WiMAX Networks: Techno-Economic Vision and Challenges

WiMAX Networks

Ramjee Prasad

l

Fernando J. Velez

WiMAX Networks Techno-Economic Vision and Challenges

Ramjee Prasad Center for TeleInFrastruktur (CTIF) Aalborg University Inst. Electronic Systems Niels Jernes Vej 12 9220 Aalborg Denmark [email protected]

Fernando J. Velez Universidade da Beira Interior Instituto de Telecomunicac¸o˜es Depto. Engenharia Electromecaˆnica Calcada Fonte do Lameiro 6201-001 Covilha Portugal [email protected] King’s College London Centre for Telecommunications Research Strand London WC2R 2LS UK

ISBN 978-90-481-8751-5 e-ISBN 978-90-481-8752-2 DOI 10.1007/978-90-481-8752-2 Springer Dordrecht Heidelberg London New York Library of Congress Control Number: 2010928698 # Springer Science+Business Media B.V. 2010 No part of this work may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission from the Publisher, with the exception of any material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. Cover design: eStudio Calamar S.L., F. Steinen-Broo, Pau/Girona, Spain Printed on acid-free paper Springer is part of Springer Science+Business Media (www.springer.com)

To our families and to our students

Preface

Attraction and aversion of the senses to their corresponding sense objects is unavoidable. One should not be controlled by them; since they are obstacles in one’s path. —The Bhagvad-Gita (3.34)

Worldwide Interoperability for Microwave Access (WIMAX) is a technology covering broad range of topics. To the best of our knowledge, WiMAX Networks is a first book that deals with all the relevant areas shown in Fig. 1 namely, quality of service (QoS), security, mobility, radio resource management (RRM), multiple input multiple output (MIMO) antenna, planning, and cost/revenue optimization, medium access control (MAC) layer, physical layer, network layer, and so on. Chapter 1 introduces the WiMAX and locates its place among the existing and future wireless systems. Aspects of OFDM and OFDMA WiMAX physical layer is well covered in Chapter 2. Chapter 3 covers link layer issues, having its main focus on Medium Access Control (MAC) Layer. The term quality of service (QoS) is clearly explained in Chapter 4, considering the WiMAX into account. Security is a primary subject for WiMAX and for secure communications, privacy and confidentiality are fundamental issues. Chapter 5 has taken care of this important subject. vii

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WiMAX Networks

Fig. 1 Tree structure of the book

Chapter 6 presents mobility architecture with integrated QoS support and the proposed architecture can accommodate different wired and wireless technologies. The radio resource management (RRM) in OFDMA based cellular networks such as WiMAX is addressed in Chapter 7. Four different sub-carriers allocation algorithm with low complexity are evaluated for WiMAX cellular systems. Chapter 8 first discusses the propagation models and then introduces the cellular planning in the context of WiMAX. A model to compute the support physical throughput is proposed for WiMAX in Chapter 9 as a function of the achievable carrier-to-noise-plus-interference ratio (CNIR). Chapter 10 first introduces general aspects about the business models for WiMAX and then address the cost/revenue optimization for these networks, for cellular configuration with and without relays.

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Multiple Input and Multiple Output (MIMO) technology options for the WiMAX has been discussed in Chapter 11. Finally, Chapter 12 concludes the WiMAX Networks by comparing WiMAX with other wireless standards and highlights its potential. We would greatly appreciate if readers would provide extra effort in improving of the quality of the book by pointing out any errors. We strongly believe nothing is errorless. Ramjee Prasad Fernando J. Velez

About Authors

Ramjee Prasad is currently Professor and Director of Center for Teleinfrastruktur (CTIF), and holds the chair of wireless information and multimedia communications. He was coordinator of European Commission Sixth Framework Integrated Project MAGNET (My personal Adaptive Global NET) and MAGNET Beyond. He was involved in the European ACTS project FRAMES (Future Radio Wideband Multiple Access Systems) as a project leader in Delft University. He was also project leader of several international, industrially funded projects of Technology. He has published over 700 technical papers, contributed to several books, and has authored, co-authored, and edited over 25 books. His latest book is “Introduction to Ultra Wideband for Wireless Communications”. Prof. Prasad has served as a member of the advisory and program committees of several IEEE international conferences. He has also presented keynote speeches, and delivered papers and tutorials on WPMC at various universities, technical institutions, and IEEE conferences. He was also a member of the European cooperation in the scientific and technical research (COST-231) project dealing with the evolution of land mobile radio (including personal) communications as an expert for The Netherlands, and he was a member of the COST-259 project. He was the founder and chairman of the IEEE Vehicular Technology/Communications Society Joint Chapter, Benelux Section, and is now the honorary chairman. In addition, Prof. Prasad is the founder of the IEEE Symposium on Communications and Vehicular Technology (SCVT) in the Benelux, and he was the symposium chairman of SCVT’93. Presently, he is the Chairman of IEEE Vehicular Technology/ Communications/Information Theory/Aerospace and Electronics Systems/Society Joint Chapter, Denmark Section. In addition, Prof. Prasad is the coordinating editor and editor-in-chief of the Springer International Journal on Wireless Personal Communications. He was the technical program chairman of the PIMRC’94 International Symposium held in The Hague, The Netherlands, from September 19 to 23, 1994 and also of the Third Communication Theory Mini-Conference in Conjunction with GLOBECOM’94, held in San Francisco, California, from November 27 to 30, 1994. He was the

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conference chairman of the fiftieth IEEE Vehicular Technology Conference and the steering committee chairman of the second International Symposium WPMC, both held in Amsterdam, The Netherlands, from September 19 to 23, 1999. He was the general chairman of WPMC’01 which was held in Aalborg, Denmark, from September 9 to 12, 2001, and of the first International Wireless Summit (IWS 2005) held also in Aalborg, Denmark on September 17–22, 2005. He was the General Chair of the First International Conference on Wireless Communication, Vehicular Technology, Information Theory and Aerospace & Electronic Systems Technology (Wireless VITAE) held on May 17–20, 2009 in Aalborg. Prof. Prasad was also the founding chairman of the European Center of Excellence in Telecommunications, known as HERMES and now he is the honorary chairman. He is a fellow of IEEE, a fellow of IETE, a fellow of IET, a member of The Netherlands Electronics and Radio Society (NERG), and a member of IDA (Engineering Society in Denmark). Prof. Prasad is advisor to several multinational companies. He has received several international awards; one of this is the “Telenor Nordic 2005 Research Prize” (website: http://www.telenor.no/om/). Fernando J. Velez received the Licenciado, M.Sc. and Ph.D. degrees in Electrical and Computer Engineering from Instituto Superior Te´cnico, Technical University of Lisbon in 1993, 1996 and 2001, respectively. Since 1995 he has been with the Department of Electromechanical Engineering of University of Beira Interior, Covilha˜, Portugal, where he is Assistant Professor. He is also researcher at Instituto de Telecomunicac¸o˜es, Lisbon. He made or makes part of the teams of RACE/MBS, ACTS/SAMBA, COST 259, COST 273, COST 290, ISTSEACORN, IST-UNITE, and COST 2100 European projects, he participated in SEMENTE and SMART-CLOTHING Portuguese projects, and he was the coordinator of four Portuguese projects: SAMURAI, MULTIPLAN, CROSSNET, and MobileMAN. Prof. Velez has authored five book chapters, around 75 papers and communications in international journals and conferences, plus 25 in national conferences, and is a senior member of IEEE and Ordem dos Engenheiros (EUREL), and a member of IET and IAENG. His main research areas are cellular planning tools, traffic from mobility, simulation of wireless networks, cross-layer design, inter-working, multiservice traffic and cost/revenue performance of advanced mobile communication systems. Susana Sargento (Ph.D. in 2003 in Electrical Engineering) joined the Department of Computer Science of the University of Porto in September 2002, and is in the University of Aveiro and the Institute of Telecommunications since February 2004. She is also a Guest Faculty of the Department of Electrical and Computer Engineering from Carnegie Mellon University, USA, since August 2008. Faculty of ICTI: Information & Communication Technologies Institute. She has been involved in several national and European projects, taking leaderships of several activities in the projects, such as the QoS and ad-hoc networks integration activity in the FP6 ISTDaidalos Project. She is currently involved in several FP7 projects (4WARD, EuroNF, C-Cast), national projects, and CMU Portugal projects (DRIVE-IN with the Carnegie Melon University). She has been organizing several conferences, such as NGI’09 and IEEE ISCC’07. She has been also in the Technical Program Committee

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of several international conferences and workshops (more than 20 in 2009), such as ACM MobiCom 2009 Workshop CHANTS and IEEE ISCC (2005–2010). She has also been a reviewer of numerous international conferences and journals, such as IEEE Wireless Communications, IEEE Networks, IEEE Communications, Telecommunications Systems Journal, IEEE Globecom, IEEE ISCC and IEEE VTC. Prof. Sargento is also Area Editor of International Journal of Communication Networks and Information Security. Her main research interests are in the areas of next generation and heterogeneous networks, infrastructure, mesh and ad-hoc networks, more specifically in QoS, mobility, routing, multicast, self-management and cognitive issues, where she has published more than 150 scientific papers. Pedro Neves received his B.S. and M.S. degrees in Electronics and Telecommunications Engineering from the University of Aveiro, Portugal, in 2003 and 2006 respectively. From 2003 to 2006 he joined the Telecommunications Institute, Portugal, and participated in the DAIDALOS-I and DAIDALOS-II European funded projects. Since 2006 he joined Portugal Telecom Inovac¸a˜o, and he is involved in the WEIRD and HURRICANE European funded projects. Furthermore, since 2007 he is also pursuing a Ph.D. in Telecommunications and Informatics Engineering at the University of Aveiro, Portugal. Eng. Neves has been involved in six, as well as more than 25 scientific papers in major journals and international conferences. His research interests are focused on broadband wireless access technologies, mobility and QoS management in all-IP heterogeneous environments, multicast and broadcast services, as well as mesh networks. Ricardo Matos is a Ph.D. student at University of Aveiro. He concluded in July 2008 his Integrated M.Sc. in Electronics and Telecommunications Engineering from the Department of Electronics, Telecommunications and Informatics of University of Aveiro. His master’s Thesis was titled “Mobility Support in WiMAX Networks”. Since September 2008 he joined Institute of Telecommunications (located in University of Aveiro Campus) as a researcher and Ph.D. student. His current research interests are related with future Internet architectures, virtualization techniques, wireless mesh networking, self-management and context-awareness. Marilia Curado is an Assistant Professor at the Department of Informatics Engineering of the University of Coimbra, Portugal, from where she got a Ph.D. in Informatics Engineering on the subject of Quality of Service Routing, in 2005. Her research interests are Quality of Service, Mobility, Routing, and Resilience. Prof. Curado has participated in several national projects, in Networks of Excellence from IST FP5 and FP6, in the IST FP6 Integrated Projects, EuQoS and WEIRD, and on ICT FP7 STREPs MICIE and GINSENG. Bruno Sousa studied computer science at the Polytechnic Institute of Leiria (B.Sc. 2005) and University of Coimbra, Portugal (M.Sc. 2008). He has participated in the IST FP6 Integrated Project WEIRD – WiMAX Extensions to Isolated Reasearch Data Networks. He is now enrolled at the University of Coimbra as a Ph.D. student, with interest areas including mobile computing; multihoming; WiMAX and simulation. Kostas Pentikousis studied computer science at the Aristotle University of Thessaloniki, Greece (B.Sc. 1996) and the State University of New York at Stony

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Brook, USA (M.Sc. 2000, Ph.D. 2004). He has published internationally in several areas, such as, network architecture and design, mobile computing, applications and services, local and wide-area networks, and simulation and modeling. Dr. Pentikousis is a Senior Research Scientist at VTT Technical Research Centre of Finland. Giada Landi received the Laurea degree “cum laude” in Telecommunication Engineering from the University of Pisa, Italy, in 2005. Currently she is R&D solutions architect at Nextworks S.r.l.. Her main research activities concern the design, development and integration of Control Plane in network architectures supporting heterogeneous wireless access technologies, with main focus on Quality of Service, Admission Control, AAA and inter-technology mobility. She participated in the IST FP6 WEIRD project and the Artemis SOFIA project. Ljupcˇo Jorguseski currently works as senior scientist/innovator on the optimization and performance estimation of wireless access networks. He has got his Dipl. Ing. degree in 1996 from the Faculty of Electrical Engineering at the university “Sts. Cyril and Methodius”, Skopje, Republic of Macedonia. From 1997 to 1999 he worked as applied scientist at TU Delft, Delft, The Netherlands on the European FRAMES project that defined the ETSI proposal for the UMTS standardization. From 1999 to 2003 he was with KPN Research, Leidschendam, The Netherlands where he was working on the radio optimization and performance estimation of the GPRS, UMTS and WLAN networks. At the same time he was affiliated with the Centre for TeleInfrastruktuur (CTiF) at Aaalbog University, Aalborg, Denmark where he has received his Ph.D. degree in 2008. Ljupcˇo is actively following 3GPP standardisation and has interactions with international fora such as e.g. NGMN. Ljupcˇo was involved in European IST research projects FP5 MOMENTUM (2001– 2004) on enhanced methods for UMTS planning, FP6 Ambient Networks (2004– 2007) on radio access selection in multi-radio access systems, and FP7 SOCRATES (2008–2010) on self-optimisation and self-healing for LTE wireless access networks. Dr. Jorguseski has one journal publications (IEEE Comm. Magazine), over 15 scientific publications in major conferences such as for example IEEE VTC-Fall, IEEE PIMRC, IEEE WPMC, etc. has contributed with editorship in two books on wireless tecommunications, and has co-authored two patents (and five pending patent applications). Pedro Sebastia˜o (S’95-M’05) received the B.Sc. degree in Electronics, Telecommunications and Computing from ISEL, Polytechnic Institute of Lisbon, Portugal, in 1992. He received his Licenciado and M.Sc. degrees in Electrical and Computer Engineering from IST, Technical University of Lisbon, in 1995 and 1998, respectively. He is a lecturer in LUI-ISCTE and research assistant at Instituto de Telecomunicac¸o˜es. He has been involved on several research projects and his interests include planning tools for Wi-Fi and WiMAX, stochastic models and efficient simulation algorithms for physical layer. Eng. Sebastia˜o is a member of IEEE, Sociedade Brasileira das Telecomunicac¸o˜es and Ordem dos Engenheiros. Rui Costa was born in Santare´m, Portugal, and received the Licenciado degree in Informatics from Instituto Matema´ticas e Gesta˜o - Universidade Lusofona in 1999. He is the responsible by the development and management of the Computer

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Services and network of the Health Sciences Faculty of University of Beira Interior, he works on the development of wireless LAN, MAN and WAN, e-Learning, b-Learning and m-Learning applications, advanced WIA (wireless Internet applications), RIA (rapid Internet applications) in University environments for Web2. He is concluding is M.Sc. on cellular planning and deployment issues for fixed and portable WiMAX. Daniel Robalo received the Licenciado and M.Sc. degrees in Electrical Engineering from University of Beira Interior (UBI), Covilha˜, Portugal, in 2005 and 2008, respectively. His M.Sc. research was done in the context of the MobileMAN project, an internal project on WiMAX deployment from Instituto de Telecomunicac¸o˜es (IT). He is currently a researcher at IT, and his research interest is in the field of Broadband Wireless Access, including design and implementation of WiMAX networks. Besides conference papers, including IEEE ones, Eng. Robalo has two journal papers and one book chapter accepted for publication. Cla´udio Comissa´rio received the Licenciado and M.Sc. degrees in Electrical Engineering from University of Beira Interior (UBI), Covilha˜, Portugal, in 2007 and 2008, respectively. His M.Sc. research was done in the context of the MobileMAN project, an internal project on WiMAX deployment from Instituto de Telecomunicac¸o˜es (IT). Eng. Comissa´rio is currently with CELFINET, a Portuguese consultancy company for mobile operators. Anto´nio Rodrigues received the B.S. and M.S degrees in electrical and computer engineering from the Instituto Superior Te´cnico (IST), Technical University of Lisbon, Lisbon, Portugal, in 1985 and 1989, respectively, and the Ph.D. degree from the Catholic University of Louvain, Louvain-la-Neuve, Belgium, in 1997. Since 1985, Prof. Rodrigues has been with the Department of Electrical and Computer Engineering, IST, where is currently an Assistant Professor. His research interests include mobile and satellite communications, wireless networks, spread spectrum systems, modulation and coding. Hamid Aghvami is the Director of the Centre for Telecommunications Research at King’s College London. He is Managing Director of Wireless Multimedia Communications Ltd., his own consultancy company. Professor Aghvami leads an active research team working on numerous mobile and personal communications projects for third and fourth generation systems. He is a Fellow of the Royal Academy of Engineering, Fellow of the IET, Fellow of the IEEE, and in 2009 was awarded a Fellowship of the Wireless World Research Forum. Prof. Aghvami was a member of the Board of Governors of the IEEE Communications Society in 2001–2003, and has been member, Chairman, and Vice-Chairman of the technical programme and organising committees of a large number of international conferences. He is also founder of the International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC). Oliver Holland obtained his B.Sc. degree (with First Class Honours) in Physics and Music from Cardiff University, and his Ph.D. in Telecommunications from King’s College London. Dr. Holland has jointly authored over 60 publications on a variety of topics, including several book chapters and one patent, and has served as an Organiser and Programme Committee member for a number of major

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conferences and journals. His interests include Beyond 3G Communications Systems, Spectrum Sharing, and Green Communications, among many others. Muhamad Kashif Nazir concluded his M.Sc. in Space Science at the University of Punjab Lahore in 2002. He is currently a “Signal Processing for Communications” M.Sc. student at King’s College London. His research is on “Modelling and Simulation of Efficient Broadband Wireless Access Architectures with Multi-hop Relays”, which also involved cost & revenue analysis for Fixed WiMAX.

Acknowledgements

First of all, the Editors would like to acknowledge Kirti Pasari from CTIF, Aalborg University for her big effort towards the completion of this book. Special thanks go to Mandalika Venkata Ramkumar and Dua Idris from CTIF for their hard effort in finalizing the manuscript. Authors also gratefully acknowledge Dr. Nicola Marchetti and Ambuj Kumar contributions and suggestions. The Editors acknowledge Thikrait Al Mosawi for the discussions and the Figure on Media independent Handover and IEEE 802.21. They also acknowledge B. Muquet, E. Biglieri, H. Sari and S. Ahamdi for using the following material from their papers: Figures 11.15 and 11.16, extracted from reference [18]/Chapter 11, and Table 12.11, extracted from reference [31]/Chapter 12. They also acknowledge IEEE for using the information from IEEE standards. Part of the work from Chapter 6 was conducted within the framework of the IST Sixth Framework Programme Integrated Project WEIRD (IST-034622), which was partially funded by the Commission of the European Union. Study sponsors had no role in study design, data collection and analysis, interpretation, or writing the book chapter. The views expressed do not necessarily represent the views of the authors’ employers, the WEIRD project, or the Commission of the European Union. We thank our colleagues from all partners in WEIRD project for fruitful discussions. The work from Chapters 8, 9 and 10 was partially funded by MobileMAN (Mobile IP for Broadband Wireless Metropolitan Area Network), an internal project from Instituto de Telecomunicac¸o˜es/Laborato´rio Associado, by CROSSNET (Portuguese Foundation for Science and Technology POSC project with FEDER funding), by “Projecto de Re-equipamento Cientı´fico” REEQ/1201/EEI/ 2005 (a Portuguese Foundation for Science and Technology project), by UBIQUIMESH, by the Marie Curie Intra-European Fellowship OPTIMOBILE (Cross-layer Optimization for the Coexistence of Mobile and Wireless Networks Beyond 3G, FP7-PEOPLE-2007-21-IEF) and by the Marie Curie Reintegration Grant PLANOPTI (Planning and Optimization for the Coexistence of Mobile and Wireless Networks Towards

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Long Term Evolution, FP7-PEOPLE-2009-RG). Authors also acknowledge the COST Action 2100 – Pervasive Mobile & Ambient Wireless Communications. The authors acknowledge the fruitful contributions on ArcGIS tools from Eng Jose´ Roma˜o, Eng Jose´ Riscado and Prof. Victor Cavaleiro from STIG-UBI, and to the final year project students Hugo Carneiro, Jorge Oliveira, Dany Santos and Rui Marcos.

Contents

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The Evolution Towards WiMAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ramjee Prasad and Fernando J. Velez 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 History of Wireless Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Broadband Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.1 The Path Towards Wireless Broadband Access . . . . . . . . . . . . . . . 1.3.2 Types of Broadband Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.3 DSL Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 Evolution of Wireless Broadband . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4.1 Narrowband Wireless Local Loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4.2 First Generation Broadband Wireless Systems . . . . . . . . . . . . . . . . 1.4.3 Second Generation Broadband Wireless Systems . . . . . . . . . . . . . 1.4.4 Emergence of Global Standard Based Wireless Broadband . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5 Fixed Wireless Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5.1 Point-to-Point Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5.2 Point-to-Multipoint Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5.3 NLoS Point-to-Multipoint Networks . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5.4 Mesh Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6 Broadband Wireless Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6.1 Licensed Frequency Bands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6.2 License-Exempt Frequency Bands . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.7 Background on IEEE 802.16 and WIMAX . . . . . . . . . . . . . . . . . . . . . . . . . . 1.7.1 IEEE 802.16 Evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.7.2 IEEE 802.16a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.7.3 IEEE 802.16-2004 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.7.4 IEEE 802.16e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.8 Fixed and Mobile WIMAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.9 Personal Broadband . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.10 WIMAX Forum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 1 3 11 11 13 15 17 17 17 18 19 20 20 21 22 22 23 23 24 25 26 26 27 27 30 32 34

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1.10.1 Difference Between WiMAX Forum and IEEE 802.16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.10.2 Members . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.10.3 Working Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.10.4 WiMAX Products Certification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.10.5 WiMAX Forum Certified Program Milestones . . . . . . . . . . . . . 1.10.6 Certification Roadmap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.10.7 Benefits of an Industry Standard and Certified Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.10.8 WiMAX Forum Certified Products . . . . . . . . . . . . . . . . . . . . . . . . . 1.11 Frequency Band Allocations for WiMAX . . . . . . . . . . . . . . . . . . . . . . . . . . 1.12 ITU Classification Adds Credibility to WiMAX . . . . . . . . . . . . . . . . . . . 1.13 WiMAX Applications and Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.13.1 Fixed Broadband Wireless Applications . . . . . . . . . . . . . . . . . . . . 1.13.2 VoIP over WiMAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.14 Salient Features of WiMAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.15 Fixed, Portable, and Mobile Terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.16 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

OFDMA WiMAX Physical Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ramjee Prasad and Fernando J. Velez 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 History and Development of OFDM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.1 Evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.2 Applications of OFDM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 OFDM Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1 OFDM Versus FDM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.2 OFDM Signal Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 OFDM Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.1 Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.2 Serial to Parallel Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.3 Demodulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 OFDM Symbol Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6 ISI and ICI Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7 Spectral Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.8 Orthogonal Frequency Division Modulation Access . . . . . . . . . . . . . . . . . 2.8.1 Improvements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.8.2 Subchannelization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.8.3 OFDMA Subchannelization: Its advantages to WiMAX . . . . . 2.9 Advantages of OFDM Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.10 Disadvantages of OFDM Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.10.1 Strict Synchronization Requirement . . . . . . . . . . . . . . . . . . . . . . . . 2.10.2 Peak-to-Average Power Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.10.3 Co-channel Interference Mitigation in Cellular OFDM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

34 34 35 35 41 41 42 44 45 48 48 49 50 55 57 60 61 63 63 64 64 67 67 67 69 71 71 73 73 74 74 77 77 77 77 78 78 80 80 80 81

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2.11 Scalable OFDMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 2.11.1 Parameters and Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 2.11.2 Reference Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 2.12 IEEE 802.16 PHY Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 2.12.1 Supported Frequency Bands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 2.12.2 Channel Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 2.12.3 IEEE 802.16 PHY Interface Variants . . . . . . . . . . . . . . . . . . . . . . . 84 2.13 WirelessMAN-SC PHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 2.13.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 2.13.2 Duplexing Techniques and PHY Type Parameter Encodings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 2.13.3 Frame Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 2.13.4 Downlink PHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 2.13.5 Uplink PHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 2.14 WirelessMAN-OFDM PHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 2.14.1 Channel Coding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 2.14.2 Concatenated Reed–Solomon-Convolutional Code (RS-CC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 2.15 WirelessMAN-OFDMA PHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 2.15.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 2.15.2 Subcarrier Allocation Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 2.16 Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 3

Medium Access Control Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ramjee Prasad and Fernando J. Velez 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 MAC Sub-layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 MAC Protocol Data Unit (PDU) and Service Data Unit . . . . . . . . . . . 3.4 Service Specific Convergence Sub-layer (CS) . . . . . . . . . . . . . . . . . . . . . 3.4.1 Mission and Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.2 Connections and Addressing, Connection ID (CID) and Service Flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5 MAC Common Part Sub-layer (MAC CPS) . . . . . . . . . . . . . . . . . . . . . . . 3.5.1 Mission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.2 MAC Addressing and Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.3 MAC PDU Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6 MAC Header Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6.1 Generic MAC Header . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6.2 MAC Header Without Payload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.7 MAC Sub-headers, Special Payloads and Sub-header Ordering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.7.1 Significance of Type Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.8 IEEE 802.16 MAC Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

137 137 138 139 140 140 142 150 150 150 151 152 152 152 155 157 158

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3.9 Basic, Primary and Secondary Management Connections . . . . . . . . . 3.9.1 MAC Management Message Format . . . . . . . . . . . . . . . . . . . . . . . . . 3.10 Fragmentation, Packing and Concatenation . . . . . . . . . . . . . . . . . . . . . . 3.10.1 Fragmentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.10.2 Packing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.10.3 Concatenation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.10.4 CRC Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.11 Encryption of MAC PDUs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.12 Automatic Repeat Request (ARQ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.12.1 Error Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.12.2 ARQ Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.12.3 ARQ Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.12.4 HARQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.13 Scheduling Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.13.1 Scheduling Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.14 Bandwidth Allocation and Request Mechanisms . . . . . . . . . . . . . . . . . 3.14.1 Role of SSs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.14.2 Requests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.14.3 Grants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.14.4 Polling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.15 Contention Resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.15.1 Transmission Opportunity and Example for Contention-Based Bandwidth Requests . . . . . . . . . . . . . . . 3.16 Network Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.16.1 Downlink Channel Synchronization . . . . . . . . . . . . . . . . . . . . . . 3.16.2 Initial Ranging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.16.3 Capabilities Negotiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.16.4 Authentication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.16.5 Registration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.16.6 IP Connectivity Stages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.16.7 Transport Connection Creation . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.17 Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Quality of Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ramjee Prasad and Fernando J. Velez 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Interpretation and Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1 Technical and Customer-Specific QoS Parameters . . . . . . . . . . 4.2.2 QoS Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 QoS Architecture for IEEE 802.16 MAC Protocol . . . . . . . . . . . . . . . . 4.4 QoS Rovisioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.1 Service Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.2 Service Flow Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

158 159 161 161 162 163 164 165 165 165 166 167 171 174 175 175 175 176 177 178 183 184 185 186 186 187 188 188 189 189 189 190 191 191 192 192 194 196 198 198 199

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4.5 Object Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.1 Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.2 Global Service Flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.3 Conventions Used for Global Service Class Name . . . . . . . . . . 4.5.4 Global Service Flow Class Name Parameters . . . . . . . . . . . . . . . . 4.5.5 Service Flow Creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6 Service Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7 Authorization Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7.1 Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7.2 Static Authorization Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7.3 Dynamic Authorization Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8 Service Flow Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8.1 Provisioned Service Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8.2 Admitted Service Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8.3 Active Service Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9 Service Flow Creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9.1 Three-Way Handshaking Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9.2 Dynamic Service Flow Creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9.3 Dynamic Service Flow Modification and Deletion . . . . . . . . . . 4.10 Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

199 199 201 201 201 203 204 205 205 205 205 206 206 207 207 208 208 209 210 214 214

Security Sublayer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ramjee Prasad and Fernando J. Velez 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Security Architecture for IEEE 802.16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.1 Architecture and Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.2 Secure Encapsulation of MPDUs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.3 Encryption Algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.4 Data Encryption Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.5 Key Management Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 Authentication Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.1 RSA Authentication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.2 PKM EAP Authentication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4 PKM Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5 PKM Protocol MAC Management Messages . . . . . . . . . . . . . . . . . . . . . . 5.5.1 PKM Version 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.6 Key Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.6.1 Authorisation Key (AK) Management . . . . . . . . . . . . . . . . . . . . . . . 5.6.2 SS Key Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.6.3 PKM Version 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.7 Network Aspects of Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.7.1 Radius . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.7.2 Extensible Authentication Protocol (EAP) . . . . . . . . . . . . . . . . . . .

215 215 216 216 218 218 219 222 223 223 224 224 224 227 240 240 244 246 247 248 248

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5.8 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 6

7

Mobility Management Architecture for WiMAX Networks . . . . . . . . Susana Sargento, Pedro Neves, Ricardo Matos, Marı´lia Curado, Bruno Sousa, Kostas Pentikousis, and Giada Landi 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 WiMAX Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.1 The WiMAX Forum Network Reference Model . . . . . . . . . . . . . 6.2.2 The IEEE 802.16 Reference Model . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.3 Mobility Management in WiMAX . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.4 IEEE 802.21 Media Independent Handover Overview . . . . . . 6.3 QoS-Aware Mobility Management: A Use Case for the WEIRD System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.1 Integrated QoS and Mobility Management . . . . . . . . . . . . . . . . . . 6.3.2 QoS-Aware Inter-technology Handovers for WiMAX . . . . . . . 6.4 Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.1 MIHF Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.2 Link Layer Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.3 NSIS: QoS and MIH Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.4 MM and CSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.5 QoS Signalling and Resource Reservation . . . . . . . . . . . . . . . . . . . 6.4.6 Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5 Testbed Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5.1 Handover Process Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5.2 Mobility Manager Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5.3 Resource Reconfiguration During HO Preparation and Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5.4 MIH Transport Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

251

Radio Resource Management in WiMAX Networks . . . . . . . . . . . . . . . . . Jorguseski Ljupco and Ramjee Prasad 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 General Radio Resource Management (RRM) Problem Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3 Radio Resource Definition in WiMAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4 Downlink RRM Algorithms for WiMAX Systems . . . . . . . . . . . . . . . . 7.4.1 Reuse-One . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4.2 Reuse-Three . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4.3 Soft Re-Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4.4 Maximum C/I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4.5 Proportional Fair (PF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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253 254 255 256 259 261 263 265 269 272 272 273 274 275 276 277 279 281 282 282 285 286 286

289 290 293 294 296 296 297 299 300

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7.5 Simulation Evaluation of Downlink Sub-Carrier Allocation Algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.6 Semi-analytical Evaluation of Downlink Sub-carrier Allocation Algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.6.1 Comparison of Semi-analytical and Simulation Results . . . . . 7.7 Conclusions and Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

9

Radio and Network Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fernando J. Velez, Pedro Sebastia˜o, Rui Costa, Daniel Robalo, Cla´udio Comissa´rio, Anto´nio Rodrigues, and A. Hamid Aghvami 8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 Propagation Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.1 SUI Versus Modified Friis Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.2 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3 Cellular Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.1 Limitations of a Simplified Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.2 Signal-to-Noise-Plus-Interference Ratio . . . . . . . . . . . . . . . . . . . . . 8.3.3 Interference-to-Noise Ratio and Reuse Pattern . . . . . . . . . . . . . . 8.3.4 CNIR and Supported Throughput . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.5 Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4 Fixed WiMAX Planning Platforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.1 Framework and Scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.2 Wireless Planning Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.3 Results with Adaptive Modulation and Coding Schemes . . . . 8.4.4 Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . System Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fernando J. Velez, M. Kashif Nazir, A. Hamid Aghvami, Oliver Holland, and Daniel Robalo 9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.2 CNIR Versus Physical Throughput Without Relays . . . . . . . . . . . . . . . 9.3 CNIR Versus Physical Throughput with Relays . . . . . . . . . . . . . . . . . . . 9.3.1 Formulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.3.2 Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.3.3 DL Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.3.4 UL Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.4 Supported Physical Throughput . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.4.1 Implicit Function Formulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.4.2 Without Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.4.3 DL with Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.4.4 UL with Relays and K = 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.4.5 Use of Sub-Channelisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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300 305 310 312 313 315

316 319 319 321 325 325 326 328 334 343 344 344 344 351 359 362 363 365

366 367 370 370 372 374 377 378 378 381 387 388 389

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9.5 Throughput with Sectorization, Relays and K = 1 . . . . . . . . . . . . . . . . . 390 9.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393 10

11

Business Models and Cost/Revenue Optimization . . . . . . . . . . . . . . . . . . . Fernando J. Velez, M. Kashif Nazir, A. Hamid Aghvami, Oliver Holland, and Daniel Robalo 10.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.2 Business Model Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.3 Broadband Communications Business . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.4 Developing a WiMAX Business Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.4.1 Market Research: Gathering the Input Parameters for a WiMAX Business Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.4.2 Market Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.5 Range of Services Offered . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.5.1 Classification of Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.5.2 Varying Terrain Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.6 Cost/Revenue Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.6.1 Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.6.2 Hypothesis Without Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.6.3 Hypothesis and Assumptions with Relays . . . . . . . . . . . . . . . . 10.6.4 Optimization and Profit Without Relays . . . . . . . . . . . . . . . . . . 10.6.5 Optimization and Profit with Relays . . . . . . . . . . . . . . . . . . . . . . 10.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

395

Multiple Antenna Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ramjee Prasad and Fernando J. Velez 11.1 Introduction to MIMO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1.1 MIMO Wireless Transmission System . . . . . . . . . . . . . . . . . . . . 11.1.2 Closed Loop MIMO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Capacity of MIMO Channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3 Multi-antenna in OFDM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.4 Space Diversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.5 Space-Time Coding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.5.1 Alamouti Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.5.2 Second-Order STC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.6 Spatial Multiplexing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.6.1 Vertical Encoding SM & Horizontal Encoding SM . . . . . . 11.7 Collaborative Spatial Multiplexing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.7.1 Collaborative SM for UL PUSC . . . . . . . . . . . . . . . . . . . . . . . . . . 11.8 Diversity Gain and Array Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.9 Comparison of MIMO Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.10 System Model for MIMO OFDM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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396 397 397 398 398 400 404 404 405 406 406 408 409 411 416 419 421

423 425 426 427 427 429 429 430 432 432 433 435 435 436 438 440

Contents

11.11 Support of MIMO Technology in the IEEE 802.16 Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.11.1 Two-Antenna Downlink STC Transmission . . . . . . . . . . . . 11.12 Beamforming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.12.1 Switched-Beam Antenna Arrays . . . . . . . . . . . . . . . . . . . . . . . . 11.12.2 Adaptive Antenna Systems (AAS) in IEEE 802.16e-2005 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.13 Trade-Off Between Spatial Multiplexing and Spatial Diversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.14 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

WiMAX and Wireless Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ramjee Prasad and Fernando J. Velez 12.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.2 Advantages of WIMAX Over DSL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.3 Wi-Fi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.4 WiBRo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.5 ETSI HiperACCESS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.6 ETSI HiperMAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.7 iBURST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.8 Flash- OFDM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.9 IEEE 802.16 and 3G . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.10 3G Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.10.1 3GPP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.10.2 3GPP2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.11 HSDPA and HSUPA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.12 IEEE 802.16m and IMT-ADVANCED . . . . . . . . . . . . . . . . . . . . . . . . . . 12.13 IEEE 802.20/Mobile FI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.14 IEEE 802.21 and Media Independent Handover . . . . . . . . . . . . . . . . 12.15 IEEE 802.22 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.16 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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441 442 444 444 446 447 448 449 451 451 452 454 457 458 458 459 460 460 461 461 462 464 467 467 469 471 473 473

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477

Chapter 1

The Evolution Towards WiMAX Ramjee Prasad and Fernando J. Velez

Abstract Convergence is a step towards the unpredictable future of wireless communications. Important increases are foreseen in supported bit rates and remarkable improvements in services, applications and wireless communication components. After presenting a brief history of wireless communications, a vision on nowadays wireless ecosystem is presented and the path towards broadband wireless access is explored. Details on IEEE 802.16 evolution are given and the reasons for the existence of the WiMAX Forum are explained. WiMAX service classes are described and salient features of WiMAX are highlighted.

1.1

Introduction

The rapid growth of wireless communication and its pervasive use in all walks of life are changing the way we communicate in all fundamental ways. It is one of the most vibrant areas in the communication field today. Wireless communication dates back to the end of the nineteenth century when Maxwell showed through his equations that the transmission of information can be achieved without the need for a wire [1]. Later, experimentations by Marconi and other scientists proved that long distances wireless transmission may be a reality. True Wireless communications have gained a momentum in the last decade of twentieth century with the success of second Generation (2G) of digital cellular mobile services. Worldwide successes of Global System for Mobile Communications (GSM), Interim Standard 95 (IS-95), Personal digital Cellular (PDC) and digital Advanced Mobile Phone System (IS-54/136) have enabled pervasive ways of life for the new information and communication technology era. Second R. Prasad (*) Center for TeleInFrastruktur (CTIF), Aalborg University, Niels Jernes Vej 12, DK–9220 Aalborg Øst, Denmark e-mail: [email protected]

R. Prasad and F.J. Velez, WiMAX Networks, DOI 10.1007/978-90-481-8752-2_1, # Springer ScienceþBusiness Media B.V. 2010

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5G

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2020 IMT-A/4G High speed WLAN

WiBro 802.16e

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5 GHz WLAN

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PN & PN Federation IEEE 802.22

WPAN IEEE 802.20

3G 2.4 GHz WLAN

Bluetooth

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ZigBee

2G

1990 1G

1980 GIMCV: Global Information Multimedia Communication Village

Fig. 1.1 The progress tree for communication technology [5, 6]

Generation (2G), 2.5G, and Third Generation (3G) standards of mobile systems are being deployed everywhere worldwide, with different versions of Universal Mobile Telecommunications System (UMTS), while efforts are going on towards the development and standardization of Beyond 3G (B3G) systems, for example, High Speed Packet Access (HSPA), Wireless Local and Personal Area Networks (WLANs/WPANs) and ultimately towards Fourth Generation (4G) [2–4]. Figure 1.1 illustrates how the progress towards the next generation in communication technology, 4G, can be perceived as a tree, with many branches. But this is not the end of the tunnel; ever increasing user demands have drawn the industry to search for always best connected solutions to support data rates of the range of tens of Mbps in a context of interoperability and cognitive radio. It will lead to 5G as shown in Fig. 1.1. This chapter is organized as follows. Section 1.2 addresses the history of wireless communications and presents convergence as a step towards the unpredictable future. Section 1.3 presents the path towards wireless broadband access, the types of broadband technologies and gives details on Digital Subscriber Line (DSL) broadband technology. Section 1.4 describes the evolution of wireless broadband, from narrowband wireless local loop to different generations of broadband wireless systems, towards the emergence of a global standard based wireless broadband. Section 1.5 addresses fixed wireless access. Section 1.6 present broadband wireless accesses and distinguishes between licensed and licensed-exempt frequency bands. Section 1.7 gives the background on IEEE 802.16 and Worldwide Interoperability for Microwave Access (WiMAX), namely IEEE 802.16 evolution,

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from IEEE 802.16 to 802.16a, 802.16b, 802.16-2004, 802.16e and 802.16m as well as their characteristics. Section 1.8 compares fixed and mobile WiMAX. Section 1.9 presents the convergence of personal broadband while Section 1.10 describes the WiMAX Forum perspective. Section 1.11 presents the frequency band allocation for WiMAX while Section 1.12 gives details about ITU classification for WiMAX. Section 1.13 addresses WiMAX services and applications. Section 1.14 presents the salient features of WiMAX. Section 1.15 presents fixed, portable and mobile WiMAX terminals. Finally, Section 1.16 presents the conclusions.

1.2

History of Wireless Transmission

The notion of transmitting information without the use of wires seemed to be a magic in the nineteenth century. But in the year 1896 Marchese Guglielmo Marconi made it possible for the first time by demonstrating the ability of radio waves instant communication [1]. Since then new wireless communication methods and technologies have been evolving in the last over 100 years. The exciting history of Wireless can be divided into four periods, as shown in Tables 1.1–1.4: Table 1.1 Pioneer Era 1600 Dr. William Gilbert detects electromagnetic activity in the human body and describes it as “electricity”. 1837 Samuel F.B. Morse invents the Morse telegraph and sends messages over wires by using Morse code. 1865 Scientists, inventors, and hobbyists begin performing experiments with wireless. 1860s James Clark Maxwell’s EM waves postulates. 1880s Proof of the existence of EM waves by Heinrich Rudolf Hertz. 1905 First transmission of wireless and first patent of wireless communications by Gugliemo Marconi. 1909 Gugliemo Marconi received the Nobel prize. 1912 Sinking of the Titanic highlights the importance of wireless communications on the seaways. In the next years marine radio is established.

Table 1.2 Pre-cellular Era 1921 Detroit police department conducts field tests with mobile radio. 1933 In the United States, four channels in the 30–40 MHz range. 1938 In the United States, ruled for regular services. 1940 Wireless communications is stimulated by World War II. 1948 First commercial fully automated mobile telephone system is deployed in Richmond, United States. 1950s Microwave telephone and communication links are developed. 1958 A-Netz was introduced in Germany. 1960s Introduction of trunked radio systems with automatic channel allocation capabilities in the United States. 1970s Commercial mobile telephone system operated in many countries (e.g. 100 million vehicles on US highways, B-Netz in (West-)Germany).

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Table 1.3 Cellular Era/ Broadband Era [1–3]

1980s 1990s 2000s

Table 1.4 Convergence/ Personalisation Era

l l l l

2010+ 2015+ 2020’

Deployment of analogue cellular systems: 1G. Digital cellular deployment and dual mode operation of digital systems: 2G. International Mobile Telecommunications 2000 (IMT-2000)/deployment with multimedia services: 3G WPAN: Bluetooth, UWB WLAN: Wi-Fi WMAN: WiMAX, WiBro

Fourth generation (4G) Mega-communications Fifth generation (5G)

Pioneer Era Pre-cellular Era Cellular/Broadband Era Convergence/Personalisation Era

The pioneer era was marked by fundamental research and development, with contributions from Oersted, Faraday, Maxwell, Helmoltz, Rudolf Hertz, Righi, Lavernock, among many others. The history of modern wireless communications started in 1896 when Marconi submitted his first patent, the first one ever in the field of wireless telegraphy, and 1901, also with Marconi, who demonstrated wireless telegraphy by sending and receiving Morse code, based on long-wave (>>1 km wavelength) radiation, using high-power transmitters [4]. It had happened at the 11 December 1901. With a transmission range larger than 3,000 km, radio waves connected wirelessly Europe and America. How was it possible if the two terminals were not in Line-of-Sight (LoS)? The answer is the reflection onto the ionosphere, whose existence was postulated by Heaviside and Kennely. In 1907, the first commercial trans-Atlantic wireless service was initiated, using huge ground stations and 30100 m antenna masts. World War I saw the rapid development of communications intelligence, intercept technology, cryptography, and other technologies that later became critical to the advent of modern wireless systems. Later, Marconi discovered shortwave (<100 m wavelength) transmission. Such waves undergo reflections, refractions, absorption, and bounce off the ionosphere, making much more efficient transmission possible. The higher frequencies needed were made possible by vacuum tubes, which were discovered by J.A. Fleming in 1904 and became available around 1906. In addition, cheaper, smaller, and betterquality transmitters became available. In 1915, wireless voice transmission between New York and San Francisco, USA, was achieved while, in 1920, the first commercial radio broadcast took place in Pittsburgh, Pennsylvania, USA. In 1921,

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police cars in Detroit, Michigan, USA, were already equipped with wireless dispatch radios. In 1935, the first telephone call around the world was made. In Europe, there have also been some advances as the inclusion of telephones in trains in the railway Hamburg-Berlin, Germany, in 1926, with cables parallel to the railway, as well as several experiences with television (TV) broadcast in 1928, across the Atlantic, colour TV and TV news. During the World War II years, although commercial exploitation was delayed, radio technology developed rapidly to assist with the war effort. After the end of the War, in 1946, the first public telephone service started in 25 major US cities. It used 120 kHz RF bandwidth in half-duplex mode. Then, in 1950, the FCC doubled the number of mobile channels, and improved the technology, which enabled to cut the RF bandwidth to 60 kHz. In 1960, in the context of the Improved Mobile Telecommunications System (IMTS), the FM bandwidth was again cut, to 30 kHz. Besides, trunking was also introduced, and telephone companies could start to offer full-duplex, auto-dial systems. In Germany, A-Netz was introduced in 1958. It was an analogue system operating at 160 MHz ant it achieved coverage of 80%. Calls could only be established from the mobile terminal. In 1971, it had reached a total of 11,000 users. In 1968, based on research initiated in 1947, AT&T proposed the cellular concept to the FCC. Bell Mobile offered 12 channels for the entire metropolitan area of New York serving 543 customers in the year 1976. Meanwhile, B-Netz was introduced in Germany in 1972. It was analogue too and operated at 160 MHz. The novelty was the possibility of establishing the calls from the fixed network if the location of the mobile terminal was known in advance. It reached 13,000 users in Germany but it was also deployed in Austria, Luxembourg and Holland. Although the concept of cellular telephony was developed by Bell Labs before, the first cellular mobile systems began its operation in August 1981 in Sweden. This was called Nordic Mobile Telephone system (NMT). NMT was followed by Total Access Communication System (TACS) in Austria (in 1984), Italy and the UK (in 1985), by C-450 in Germany and by Radiocom2000 in France. These different European systems belong to the first generation (1G) and were totally incompatible with each other. In 1983, cellular service began in USA when FCC allocated 666 duplex channels for the Advanced Mobile Phone System (AMPS) .The market situation in Europe was not favourable as there was no single standard to provide economies of scale. This pushed Europe to develop a unified and single Digital Pan-European standard called GSM, which was developed in early 1980s and deployed in 1992. In 1989, the FCC granted an additional 166 channels (10 MHz worth) to AMPS. In 1991, US digital cellular (USDC), or IS-54, which supports three users in each 30 kHz channel, was released. This was later improved to accommodate six users per channel. All the standards were developed in the 1980s for voice communications and used frequency modulation (FM) for speech, frequency shift keying (FSK) for signalling and Frequency Division Multiple Access (FDMA). AMPS and IS-54 were 1G systems, too. Only later, in the 1990s, GSM and IS-95 standards evolved to include wireless data transmission as an integral part of their set of services. The standards deployed later in 1090s were based in Time Division Multiplexing

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(TDMA), FDMA, or Code Division Multiple Access (CDMA). Frequency Division Multiplexing (FDD) was employed. In 1993, the 1.8 GHz band was released for the digital Personal Communications System (PCS), followed in 1994 by the introduction of IS-95 CDMA. With the advent of new digital standards, wireless data communication became more prevalent. These standards enabled data capabilities from 9.6 to 14.4 kb/s and were termed second Generation (2G) mobile systems. Fundamentally, 2G networks use telephone-like circuit switching that proved to be optimal for voice communications, which require low latency. But this system is relatively inefficient for data communications, and research efforts to move towards packet switching communications were needed. Meanwhile, intermediate systems were introduced beginning in the late 1990s to achieve higher data rates. These systems are designed “Towards 3G” (sometimes called 2.5G) since they perform better than 2G. The first GSM upgrade was the High Speed Circuit Switched Data (HSCSD) system. HSCSD is the first multi-slot data deployed based in software only upgrade. In 2001, General Packet Switched Service (GPRS) emerged and enabled data streams to flow more easily via packet switching. It proved to be better than HSCSD for higher data rates. As GPRS is a packet switched solution, it enables billing to be based on data volume rather than on time .There also were protocol enhancements to the cdmaOne protocol (originally called IS/95) named IS-95B, and Single Carrier (1x) Radio Transmission Technology (IXRTT) with an extension of GPRS called EDGE (Enhanced Data Rates for GSM Evolution). EDGE is an evolution of GPRS towards 3G standards, compatible with other TDMA systems such as D-AMPS and Japan’s Pacific Digital Cellular, PDC, originally embodied in the UMTS WCDMA and CDMA2000 standards and have now been included in IMT2000, discussed below [4, 5]. In the context of fixed access, traditionally, most users connected to the Internet through the same telephone line that can be used for traditional voice communication. A personal computer equipped with a modem is used to hook into an Internet dial-up connection. These lines provided a relatively low data transmission rate (called “narrowband”) of 56 kbps. As Internet market continued to explode and the content on the World Wide Web became more sophisticated, the need for greater bandwidth and faster connection speeds was felt. This led to the development of several technological approaches to provide broadband. Broadband service provides higher data transmission speed and facilitates more content to be carried through the transmission “pipeline”. Users can view video, make telephone calls, or download software and other data rich files in a matter of seconds. In addition to offering speed, broadband is “always on” connection (no need to “dial-up”), does not block phone lines and no need to reconnect to network after logging off. Broadband also has “two-way” capability that means, the ability to both receive (download) and transmit (upload) data at very high speeds. In the context of wireless access, the growing demand for Internet also fuelled with the triple play multimedia required packet based higher bit data rate communication. The term 3G was coined in the 1990s by the global industry to indicate the next generation of mobile devices. The development of third-generation (3G)

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mobile systems began when the World Administrative Radio Conference (WARC) in 1992.The international 3G standards have been accepted by the ITU (International Telecommunications Union) under the name of International Mobile Telecommunications 2000 (IMT-2000). The WARC’92 identified 1885–2025 and 2110–2200 MHz as the frequency bands for the IMT-2000 [7]. The goal of the 3G standards is to provide users with worldwide coverage via handsets that the capability to seamlessly roam among multiple cellular networks. ITU has recommended several different air interfaces for third-generation systems, based on either CDMA or TDMA technology. The specifications for IMT-200 standards are developed by the Third Generation Partnership Project (3GPP) and 3GPP2 [5]. Amongst the most important 3G concerns for operators are backward compatibility and protection of existing investments. Compatibility with 2G systems is also one of the main goals of 3G system. Thus, an evolution rather than a revolution to 3G from 2G would succeed in this scenario. Finally, third-generation (3G) wireless systems, based on CDMA technologies, are being developed and deployed, with data and voice communications in tight integration. It is now projected that wireless data traffic will actually surpass that of voice traffic. Moreover, the cost of wireless data devices is now low enough to allow wide penetration in the home and office markets. Today in every sphere of life (vertically and horizontally), from ‘ways of transition the way it has always been done’ to more flexible, seamless and effective way of communicating and managing data must be explored. This will facilitate new and competitive services, delivered to new broader markets, beyond the boundaries of the existing communities. This will lead to new revenue streams and higher profit margins. Existing business processes and workflows will be automated and optimized, which will lead to cost control and increased use of assets and resources, and consequently increased revenues. Wireless Innovative System for Dynamic Operating Mega-communications (WISDOM) adopts the thesis that the digital evolution and successful businesses can be made financially viable, only if the complexity of rapidly increasing costs against rapidly declining real payments is balanced against the backdrop of a complex technological uptake that will leave certain players obsolete, Fig. 1.2. Wireless data rates have recently been increasing starting from Mbps to Gbps and possibly moving onto Tbps [8]. A concept which has gained high popularity for the future of the telecommunications sector in the recent years is that of convergence. Convergence can be defined as the coming together of voice, facsimile, data, video, and image applications, systems, and networks, both wire line and wireless and several others. It is a fundamental change in the relationship between content producers and content consumers with economic, social and political implications. Converging Technologies are changing the way we live, work and play. Information and knowledge is readily accessible in rich media formats from a very early age. The boundaries between what is real and virtual are blurring. Convergence is really what future generation is all about and is illustrated in Fig. 1.3. WISDOM proposes to combine two innovative concepts to achieve global dynamic

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Fig. 1.2 Dynamic mega-communications to assist the digital world evolution (the C3W approach of WISDOM)

Networks:

Convergence

Applications: Speech, Data, Graphics, Video, Multimedia

Wired, Wireless, Broadcast

Technology: Computers, Communications, Consumer electronics

Fig. 1.3 Convergence of networks, applications and technology

mega-communications in the convergence/personalization Era, namely, cognitive technology and personal networks. The combination of these two concepts by WISDOM offers a dynamic communication system that breaks down the barriers between communications modes, in a comprehensive and cost-effective manner. The offered benefits include the following aspects: l

l

l

l

Consolidation and cost reduction with a secure and easily managed converged network infrastructure Knowledge sharing and improved user safety through intelligent rich presence and collaboration Accessibility of users and knowledge by integrating WISDOM-based services into workflow and applications, regardless of the device Protection of existing investments with a migration path from traditional to WISDOM-based services

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Networks

Components

Convergence Terrestrial, Stratospheric, Space Wired, Wireless, Broadcast

Technology Applications Services

Computers, Communications, Consumer electronics

Speech, Data, Graphics, Video, Multimedia

Navigation and Communications, Earth Observation and Communications

Fig. 1.4 Important elements of convergence

l

The freedom for users to work from home, office or other location using highspeed internet connections

Gilder’s Law predicts a sixfold increase of the available Bit Rate every 1.5 years. It will take approximately 6 years to achieve the 1 Tbps (Megacommunications). Other two important elements of convergence in the future will be services and components as shown in Fig. 1.4. Various examples for 1 Tb/s wireless aggregation are given as follows: l

l

l

Indoor/Outdoor/In Car (M2M): Assuming an average of 1,000 sensors per person, and a sampling rate of 1 kbps/sensor for environmental monitoring purposes, in the case of country of population 1 M, we have an aggregate network capacity of 1 Tbps (1,000 sensors per person  1 kbps  population 1 M = 1 Tbps). Human Centric: “your own pocket Internet” on a burst, with very fast downloads from hotspots, for example, a movie about 10 GB, transmitted in less than 1 s when you pass with your “multimedia cell” over a portal. The whole network becomes a fast burst environment, thanks to the high speed short range portals widely available (a movie of about 10 GB in 1 s  100 users = 1 Tbps). Outdoor micro/macro cellular: At the WMAN scale, the vision of Tbps wireless corresponds to aggregate capacity of all users served in a metropolitan area. For instance 400 radio cells in a metropolitan city, each cell serving 10 users, using 250 Mbps each for virtual reality applications (400 radio cells  10 user/cell  250 Mbps = 1 Tbps).

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National and International zones

Microcells: City-centers Highways

Global Information Village Macrocells: Suburban Regional National

Personal Area Network (PAN)

Picocells: In-house

Megacommunications (1 Tb/s)

Fig. 1.5 Global Information Multimedia Communication Village (GIMCV)

l

Regional Continental Scales: The regional/continental scenario covers the need for global and reliable connectivity anywhere and anytime, such as on trains, airplanes, ships, remote areas and dense urban areas, as well as during emergency and disaster scenarios. For instance, delivering via satellite, high-quality video at a rate of 250 Mbps, to an average of 40 people on-board a plane, to a fleet of 100 planes calls for an aggregate traffic of 1 Tbps at the system level (40 people  100 planes  250 Mbps = 1 Tbps).

So finally, in the future one can expect to see a global information multimedia communication village (GIMCV) as shown in Fig. 1.5. The various applications of such GIMCV networks are summarized in Fig. 1.6. The evolution of GIMCV can be understood from the family tree of wireless communications shown in Fig. 1.1. In Fig. 1.1, IMT-A is defined as the integration of existing systems to interwork with each other and with a new interface. It envisions new radio interfaces which are as follows: mobile class targets 100 Mbps with high mobility and nomadic/local area class targets 1 Gbps with low mobility (Licensed or maybe licensed-exempt). 4G ¼ IMT-A þ Pers

(1.1)

Pers stands for Personalisation and this topic has been investigated in My Personal Adaptive Global NET (MAGNET) & MAGNET-Beyond project. The emerging 4G technologies and the proposed Wireless Innovative System for Dynamic Operating Megacommunications (WISDOM) concept (explained in next

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EDUCATION

COMMUNITY

GIMCV networks EMERGENCY CARE

HEALTH

ITS SERVICES

HOME AND OFFICE

Fig. 1.6 Applications for GIMCV networks

section) will lead the wireless communication towards the realization of true 5G systems. 5G ¼ 4G þ WISDOM

1.3 1.3.1

(1.2)

Broadband Access The Path Towards Wireless Broadband Access

Since the beginning of 1990s, the development of innovative Wireless communication systems has marked the start of the new Era. The transition from fixed to Wireless really started during the Internet revolution. The Internet world evolved as an exchange mechanism for electronic data, but soon sparked worldwide demand for anytime/anywhere computing and communications. Today the role of broadband is changed from a limiting user wired experience to an anytime, anywhere, anyway personal experience for use at home, office, or away. In an Era when both Wireless and broadband have achieved mass market adoption, Wireless broadband technologies provide ubiquitous broadband access to users, enabling services that were previously only available to wireline users. This wireless revolution is occurring mainly at the last mile, the final point at which connectivity is delivered from a service provider to a customer. This includes end user access, for example, via Wireless Local Loop (WLL), but also Broadband Wireless Access (BWA). BWA features several techno-economic advantages over wireline solution. It provides a cost effective solution along with straightforward

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2010 2000 Cellular 1G (Analog)

2G (Digital)

r

ula

hic

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AMPS ETACS NTT

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(System

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W-CDMA/HSDPA CDMA2000 EV-DO/DV

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.16e 802 ile Mob

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Bluetooth 802.15.1

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ZigBee 802.15.4

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Data Rate Spectral Efficiency Radio access Tecnologies

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TDMA QPSK

TDMA QPSK

Adaptive QAM

OFDM/QAM Adaptive coding

1G

b/s

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b/s/Hz

MIMO Adaptive array

Fig. 1.7 Evolution of wireless towards wireless broadband systems [1, 4, 6, 7]

scalability and extensibility to support growth and expansion of the user base. These systems will not only provide wireless high speed data but also an alternative wireless backhaul solution for existing cellular systems. WLL provides a non-wired loop for customer access. It has already established itself as the primary alternative to the twisted pair copper wire (local loop) in providing central office connectivity to homes and small offices. The successful deployment of WLL in rural and congested metropolitan area is enticing BWA to address both point-to-point (PtP) and point-to-multipoint (PtM) metropolitan coverage. As depicted in Fig. 1.7, Wi-Fi, WiMAX, 3G and Ultra-Wideband (UWB) technologies are essential to form the global wireless infrastructure needed to deliver high-speed communications and Internet access. While Wi-Fi is ideal for isolated connectivity “islands”, WiMAX and 3G are needed for long distance wireless connectivity. Meanwhile, WiMAX and 3G are both required because their optimum platforms differ: WiMAX is conceived for computing platforms, such as laptops, while 3G envisages mobile devices, like PDAs and cell phones. In turn, UWB offers very short range connectivity, perfect for the home entertainment environment or wireless USB.

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In short, each technology envisages a different niche of the Wireless market and supports different types of mobility, being important for different reasons. Mobile WiMAX is a step towards the evolution of WiMAX. Mobile WiMAX was the first mobile broadband wireless-access solution based on the IEEE 802.16e2005 standard [1] that enabled convergence of mobile and fixed broadband networks through a common wide-area radio-access technology and flexible network architecture. The mobile WiMAX air interface utilizes OFDMA as the preferred multiple-access method in the downlink (DL) and uplink (UL) for improved multipath performance and bandwidth scalability. Since January 2007, the IEEE 802.16 Working Group has embarked on the development of a new amendment of the IEEE 802.16 standard (i.e., IEEE 802.16m) as an advanced air interface to meet the requirements of the International Telecommunication Union — Radiocommunication/International Mobile Telecommunications (ITU-R/IMT)-advanced for fourth-generation (4G)systems, as well as the next-generation mobile network operators [9]. Depending on the available bandwidth and multi-antenna mode, the nextgeneration mobile WiMAX will be capable of over-the-air data-transfer rates in excess of 1 Gb/s and support a wide range of high-quality and high-capacity IPbased services and applications while maintaining full backward compatibility with the existing mobile WiMAX systems to preserve investments and continuing to support first-generation products. There are distinctive features and advantages such as flexibility and the extensibility of its physical and medium access layer protocols that make mobile WiMAX and its evolution more attractive and more suitable for the realization of ubiquitous mobile Internet access. The next-generation mobile WiMAX will build on the success of the existing WiMAX technology and its time-to-market advantage over other mobile broadband wireless access technologies. In fact, all OFDM-based, mobile broadband access technologies that have been developed lately exploit, enhance, and expand fundamental concepts that were originally used in mobile WiMAX. The IEEE 802.16m will be suitable for both green-field and mixed deployments with legacy mobile stations (MSs) and base stations (BSs). The backward compatibility feature will allow smooth upgrades and an evolution path for the existing deployments. It will enable roaming and seamless connectivity across IMTadvanced and IMT-2000 systems through the use of appropriate interworking functions. In addition, the IEEE 802.16m system utilizes multi-hop relay architectures for improved coverage and performance.

1.3.2

Types of Broadband Services

There are various transmission media or technologies that can be used to provide fixed broadband access. These include cable modem, digital subscriber line (DSL, an enhanced telephone service), satellite technology and terrestrial wireless technologies for providing wireless access. Among all these cable and DSL are the

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currently the most widely used Broadband services are provided by using a variety of different technologies, network architectures, and transmission paths. Broadband includes therefore several high-speed transmission technologies as the following ones: l l l l l l

Digital Subscriber Line (DSL) Cable Modem Fiber Wireless Satellite Broadband over Powerlines (BPL)

The Organisation for Economic Co-operation and Development (OECD) recently opened a new broadband data portal containing a wealth of information on broadband statistics among OECD member countries, Fig. 1.8, including graphs that track broadband prices, speeds, and technologies as well as overall penetration. The number of broadband subscribers in the OECD reached 267 million in December 2008, or the equivalent of 22.6 subscribers per 100 inhabitants that is 13% during 2008, Fig. 1.9. The broadband growth during the last 6 months of the year was slightly stronger at 6.23% than in the first 6 months at 6.16% showing no slow down due to economic crisis. It is worthwhile to highlight the following facts: l

l

Denmark, the Netherlands, Switzerland, Korea and Norway and Iceland lead the OECD in broadband penetration, each with over 30 subscribers per 100 inhabitants. The strongest per-capita subscriber growth over the year was in Slovak Republic, Greece, New Zealand and Norway, Germany, France and the United States. Each country added more than three subscribers per 100 inhabitants during the past year. OECD Broadband subscriptions, by technology, December 2008 Cable Modem 29%

DSL 59%

Fibre + LAN 10% Total subscribers: 266 million Source : OECD

Fig. 1.8 OECD broadband subscriptions

Other 2%

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15 Broadband penetration (subscribers per 100 inhabitants, Dec 2008)

35 30 25 20 15 10 5 0

Fig. 1.9 Broadband penetration

l

l

Operators in several countries continue upgrading subscriber lines to fibre. Fibre-to-the-home (FTTH) and Fibre-to-the-building (FTTB) subscriptions now comprise 10% of all broadband connections in the OECD (up from 9% in June 2008). Fibre is the dominant connection technology in Korea and Japan and now accounts for 48% of all Japanese broadband subscriptions and 43% in Korea. Korea has the highest fibre penetration rate at 13.8 fibre subscribers per 100 inhabitants. The United States (US) is the largest broadband market in the OECD with 80 million subscribers. US broadband subscribers represent 30% of all broadband connections in the OECD.

1.3.3

DSL Technology

DSL is an entire family of technologies, all of which provide digital transmission over the copper wires used in the local loop, or last mile. The xDSL technologies offer many home users their first taste of broadband, and most users find that once they have tried broadband, they will never go back. It is exciting how much broadband can improve performance; despite the fact that today’s broadband is not as fast as the data rates we will see in the coming years. As discussed in detail in the following sections, the xDSL family of standards includes a large variety of speeds and distance specifications: l l

High-Bit-Rate Digital Subscriber Line (HDSL) Symmetrical (or Single-Line) Digital Subscriber Line (SDSL)

Speeds for DSL can depend on the condition of the telephone wire and the distance between the home and the telephone company’s central office. Because ADSL uses frequencies much higher than those used for voice communication,

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both voice and data can be sent over the same telephone line. Thus, customers can talk on their telephone while they are online, and voice service will continue even if the ADSL service goes down. ADSL line is an “always on” connection with no dialup required. Unlike cable, however, ADSL has the advantage of being unshared between the customer and the central office. Thus, data transmission speeds will not necessarily decrease during periods of heavy local Internet use. The disadvantage relative to cable is that ADSL deployment is constrained by the distance between the subscriber and the central switching centre.

1.3.3.1

Cable Modem Service

The same cable network that currently provides television service to consumers is being modified to provide broadband access. The cable modems use the existing cable TV networks and coaxial cable to give subscribers higher Internet speeds. However as a means of providing broadband Internet cable have several shortcomings. As cable networks are shared by users, access speeds can decrease during peak usage hours, when bandwidth is being shared by many simultaneous customers. Network sharing has also led to security concerns and fears that hackers might be able to eavesdrop on a neighbour’s Internet connection. The cable industry is developing “next generation” technology which will significantly extend downloading and uploading speeds.

1.3.3.2

Fiber

Another broadband technology is optical fiber to the home (FTTH). Fiber optic technology converts electrical signals carrying data to light and sends the light through transparent glass fibers about the diameter of a human hair. Optical fiber cable is used by businesses as high speed links for long distance voice and data traffic. It has tremendous data capacity, with transmission speeds dramatically higher than what is offered by cable modem or DSL broadband technology. While the high cost of installing optical fiber in or near users’ homes has been a major barrier to the deployment of FTTH, both Verizon and AT&T (formerly SBC) are rolling out fiberbased architectures that will offer consumers voice, video, and high-speed data (sometimes referred to as a “triple play”). Some public utilities are also exploring or beginning to offer broadband access via fiber inside their existing conduits. Networks that depend on a fiber-optic cable backbone are capital-intensive and usually more profitable in high-density urban areas. A number of rural communities have used their resources to install fiber-optic broadband services in part because they were too small a market to interest for-profit companies. Increasingly, communities are looking at wireless technologies to support their networks.

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1.4 1.4.1

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Evolution of Wireless Broadband Narrowband Wireless Local Loop

The primary need for the development and deployment of Wireless Broadband was voice telephony. In developed countries like India, China, Indonesia, Brazil, and Russia, where there was lack of basic infrastructure WLL served basic need for telephone services [5]. Nevertheless, in the developed markets, where voice telephony infrastructure already existed, WLL led to the advent of new consumer telecommunications services such as video conferencing and increased usage of existing services such as email and web access. After the commercialization of the Internet in 1993, the demand for Internet-access service began to surge, as many provided high speed Internet access as a way for wireless systems to differentiate themselves. In 1997, AT&T announced that it had developed a wireless access system for 1,900 MHz personal communications service (PCS) band that could deliver a wireless phone service similar to cellular telephone service but emphasizing personal service and extended mobility. It is sometimes referred to as digital cellular (although cellular systems can also be digital). Like cellular, PCS is for mobile users and requires a number of antennas to blanket an area of coverage. In the mean time many start-up companies also started focusing on Internet access services using wireless These wireless Internet service providers (WISP) companies deployed systems in the license exempt bands, typically 900 MHz and 2.4 GHz [10].

1.4.2

First Generation Broadband Wireless Systems

Wireless systems started to be evolved to support much higher speeds as Digital Subscriber Line (DSL) and cable modems began to be deployed. Proprietary technologies like Local Multipoint Distribution System (LMDS) began to be developed for higher frequencies such as 2.5 and 3.5 GHz. LMDS is a broadband wireless PtM communication system that can be used to provide digital two-way voice, data, Internet, and video services. It is a microwave system that provides two-way transmission in the 28 GHz range. It became known as “wireless cable” for its potential to enable competition with the cable television companies for broadband video to the home. Due to the very high frequency range in which it operates, it has very severe line of sight requirements and needs a transmitter every couple of miles. LMDS has a range of up to only 5 km and is only really suitable for urban settings [11, 12]. In late 1990s, some telephony companies started deployments of wireless broadband in the Multichannel Multipoint Distribution Services (MMDS) band at 2.5 GHz. These services, called MMDS, target data rates of several Mbps. In 1998, FCC allocated frequency bands for these services. This band was historically used

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to provide cable broadcast video services, especially in rural areas where cable TV services were not available. But after the introduction of satellite TV the wireless cable business was ruined and the band was set free. MMDS is a microwave system that provides 33 analogue channels and from five to ten times as many digital channels. Operating in the 2.5 GHz range, it requires line of sight between the transmitter and receiving antenna. Digital signals let MMDS support more channels and also deal better with the topography. Signals can be beamed to a high building, which can serve as one or more cell sites transmitting in various directions. MMDS systems were only available in a specific frequency band and available through licenses from the regulatory agency. This method limited the number of operators in a given geography to only one. The success of BWA in that market became dependent on the success of that one operator. Today, there is a large swath of unused spectrum as a result of those operators not succeeding with their MMDS deployments. In the last 3 years, the use of license-exempt spectrum has been an attractive way for a competitive BWA market to emerge. Operators can enter a market quickly and with minimal expense to provide either the first broadband connection or a competitive service to wired offerings. First generation networks were designed by applying cable modem technology to create a wireless solution. These networks have substantial performance limitations due to the following to issues: l

l

First generation systems do not respond well to rain fades, obstructions, or nonline-of-sight (NLoS) conditions. They require very tall base station antennas and line-of-sight (LoS) access to all of the customer-premise equipment (CPE). They suffered poor response to link impairments. Also these systems had poor response to co-channel interference.

These distinctive issues put restrictions on their deployment on the First Generation Broadband Wireless Systems.

1.4.3

Second Generation Broadband Wireless Systems

The LoS issue was resolved in second generation broadband systems and were able to provide more capacity. The companies tried to develop advanced proprietary solutions to overcome the short comings of the first generation broadband wireless systems. This was done by the use of a cellular architecture and implementation of advanced –signal processing techniques to improve the link and performance systems. The use of Orthogonal frequency division multiplexing (OFDM), code division multiple access (CDMA), and multi antenna processing solved the problem of NLoS. The second generation fixed wireless systems offered a few megabits per second throughput over cell ranges of few miles. Proprietary systems developed by Navini Networks and Soma Networks offered adequate link performance over a few miles without the need of antenna mounted outside. Thus, Second Generation

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Broadband Wireless Systems were able to overcome the LoS issue and to provide more capacity.

1.4.4

Emergence of Global Standard Based Wireless Broadband

LMDS and MMDS failed to be considered as viable means of providing wireless broadband access because of combination of factors like lack of economies in silicon, expensive equipment, poor deployments, weather conditions, and ultimately, over-hyping and under-delivering on performance. There was a growing need of a global standard based broadband access technology that can provide high speed packet data services for IP applications, support portability as well as mobility, give nationwide coverage (including rural areas), voice support at high speeds, and provide moderate data rates. To address these needs for next generation broadband wireless Access Systems, IEEE formed The Work Group 16 in 1998 [13, 14].This group called 802.16 developed a wireless metropolitan area network or Wireless MAN .The standard was completed and approved in December 2001, Table 1.5.

Table 1.5 Important dates in the development of broadband wireless [5] Date Event Feb 1997 AT&T announces development of fixed wireless technology code named “Project Angel”. Feb 1997 FCC auctions 30 MHz spectrum in 2.3 GHz band for wireless communications services (WCS). Sept 1997 American Telecasting (acquired later by Sprint) announces wireless Internet access services in the MMDS band offering 750 kbps downstream with telephone dial-up modem upstream. Sept 1998 FCC relaxes rules for MMDS band to allow two-way communications. Apr 1999 MCI and Sprint acquire several wireless cable operators to get access to MMDS spectrum. July 1999 First working group meeting of IEEE 802.16 group. Mar 2000 AT&T launches first commercial high-speed fixed wireless service after years of trial. May 2000 Sprint launches first MMDS deployment in Phoenix, Arizona, using firstgeneration LOS technology. June 2001 WiMAX Forum established. Oct 2001 Sprint halts MMDS deployments. Dec 2001 AT&T discontinues fixed wireless services. Dec 2001 IEEE 802.16 standards completed for > 11 GHz. Feb 2002 Korea allocates spectrum at 2.3 GHz for wireless broadband (WiBro). Jan 2003 IEEE 802.16a standard completed. June 2004 IEEE 802.16-2004 standard completed and approved. Sept 2004 Intel begins shipping the first WiMAX chipset, called Rosedale. Dec 2005 IEEE 802.16e standard completed and approved. Jan 2006 First WiMAX Forum–certified product announced for fixed applications. June 2006 WiBro commercial services launched in Korea.

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1.5

Fixed Wireless Access

Three options are popular today for design of wireless networks – Point-to-Point (PtP), Point-to-Multipoint (PtM), and Mesh topologies. The types of fixed wireless network topologies can be categorized into four types: l l l l

PtP networks PtM networks NLoS PtM networks Mesh networks

1.5.1

Point-to-Point Networks

As the name implies, a point-to-point wireless network is a direct link between two distinct locations. In the diagram, PtP connections are represented by the red lines. These connections are commonly used in cellular backhaul (from the Base Station, BTS, site towards the network operations centre) and for building-to-building extensions of IP and circuit-switched services (i.e. analogue PBX). Fiber optics and leased copper connections are examples of “wired” PtP networks. PtP networks consist of one or more fixed PtP links, usually employing highly directional transmitting and receiving antennas, as illustrated in Fig. 1.10. Networks of such links connected end to end can span great distances. Links connected end to end are often referred to as tandem systems, and the analysis for the end-to-end reliability or availability of the whole network must be calculated separately from the availability of individual links [15].

Line of Sight (LOS) Non Line of Sight (NLOS)

Not optimal some loss of signal

Base Station

Fig. 1.10 PtP network connecting two cities through mountaintop repeaters

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1.5.2

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Point-to-Multipoint Networks

PtM networks used a ‘hub and spoke’ approach to deliver data services as illustrated in Fig. 1.11. The hub is analogous to the base station in a cellular system. It consists of one or more broad-beam antennas that are designed to radiate toward multiple end-user terminals. Depending on the frequency band employed, and the data rates to be provided to end users, normally several hubs are needed to achieve ubiquitous service to a city. The remote end-user terminals are engineered installations in which directional antennas have been installed in locations that are in the LoS to the hub and oriented by a technician to point at the hub location. In some cases this may require extensive work at each terminal location. PtM network architecture is by far the most popular approach to fixed broadband wireless construction. It mimics the network topology successfully used for decades in wired telephone networks, cable television networks, and even electrical, gas, and water utilities of all sorts. For wireless, the major drawback is the cost of the infrastructure to construct the hubs needed to achieve comprehensive LoS visibility to a large percentage of the service.

Subscriber Station (SS)

Fig. 1.11 PtM network

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NLoS Point-to-Multipoint Networks

NLoS PtM networks are identical in topology to the PtM networks described above. The difference lies in the nature of the remote terminals. Instead of the remote terminals being engineered and professionally installed to achieve successful performance using an outside antenna, the terminals are arbitrarily positioned at the convenience of the end user inside a house or office. In most cases, the location of these terminals will be places that do not have a clear, obstruction-free view of a network hub and are thus called NLoS. The signal attenuation and amplitude variability that occurs along the wireless signal path from the network hub to NLoS location present new challenges to system designers in their efforts to provide a reliable high-speed data service to every terminal.

1.5.4

Mesh Networks

Mesh networks are a relatively new, evolving type of wireless broadband technology that may enable more flexible and more efficient expansion of wireless broadband services, Fig. 1.12. In the mesh topology each node has redundant connections to other nodes in the network, as shown in the figure. Unlike traditional Wireless Metropolitan area Networks (WMANs) or Wireless Local Area networks (WLANs), in which each “node” (or consumer device) in the network communicates only with a central antenna or base station, in a mesh network, each node

Fig. 1.12 Mesh networks

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can function as an access point and transmit information to other nodes in close proximity. If one node goes out of service, the other nodes will route the traffic around it, making mesh networks a relatively robust communications technology. One of the key aspects of a mesh network is the routing functionality of its nodes which allows them to take the best route in communication with other nodes or networks. When a backhaul-based network is deployed in mesh mode, it does not only increase the wireless coverage, but it also provides features such as lower backhaul deployment cost, rapid deployment, and reconfigurability. Various deployment scenarios include citywide wireless coverage, backhaul for connecting 3G RNC with base stations, and others.

1.6 1.6.1

Broadband Wireless Access Licensed Frequency Bands

International Telecommunications Union (ITU) regulates the use of radio spectrum worldwide, which operates with the participation of all member nations [16]. The spectrum available for the construction of broadband wireless systems can be divided into licensed and license-exempt frequency bands. In general, licensed spectrum provides for some degree of interference protection because each new licensee must demonstrate compliance with certain standards for limiting interference to other existing nearby licensed systems. There are also radiated transmitter power level and other parameter limitations that each licensee must observe. License-exempt bands do not require individual transmitters to be licensed in order to operate, but there are still radiated power restrictions that usually keep power at low levels as a de facto way of limiting interference. There may also be a rudimentary channelization scheme and modulation standard; again, to make possible as many successful operations as possible without destructive interference. Some cooperation and coordination may sometimes be necessary to make the most of these measures. Cordless telephones, remote control toys, and IEEE802.11b/802.11a wireless LAN devices are examples of license-exempt systems. There are a number of frequency bands that have been allocated throughout the world for use by licensed fixed broadband services. Within the general ITU band designations, individual countries may elect to implement or not implement policies that allow those frequencies to be licensed and used within their country boundaries. This is especially true for fixed broadband wireless services. However, Table 1.6 provides a convenient summary for most of the European countries. The frequency bands listed are intended as examples of the variety of services that have access to the microwave spectrum for fixed services. The table include the major bands used for newer PtP and PtM broadband services such as Local Multipoint Distribution Service (LMDS).

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Table 1.6 European licensed fixed wireless bands [16–19] Frequency band Description (GHz) 3.4–3.6 Duplex spacing’s of 50 or 100 MHz are employed. 3.7 GHz is the upper limit of this band is in some countries. 3.8–4.2 High capacity public operator band for PtP link systems. 5.9–7.1 High capacity public operator band for PtP link systems. 7.1–8.5 Medium and high capacity public operator band for long haul PtP systems. 10.15–10.65 5  30-MHz channels with duplex spacing of 350 MHz. 10.7–11.7 High capacity public operator band for PtP link systems. 12.7–13.3 Low and medium capacity public operator band. 14.4–15.4 Fixed link operations of various types. 17.7–19.7 Public operator band for low and medium capacities. 21.2–23.6 Public operator band for PTP link systems of various types. 24.5–26.5 ETSI 26-GHz band. 3.5- to 112-MHz FDD channels with 1008-MHz duplex spacing. 37–39.5 Common carrier band for PtP link systems.

In addition to requirements to obtain a license for systems operating in these bands, each band also has a number of technical criteria that each system must satisfy. In general, these criteria are established to reduce or minimize interference among systems that share the same spectrum, and to ensure that the spectrum efficiency is sufficiently high to justify occupying the spectrum. In a given band, there may be requirements for minimum and maximum radiated power levels, particular efficient modulation types, and even standards for the radiation patterns of directional antennas to reduce interference to other operators in the band. These technical standards can be detailed and complex, and may vary from country to country. Designing and deploying a fixed wireless system in any particular country requires a careful review and functional understanding of the administrative rules that govern the use of the intended licensed spectrum space.

1.6.2

License-Exempt Frequency Bands

There is a growing interest in using the so-called license-exempt bands. One of the primary reasons is that it allows users of the wireless service to purchase offthe-shelf wireless modems for connecting to a system. In the United States, the 11 Mbps IEEE 802.11b standard that specifies Direct Sequence Spread Spectrum (DSSS) technology operating in the 2.4 GHz band is the best current example of self deployed license-exempt technology. However, license-exempt bands offer no regulatory interference protection except that afforded by the interference immunity designed into the technology itself. With relatively modest penetration of these systems to date, the robustness of the design for providing the expected quality of service in the presence of widespread interference and many

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Table 1.7 US license-exempt fixed wireless bands [16–19] Frequency band Service Description (GHz) name 2.4–2.483 ISM Industrial, Scientific and Medical (ISM). This is the band for IEEE 802.11b DSSS networks operation 5.15–5.35 U-NII Unlicensed National Information Infrastructure (U-NII). This band is where IEEE 802.11a OFDM systems operate among several other proprietary standards. Channel bandwidth is 20 MHz. Particular power limits apply for segments of this band, intended for indoor and outdoor applications of are 20 MHz 5.725–5.825 GHz U-NII Same as 5.15–5.35-GHz U-NII band except that this band is intended only for outdoor applications with radiated power levels up to 4 W

Table 1.8 European license-exempt fixed wireless bands [16–19] Frequency band Service name Description (GHz) 2.4–2.483 Wi-Fi Industrial, Scientific and Medical (ISM). This is the same band where IEEE 802.11b DSSS networks operate in the United States 5.15–5.35 HiperLAN HiperLAN is the fast wireless network standard for Europe, which uses an OFDM transmission standard similar to IEEE 802.11a. This band is intended for indoor operations with radiated powers limited to 200 mW 5.470–5.725 GHz HiperLAN/2 Proposed frequency band for outdoor operation with radiated power levels limited to 1 W

contending users has yet to be fully tested. As the number of people using licenseexempt equipment increases in a given area, the ultimate viability of having a multitude of people using a limited set of frequencies will be tested. Table 1.7 shows the license-exempt bands currently used in the US for fixed broadband communications. The license-exempt spectrum has been designated in Europe, though the uptake of the technology has been slower than in the United States. As discussed in the next section, several long-running standard-setting efforts designed for this purpose did not bear fruit in a timely fashion, resulting in many of these efforts being suspended or abandoned in favour to US standards already in place. Table 1.8 shows the license-exempt bands currently available for use in Europe.

1.7

Background on IEEE 802.16 and WIMAX

The 802.16 activities were initiated in August 1998 in a meeting called by the National Wireless Electronics Systems Testbed (N-WEST) of the U.S [20] National Institute of Standards and Technology. The effort was welcomed in IEEE 802,

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which opened a Study Group. The 802.16 Working Group has held weeklong meetings at least bimonthly since July 1999.

1.7.1

IEEE 802.16 Evolution

The IEEE 802.16 group was formed in 1998 to develop an air-interface standard for Broadband Wireless Access (BWA) and to support the development and deployment of wireless metropolitan area networks, Table 1.9. The main task of the Working Group is addressing primarily applications of wireless technology to link commercial and residential buildings to high-rate core networks and thereby provide access to those networks. This link is known popularly as the “last mile”. The evolution of the IEEE 802.16 standard is shown in Table 1.9. The standard has adapted many of the concepts from the popular cable modem Data Over Cable Service Interface Specification (DOCSIS) standard related to the MAC layer. The group released the first standard in December 2001. This standard was designed for 10 GHz–66 GHz fixed frequencies that require LoS conditions as in LMDS.

1.7.2

IEEE 802.16a

The IEEE 802.16 group subsequently produced 802.16a, an amendment to the standard, to include NLOS applications in the 2–11 GHz band instead of LOS 266 GHz. The significant difference between these two frequency bands lies in the ability to support Non-Line-of-Sight (NLOS) operation in the lower frequencies, something that is not possible in higher frequency bands [20, 21]. Consequently, the 802.16a amendment to the standard opened up the opportunity for major changes to the PHY layer specifications specifically to address the needs of the 2–11 GHz bands. This is achieved through the introduction of three new PHY-layer specifications (a new Single Carrier PHY, a 256 point FFT OFDM PHY, and a 2048 point FFT OFDMA PHY); major changes to the PHY layer specification as compared to Table 1.9 The evolution of the IEEE 802.16 standard [20] Date IEEE standard Description Dec 2001 802.16 First Standardisation Using 10–66 GHz spectrum band, only LoS Only Point to Multipoint configuration supported Jan 2003 802.16a Amendment that supports NLoS using 2-11 GHz band Both PtM and mesh configuration supported OFDM(A) are adopted as principal PHY implementations Oct 2003 802.16b QoS Provisioning Oct 2004 802.16-2004 This revised standard replaced previous versions Dec 2005 802.16e Enhancements for mobility support (Mobile WiMAX)

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the upper frequency, as well as significant MAC-layer enhancements. Additions to the MAC layer, such as support for Orthogonal Frequency Division Multiple Access (OFDMA), were also included.

1.7.3

IEEE 802.16-2004

This standard was the first practical standard of the IEEE 802.16 family. It is popularly called as fixed WiMAX, the name of the industrial alliance for its production. IEEE 802.16-2004 air interface standard was published in October 2004. This version replaced all previous versions of the IEEE 802.16 standard including 802.16-2001, 802.16a-2003, 802.16c and 802.16-REVd, Table 1.10. It integrated all the previous standards and re-edited PHY and MAC layer contents to improve the system performance. Although IEEE 802.16-2004 specifies a standard for fixed access, the actual applications supports nomadicity. Nomadicity means that user devices can move as long as they do not operate while doing so. The standard is specified to allow nomadicity, where users can access the service from various locations covered by the network. The complete edition of IEEE 802.16-2004 was approved in December 2004. The types of PHY layers and the respective frequency bands in which they are operating are shown in Table 1.10.

1.7.4

IEEE 802.16e

In December 2005, the IEEE group completed and approved IEEE 802.16e-2005, an amendment to the IEEE 802.16-2004 standard that added mobility support. The IEEE 802.16e-2005 forms the basis for the WiMAX solution for nomadic and mobile applications and is often referred to as mobile WiMAX [23]. Mobility has become the necessity of time and will create a new market for mobile broadband services. With the introduction of 802.16e standard seamless handover and roaming are possible when users move from one cell site area to another. It adds 128, 512 Table 1.10 IEEE 802.16-2004 nomenclature [20, 22] Frequency spectrum Physical layer type 10–66 GHz WirelessMAN-SC <11 GHz(licensed band) WirelessMAN-SCa <11 GHz(licensed band) WirelessMAN-OFDM <11 GHz(licensed band) WirelessMAN-OFDMA <11 GHz(unlicensed band) WirelessHUMAN(high speed unlicensed MAN

Duplexing mode TDD, FDD TDD, FDD TDD, FDD TDD, FDD TDD

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and 1024 OFDMA in addition to 2048 FFT modes to facilitate a scalable OFDMA (S-OFDMA) [20, 24, 25]. WiMAX is an exciting new technology that delivers carrier class, high-speed, wireless broadband at a much lower cost than cellular and over a much greater range than Wi-Fi. WiMAX will not only deliver significant improvements in speed, throughput and capacity to home and small business users, but will also enable portable and mobile services to laptops and handheld devices. The appeal of WiMAX systems lies in the fact that they can be applied to a host of applications offered by a range of different providers, including cellular operators, wireline carriers, cable operators and new entrants. WiMAX is widely supported by an ecosystem of infrastructure and device vendors and has been endorsed by network operators from around the globe. WiMAX delivers non-line-of-site (NLoS) coverage using outdoor transmitters mounted on towers or rooftops to deliver multimegabit service in both urban and rural environments. For practical reasons related to interoperability, the scope of the standard needs to be reduced, and a smaller set of design and implementation choices need to be defined. The WiMAX Forum defines a limited number of system profiles and certification profiles [26]. A system profile defines the subset of mandatory and optional physical- and MAC-layer features selected by the WiMAX Forum from the IEEE 802.16-2004 or IEEE 802.16e-2005 standard. Currently, the WiMAX Forum has two different system profiles: one based on IEEE 802.16-2004, OFDM PHY, called the fixed system profile; the other one based on IEEE 802.16e-2005 scalable OFDMA PHY, called the mobility system profile. A certification profile is defined as a particular instantiation of a system profile where the operating frequency, channel bandwidth, and duplexing mode are also specified. WiMAX equipment are certified for interoperability against a particular certification profile. IEEE 802.16 is a collection of standards, not one single interoperable standard. These standards were developed to suit a variety of applications and deployment scenarios, and hence offer a plethora of design choices for system developers. The basic characteristics of the various IEEE 802.16 standards are summarized in Table 1.11. The 802.16 standards offer a variety of fundamentally different design options. For example, there are multiple physical-layer choices: a single-carrier-based physical layer called Wireless- MAN-SCa, an OFDM-based physical layer called WirelessMAN-OFDM, and an OFDMA based physical layer called Wireless-OFDMA. Similarly, there are multiple choices for MAC architecture, duplexing, frequency band for operation, etc. Meanwhile, there have been several amendments to the IEEE 802.16e standard. The amendments are the following: l l l l l

802.16e-2005 — Mobile 802.16 802.16f-2005 — Management Information Base (Fixed MIB) 802.16g-2007 — Management Plane Procedures and Services 802.16k-2007 — Bridging of 802.16 (an amendment to 802.1D) 802.16h — Improved Coexistence Mechanisms for License-Exempt Operation

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Table 1.11 Salient features of IEEE 802.16 standards family [20–23, 27] Features 802.16 802.16-2004 802.16e-2005 Frequency band 10–66 GHz 2–11 GHz for fixed 2–11 GHz for fixed 2–6 GHz for mobile applications Point-to-multipoint Point-to-multipoint mesh MAC architecture Point-tomesh multipoint mesh Transmission Single carrier Single carrier, Single carrier, 256 OFDM scheme only 256’OFDM or 2,048 or scalable OFDM with OFDM 128, 512, 1,024, or 2,048 Subcarriers Modulation QPSK, 16 QAM, QPSK, 16 QAM, 64 QPSK, 16 QAM, 64 QAM 64 QAM QAM Multiplexing Burst TDM/ Burst TDM/TDMA/ Burst TDM/TDMA/ TDMA OFDMA OFDMA Duplexing TDD and FDD TDD and FDD TDD and FDD Channel bandwidths 20, 25, 28 MHz 1.75, 3.5, 7, 14, 1.25, 5, 1.75, 3.5, 7, 14, 1.25, 5, 10, 15, 8.75 MHz 10, 15, 8.75 MHz Gross data rate 32–134.4 Mbps 1–75 Mbps 1–75 Mbps Air-interface WirelessMANWirelessMAN-SCa WirelessMAN-SCa designation SC WirelessMAN-OFDM WirelessMAN-OFDM WirelessMAN-OFDMA WirelessMAN-OFDMA Application Fixed LOS Fixed NLoS Fixed and Mobile NLoS Time of completion December 2001 June 2004 December 2005

Table 1.12 IEEE 802.16m requirements [29]

l l l

Item Operating bandwidth Duplex Normalised peak data rate User throughput Mobility

Requirements Scalable bandwidth between 5–20 MHz Full duplex FDD, half duplex FDD, TDD Downlink: > 8.0 bps/Hz, uplink: > 2.8 bps/Hz Downlink: > 2*802.16e, uplink: > 2*802.16e Up to 350 km/h

802.16i — Mobile Management Information Base (Mobile MIB) 802.16j — Multihop Relay Specification 802.16Rev2 — Consolidate 802.16-2004, 802.16e, 802.16f, 802.16g and possibly 802.16i into a new document

There will also be a future development towards the air interface, the IEEE 802.16m. The data rates will be 100 Mbps for mobile applications and 1 Gbps for fixed applications, cellular, macro and micro cell coverage. Nowadays, there is no restrictions on the RF bandwidth (which is expected to be 20 MHz or higher) [28]. Table 1.12 shows the IEEE 802.16m requirements.

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Fixed and Mobile WIMAX

Mobile WiMAX, referred to by the standard 802.16e, adds mobility to the WiMAX specifications. PC data cards, mobile handsets and laptops with embedded WiMAX chips are being planned by vendors on this standard. In countries where regulation prohibits full mobility for alternative wireless technologies such as WiMAX, operators can also deploy 802.16e networks for fixed and nomadic access. The Telecom industries faith in this new technology is reflected in the decision of leading chip vendors to invest heavily into the manufacturing of miniaturized 802.16e chipsets. Economies of scale are expected to drive price once large scale production starts. A comparison between fixed and mobile WiMAX is shown in Table 1.13 while Fig. 1.13 illustrates the concept. HOW DOES IT WORK? WiMAX uses microwave radio technology to connect computers to the Internet in place of wired connections such as DSL or cable modems, Fig. 1.14. WiMAX works very much like cell phone technology in that reasonable proximity to a base station is required to establish a data link to the Internet. Users within 3–5 miles of the base station will be able to establish a link using NLoS technology with data rates as high as 75 Mbps. Users up to 30 miles away from the base station with an antenna mounted for LoS to the base station will be able to connect at data rates approaching 280 Mbps. IEEE 802.16-based broadband and mobile wireless access is expected to be a significant component in the next-generation wireless systems. The IEEE 802.16 standard, which incorporates several advanced radio transmission technologies such as orthogonal frequency-division multiplexing (OFDM), adaptive modulation and coding (AMC), and adaptive forward error correction (FEC), is designed to

Table 1.13 Fixed and mobile WiMAX comparison [20, 24, 25] Parameter Fixed WiMAX Mobile WiMAX Definition Allows BWA when the user is in the Allows for handover of a call/data session as the user moves range of a WiMAX BS but not between radio towers when the user is roaming. Standard 802.16d 802.16e Release date Q3 2004 December 2005 Frequency 2–66 GHz Licensed bands 2–6 GHz l Allows for line of sight as well l Amendment for mobile wireless Key feature as non-line of sigh deployments broadband up to vehicular l Selectable channel bandwidth speeds l At vehicles, user data rates will be ranging from 1.25 to 20 MHz lower than for pedestrians Application Fixed and Nomadic Access Supports mobile and Nomadic Wireless Access CPE requirement Outdoor directional antenna, indoor PC data cards, laptops and mobile modems handsets with embedded CPE Required WiMAX chips

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Fixed WiMAX

Mobile WiMAX

Embedded WiMAX Laptopts

Wi-Fi

Indoor Modem

Outdoor CPE

WiMAX PC Cards WiMAX Mobile Phone

Fig. 1.13 Fixed and mobile WiMAX

Nomadic Broadband complementary to 3G, EDGE & Wi-Fi

Broadband Access for Enterprise

802.16-e

802.16-2004

Broadband Access for Public hotspots 802.16-2004 004

Broadband Access @ Home complementary to DSL & Cable 802.16-2004

Wi-Fi

Fig. 1.14 WiMAX operation

provide broadband wireless capability using a well defined quality of service (QoS) framework. Therefore, this is a promising technology to provide wireless services requiring high-rate transmission (in the range of tens of megabits per second) and strict QoS requirements in both indoor and outdoor environments.

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Similar to the Wi-Fi Forum for the IEEE 802.11 WLAN standard, the WiMAX (worldwide interoperability for microwave access) Forum, which is a non-profit organization, encourages and supports IEEE 802.16-based broadband wireless access (BWA). The main role of the WiMAX Forum is to standardize and maintain the process of testing and the certification program for compatibility and interoperability of IEEE 802.16 equipment. IEEE 802.16/WiMAX technology intends to provide broadband connectivity to both fixed and mobile users in a wireless metropolitan area network (WMAN) environment. To provide flexibility for different applications, the standard supports two major deployment scenarios: Last-mile BWA: In this scenario, broadband wireless connectivity is provided to home and business users in a WMAN environment. The operation is based on a point-to-multipoint single- hop transmission between a single base station (BS) and multiple subscriber stations (SSs). Backhaul networks: This is a multihop (or mesh) scenario where a WiMAX network works as a backhaul for cellular networks to transport data/voice traffic from the cellular edge to the core network (Internet) through meshing among IEEE 802.16/WiMAX SSs.

1.9

Personal Broadband

Personal broadband expands the availability of a true broadband connection beyond the home and the office, allowing subscribers to have access to the same level of service and the same applications regardless of location. Figure 1.15 presents the evolution of broadband connectivity around the world in residential and commercial settings. 4.5 4 3.5 MidEast/Africa

3

Asia

2.5 2

Europe

1.5

Americas

1 0.5 0 2003

2004

2005

2006

2007

2008

Fig. 1.15 Accelerating demand for broadband connectivity around the world in residential and commercial settings continues to grow (From Intel Capital)

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Fixed WiMAX based on IEEE 802.16-2005

Mobile WiMAX based on IEEE 802.16-2004 Fixed Access Portable Access Mobile Access

Fig. 1.16 Personal broadband requires a wireless interface that supports fixed, portable & mobile access

Depending on the technologies deployed, personal broadband may provide less throughput than its wired broadband last mile technologies, or not be as ubiquitous as cellular networks. Personal broadband, however, brings a precious advantage: convenience. With a single subscription, personal broadband subscribers can get online regardless of location, without having to worry about throughput, service availability, or metered charges at some locations. Personal broadband is located at intersection of the evolution trends in Internet access, from dial-up to always-on broadband to Wi-Fi wireless network, and the shift towards mobility in voice communications, which in the US now account for more minutes than the fixed lines for the average subscriber: subscribers value a flexible service that follows them wherever they go. Some 3G users with flat-fee plans have started to use their subscription as a sort of personal broadband service: they keep their 3G connection active regardless of location and, when they need more bandwidth and they are at home or in the office, they switch to the wired network, Fig. 1.16. In the current 3G networks, this is only possible because there are still very few users using the service and therefore congestion is not a problem. At the current price levels of $60–80 per month and above, this is also clearly a service aimed at a small niche of business users that are relatively price insensitive. Personal broadband is aimed at a wider subscriber base that includes both business and consumer users and therefore needs to rely on technologies that are scalable and costeffective, and provide high throughput. It is still too early to know which applications personal broadband subscribers will use, but one thing is clear: there will be no killer application. Instead, the appeal of personal broadband is to make available all the existing applications everywhere. Web surfing, VoIP, email and VPN connectivity, downloads are likely to be among the most popular applications. Service providers do not need to develop specific applications or content before rolling out the service, as they did for cellular data services, where the throughput limitations have required the development of optimized applications. This removes a big burden from service providers which have been to date not very successful at this task and allows them to focus on their core business.

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R. Prasad and F.J. Velez

WIMAX Forum Difference Between WiMAX Forum and IEEE 802.16

Wireless Interoperability for Microwave Access (WiMAX) is an industrial forum that is responsible for the task of ensuring interoperability and conformance among the systems and solutions developed by various vendors based, on IEEE 802.16 standard for Broadband Wireless Access (BWA). WiMAX Forum is coalition of vendors, service providers, technology providers, and manufacturers, etc. Its union symbolises industry leaders who are committed to promote broadband wireless access based on WiMAX technology. The WiMAX forum is a non profit organization and was formed in July 2001. This forum defines and conducts interoperability tests and awards the equipment manufacturers with the ‘WiMAX Certified’ label [20]. WiMAX Forum and WiMAX Forum Certified are both trademark names of an industry trade organisation. The difference between WiMAX and IEEE 802.16 is that the WiMAX Forum is a non-profit trade association industry group. The mission of IEEE 802.16, ETSI HIPERMAN and the WiBro working groups is to formulate the specifications. In contrast the aim of the WiMAX Forum is to incorporate the variations in the specifications of the three different working groups to ensure interoperability amongst them. This ultimately would benefit the end users who can buy the brand of their choice, with all the features they are interested in and with the full confidence that this would work with all other certified products. The IEEE Working Group 802.16 is responsible for the development of the 802.16 standard including the air interface for Broadband Wireless Access. The activities of this working group were initiated in a meeting in August 1998, called by National Wireless Electronics Systems Testbed (N-WEST) which is a part of U.S. National Institute of Standards and Technology [20]. Initially the group focused on the development of standards and air interface for the 10–66 GHz band. Later an amendment project led to the approval of the IEEE 802.16a standard meant for 2–11 GHz band. The final approval of the 802.16a Air Interface specification came in January 2003 [30]. It comprises of Industry leaders who are committed to promote broadband wireless access based on WiMAX technology.

1.10.2

Members

The WiMAX Forum has more than 522 members [30] comprising the majority of operators, component and equipment companies in the communications ecosystem, Fig. 1.17.

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Content / Ecosystem

Component Suppliers

WiMAX Forum Members

Service Providers

System Vendors

Fig. 1.17 Composition of WiMAX forum members [30]

1.10.3

Working Groups

The WiMAX Forum has organized the Working Groups shown in Table 1.14 to address critical areas of focus in bringing WiMAX Forum Certified products to the marketplace. The WiMAX Forum works closely with service providers and regulators to ensure that WiMAX Forum Certified systems meet customer and government requirements. “WiMAX Forum” is a registered trademark of the WiMAX Forum. “WiMAX”, the WiMAX Forum logo, “WiMAX Forum Certified”, and the WiMAX Forum Certified logo are trademarks of the WiMAX Forum. All other trademarks are the properties of their respective owners [30].

1.10.4

WiMAX Products Certification

WiMAX Forum is the exclusive organization dedicated to certifying the interoperability of products based upon IEEE 802.16/ETSI HiperMAN. It defines and conducts conformance and interoperability testing to ensure that different vendor systems work seamlessly with one another. Those that pass conformance and interoperability testing will receive the “WiMAX Forum Certified™” designation [26, 30]. Today in the market there are many vendors claiming their equipment is “WiMAX-like”, WiMAX-compliant”, etc. These products do not have WiMAX Forum Certified on it, which means that their equipment is not independently

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Table 1.14 Working groups of WiMAX forum Working group name Scope Application Working Define applications over WiMAX that are necessary to meet core Group (AWG) competitive offerings and that are uniquely enhanced by WiMAX Certification Working Handles the operational aspects of the WiMAX Forum Certified Group (CWG) program Evolutionary Technical Maintains existing OFDM profiles, develops additional fixed OFDM profiles, and develops technical specifications for the evolution Working Group of the WiMAX Forum’s OFDM based networks from fixed to (ETWG) nomadic to portable, to mobile Assures the availability of global roaming service for WiMAX Global Roaming networks in a timely manner as demanded by the marketplace Working Group (GRWG) Marketing Working Promotes the WiMAX Forum, its brands and the standards which form Group (MWG) the basis for worldwide interoperability of BWA systems Network Working Creates higher level networking specifications for fixed, nomadic, Group (NWG) portable and mobile WiMAX systems, beyond what is defined in the scope of 802.16 Regulatory Working Influences worldwide regulatory agencies to promote WiMAXGroup (RWG) friendly, globally harmonized spectrum allocations. Gives service providers a platform for influencing BWA product and Service Provider spectrum requirements to ensure that their individual market needs Working Group are fulfilled (SPWG) Technical Working The main goal of the TWG is to develop technical product Group (TWG) specifications and certification test suites for the air interface based on the OFDMA PHY, complementary to the IEEE 802.16 standards, primarily for the purpose of interoperability and certification of Mobile Stations, Subscriber Stations and Base Stations conforming to the IEEE 802.16 standards

certified to be interoperable with other vendors’ equipment. Only WiMAX Forum Certified™ equipment is proven interoperable with other vendors’ equipment. The logo “WiMAX Forum Certified” means users can buy a product or service based on the IEEE 802.16 standard from different companies and be confident that everything will work together. This approach is similar to what 802.11-based Wi-Fi networks used and has proved to be very successful. The IEEE 802.11 standard set the requirements, and the Wi-Fi Alliance ensured product compliance for interoperability. The WiMAX Forum manages the certification process by developing and adopting the relevant specifications, establishing the process and test suites to be used, selecting the testing labs, issuing the certification certificates, and maintaining a registry of WiMAX Forum Certified products. However, it is not directly involved in certification testing; this keeps the program independent and gives vendors the freedom and flexibility to choose their preferred lab. Vendors primarily work with the WFDCL of their choice, which accepts the certification application, conducts the tests, and, if tests are successful, issues a certification certificate. Current certification labs are located in China, Spain, South Korea, Taiwan, and the USA listed in Table. The WiMAX Forum is evaluating additional labs in Brazil, Japan, and India.

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37

Certification Process

The WiMAX Certification label, guarantees both WiMAX/802.16-compliance and equipment interoperability. The certification process is divided into the development of conformance testing and interoperability testing. Development of the certification program is done by the WiMAX Certification Working Group (CWG). Certification testing is intended only for complete systems such as a BS or an SS, not individual solution components such as radio chips or software stacks. The introduction of BS/SS reference designs may also be considered for testing to show that the design conforms to the IEEE 802.16 specification and is interoperable with other WiMAX Forum Certified equipment. Conformance testing is a process where BS and SS manufacture test units to ensure that they perform in accordance with the specifications. Conformance test ensures interoperability with other WiMAX equipment and a positive end-user experience for your customers. WiMAX conformance testing can be done by either the certification lab or another test lab. At the lab, the manufacturers (both BS and SS) test their pre-production or production units to ensure that they perform in accordance with the specifications called out in the WiMAX Protocol Implementation Conformance Specification (PICS) document. Based on these results manufacturers may choose to modify their hardware and/or firmware and formally re-submit these units for conformance testing. WiMAX interoperability involves multi-vendor test process .This is hosted by the certification lab. Interoperability testing to verify that equipment from different vendors works within the same network. At least three vendors have to submit equipment within the same certification profile (defined by spectrum band, channelization and duplexing) to start interoperability testing.

1.10.4.2

Certification Testing

WiMAX Forum conducts Certification testing in independent laboratories. Table 1.15 lists the various certification laboratories termed as WiMAX Forum Designated Certification Laboratories (WMDCLs). The certification methodology is defined by the WiMAX Forum while the testing is conducted at the lab chosen by the vendor. Upon successful completion Table 1.15 WiMAX Forum Designated Certification Laboratories (WMDCLs)

AT4 Wireless (Spain, USA) www.at4wireless.com Bureau Veritas ADT (Taiwan) www.adt.com.tw CCS/TTC (Taiwan) Compliance Certification Services (CCS) www.ttc.org.tw China Academy of Telecommunication Research (China) www.catr.cn Telecommunications Technology Association (South Korea) www.tta.or.kr

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of all tests, vendors receive a WiMAX Forum Certified certificate and a test report, and can list their certified equipment on the WiMAX Forum Certified Product Registry. Certification testing is performed against the backdrop of the following test suites/purposes: l

l

l

Protocol Implementation Conformance Statement (PICS) Proforma — Is a document listing the required, optional and conditionally required features of a device assigned to conform to a standard. This document helps determine whether a device intends to meet all or a subset of the requirements for conformance with the view of helping to direct the test lab as to which tests to perform. Test Suite Structure & Test Purposes (TSS&TP) — All the tests that should be performed for all system options are listed in this document. It is structured in such a way that testing like topics are grouped together. The test “purposes” include the initial condition, stimulus and expected results but not necessarily the detailed steps. In addition to covering the requirements, it should be structured such that answers given by the manufacturer in the PICS Proforma can be mapped to the set of tests that need to be run for a particular device. Abstract Test Suite (ATS) — This consists of the detailed test procedures for the test purposes outlined in the TSS&TP. The ATS is abstract in that it’s usually written in a test language, such as TTCN8, for portability amongst a variety of test labs rather than containing specific detailed instructions for specific models of test equipment.

1.10.4.3

Plugfest

The Plugfest is a preview of full interoperability testing which allows vendors to get an early look at how well their equipment interoperates, Fig. 1.17. The plugfest conducted by WiMAX Forum generally last for 1 week at contracted testing site. Equipment is validated and verified “interoperable” when it is tested to be interoperable with other vendors’ equipment. This is done by demonstrating that their respective hardware is able to send and receive packets with two other vendors involving base stations and subscriber stations for a selected. Before the Plugfest, participating vendors must agree on a set of RF/PHY characteristics within a given certification profile. In all instances, a minimum of three vendors must be available to conduct interoperability testing in a certification profile. Ideally, the WiMAX Forum requires a minimum of five to six vendors to execute the planning of a Plugfest. WiMAX equipment can operate at any frequency below 11 GHz, using channel bandwidths ranging from 1.75 to 10 MHz, and with both TDD and FDD duplexing1. To make interoperability effective and testable, the WiMAX Forum has created system profiles and certification profiles (Fig. 1.18) that define classes of products. The WiMAX system profiles are as follows: l

System profiles are based on versions of the IEEE 802.16 and ETSI HiperMAN standards and define the key mandatory and optional features that are tested in

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Equipment Submission Vendor to: Select certification profile and optimal modules Participate in plugfests and conduct self testing

Conformance Testing Certification Lab to: Test Protocol Compliance Test Radio Compliance

No

Pass

Yes Interoperability Testing Certification Lab to: Test Interoperability with products from other vendors

No

Pass

Yes Certification Issue WiMAX Forum to: Announce certification Issue Certificate Issue test report to vendor

Fig. 1.18 Plugfest algorithm (From WiMAX forum)

l

WiMAX equipment. The list of features tested in system profiles is more stringent than the underlying standards (features that are optional in the standards may be tested as mandatory by the WiMAX Forum Certified program), but does not include any new feature that is not included in the standards. For instance, the Fixed WiMAX profile is based on IEEE 802.16-2004 and only allows testing on equipment using point to multipoint operations up to 11 GHz, while IEEE 802.16-2004 equipment can operate up to 66 GHz, Table 1.16. Similarly, Fixed WiMAX uses OFDM multiplexing with 256 carriers, even though IEEE 802.16-2004 also supports an Orthogonal Frequency Division Multiple Access (OFDMA) mode. Mobile WiMAX is a second system profile, Table 1.17. The WiMAX Forum defines a list of test cases to use during the certification process for all equipment based on the same system profile. Certification profiles define classes of interoperable equipment for the testing process. They are instances of a system profile, defined by three parameters:

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Table 1.16 Fixed WiMAX certification profiles

Profile name ET01 ET02

Spectrum band (GHz) 3.4–3.6 3.4–3.6

Channel Duplexing Status bandwidth (MHz) 3.5 TDD Active 3.5 FDD Active

Table 1.17 Mobile WiMAX certification profiles [26] Profile name Spectrum band (GHz) Channel bandwidth (MHz) MP01 2.3–2.4 8.75 MP02 2.3–2.4 5 and 10 MP05 2.496–2.69 5 and 10 MP09 3.4–3.6 5 MP10 3.4–3.6 7 MP12 3.4–3.6 10 a Projected start date of certification testing, subject to change

l l l

Duplexing TDD TDD TDD TDD TDD TDD

Status Active 2009a Active 4Q2008a 4Q2008a 4Q2008a

Spectrum band (<11 GHz) Channel size (1.75 to 10 MHz) Duplexing (TDD or FDD)

All WiMAX Forum Certified equipment fully interoperates with other equipment in the same certification profile that is tested under the same Release and Wave, and is backward compatible with equipment tested under previous Releases and Waves. Certification profiles limit the number of WiMAX implementations allowed under a system profile to avoid market fragmentation, while meeting the demand from operators. The definition of certification profiles depends on market and vendor demand, which in turn are strictly linked to the availability of spectrum worldwide. As shown in Table 1.16, there are two spectrum bands covered by Fixed WiMAX. More may be added at a later stage through the definition of additional certification profiles. The 3.5 GHz licensed band, widely available around the world with the exception of the US and a few other countries, has certification profiles for both TDD and FDD. The WiMAX Forum Certified products certified so far operate in this band with 3.5 MHz channels for both TDD and FDD. The 5.8 GHz band is the second spectrum band. It is also commonly available worldwide, typically within a license-exempt regime. The 5.8 GHz profile is based on TDD as this is the prevalent duplexing mechanism used in this band and offers better cost performance than FDD. The effective range of interoperability among commercial products, however, will be wider because of multi-mode base stations or subscriber stations that will work at different frequencies or channel bandwidths, or even use a different duplexing mechanism. A multi-mode subscriber station, for instance, will interoperate with any base station that supports any of the certification profiles for which the subscriber station is certified.

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41

WiMAX Forum Certified Program Milestones

The WiMAX Forum was established in 2001 to promote and certify wireless broadband equipment based on the IEEE 802.16 and ETSI HiperMAN standards. As of September 2008, it has attracted 530 member companies from 51 countries, representing the entire value chain – from component suppliers (92 members), to system vendors (132), to service providers (162), to content providers and ecosystem players (144). The WiMAX Forum has established a rigorous program to test equipment for compliance with the standards and for interoperability among vendors that is trusted, flexible, and cost effective, and that meets the requirements of subscribers, operators, and ecosystem vendors. Key milestones of the certification program include: l

l

l

l

October 2004: After the ratification of the IEEE 802.16-2004 version of the standard, work on the certification program started with the creation of specifications and test suites to guide subsequent certification testing January 2006: The WiMAX Forum announced the certification of the first base stations, and indoor and outdoor subscriber devices operating in the 3.5 GHz band based on IEEE 802.16-2004. As of September 2008, there are 16 base stations and 18 subscriber devices certified under the Fixed WiMAX™ certification profiles April 2008: Three base stations and four subscriber devices were announced as the first Mobile WiMAX Forum Certified products operating in the 2.3 GHz band and based on IEEE 802.16e-2005. Products in this certification group meet the South Korean regulatory requirements and are mainly targeted at that market June 2008: The WiMAX Forum announced the first Mobile WiMAX Forum Certified base stations (six) and subscriber devices (four) based on IEEE 802.16e-2005 and operating in the 2.5 GHz. As of September 2008, there are 11 base stations and 17 subscriber devices certified under the Mobile WiMAX certification profiles

By end of 2008, 31 vendors had successfully completed the certification process and 81 products have received the WiMAX Forum certification [26]. Many more have submitted their products for certification, and the WiMAX Forum expects to have certified additional products in 2009.

1.10.6

Certification Roadmap

WiMAX technology is evolving rapidly to meet demand in a growing number of countries and to provide improved performance and support for applications. The WiMAX Forum Certified program will continue to drive the evolution of the technology through an aggressive Mobile WiMAX certification roadmap over the next few years.

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Products are currently certified under Release 1.0, which is based on the IEEE 802.16e-2005 standard. The focus of certification during the initial stages of Release 1.0 is on radio and protocol conformance, and on interoperability testing. Towards the end of 2008, Release 1.0 will include testing for baseline network services, based on the WiMAX Network specifications developed by the NWG. Release 1.5 is expected for 2009. It will be an expansion of Release 1.0 and will have an increased emphasis on the WiMAX Network specifications. Radio and protocol conformance, and interoperability testing will be based on IEEE 802.16e Revision 2 and the corresponding updated version of the Mobile WiMAX System Profile. Release 1.5 will also include new certification profiles that will support FDD duplexing in response to a growing demand for FDD in markets where FDD is mandated or more easily supported by regulatory mandates. Mobile WiMAX was added as the sixth radio interface in the International Mobile Telecommunications (IMT) 2,000 family, in recognition of the worldwide demand to deploy WiMAx technology. The International Telecommunications Union (ITU) decision opened the way towards wider opportunities for operators to deploy WiMAX within existing and new spectrum allocations. Release 2 will be a major step forward in the evolution of WiMAX technology and is expected for 2010–2011. It will rely on the IEEE 802.16m version of the standard, which is a candidate for inclusion among IMT-Advanced technologies. IEEE 802.16m will feature higher throughput and wider channels, in addition to improved support for voice services. Certification testing will rely on an updated version of the Mobile WiMAX System Profile and on an updated version of the WiMAX Network Specifications (NWIOT Release 2.0).

1.10.7

Benefits of an Industry Standard and Certified Products

It has been seen that ultimate success of any wireless technology is dependent on having an open standard with guaranteed equipment interoperability. The use of standards based technologies helps to drive up volume and minimize equipment variations lowering the manufacturer costs. This virtuous cycle has been seen in Ethernet products, DSL products and Wi-Fi products; the more popularity a standard gains the lower the eventual cost of the CPE and associated common equipment is. WiMAX systems are based on the IEEE 802.16 air interface standard. The standard has evolved over a number of years with broad industry participation from service providers, equipment vendors, and device and semiconductor manufacturers. The IEEE standard however, is quite broad and simply being IEEE 802.16-compliant does not guarantee that equipment from one vendor will interoperate with equipment from another vendor. The collaboration of IEEE 802.16, HiperMAN and ETSI has promoted worldwide adoption and harmonization of a standards-based broadband wireless solution b802.16 air interface standard with guaranteed interoperability.

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43

Vendors Promote Faster Innovation

Broadband Wireless Access system vendors currently develop the entire system, the hardware system, and the software architecture. Because a single vendor is responsible for the entire ecosystem, development cycles are long and products are designed for a broad set of users and applications. With standardization, component suppliers are able to enter the market in greater numbers, allowing for faster development cycles as multiple companies innovate in different areas of the solution. 1.10.7.2

Ease of Deployment for Service Providers

Service providers who engage with WiMAX member companies can help drive the development of standards-based products that will support their desired business models. When a service provider or end user selects a WiMAX Forum Certified product they are allowing themselves the option of building a multi-vendor network. This can allow them to adopt the standard earlier by being assured that if their primary vendor cannot deliver a product with the desired features at the desired price point another vendor will be able to meet their needs. This multi-vendor approach will also allow service providers to develop business relationships with abroad base of WiMAX vendors that may result in industry-wide collaborative efforts such as field trials that create awareness about WiMAX in their region and driving the demand for wireless broadband services. 1.10.7.3

Increased End User Confidence

Successful deployments of BWA systems have been made by thousands of enterprise customers and community-based service providers. While the number of total customers is large, most BWA deployments tend not to be dense in customer size or large scale. Lack of interoperability amongst vendor systems has been a contributing factor in limiting deployment size and scale. Since each system is proprietary to a vendor, large operators have not been able to source multiple vendors’ equipment to use interchangeably within their networks. For example, a service provider may prefer some of the management characteristics from one vendor’s Base Station Unit, while preferring the form-factor or functionality found in a different vendor’s Subscriber Station. The flexibility for a network operator to choose the equipment that meets their network requirements best for both ends of the service is unprecedented today. 1.10.7.4

Continued Improvement in Cost Points

While BWA Subscriber Unit prices have come down in price from the high of $5,000 to only about $300 today, continued price pressure from wired broadband

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customer premise equipment and the need of network operators to obtain a payback period of under 18 months necessitates that the Subscriber Unit price needs to become even more affordable. Standardization drives higher volumes, which ultimately can deliver lower cost points to end customers.

1.10.8

WiMAX Forum Certified Products

One of the goals of the WiMAX Forum is to develop and manage a certification program where vendors can submit their products for conformance and interoperability testing to independent laboratories, Tables 1.18 and 1.19. Upon completing the requirements, the products earn the WiMAX Forum Certified mark denoting that they will interoperate with other WiMAX Forum Certified products bearing the same mark. Two types of products that can be submitted for WiMAX Forum Certified testing: Base Stations (BS) and Subscriber Stations (SS). The BS and SS products will be tested against profiles established by the WiMAX Forum. These profiles define many of the characteristics, such as frequency band, modulation type, and channel bandwidth, which determine the countries and applications for each product. In June 2004, WiMAX Forum had approved three profiles for WiMAX Forum Certified testing – one at 2.5 GHz, one at 3.5 GHz, and one at 5.8 GHz.

Table 1.18 WiMAX forum timeline for product certification

2005

802.16-2004 lab opens Air protocol certification Service certification Indoor certification 802.16 lab opens 802.16e first certification

▾ ▾

2006

▾ ▾ ▾

2007

▾

Table 1.19 Expected commercial availability of WiMAX user product equipment (From WiMAX Forum) 802.16-2004 WiMAX 802.16e WiMAX 2006 First certified products _ Outdoor CPE Indoor, self-installable CPE PCMCIA card for laptops 2007 _ First certified products PCMCIA card for laptops, indoor self installable 2008 _ Mini-PCMCIA card for laptops, PDA, smart phones

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45

Frequency Band Allocations for WiMAX

The electromagnetic spectrum is the fundamental resource in a wireless communication system. This spectrum is divided into several bands that are used for specific applications. WiMAX operates in a mixture of licensed and unlicensed bands. The unlicensed bands are typically the 2.4 and 5.8 GHz bands, Table 1.20. Licensed spectrum provides operators control over the usage of the band, allowing them to build a high-quality network, Fig. 1.19. The unlicensed band, on the other hand, allows independents to provide backhaul services for hotspots, Fig. 1.19. Initial WiMAX implementations are focused on three bands in the RF spectrum as shown in Fig. 1.19. l

3.5 GHz Band: The 3.5 GHz is licensed spectrum available for BWA use in many European and Asian countries, except US. This is the most heavily allocated band, representing the largest global BWA market. Covering the bandwidth of 300 MHz from 3.3 to 3.6 GHz, the band supports great flexibility for large-pipeline backhauling to WAN services.

Table 1.20 WiMAX frequencies [31, 32] Frequency range Band description 2.305 to 2.320 GHz WCS (Wireless Communications Service) 2.345 to 2.360 GHz WCS (Wireless Communications Service) 2.495 to 2.686 GHz MMDS (Multichannel Multipoint Distribution System), BRS (Broadband Radio Service) 3.3 to 3.8 GHz BWA (Broadband Wireless Access), WLL (Wireless Local Loop) 5.150 to 5.350 GHz U-NII (Unlicensed National Information Structure) 5.750 to 5.825 GHz U-NII (Unlicensed National Information Structure)

Licensed Yes Yes Yes Yes No No

Unlicensed Band ISM 2.4 – 2.48 GHz

WRC 5.47 – 5.725 GHz

3.3 – 3.4 GHz

2

US WCS 3 3.4 – 3.6 GHz 2.305 – 2.320 GHz MMDS 2.345 – 2.360 GHz 2.5 – 2.69 GHz

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6 GHz UNII/ISM UNII 5.15 – 5.35 GHz 5.7255 – 5.85 GHz Unlicensed Band

Licensed Band

ISM: Industrial, Scientific & Medical Band UNII: Unlicensed National Information Infrastructure band

Fig. 1.19 2–6 GHz band available for WiMAX [19, 20]

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Table 1.21 U-NII bands and frequency groups [19, 20]

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UNII bands Lower and middle U-NII World Radio Conference(WRC) Upper U-NII/ISM band

Frequency group 5,150–5,350 MHz 5,470–5,725 MHz 5,725–5,850 MHz

5 GHz U-NII & WRC Bands: The second band is the 5.8-GHz band, which has a range of 5,725–5,850 MHz, Table 1.21. This band also is known as the upper Unlicensed National Information Infrastructure (U-NII) band. Many overlapping 5-GHz frequency bands are earmarked for BWA growth worldwide. The World Radio Conference’s 5470-to-5725-MHz band adds significant licenseexempt bandwidth. Most WiMAX activities are in the upper U-NII band because at there are lesser competing internet subscribers and interferences. WCS (Licensed 2.3 GHz): The two Wireless Communication Service ban are identical 15 MHz slots and range from 2.305 to 2.320 GHz and 2.345 to 2.360 GHz, respectively. This band, called the WCS band in the United States, is also available in many other countries such as Australia, South Korea, and New Zealand. But the major constraint in this spectrum is the 25 MHz gap which is assigned to Digital Audio Radio Service (DARS). This makes broadband services, particularly mobile services, difficult in the sections of this band. For the successful deployment of WiMAX technology in these bands exceptional spectral efficiency is the prerequisite. MMDS: The third band is Multichannel Multipoint Distribution Service (MMDS). Two frequency ranges reside in MMDS: the 2500-to-2690-MHz band and the 2700-to-2900-MHz band. MMDS spectrum includes 31 channels of 6-MHz spacing in the first range. It also includes the Instructional Television Fixed Service (ITFS), which was underutilized and reallocated for BWA service in the U.S. In the longer term, other bands may be useful. Examples include the two Wireless Communications Service (WCS) bands and the 2.4-GHz Industrial, Scientific, and Medical (ISM) band.

Initially, the WiMAX Forum is focusing its profiling and certification on the MMDS, 3.5-GHz licensed, and unlicensed upper U-NII 5-GHz bands. The upper U-NII band boasts less interference, reasonable power levels, and adequate bandwidth. Frequency bands in the 2-to-6-GHz portion have relatively narrow allocated bandwidths. The microwave frequencies below 10 GHz are referred to as centimetre bands. Above 10 GHz, they’re known as millimetre bands. The millimetre bands have much wider allocated channel bandwidths to accommodate the larger data capacities that are suitable for high-data-rate, line-of-sight backhauling applications. The centimetre bands are best for multipoint, near-line-of-sight (NLOS), tributary, and last-mile distribution. The centimetre spectrum contains both tributary and last-mile potential. IEEE 802.16-2004 supports fixed-NLOS BWA to supplement DSL and cable access for last-mile service. For spectrums below the 6-GHz range, however, IEEE 802.16e

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Fig. 1.20 Spectrum by region (From WiMAX forum)

will add mobility and portability to applications like notebooks and PDAs. Both licensed and unlicensed spectrums will be utilized in these deployments. Additional bands are being considered today by different regions around the world for the deployment of WiMAX and other similar broadband wireless access services. In Japan the 4.9 GHz–5.0 GHz band will be used after 2007 while the 5.47 GHz–5.725 GHz band is also being considered for future use, Fig. 1.20. The first one will require a license for BS deployment and will support 5, 10 and 20 MHz bandwidths, while the second one will possibly not require a license and would support 20 MHz bandwidths. The North American market is indicating some interest in deploying WiMAX in the 4.9 GHz broad-spectrum public-safety band. There is even some interest in using lower frequency bands such as the licensed 800 MHz and the unlicensed 915 MHz ISM bands for WiMAX and similar types of services and deployments. The WiMAX standard is set to bring the long-awaited spectral efficiency and throughput to meet users’ needs for combined mobility, voice services and high data rates. It will enable access for more users due to its non-line-of-sight capability, lower deployment costs, wide range capability and penetration into the mass consumer market with lower CPE costs as a result of standardization and interoperability. Needless to say, it is the clear path to broadband mobility and will form the basis of 4G, offering a true freedom for mobility.

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ITU Classification Adds Credibility to WiMAX

The Radio communication Sector of the International Telecommunication Union (ITU-R), which is affiliated with the United Nations, has approved WiMAX mobile broadband technology as a global 3G communications standard. The agreement was reached in a meeting in Geneva on 19 October 2007, after a number of countries objected to the inclusion of WiMAX in the IMT-2000 standard for advanced mobile technologies. The application was first presented to the ITU in January 2007 [33]. WiMAX is the sixth new standard, called “IMT-2000 OFDMA TDD WMAN”, to be admitted to the family of IMT-2000 radio interface specifications. The ITU-R voted to support WiMAX’s underlying technology, Orthogonal Frequency Division Multiplexing (OFDMA), which is also set to power future technologies, including Long Term Evolution (LTE) – designed as the next step in GSM and UMTS evolution, and expected to be deployed in 2009/10. IMT-2000 is a global standard for third generation (3G) mobile wireless communications that was defined by the ITU in 1999. The original members of the IMT-2000 family included the UMTS, CDMA2000, TD-CDMA, EDGE and DECT technologies. The underlying characteristic of this new technical interface is OFDMA, which, in terms of network connectivity, allows for the simultaneous transmission of low data rates amongst multiple users. It is specifically ODFMA that provides mobility for the IEEE 802.16 WirelessMan (WMAN) interface standard [29, 34]. In simple terms, the ratification of this new standard makes WiMAX, the industrial alliance name for the IEEE 802.16 family of products, a full member of the IMT-2000 family of mobile wireless technologies. In commercial terms, the decision of the ITU means that certain global radio frequencies that are classified for use only with IMT-2000 technologies now can be used by networks that employ WiMAX technology. In particular, the 2,500–2,690 MHz frequency that is reserved for use by IMT-2000 also became a prime frequency for WiMAX. This was an important step from the ITU side, as many countries have been waiting for this ITU classification before licensing these frequencies for use with WiMAX.

1.13

WiMAX Applications and Services

Practical limitations underlying in DSL and cable technologies make them incapable of reaching many potential broadband customers. For the service provider the cost of deploying cable is very high in low density subscriber areas. Furthermore, the traditional DSL connections can only reach 18,000 ft from central office switch limiting it to a specific range. Thus, lack of copper and lack of long ‘last mile’ allows wired deployments difficult. Also for mass deployment, the current

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Table 1.22 WiMAX service classes and applications (From WiMAX forum) Type of service class Application Required bandwidth Interactive gaming Interactive gaming 50–85 kbps VoIP, video conference VoIP 4–64 kbps Video phone 32–384 kbps Streaming media Music/speech 5–128 kbps Video clips 20–384 kbps Movies streaming > 2 Mbps Media content download Bulk data, movie download > 1 Mbps (store and forward) Peer-to-peer > 500 kbps

generation of wireless systems is relatively expensive as without a standard few economies of scale are possible. These limitations of traditional wired and proprietary wireless technologies can be overcome by the absence of LoS requirement, high bandwidth, inherent flexibility and range of IEEE 802.16 solutions. Therefore, fixed/nomadic WiMAX is ideally suited to be the best alternative to both broadband internet and voice telephony. The family of IEEE 802.16 standards effectively addresses several different types of potential customers and situations, especially where alternative DSL solutions are neither available nor economically viable. It is expected that standards based solutions will enable the largest and most flexible available ecosystem, driving competition and features up. Furthermore, this will bring prices down enabling to create new applications and services. Its ability to support both LoS and NLoS connections make WiMAX suitable for ubiquitous service offering in rural and urban areas alike. High speed and symmetrical bandwidth may satisfy the needs of individual customers, public administrations, and enterprises of all sizes. Cellular coverage makes its deployment extremely fast and relatively inexpensive. There is a vast number of real time services and applications that are already provided on WiMAX networks. This means that service providers are not forced to develop special applications specifically for WiMAX. Few of such applications, which already exist on wired networks are classified under service classes and listed in Table 1.22. The high bandwidth provided by WiMAX facilitates to deliver real-time applications much faster than other technologies do today. Thus, in terms of applications, WiMAX means freedom to both subscribers and service providers. Mobile WiMAX (IEEE 802.16e) will also encourage the early emergence of mobile applications that address the specific needs of mobile Internet users. IMS support in WiMAX will facilitate the ubiquitous deployment of managed services for subscribers across wired and wireless platforms.

1.13.1

Fixed Broadband Wireless Applications

The market for Fixed Broadband Wireless Access (FBWA) is huge. New and lucrative broadband access markets are springing up everywhere while new carriers

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and service providers are being created. In emerging countries, Plain Ordinary Telephone System (POTS) penetration is still low. Also, the low quality of the copper pair prevents mass scale DSL deployment fostering the need for alternate broadband technologies. FBWA fills the void at markets where cable or copper infrastructures are either saturated, outdated or simply out of reach, providing highly efficient and cost effective access services for millions of subscribers who would otherwise be left out of the loop. The BWA market targets wireless multimedia services to Small Offices/Home Offices (SOHOs), small and medium-sized businesses, and residences. The fixed wireless market for broadband megabit per second transmission rates is growing for providing an easily deployable low-cost solution, compared with existing cable and digital subscriber line (xDSL) technologies, for dense and suburban environments.

1.13.2

VoIP over WiMAX

Voice over IP (VoIP) is expected to be one of the dominating WiMAX services in future. VoIP over WiMAX is attractive both for enterprises and carriers. In VoIP, voice is transferred as data packets through personal broadband networks or public Internet. This makes VoIP service provider bypass the high operation costs for PSTN by using the cheapest resource of Internet. Although WiMAX is not designed for switched cellular voice traffic as cellular technologies, like CDMA and WCDMA, its rich set of QoS classes, supporting low latency, provide full support for VoIP traffic. VoIP calls can be received or placed at a very low or, in some cases, no additional cost. Therefore, the VoIP over WiMAX solution is the combination between the wireless technology and the low price VoIP. WiMAX is not a technology specifically built for voice communications; therefore, it will not challenge the voice revenues of mobile operators. This is mainly because cellular networks offer a cost-effective infrastructure for voice communications, with an extensive coverage that WiMAX is not designed to replace. But in some cases a mobile operator may move some voice traffic to the WiMAX infrastructure due to capacity constraints. Other real-time applications, like mobile video and audio streaming, videoconferencing and gaming, will strongly benefit from QoS support and low latency. They will become increasingly important when new devices optimized for these applications are introduced. Broadcast is another potential WiMAX application. Work is currently under way within the WiMAX Forum to further develop the Multicast and Broadcast Services (MBS) protocols within the standard, to allow for efficient multicasting of content. Vertical applications like surveillance, public safety, connectivity to remote devices, inventory tracking, fleet management and educational services can also

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FRACTIONAL E1 for SMALL BUSINESS BACKHAUL for HOTSPOTS

T1+ LEVEL SERVICE ENTERPRISE

Mobile Backhaul

RESIDENTIAL & SoHo DSL LEVEL SERVICE

802.16d WMAN Nomadic Coverage --> handoff from HOT SPOTS H

H

H

H

802.16e

H

H H

H H

= wide area coverage outside of Hot Spots

INTERNET BACKBONE BWA Operator Network Backbone

Fig. 1.21 WiMAX applications and missions [35]

be supported by mobile WiMAX networks with little or no incremental cost to network operators. These applications require robust and reliable connectivity, but in most of the cases it would be prohibitively expensive to build separate networks to support them. A WiMAX operator is thus well placed to support these applications and to secure new revenue streams either by providing the service to new market segments or by establishing wholesale relationships with service providers that focus on specific verticals. In fact, WiMAX is ideally suited for the following the following applications and missions, Fig. 1.21: l l

l l

l

l

Extending DSL/cable modem services to rural areas Backhauling traffic for wireless service providers or cable operators at a reduced cost Interconnecting and backhauling Wi-Fi hot zones Enabling ISPs, cable and satellite operators to deliver existing content through a new channel, which is even more attractive with WiMAX 802.16e Providing robust, secure bandwidth for data traffic at widely dispersed enterprises, such as financial and educational institutions and municipalities Enabling secure communications in-the-field for the military or public safety institutes

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The IEEE 802.16 standard can help the industry to provide solutions across multiple broadband segments, namely, (1) cellular backhaul, (2) broadband ondemand, (3) residential broadband, and (4) underserved areas [35]. The robust high bandwidth support of IEEE 802.16 technology makes it also a good choice for commercial enterprises backhaul. The on-demand connectivity is useful in trade shows and also in businesses such as construction sites. The deployment of IEEE 802.11 hotspots and home/small office wireless LANs in areas not served by cable or DSL will be accelerated by last-mile broadband wireless access provided by WiMAX. For many businesses, the broadband connectivity is so much important that relocation of organizations to areas where service is available is done. If the service is not available, a local exchange carrier may take 3 months or more to provide a T1 line to business customer. IEEE 802.16 wireless technologies enable to provide high speed services (with a speed comparable to wired services) at low cost, with a response time of only some days. The service providers with IEEE 802.11 wireless technologies also offer instantly configurable on-demand high-speed connectivity for temporary events, generating hundreds or thousands of users through 802.11 hotspots.

1.13.2.1

Wi-Fi Backhaul

Hotspots are becoming a very popular means of surfing on public places like coffee shops, airports, train stations, etc. These hotspots continue to be set up on worldwide basis at a very fast rate. For every hotspot, there is a DSL or dedicated broadband medium which is used to backhaul its traffic from the wireless access point to the telephone company central office, enabling to connect to the Internet. For these hotspots WiMAX may therefore serve as high bandwidth Internet backhaul. Another area where WiMAX connectivity may be very useful is Wi-Fi hot spots connectivity. There may be several Wi-Fi hotspots whose WiMAX backhaul provides a full wireless solution. Thus, last-mile broadband wireless access will help to accelerate the deployment of IEEE 802.11 hotspots and home/small office wireless LANs, especially in those areas not served by cable or DSL or in areas where the local telephone company may have a long lead time for provisioning broadband service.

1.13.2.2

Cellular Backhaul

Backhaul for cell towers is currently enabled through either a dedicated T1/E1 medium or a microwave radio link but WiMAX may be a better alternative for these types of backbone. Also, given the limited availability of a wired infrastructure in some developing countries, the costs to install a WiMAX station in conjunction with an existing cellular tower (or even as a solitary hub) are likely to be lower in comparison to developing a wired solution. Areas of low population density and flat

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terrain are particularly suited to WiMAX, whose coverage range is appropriate. For countries that have skipped wired infrastructure as a result of prohibitive costs and irregular geography, WiMAX can enhance the Wireless infrastructure in an inexpensive and decentralized deployment – in a friendly and effective manner. There are number of advantages such as reduced operating expense (OPEX). Besides, no monthly rent for fixed line service need to paid as well as a new network is made available supporting broadband roaming.

1.13.2.3

Rural Connectivity

Rural areas are typically small city or towns that are located far from metropolitan area. Such areas are underserved and do not have enough wired broadband connection. For small businesses in remote areas, such as rural towns and mountain communities, high-speed Internet access has been hard to come by. The conventional broadband services providers, like DSL and cable companies, have not typically extended their services outside of well-to-do cities and suburbs because such a build-out may be very expensive. However, being off-the-Internet is not a plausible possibility for any business these days. High-speed Internet access is essential to gather information, and communicate with partners, clients and potential customers. The companies also need to maintain a presence on the Web in today’s global marketplace. Rural connectivity is therefore critical in many developing countries and underserved areas of developed country. Rich WiMAX QoS features ensure the real time voice transmission as well as low latency. Rural connectivity is therefore essential for voice telephony and Internet services. As the WiMAX solution provides extended coverage, it is a cost effective solution, and it can be preferable to wired technology in areas with low population density. Furthermore, WiMAX solutions may be quickly deployed.

1.13.2.4

Last Mile to the Home

The residential market segment primarily depends on the availability of DSL or cable access, which are however poor and expensive to build up connectivity in the rural or suburban areas. The lowest cost and highest capacity of the WiMAX solution will replace these conventional wired broadband technologies. Thus, low cost WiMAX solutions may replace cable and ADSL solutions while really making the broadband home revolution happen.

1.13.2.5

Business Users

Worldwide, only 5% of commercial structures are served by fibre networks, the main method for the largest enterprises to access broadband multimedia data services. These networks are extended to the business or residence via cable or

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DSL. Both are expensive options because of the infrastructure changes required. Enterprises can use WiMAX instead of T1 for about 10% of the cost, while SMEs can be offered fractional T1 services. Base stations will cost under $20,000 and support 60 enterprise customers with T1-class connections.

1.13.2.6

Municipal and Law Enforcement

A number of local municipalities have already started city-wide implementation of wireless networks or at least they have announced plans to do so. The city councils want to make affordable ubiquitous broadband access available to residences and small medium enterprises (SMEs). In many cases, Wi-Fi would be the natural choice, primarily for its low cost and wide availability, including places as public libraries, schools, parks, and municipal buildings. WiMAX will play a key role in backhaul or backbone access to these Wi-Fi hot spots while providing the last mile link to SMEs. Additionally, WiMAX is an excellent technology with the following envisaged application scenarios: l l l l l l

Public safety Traffic management Parking meter reading Public utilities Remote utility reading Toll collection

1.13.2.7

Emergency Response and Monitoring

During national crisis, wireless communications play a critical role. For example, in fire emergency, WiMAX can play a critical role by providing mobile transmission of maps, floor layouts and architectural drawings. This can assist fire-fighter brigades and other response personnel in the rescue of individuals involved in emergency situations. In situations of national crisis, such as terrorist attacks or natural disaster (e.g., hurricanes, earthquakes and floods), where the terrestrial infrastructure is broken and speed of deployment is of utmost importance, IEEE 802.16 can provide quick relief. In addition to disaster relief, WiMAX could be used in law enforcement applications. Examples are the following such as: l

l l l

Video/sensor surveillance: Wireless video surveillance is a cost-effective, flexible and reliable tool for monitoring traffic, roads, bridges, dams, offshore oil and gas, military installations, perimeter, borders and many more critical locations Public safety City workforce mobility Real-time video-based criminal checks

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WiMAX may also be used in remote monitoring of patients to provide continuous information and immediate response in the event of a patient crisis.

1.14

Salient Features of WiMAX

WiMAX is a wireless broadband solution that offers a rich set of features, with a lot of flexibility in terms of deployment options and diversity of service offerings. Some of the most salient WiMAX features are the following [20, 29]: l

l

l

l

OFDM-based PHY layer – The WiMAX PHY layer is based on OFDM, a scheme that uses many subcarriers, or tones, to carry a signal. OFDM signalling consists of a large set of spaced subcarriers with no mutual interface to perform parallel data transmission in the frequency domain. The primary advantage of OFDM is that it eliminates the multi-path channel-induced self-interference that occurs with high speed data transmission over the wireless channel, which can limit transmission speed and spectral efficiency. OFDM offers good resistance to multipath, and allows WiMAX to operate in NLOS conditions. Very high peak data rates – The peak data rate indicates the bit-rate a user in good radio conditions can reach when not sharing the channel with other users. WiMAX is capable of supporting very high peak data rates. In fact, the peak PHY data rate can be as high as 70 Mbps when operating using a 20 MHz wide bandwidth. More typically, using a 10 MHz spectrum operating using TDD scheme with a 3:1 downlink-to-uplink ratio, the peak PHY data rate is about 25 Mbps and 6.7 Mbps for the downlink and the uplink, respectively. These peak PHY data rates are achieved when using 64 QAM modulation with rate 5/6 error-correction coding. Under very good signal conditions, even higher peak rates may be achieved using multiple antennas and spatial multiplexing. Scalable bandwidth and data rate support – WiMAX has a scalable PHY layer architecture that allows for the data rate to scale easily with available channel bandwidth. This scalability is supported in the OFDMA mode, where the FFT (fast Fourier transform) size may be scaled based on the available channel bandwidth. For example, a WiMAX system may use 128-, 512-, or 1,048-bit FFTs based on whether the channel bandwidth is 1.25 MHz, 5 MHz, or 10 MHz, respectively. This scaling may be done dynamically to support user roaming across different networks that may have different bandwidth allocations. Adaptive modulation – During the time of transmission the quality of the radio link always varies. To overcome the transmission challenges, WiMAX supports a number of modulation schemes. Adaptive modulation allows the WiMAX system to adjust the signal modulation scheme depending on the signal to noise ratio (SNR) of the channel conditions. When the radio link is high in quality, the highest modulation scheme is used increasing the system capacity. The system shifts to a lower modulation scheme during a signal fade. This increases the

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range, as higher modulation scheme is used over as opposed to having a fixed scheme for worst channel conditions. Error Correction Techniques – WiMAX incorporates strong error correction techniques like FEC and ARQ to improve throughput. In FEC errors are detected and corrected upon reception by adding redundancy to the transmitted signal. Reed Solomon FEC, convolutional coding and interleaving algorithms are used in WiMAX systems. ARQ is a MAC level error control scheme and is used to correct errors not corrected by FEC. In ARQ scheme the information with error is resent. WiMAX systems also support hybrid technique, called H-ARQ, where a combination of FEC and ARQ is used. Support for TDD and FDD – IEEE 802.16-2004 and IEEE 802.16e-2005 supports both FDD (Frequency division duplexing) and TDD (Time division duplexing), as well as a half-duplex FDD. FDD is the legacy duplexing method that has been deployed in cellular telephony. In regulatory environments where structured channel pairs do not exist, TDD uses a single channel for both upstream and downstream transmissions, dynamically allocating bandwidth depending on traffic requirements. TDD is also favoured by a majority of implementations because of its advantages like, ability to exploit channel reciprocity, ability to implement in non-paired spectrum, and less complex transceiver design. All the initial WiMAX profiles are based on TDD, except for two fixed WiMAX profiles in 3.5 GHz. Orthogonal frequency division multiple access (OFDMA) – Mobile WiMAX uses OFDM as a multiple-access technique, whereby different users can be allocated different subsets of the OFDM tones. As discussed in detail in Chapters 2 and 11, OFDMA facilitates the exploitation of frequency diversity and multiuser diversity to significantly improve the system capacity. Flexible and dynamic per user resource allocation – Both uplink and downlink resource allocation are controlled by a scheduler in the base station. Capacity is shared among multiple users on a demand basis, using a burst TDM scheme. When using the OFDMA-PHY mode, multiplexing is additionally done in the frequency dimension, by allocating different subsets of OFDM subcarriers to different users. Resources may be allocated in the spatial domain as well when using the optional advanced antenna systems (AAS). The standard enables bandwidth resources to be allocated in time, frequency, and space and has a flexible mechanism to convey the resource allocation information on a frame-by-frame basis. Support for advanced antenna techniques – Advanced multi-antenna technologies are one of the most important methods of improving spectral efficiency in non-cellular wireless networks. 802.16 standards allow vendors to support a variety of these mechanisms, which can be a key performance differentiator. The WiMAX solution has a number of built in features into the physical-layer design, which allows for the use of multiple-antenna techniques, such as beamforming, space-time coding, and spatial multiplexing. These schemes can be used to improve the overall system capacity and spectral efficiency by deploying

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multiple antennas at the transmitter and/or the receiver. Chapter 11 presents detailed overview of the various multiple antenna techniques. Quality-of-service support – WiMAX system supports a multiplicity of widely varying transport demands over an inherently fluctuating wireless medium. Therefore the network must include rigorous support for differentiated QoS as a fundamental design feature. WiMAX MAC layer has a connection-oriented architecture that is designed to support a variety of applications, including voice and multimedia services. The grant/request mechanism enables an operator to simultaneously provide premium guaranteed levels of service to businesses, such as T1-level service, and high-volume “best-effort” service to homes, similar to cable-level service, all within the same base station service area cell. Also the MAC is designed to support a large number of users, with multiple connections per terminal, each with its own QoS requirement. The system offers support for constant bit rate, variable bit rate, real-time, and non-real-time traffic flows, in addition to best-effort data traffic. Robust security – WiMAX supports strong encryption, using Advanced Encryption Standard (AES), and has a robust privacy and key-management protocol. The system also offers a very flexible authentication architecture based on Extensible Authentication Protocol (EAP), which allows for a variety of user credentials, including username/password, digital certificates, and smart cards. Support for mobility – The mobile WiMAX variant of the system has mechanisms to support secure seamless handovers for delay-tolerant full-mobility applications, such as VoIP. The system also has built-in support for powersaving mechanisms that extend the battery life of handheld subscriber devices. Physical-layer enhancements, such as more frequent channel estimation, uplink subchannelization, and power control, are also specified in support of mobile applications. IP-based architecture – Network Working Group (NWG) in the WiMAX Forum has defined a reference network architecture that is based on an all-IP platform. WiMAX has been at the forefront of the move to all-IP end-to-end networks based on open systems. All end-to-end services are delivered over an IP architecture relying on IP-based protocols for end-to-end transport, radio resource management, QoS management, security, and mobility. Service providers can concentrate on a core packet based network and have services that enable them provide voice, WLAN and broadcast services over WiMAX. Reliance on all-IP allows WiMAX systems to facilitate easy convergence with other networks and enter the rich ecosystem for application development that exists for IP.

1.15

Fixed, Portable, and Mobile Terminals

The term Wireless does not exactly mean mobile. There is therefore often a need to make a conceptual difference between the terms ‘Wireless’, ‘Portable’ and ‘Mobile’. Wireless systems may be classified into two types: Mobile and Fixed.

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Fixed wireless system include traditional broadcast television, direct to home satellite service and the microwave backhaul networks that transport telephone traffic from individual cell sites to the mobile switching centre. In these systems the transmitters and receivers are permanently fixed in one geographical location. For example, PtP microwave links are permanently located and aimed so that each radio station is in LoS with the corresponding ones. If the sites are moved or misaligned, then the radio contact is lost. In the Wireless context, the term fixed is clear: the transmitting and receiving terminals of the wireless transmission circuit are physically fixed in a place. A microwave link system, with the transmitting and receiving antennas mounted on towers attached to the ground, a rooftop or to some other structure is a reference example of a fixed Wireless system. Television broadcast systems are fixed systems in this sense. The transmitting and receiving antennas are fixed, as is the TV itself while it is being watched. An exception to this are high-gain antennas receiving satellite signals on board ships where sophisticated gimbaling systems are required to keep the antenna pointed in the correct orientation regardless of the movements of the ship. The IEEE 802.11 standards are primarily designed for fixed and ‘portable’ terminal devices. Also referred to as nomadic in the context of ITU and other European standardization bodies, a portable terminal is one that stays in one place while it is being used but can readily be picked up and moved to another location. A notebook computer, with an 802.11b wireless access PC card, is a good example of such a portable device. Another portable device is a desktop wireless modem that is connected to a computer via a USB port. While operating, the modem is expected to steadily be in one place – on a desktop, for example. Moving it across the desk or to another room makes it portable but while it is in use it is stationary. The classification of fixed systems can be further refined by recognizing that for some networks, one terminal of the transmission link is at an ad-hoc location rather than an ‘engineered’ (or ‘planned’) location; that is, no planning effort has been made to optimize the location for the terminal device. Instead, the terminal location has been chosen by the user as the most convenient one. A notebook computer with a wireless modem of some sort, placed on an arbitrarily located desk, is an example of such a system. Ad-hoc fixed systems present new challenges to system design since the problem of analyzing coverage and interference, and ultimately performance is quite similar to that of mobile radio or cellular systems in which the design must provide for terminals located essentially anywhere in the system service area. The differences between engineered and ad-hoc fixed wireless systems have an important impact on the commercial success of the system. An engineered system requires the expensive step of sending a trained engineer or technician to every terminal location at least once to complete a successful installation. The value to the operator of this customer’s business must be significant enough to justify the cost of this ‘truck roll’. Certainly, for some customers, such as large businesses that require microwave links carrying hundreds of megabits of data, this may very well be the case. However, for systems designed to serve thousands of more casual communication users, for example, at homes, home offices, and small businesses, a system

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Fig. 1.22 Mobile WiMAX enabled device can move from one Base Station (BS) to another in a seamless session [36]

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BS PDA (WiMAX Mobile Ennabled)

BS

design that can work effectively with ad-hoc ‘self-installed’ terminals, without the necessity of truck roll, is essential for commercial viability. Mobile phones, pagers Family Radio Service (FRS) also called walkie-talkies and some satellite phones are the example of Mobile Wireless Systems. These radio systems are designed for situations where the handset is expected to be in motion while being used. As shown in Fig. 1.22, communication is not interrupted when Mobile WiMAX enabled device moves from the range of one Base Station (BS) to another while the user moves in seamless manner. With mobility there is no realtime speed limit. High mobility is accomplished when a Broadband Wireless Access (BWA) device can be used in some high speed trains with speeds exceeding 300 km/h, or more. WiMAX Ecosystem The WiMAX ecosystem is a common platform created by all industry players in theWiMAX value chain. For WiMAX to succeed, all the stakeholders of this ecosystem must come together to develop, produce, certify, promote and deliver a quality product. The WiMAX ecosystem consists of standardization bodies, operators, service providers, equipment vendors, system integrators, component vendors, and users, Fig. 1.23. The success of the BWA business depends on a stable and comprehensive industrial ecosystem. WiMAX forum offers a platform of cooperation for stakeholders to build up such ecosystem. This ecosystem is open and dynamic allowing its members to join in the process of value creation. Just at the chip level, the variety of companies delivering solutions ranging from the OFDM technology being used in Mobile WiMAX to a wide variety of systemon-a-chip silicon providers, offer the variety of support and implementation strategies that will either ensure or fail to ensure that the technology supports the range of optional features that will garner customer attention. The various equipment vendors as well as the component and system integrators deliver unique solutions tailored to the driving market needs. They offer opportunities to them and their service provider customers.

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Component Vendor

System Integrator

User Residential Enterprise Mobile

Operator

Service provider

WiMAX Forum

Equipment Vendor

Fig. 1.23 WiMAX ecosystem [30, 37]

The WiMAX ecosystem is a crucial element of success for this technology. The widespread quantity and quality of the companies supporting WiMAX in their various ecosystem roles is a major reason that the market place has taken the technology so seriously. It is also the industry’s greatest hope for success. Many famous vendors from different industry area have come together and joined hands for the development of WiMAX equipment and enhance interoperability for various products. WiMAX Forum promotes the development of WiMAX profile and undertakes the certification of the products to ensure the interoperability of equipment from different vendors. The end user, that is, the customer, is certainly being benefited from such a healthy ecosystem.

1.16

Conclusions

WiMAX is an emerging and exciting wireless technology that will support a variety of business and consumer applications, from network backhauling and interconnecting Wi-Fi and LANs, to voice, video, data, and mobility support. WiMAX will change the way people access data, e-mail, and instant messaging service. It may coexist with 3G or even replace 3G, and it can seamlessly integrate with cellular handsets or serve as a standalone technology to provide mobile voice and data services. Moreover, WiMAX technology can be used in a variety of commercial, municipal, and law enforcement business applications. The success of WiMAX deployment will depend on its adoption rate, equipment pricing, business models, availability and affordability of licensed spectrum. Based on Internet access is becoming a necessity, and 3G and Research in Motion (RIM) capturing a large business market share, the WiMAX market is continuously growing. It will change the way people access the Internet and

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download media, such as streaming video and MP3 files. Successful deployments have so far been limited to a few niche applications and markets. Clearly, broadband wireless until now had not reached to the required record, in part because of the fragmentation of the industry due to the lack of a common standard. The emergence of WiMAX as an industry standard is expected to change this situation.

References 1. R. Prasad, Universal Wireless Personal Communications (Artech House, Norwood, MA, 1998) 2. A.R. Prasad, The future re-visited. Wireless Pers. Commun. Int. J. 37(3–4), 187–211 (May 2006) 3. R. Bekkers, Mobile Telecommunication Standards, GSM, UMTS, TETRA, ERM S (Artech House, Norwood, MA, 2001) 4. V.K. Garg, Wireless Network Evolution: 2G to 3G (Prentice Hall, Upper Saddle River, NJ, 2002) 5. Y.K. Kim, R. Prasad, 4G Roadmap and Emerging Communication Technologies (Artech House, Boston, MA, 2006) 6. R. Prasad, R.L. Olsen, The unpredictable future: personal networks paving towards 4G. Telektronikk 1.2006, Real-time communication over IP. 7. S. Ahamdi, An overview of next-generation mobile WiMAX technology. Commun. Mag. 47(6), 84–98 (June 2009) 8. R. Prasad, Convergence: a step towards unpredictable future (keynote speech), in Proceedings of EuWIT2009 – European Wireless Technology Conference 2009 (Rome, Italy, Sept 2009) 9. R. Prasad, M. Ruggier, Technology Trends in Wireless Communication (Artech House, Norwood, MA, 2003) 10. B. Fong, N. Ansari, A.C.M. Fong, G.Y. Hong, P.B. Rapajic, On the scalability of fixed broadband wireless access network deployment. IEEE Radio Communications (Sept 2004) 11. A. Ghosh, R. Muhamed, J.G. Andrews, Fundamentals of WiMAX: Understanding Broadband Wireless Networking (Prentice Hall, Upper Saddle River, NJ, 2007) 12. V. Gunasekaran, F.C. Harmantzis, Emerging wireless technologies for developing countries. Technol Soc 29(1), 23–42 (Jan 2007) 13. R.B. Marks, Status of 802.16 Efforts: successes, new products & next steps, in Wireless Communication Association 8th Annual Technical Symposium (Jan 2002) 14. IEEE 802.16 Working Group web site. http://WirelessMAN.org (March 2010) 15. F. Ohrtman, WiMAX Handbook: Building 802.16 Wireless Networks (McGraw-Hill, New York, 2005) 16. International Telecommunications Union (ITU). http://www.itu.int/net/home/index.aspx (March 2010) 17. European Telecommunication Standardization Institute (ETSI). http://www.etsi.org/ (March 2010) 18. Rules of the Federal Communication Commission. Part 101.101. CFR Title 47. United States Government Printing Office 19. Rules of the Federal Communication Commission. Part 74. CFR Title 47. United States Government Printing Office 20. C. Eklund, R. Marks, K. Stanwood, S.Wang, IEEE standard 802.16: a technical overview of the WirelessMANTM air interface for broadband wireless access

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21. IEEE 802.16a-2003, IEEE standard for Local and Metropolitan Area Networks – Part 16: Air Interface for Fixed Broadband Wireless Access Systems – Medium Access Control Modifications and Additional Physical Layer Specifications for 2–11 GHz (Jan 2003) 22. IEEE 802.16-2004, IEEE Standard for Local and Metropolitan Area Networks – Part 16: Air Interface for Fixed Broadband Wireless Access Systems (Oct 2004) 23. IEEE 802.16e-2005, IEEE Standard for Local and Metropolitan Area Networks – Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems Amendment 2: Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands (Feb 2006) 24. S. Shepard, WIMAX Crash course (McGraw-Hill, New York, 2006) 25. D. Pareek, The Business of WiMAX (Wiley, Hoboken, NJ, 2006) 26. White Paper (The WiMAX Forum Certified TM Program). www.wimaxforum.org (March 2010) 27. IEEE 802.16c-2002, IEEE Standard for Local and Metropolitan Area Networks – Part16: Air Interface for Fixed Broadband Wireless Access Systems – Amendment1: Detailed System Profiles for 10-66 GHz (Dec 2002) 28. http://en.wikipedia.org/wiki/IEEE_802.16#cite_note-0 (March 2010) 29. Mobile WiMAX – Part I: A Technical Overview and Performance, WiMAX Forum (Mar 2006) 30. www.wimaxforum.org (March 2010) 31. Fujitsu Microelectronics America Inc., RF Spectrum Utilization in WiMAX, white paper (2004) 32. Maravedis Inc, Spectrum Analysis – The Critical Factor in BWA/WiMAX versus 3G (Jan 2006) 33. White Paper (WiMAX and IMT-2000). www.wimaxforum.org (March 2010) 34. WiMAX Forum (Mobile WiMAX – Part II: Competitive Analysis). www.wimaxforum.org (March 2010) 35. Can WiMAX Address Your Applications? Westech on Behalf of the WiMAX Forum (Oct 24, 2005) 36. WiMAX Forum, Fixed, nomadic, portable ad mobile applications for 802.16-2004 and 802.16e WiMAX networks (2005). www.wimaxforum.org (March 2010) 37. White Paper (M-Taiwan Program: A WiMAX Ecosystem). www.wimaxforum.org (March 2010)

Chapter 2

OFDMA WiMAX Physical Layer Ramjee Prasad and Fernando J. Velez

Abstract IEEE 802.16 physical (PHY) layer is characterized by Orthogonal Frequency Division Multiplexing (OFDM), Time Division Duplexing, Frequency division Duplexing, Quadrature Amplitude Modulation and Adaptive Antenna Systems. After discussing the basics of OFDM and Orthogonal Frequency division Multiple Access (OFDMA), scalable OFDMA is presented and supported frequency bands, channel bandwidth and the different IEEE 802.16 PHY are discussed. The similarities and differences between wireless MAN-SC, wireless MAN-OFDM and wireless MAN-OFDMA PHY are finally highlighted.

2.1

Introduction

The IEEE 802.16 standard belongs to the IEEE 802 family, which applies to Ethernet. WiMAX is a form of wireless Ethernet and therefore the whole standard is based on the Open Systems Interconnections (OSI) reference model. In the context of the OSI model, the lowest layer is the physical layer. It specifies the frequency band, the modulation scheme, error-correction techniques, synchronization between transmitter and receiver, data rate and the multiplexing techniques. For IEEE 802.16, Physical layer was defined for a wide range of frequencies from 2–66 GHz. In sub frequency range of 10–66 GHz there essentially is LoS propagation. Therefore, single carrier modulation was chosen, because of low

R. Prasad (*) Center for TeleInFrastruktur (CTIF), Aalborg University, Niels Jernes Vej 12, DK–9220 Aalborg Øst, Denmark e-mail: [email protected]

R. Prasad and F.J. Velez, WiMAX Networks, DOI 10.1007/978-90-481-8752-2_2, # Springer ScienceþBusiness Media B.V. 2010

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system complexity. Downlink channel is shared among users with TDM signals. Subscriber unit are being allocated individual time slots. Access in uplink is being realized with TDMA. In the 2–11 GHz bands, communications can be achieved for licensed and non-licensed bands. The communication is also available in NLoS conditions. To ensure the most efficient delivery in terms of bandwidth and available frequency spectrum, the IEEE 802.16 physical layer uses a number of legacy technologies. These technologies include Orthogonal Frequency Division Multiplexing (OFDM), Time Division Duplexing (TDD), Frequency Division Duplexing (FDD), Quadrature Amplitude Modulation (QAM), and Adaptive Antenna System (AAS). The WiMAX physical layer is based on OFDM. OFDM is the transmission scheme of choice to enable high speed data, video, and multimedia communications and presently, besides WiMAX, it is used by a variety of commercial broadband systems, including DSL, Wi-Fi, Digital Video Broadcast-Handheld (DVB-H). Above the physical layer are the functions associated with providing service to subscribers. These functions include transmitting data in frames and controlling access to the shared wireless medium, and are grouped into a media access control (MAC) layer. This Chapter is organized as follows. Section 2.2 addresses the history, evolution and applications of OFDM. Section 2.3 presents the OFDM fundamentals by comparing it with FDMA as well as describing OFDM signal characteristics. Section 2.4 describes the concepts behind OFDM transmission and presents the serial to parallel converter as well as the OFDM demodulator. The OFDM symbol is described in Section 2.5 while Section 2.6 presents ISI and ICI mitigation. Section 2.7 addresses spectral efficiency. Section 2.8 presents the improvements of OFDMA and the advantages of subchannelisation. Section 2.9 and 2.10 present the advantages and disadvantages of OFDM systems. The details on scalable OFDMA are presented in Section 2.11, including the parameters, principles, and the reference model. Section 2.12 addresses specific issues of PHY layer, including WirelessHUMAN PHY, while Section 2.13 addresses WirelessMANSC (single carrier) PHY. Section 2.14 covers WirelessMAN-OFDM PHY while Section 2.15 describes WirelessMAN-OFDMA PHY. Finally, Section 2.16 presents the conclusions.

2.2 2.2.1

History and Development of OFDM Evolution

OFDM has recently been gaining interest from telecommunications industry. It has been chosen for several current and communications systems all over the world. Nevertheless, OFDM had a long history of existence (Table 2.1). The first multichannel modulation systems appeared in the 1950s as frequency division multiplexed

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Table 2.1 A brief history of OFDM Dates OFDM Landmark Achieved 1966 Chang postulated the principle of transmitting messages simultaneously through a linear band limited channel without ICI and ISI [3]. This is considered the first official publication on multicarrier modulation. Earlier work on OFDM was Holsinger’s 1964 MIT dissertation [4] and some of Gallager’s early work on waterfilling [5]. 1967 Saltzberg observed that, in order to increase efficiency of parallel system, cross talk between adjacent channels should be reduced [6]. 1971 Weinstein and Ebert show that multicarrier modulation can be accomplished by using a DFT [7]. 1980 Peled and Ruiz introduced use of Cyclic Prefix (CP) or cyclic extension instead of guard spaces [8]. 1985 Cimini at Bell Labs identifies many of the key issues in OFDM transmission and does a proof-of-concept design [9]. 1990–1995 OFDM was exploited for wideband data communications over mobile radio FM radio, DSL, HDSL, ADSL and VDSL. First commercial use of OFDM in DAB and DVB. 1999 The IEEE 802.11 used OFDM at the physical layer. HiperLAN and HiperLAN/ 2 also adopted OFDM at the physical layer. 2002 The IEEE 802.16 committee released WMAN standard 802.16 based on OFDM. 2003 The IEEE 802.11 committee releases the 802.11g standard for operation in the 2.4 GHz band. The multiband OFDM standard for ultra wideband is developed. 2004 OFDM is candidate for IEEE 802.15.3a standard for wireless PAN (MB-OFDM) and IEEE 802.11n standard for next generation wireless LAN [33]. 2005 OFDMA is candidate for the 3GPP Long Term Evolution (LTE) air interface E-UTRA downlink [33]. 2007 The first complete LTE air interface implementation was demonstrated, including OFDM-MIMO, SC-FDMA and multi-user MIMO uplink [34]. 2008 Mobile WiMAX base stations and subscriber devices were first certified by WiMAX Forum.

military radio links. OFDM had been used by US military in several high frequency military systems, such as KINEPLEX, ANDEFT and KATHRYN [1, 2]. In December 1966, Robert W. Chang outlined first OFDM scheme. This was a theoretical way to transmit simultaneous data stream through linear band limited channel without Inter Symbol Interference (ISI) and Inter Carrier Interference (ICI). Chang obtained the first US patent on OFDM in 1970 [12]. Around the same time, Saltzberg performed an analysis of the performance of the OFDM system and concluded that the strategy should concentrate more on reducing cross talk between adjacent channels than on perfecting the channels [6]. Until this time, we needed a large number of subcarrier oscillators to perform parallel modulations and demodulations. This was the main reason why the OFDM technique has taken a long time to become a prominence. It was difficult to generate such a signal, and even harder to receive and demodulate the signal. The hardware solution, which makes use of multiple modulators and demodulators, was somewhat impractical for use in the civil systems. In the year 1971, Weinstein and Ebert used Discrete Fourier Transform (DFT) to perform baseband modulation and demodulation. The use of DFT eliminated the

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need for bank of subcarrier oscillators. These efforts paved the way for the way for easier, more useful and efficient implementation of the system. The availability of this technique, and the technology that allows it to be implemented on integrated circuits at a reasonable price, has permitted OFDM to be developed as far as it has. The process of transforming from the time domain representation to the frequency domain representation uses the Fourier transform itself, whereas the reverse process uses the inverse Fourier transform. All the proposals until this moment in time used guard spaces in frequency domain and a raised cosine windowing in time domain to combat ISI and ICI. Another milestone for OFDM history was when Peled and Ruiz introduced Cyclic Prefix (CP) or cyclic extension in 1980 [8]. This solved the problem of maintaining orthogonal characteristics of the transmitted signals at severe transmission conditions. The generic idea that they placed was to use cyclic extension of OFDM symbols instead of using empty guard spaces in frequency domain. This effectively turns the channel as performing cyclic convolution, which provides orthogonality over dispersive channels when CP is longer than the channel impulse response [1]. It is obvious that introducing CP causes loss of signal energy proportional to length of CP compared to symbol length but, in turn, it facilitates a zero ICI advantage which pays off. By this time, inclusion of FFT and CP in OFDM system and substantial advancements in Digital Signal Processing (DSP) technology made it an important part of telecommunications landscape. In the 1990s, OFDM was exploited for wideband data communications over mobile radio FM channels, High-bitrate Digital Subscriber Lines (HDSL at 1.6 Mbps), Asymmetric Digital Subscriber Lines (ADSL up to 6 Mbps) and Very-high-speed Digital Subscriber Lines (VDSL at 100 Mbps). The first commercial use of OFDM technology was made in Digital Audio Broadcasting (DAB).The development of DAB started in 1987 and was standardized in 1994. DAB services started in 1995 in UK and Sweden. The development of Digital Video Broadcasting (DVB) was started in 1993. DVB along with High-Definition TeleVision (HDTV) terrestrial broadcasting standard was published in 1995. At the dawn of the twentieth century, several Wireless Local Area Network (WLAN) standards adopted OFDM on their physical layers. Development of European WLAN standard HiperLAN started in 1995. HiperLAN/2 was defined in June 1999 which adopts OFDM in physical layer. OFDM technology is also well positioned to meet future needs for mobile packet data traffics. It is emerging as a popular solution for wireless LAN, and also for fixed broad-band access. OFDM has successfully replaced DSSS for 802.11a and 802.11g. Perhaps of even greater importance is the emergence of this technology as a competitor for future fourth Generations (4G) wireless systems. These systems, expected to emerge by the year 2010, promise to at last deliver on the wireless ‘Nirvana’ of anywhere, anytime, anything communications [14]. It is expected that OFDM will become the chosen technology in most wireless links worldwide [13] and it will certainly be implemented in 4G radio mobile systems.

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Table 2.2 Wireless systems using OFDM [10] Application WMAN Technology OFDM Cell Radius 1–20 km Mobility High and low Freq Band 2–66 GHz Data Rate Few Mbps Deployment IEEE 802.16a, d, e, WiMAX, 3GPP-LTE

2.2.2

67

WLAN OFDM up to 300 m Low 2–5 GHz up to 100 Mbps IEEE 802.11a, g, HiperLAN2

WPAN OFDM few tens of meter very low 5–10 GHz up to 10 Mbps IEEE 802.15, Zig-Bee

Applications of OFDM

OFDM has been incorporated into four basic applications: (1) Digital Audio Broadcasting (DAB); (2) Digital Video Broadcasting (DVB), over the terrestrial network Digital Terrestrial Television Broadcasting (DTTB); (3) Magic WAND (Wireless ATM Network Demonstrator); and (4) IEEE 802.11a/HiperLAN2 and MMAC WLAN Standards. DAB and DVD were the first standards to use OFDM. Next Magic WAND was introduced, which demonstrated the viability of OFDM. Lastly, and most importantly, the most recent 5 GHz applications evolved which were the first to use OFDM in packet-based wireless communications. Few of the OFDM application and their details based on the type of wireless access technique are summarized in Table 2.2.

2.3 2.3.1

OFDM Fundamentals OFDM Versus FDM

Orthogonal Frequency Division Multiplexing is an advanced form of Frequency Division Multiplexing (FDM) where the frequencies multiplexed are orthogonal to each other and their spectra overlap with the neighbouring carriers. As shown in the Fig. 2.1 the subcarriers never overlap for FDM. In contrast to FDM, OFDM is based on the principle of overlapping orthogonal sub carriers. The spectral efficiency of OFDM system as compared to FDMA is depicted in the Fig. 2.2. The overlapping multicarrier technique can achieve superior bandwidth utilization. There is a huge difference between the conventional non-overlapping multicarrier techniques such as FDMA and the overlapping multicarrier technique such as OFDM. In frequency division multiplex system, many carriers are spaced apart. The signals are received using conventional filters and demodulators. In these receivers guard bands are introduced between each subcarriers resulting into reduced spectral efficiency. But in an OFDM system it is possible to arrange the carriers in such a

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Ch.2

Ch.3

Ch.4

Ch.5

Ch.6

Ch.7

Ch.8

Ch.9

Ch.10

Conventional multicarrier techniques

frequency

Ch.2 Ch.4 Ch.6 Ch.8 Ch.10 Ch.1 Ch.3 Ch.5 Ch.7 Ch.9 Saving of bandwidth

50% bandwidth saving frequency

Orthogonal multicarrier techniques

Fig. 2.1 Concept of OFDM signal

N=1

N=2

B = 2R

N=3 B = 2R

B = 2R

FDMA

–R

R

f

–R

f

R

–R

B = 3/2R

B=2R

–R/3

R/3

2R

f

B = 4/3R

OFDM –R

R

f

–3R/4 –R/4 R/4 3R/4

f

–2R/3 –R/3 R/3 2R/3

f

Fig. 2.2 Spectrum efficiency of OFDM compared to FDMA

fashion that the sidebands of the individual subcarriers overlap and the signals are still received without adjacent carrier interference. The main advantage of this concept is that each of the radio streams experiences almost flat fading channel. In slowly fading channels the inter-symbol interference (ISI) and inter-carrier interference(ICI) is avoided with a small loss of energy using cyclic prefix. In order to assure a high spectral efficiency the subchannel waveforms must have overlapping transmit spectra. But to have overlapping spectra, subchannels need to

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Subcarrier Peaks

Magnitude

Frequency

Subcarrier Nulls

Fig. 2.3 Orthogonal subcarriers in multicarrier systems (OFDM)

be orthogonal. Orthogonality is a property that allows the signals to be perfectly transmitted over a common channel and detected without interference. Loss of orthogonality results in blurring between the transmitted signals and loss of information. For OFDM signals, the peak of one sub carrier coincides with the nulls of the other sub carriers. This is shown in Fig. 2.3. Thus there is no interference from other sub carriers at the peak of a desired sub carrier even though the sub carrier spectrums overlap. OFDM system avoids the loss in bandwidth efficiency prevalent in system using non orthogonal carrier set.

2.3.2

OFDM Signal Characteristics

An OFDM signal consists of N orthogonal subcarriers modulated by N parallel data streams, Fig. 2.4. The data symbols (dn,k ) are first assembled into a group of block size N and then modulated with complex exponential waveform {fk(t)}. After modulation they are transmitted simultaneously as transmitter data stream. The total continuous-time signal consisting of OFDM block is given by xðtÞ ¼

1 X n¼1

"

N 1 X k¼0

# dn; k ’k ðt  nTd Þ

(2.1)

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Relative Amplitude

0.6 0.4 0.2 0 –0.2 –0.4 –5

–4

–3

–2

–1

0

1

2

3

4

1

2

3

4

5

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Relative Amplitude

0.6 0.4 0.2 0 –0.2 –0.4 –5

–4

–3

–2

–1

0

5

Sample Duration Fig. 2.4 Spectra for OFDM subcarriers

where, fk(t) represents each baseband subcarrier and is given by  ’k ðtÞ ¼

e j2pfk t t 2 ½0; Td  0 otherwise

(2.2)

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where dn,k is the symbol transmitted during nth timing interval using kth subcarrier, Td is the symbol duration, N is the number of OFDM subcarriers and fk is kth subcarrier frequency, which is calculated as fk ¼ fo þ Tkd ; k ¼ 0 . . . N  1. Note that f0 is the lowest frequency used.

2.4 2.4.1

OFDM Transmission Concept

The OFDM based communication systems transmit multiple data symbols simultaneously using orthogonal subcarriers .The principle behind the OFDM system is to decompose the high data stream of bandwidth W into N lower rate data streams and then to transmit them simultaneously over a large number of subcarriers. Value of N is kept sufficiently high to make the individual bandwidth (W/N) of subcarriers narrower than the coherence bandwidth (Bc) of the channel. The flat fading experienced by the individual subcarriers is compensated using single tap equalizers. These subcarriers are orthogonal to each other which allows for the overlapping of the subcarriers. The orthogonality ensures the separation of subcarriers at the receiver side. As compared to FDMA systems, which do not allow spectral overlapping of carriers, OFDM systems are more spectrally efficient. OFDM transmitter and receiver systems are described in Figs. 2.5 and 2.6. At the transmitter, the signal is defined in the frequency domain. Forward Error Control/Correction (FEC) coding and interleaving block is used to obtain the robustness needed to protect against burst errors. The modulator transforms the encoded blocks of bits into a vector of complex values, Fig. 2.7. Group of bits are mapped onto a modulation constellation producing a complex value and representing a modulated carrier. The amplitudes and phases of the carriers depend on the data to be transmitted. The data transitions are synchronized at the carriers, and may be processed together, symbol by symbol.

Complex data constellations

BITS

Error Correction coding and Interleaving

Symbol Mapping (data modulation)

Fig. 2.5 OFDM transmitter

Baseband transmitted signal

Pilot symbol insertion

Serial-toparallel

OFDM Modulation via FFT

CP

DAC

IQ Modulation and upconverter

RF

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Received Complex data constellations

Received Signal at Baseband

Data conversion and I/Q demodulation

Carrier Synchronization

ADC

CP

OFDM Demodulation via IFFT

Parallel -to Serial-

Channel Estimation based on Pilot symbol

Symbol demapping (data demodulation)

Error correction decoding and Deinterleaving

O/P Binary data

Time Synchronization

Fig. 2.6 OFDM receiver

dn,0

ejw0t

S

x(t)

dn,N–1

Fig. 2.7 OFDM modulator

ejwN–1t

As the OFDM carriers are spread over a frequency range, chances are there that some frequency selective attenuation occurs on a time varying basis. A deep fade on a particular frequency may cause the loss of data on that frequency for that given time, thus some of the subcarriers can be strongly attenuated and that will cause burst errors. In these situations, FEC in COFDM can fix the errors [15]. An OFDM system with addition of channel coding and interleaving is referred to as Coded OFDM (COFDM). An efficient FEC coding in flat fading situations leads to a very high coding gain. In a single carrier modulation, if such a deep fade occurs, too many consecutive symbols may be lost and FEC may not be too effective in recovering the lost data. In a digital domain, binary input data is collected and FEC coded with schemes such as convolutional codes. The coded bit stream is interleaved to obtain diversity gain. Afterwards, a group of channel coded bits are gathered together (1 for BPSK, 2 for QPSK, 4 for QPSK, etc.) and mapped to the corresponding constellation points.

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Serial to Parallel Converter

Data to be transmitted is typically in the form of a serial data stream. Serial to parallel conversion block is needed to convert the input serial bit stream to the data to be transmitted in each OFDM symbol. The data allocated to each symbol depends on the modulation scheme used and the number of subcarriers. For example, in case a subcarrier modulation of 16-QAM each subcarrier carries 4 bits of data, and so for a transmission using 100 subcarriers the number of bits per symbol would be 400. During symbol mapping the input data is converted into complex value constellation points, according to a given constellation. Typical constellations for wireless applications are, BPSK, QAM, and 16 QAM. The amount of data transmitted on each subcarrier depends on the constellation. Channel condition is the deciding factor for the type of constellation to be used. In a channel with high interference a small constellation like BPSK is favourable as the required signal-to-noise-ratio (SNR) in the receiver is low. For interference free channel a larger constellation is more beneficial due to the higher bit rate. Known pilot symbols mapped with known mapping schemes can be inserted at this moment. Cyclic prefix is inserted in every block of data according to the system specification and the data is multiplexed to a serial fashion. At this point of time, the data is OFDM modulated and ready to be transmitted. A Digital-to-Analogue Converter (DAC) is used to transform the time domain digital data to time domain analogue data. RF modulation is performed and the signal is up-converted to transmission frequency. After the transmission of OFDM signal from the transmitter antenna, the signals go through all the anomaly and hostility of wireless channel. After the receiving the signal, the receiver downconverts the signal; and converts to digital domain using Analogue-to-Digital Converter (ADC). At the time of down-conversion of received signal, carrier frequency synchronization is performed. After ADC conversion, symbol timing synchronization is achieved. An FFT block is used to demodulate the OFDM signal. After that, channel estimation is performed using the demodulated pilots. Using the estimations, the complex received data is obtained which are de-mapped according to the transmission constellation diagram. At this moment, FEC decoding and deinterleaving are used to recover the originally transmitted bit stream. OFDM is tolerant to multi path interference. A high peak data rate can be achieved by using higher order modulations, such as 16 QAM and 64 QAM, which improve the spectral efficiency of the system.

2.4.3

Demodulator

The OFDM demodulator is shown in the form of a simplified block diagram is shown in Fig. 2.8. The orthogonality condition of the signals is based orthogonality of subcarriers {fk(t)}, defined by:

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R. Prasad and F.J. Velez Td

∫ ( •)

dn,0

Td

e —jw0t x(t) Td

∫ (•)

dn,N–1

Td

e —jNw0t Fig. 2.8 OFDM demodulator

Z

’k ðtÞ’l ðtÞdt ¼ Td dðk  lÞ ¼



Td k ¼ l 0 otherwise

(2.3)

<

The demodulator satisfies the above condition for orthogonality of the subcarriers.

2.5

OFDM Symbol Description

OFDM boosts throughput by using several subcarriers in parallel while multiplexing data over the set of subcarriers. Inverse-Fourier-transforming (IFT) creates the OFDM waveform. This time duration is referred to as the useful symbol time Tsym. A copy of the last TCP of the useful symbol period, termed Cyclic Prefix (CP), is used to mitigate multipath, while maintaining the orthogonality of the tones. Figure 2.9 illustrates this structure in the time domain. The frequency domain description includes the basic structure of an OFDM symbol (Fig. 2.10). An OFDM symbol shown in Fig. 2.9 is made up from subcarriers, the number of which determines the FFT size used. There are three subcarrier types: (1) data subcarriers, for data transmission, (2) pilot subcarriers, for various estimation purposes, and (3) null subcarriers, for no transmission at all, for guard bands, nonactive subcarriers and for the DC subcarrier.

2.6

ISI and ICI Mitigation

Two types of difficulties arise when a signal is transmitted through a timedispersive channel. First, channel dispersion destroys the orthogonality between subcarriers and cause intercarrier interference (ICI) for the signal. Second, the

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Fig. 2.9 OFDM symbol time structure (From [19])

TCP

Tsym Ttotal

Data Subcarriers

Guard Band

DC Subcarrier

Channel

Pilot Subcarriers

Guard Band

Fig. 2.10 OFDM frequency description (From [20])

system may sometimes transmit multiple OFDM symbols in a series causing intersymbol interference (ISI) between successive OFDM symbols. Guard intervals were proposed as the solution. A guard interval is defined by an empty space between two OFDM symbols, which serves as a buffer for the multipath reflection. When guard bands are inserted between successive OFDM symbols avoids ISI but cannot cope with the loss of the subcarrier orthogonality. This problem was addressed by Peled and Ruiz, in 1980, by introducing cyclic prefix (CP) instead of guard interval between successive OFDM symbols. CP is a copy of the last part of OFDM symbol which is appended to front the transmitted OFDM symbol. The cyclic prefix preserves the orthoganility of the subcarriers and prevents ISI between successive OFDM symbols. CP helps to maintain orthogonality between the sub carriers. The interval must be chosen to be larger than the expected maximum delay spread, such that multi path reflection from one symbol would not interfere with another. As shown in the Fig. 2.11, CP still occupies the same time interval as guard period but, in turn, ensures that the delayed replicas of the OFDM symbols will always have a complete symbol within the FFT interval. Thus, the transmitted signal is still periodic and this periodicity plays a very significant role as this helps maintaining the orthogonality. In a Fourier transform, all the resultant components of the original signal are orthogonal to each other. CP makes sure that subsequent subcarriers are orthogonal to each other.

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End of symbol is prepended to the beginning

OFDM Symbol time Guard time

FFT time

Delay Spread

No ISI

Fig. 2.11 Use of cyclic prefix to combat ISI and ICI

At the receiver side, CP is removed before any processing starts. As long as the length of CP interval is larger than maximum expected delay spread, all reflections of previous symbols are removed and orthogonality is restored. The orthogonality is lost when the delay spread is larger than length of CP interval. Although the generated signals are always orthogonal, inserting CP has its own cost. Part of signal energy is lost since it carries no information. The loss may be calculated by SNRloss

CP

  TCP ¼ 10log10 1  Tsym

(2.4)

where TCP is the interval length of CP and Tsym is the OFDM symbol duration. The total symbol duration is Ttotal ¼ TCP þ Tsym :

(2.5)

The advantage gained by introducing CP is the zero ICI and ISI (although part of the signal energy is lost). Thus, CP combats two main problems of signal transmission, first it removes the effect of ISI, and second, by maintaining orthogonality, it completely removes the ICI.

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Spectral Efficiency

Figure 2.2 illustrates the different between FDMA and OFDM systems. In the case of OFDM, an higher better spectral efficiency is achieved by maintaining orthogonality between the subcarriers. If orthogonality is maintained between different subchannels during transmission, then it is possible to separate the signals very easily at the receiver side. This is ensured by classical FDM by inserting guard bands between sub channels. These guard bands keep the subchannels far enough so that separation of different subchannels is possible. Naturally, inserting guard bands results to inefficient use of spectral resources. In OFDM, orthogonality makes it possible in OFDM to arrange the subcarriers in such a way that the sidebands of the individual carriers overlap and still the signals are received at the receiver without being interfered by ICI. The receiver acts as a bank of demodulators, translating each subcarrier down to DC, with the resulting signal integrated over a symbol period to recover raw data. If the other subcarriers all down converted to the frequencies that, in the time domain, have a whole number of cycles in a symbol period Tsym, then the integration process results in zero contribution from all other carriers. As a consequence, the subcarriers are linearly independent (i.e., orthogonal) if the carrier spacing is a multiple of 1/Tsym [18].

2.8 2.8.1

Orthogonal Frequency Division Modulation Access Improvements

In the previous section, we discussed the OFDM as a multiplexing scheme that provides better spectral efficiency and immunity to multipath fading. The OFDM system is also simpler to design based on FFT/IFFT method. These advantages are further extended for multiple access schemes by assigning a subset of subcarriers or tones of OFDM to individual users. This multiple access technique is termed as OFDMA. The allocation of subsets of tones to various users allows for simultaneous transmission of data from multiple users, allowing for sharing the physical medium. Although this technique looks very much like FDMA, the large guard bands required in FDMA are not needed in OFDMA.

2.8.2

Subchannelization

In OFDMA, the active subcarriers are divided into subsets of subcarriers. Each subset represents a subchannel, as shown in the Fig. 1.2. These sub-carriers that

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form a single subchannel need not be adjacent. Thus, an OFDM symbol is subdivided into several subchannels by grouping the subcarriers. In the DL, a single subchannel may be intended for different receivers whereas, in the uplink, a transmitter may be assigned one or more subchannels, and several transmitters may transmit simultaneously.

2.8.3

OFDMA Subchannelization: Its advantages to WiMAX

In OFDMA, subchannelization defines subchannels that can be allocated to subcarrier stations depending on their channel conditions and data requirements. Several SS can transmit in the same time slot over several subchannels. Depending on the channel conditions and data requirements modulation and coding is set individually for each subscriber. The transmitter power can be adapted separately as well, which optimizes the use of network resources. Because of subchannelization OFDMA signals are more complex than OFDM ones but offer better performance and scalability. This feature is very useful for WiMAX BSs. By using subchannelization, within the same time slot, the BS is able to allocate more transmitter power to those SSs with lower SNR and less power to the ones with higher SNR. Subchannelization also enables the BS to allocate higher power to subchannels assigned to indoor SSs, which results in better in-building coverage. Subchannelization in the uplink saves the power of the user device by concentrating power to the selected subchannels allocated to it. This power saving feature is indeed very useful for battery powered SSs. Subchannelisation uses orthogonal frequency-division multiple access with a 2048-point transform [11] and is designed for NLoS operation in the frequency bands below 11 GHz. For licensed bands, channel bandwidths allowed is limited to the regulatory provisioned bandwidth divided by any power of 2 no less than 1.0 MHz. The concept is shown in Fig. 2.12.

2.9

Advantages of OFDM Systems

The following advantages of OFDM may be identified: l

l

l

OFDM is spectrally efficient; IFFT/FFT operation ensures that sub-carriers do not interfere with each other. OFDM has an inherent robustness against narrowband interference. Narrowband interference will affect at most a couple of subchannels. Information from the affected subchannels can be erased and recovered via the forward error correction (FEC) codes. Equalization is very simple compared to Single-Carrier systems.

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OFDM

UL part

Preamble UL

FCH

Preamble DL

Sub-Carriers

DL part

79

Time

DL part

OFDM UL part

User1

User3

FCH

Preamble DL

Sub-Channels

User2

User4 User5 Time

Fig. 2.12 OFDMA versus OFDM: subchannels and sub-carriers

l

l

l

l

l

l

The OFDM transmitter is low cost as the design is simple because the modulation technique is simpler implementation based on a highly optimized FFT/IFFT block. Also OFDM transmitters posses the ability to implement the mapping of bits to unique carriers via the use of the Inverse Fast Fourier Transform (IFFT) [13]. As the OFDM transmitter simplifies the channel effect, thus a simple receiver structure is enough for recovering transmitted data. If we use coherent modulation schemes, then very simple channel estimation (and/or equalization) is needed. In turn, no channel estimator is needed if differential modulation schemes are used [14]. In a relatively slow time-varying channel, it is possible to significantly enhance the capacity by adapting the data rate per subcarrier according to the value of SNR for that particular subcarrier [1]. In contrast to CDMA, OFDM receiver collects signal energy in frequency domain, thus it is able to protect energy loss at frequency domain. OFDM is more resistant to frequency selective fading than single carrier systems. The orthogonality preservation procedures in OFDM are much simpler compared to CDMA or TDMA techniques even in very severe multipath conditions.

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OFDM can be used for high-speed multimedia applications with lower service cost. OFDM can also support dynamic packet access. Ability to comply with world-wide regulations: Bands and tones can be dynamically turned on/off to comply with changing regulations. Single frequency networks are possible in OFDM, which is especially attractive for broadcast applications. Smart antennas can be integrated with OFDM. MIMO systems and space-time coding can be realized on OFDM and all the benefits of MIMO systems can be obtained easily. Adaptive modulation and tone/power allocation are also realizable on OFDM.

2.10 2.10.1

Disadvantages of OFDM Systems Strict Synchronization Requirement

OFDM is highly sensitive to time and frequency synchronization errors, especially at frequency synchronization errors, everything can go wrong. Demodulation of an OFDM signal with an offset in the frequency can lead to a high bit error rate. These are two sources of synchronization errors. One is caused by the difference between local oscillator frequencies in transmitter and receiver, while the other is due to the relative motion between the transmitter and receiver that gives Doppler spread. Local oscillator frequencies at both points must match as closely as they can. For higher number of subchannels, the matching should be even more perfect. Motion of transmitter and receiver causes the other frequency error. So, OFDM may show significant performance degradation at high-speed moving vehicles [12]. To optimize the performance of an OFDM link, accurate synchronization is therefore of prime importance. Synchronization needs to be done into three aspects: symbol, carrier frequency and sampling frequency synchronization. A description of synchronization procedures is given in [1].

2.10.2

Peak-to-Average Power Ratio

Peak to Average Power Ratio (PAPR) is proportional to the number of subcarriers used for OFDM systems. The PAPR for an OFDM system is given by 10 log (N) where N is the number of subcarriers. For example for a 48 subcarrier system, such as 802.11a where 48 out of 64 subcarriers are active, the PAPR is approximately 17 dB. Therefore OFDM system with large number of sub-carriers will thus have a very large PAPR when the sub-carriers add up coherently. An

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Large PAPR of a system makes the implementation of Digital-to-Analog Converter (DAC) and Analog-to-Digital Converter (ADC) to be extremely difficult. The design of RF amplifier also becomes increasingly difficult as the PAPR increases. To mitigate the effect of such large PAPRs on performance degradation of the OFDM system, the design of the OFDM system needs to incorporate costly RF hardware, such as efficient and large linear dynamic range power amplifiers. Incorporating costly RF hardware, however, increases the cost of the OFDM system. There are basically three techniques that are used at present to reduce PAPR, they are Signal Distortion Techniques, Coding Techniques and finally the Scrambling Technique.

2.10.3

Co-channel Interference Mitigation in Cellular OFDM

A conventional OFDM system exhibits performance degradation due to frequency coherence of the channel. The closer the spacing between the adjacent subcarriers or the narrower the required coherence bandwidth is. In many channels, adjacent subcarriers will fall within the coherence bandwidth and will thereby experience flat fading. In cellular communications systems, co-channel interference (CCI) is combated by combining adaptive antenna techniques, such as sectorization, directive antenna, antenna arrays, etc. Some are just avoidance techniques but others may be truly interference cancellation methodologies. Using OFDM in cellular systems will give rise to CCI. Similarly with the traditional techniques, with the aid of beam steering, it is possible to focus the receiver’s antenna beam on the served user, while attenuating the co-channel interferers. This is significant since OFDM is sensitive to CCI.

2.11 2.11.1

Scalable OFDMA Parameters and Principles

When designing OFDMA wireless systems the optimal choice of the number of subcarriers per channel bandwidth is a tradeoff between protection against multipath, Doppler shift, and design cost/complexity. Increasing the number of subcarriers leads to better immunity to the inter-symbol interference (ISI) caused by multipath (due to longer symbols); in turn, it increases the cost and complexity of the system (it leads to higher requirements for signal processing power and power amplifiers with the capability of handling higher peak-to-average power ratios). Having more subcarriers also results in narrower subcarrier spacing and therefore the system becomes more sensitive to Doppler shift and phase noise. Calculations

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Table 2.3 SOFDMA parameters System Parameters Channel Bandwidth (MHz) Sampling Frequency (MHz) FFT Size (NFFT) Number of used data subcarriers Number of pilot subcarriers Number of null guard band subcarriers Number of Subchannnels Subcarrier frequency spacing Useful symbol time (Tb ¼ 1/f ) Guard time (Tg ¼ Tb/8) OFDMA symbol duration (Ts ¼ Tb + Tg) Number of OFDMA symbols in 5 ms

Numerology 1.25 1.4 128 72 12 44 2 10.94 kHz 91.4 11.4 102.9 48

5 5.6 512 360 60 92 8

10 11.2 1,024 720 120 184 16

20 22.4 2,048 1,440 240 368 32

show that the optimum tradeoff for mobile systems is achieved when subcarrier spacing is about 11 kHz [28]. Unlike many other OFDM-based systems such as IEEE 802.11a/g WLANs, the 802.16 standard supports variable bandwidth sizes for NLoS operations. In order to keep optimal subcarrier spacing, the FFT size should scale with the bandwidth. This concept is introduced in Scalable OFDMA (SOFDMA) [23, 28]. The concept of scalability was introduced to the IEEE 802.16 WirelessMAN OFDMA mode by the 802.16 Task Group e (TGe). A scalable physical layer enables standard-based solutions to deliver optimum performance in channel bandwidths, ranging from 1.25 MHz to 20 MHz with fixed subcarrier spacing for both fixed and portable/ mobile usage models, while keeping the product cost low. Possible SOFDMA profiles are shown in Table 2.3. In order to reduce system complexity and facilitate interoperability the decision was taken to limit the number of profiles for WiMAX. Currently, only two FFT sizes, 512 and 1024, are recommended in WiMAX. Besides the fixed (optimal) subcarrier spacing SOFDMA specifies that the number of subcarriers per subchannel should be independent of bandwidth, too. This results in the property that establishes the number of subchannels scales with FFT/bandwidth. The basic principles of SOFDMA are the following: l l l

l

Subcarrier spacing is independent of bandwidth The number of subcarriers scales with bandwidth The smallest unit of bandwidth allocation, based on the concept of subchannels, is fixed and independent of bandwidth and other modes of operation The number of subchannels scales with bandwidth and the capacity of each individual subchannel remains constant

In addition to variable FFT sizes, the specification supports other features such as Advanced Modulation and Coding (AMC) subchannels, Hybrid Automatic Repeat Request (H-ARQ), high-efficiency uplink subchannel structures, MultipleInput-Multiple- Output (MIMO) diversity and coverage enhancing safety channels, as well as other OFDMA default features, such as different subcarrier allocations and diversity schemes.

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The SOFDMA modulation schemes make IEEE 802.16e system backward compatible to the FBWA IEEE 802.16-2004 specification, which simplifies “interoperability” because it would require user equipment for roaming between fixed and mobile BWA systems based on the IEEE 802.16 family of standards.

2.11.2

Reference Model

The Reference model for IEEE 802.16 is shown in the Fig. 2.13. IEEE 802.16 standard describes both the MAC and PHY for fixed and the mobile broadband wireless access. The major components of the reference model are Data/Control plane, management plane and the network management plane. The functions of each plane are defined in Table 2.4.

Scope of standard

CS SAP

MAC

ATM Convergence Layer

Packet Convergence Layer

Management Entity Service-Specific Convergence Sublayer

MAC SAP MAC Common Part Sublayer (MAC CPS)

Security Sublayer

Management Entity MAC Common Part Sublayer Security Sublayer

PHY

PHY SAP

Physical Layer (PHY)

Data/Control Plane

Managemnent Entity PHY

Network Management System

Service-Specific Convergence Sublayer

Management Plane

Fig. 2.13 IEEE 802.16 reference model (adapted from [19]) Table 2.4 IEEE 802.16 Planes and their functions Various IEEE 802.16 Planes Functions Control Plane Short term control actions such as admission control, resource control, congestion control and load balanced routing Management Plane Long term management actions such as network provisioning, traffic engineering, monitoring Data Plane Operations on data to allow the transport of information

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IEEE 802.16 PHY Layer Supported Frequency Bands

The IEEE 802.16 standard supports multiple physical layer specifications. The first version of the standard only supported single carrier modulation in 10–66 GHz range of (licensed) spectrum. With the addition of OFDM and scalable OFDMA to the PHY layers, IEEE 802.16 now operates in NLoS environment and also provides mobility. Thus the scope of the IEEE 802.16 has been extended for use in below 11 GHz frequency bands along with the initially supported 10–66 GHz bands. The range of frequencies supported in the licensed as well as unlicensed bands for IEEE 802.16 is as described below: 10–66 GHz licensed band – IEEE 802.16-2004 defines the PHY layer for the 10–66 GHz licensed spectrum. This frequency bands require LoS operation and the effect of multipath is negligible. The channel size within these bands is typically wide, between 25 and 28 MHz. 2–11 GHz licensed and licensed exempt – In this frequency bands, both licensed and licensed exempt bands are addressed. Additional physical functionality supports have been introduced to operate in LOS and NLOS environment and to mitigate the effect of multipath propagation. In fact, many of the IEEE 802.16 PHY’s most advantageous capabilities are found in this frequency range. Operation in licensed exempt band experiences additional interference and coexistence issue. The PHY and MAC address mechanism like dynamic frequency selection (DFS) to detect and avoid interference for licensed exempt band. Although service provision in this frequency band is highly depends on design goals, vendors typically cite target aggregate data rates of up to 70 Mb/s in a 14 MHz channel.

2.12.2

Channel Bandwidth

IEEE 802.16 supports flexible channel bandwidth in integer multiple of 1.25 MHz, 1.5 MHz, 1.75 MHz, 2 MHz and 2.75 MHz with a maximum of 20 MHz. However, to ensure interoperability between different vendors’ products, WiMAX forum has initially narrowed down the large choice of possible bandwidth to a few possibilities [19, 32].

2.12.3

IEEE 802.16 PHY Interface Variants

The standard has assigned a unique name to each physical interface. They have been described below along with their supported features in brief with the tabular representation in Table 2.5.

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Table 2.5 IEEE 802.16 air interface nomenclature and description (Source: [11]) Designation Band of Operation Duplexing Notes Mode WirelessMAN-SC 10–66 GHz TDD, FDD Single Carrier WirelessMANSCa 2–11 GHz Licensed TDD, FDD Single Carrier technique for NLOS band WirelessMAN 2–11 GHz TDD OFDM for NLOS operation OFDM Licensed band FDD WirelessMAN 2–11 GHz TDD OFDM Broken into subgroups to OFDMA Licensed band FDD provide multiple access in a single frequency band WirelessHUMAN 2–11 GHz Licensed TDD May be SC, OFDM, OFDMA. Must Band Exempt include Dynamic Frequency Selection to mitigate interference

The PHY layer (or simply PHY) of IEEE 802.16 supports five different modes, as follows: WirelessMAN-SC PHY – WirelessMAN-SC PHY specification is intended for operation in the 10–66 GHz frequency band. At these frequencies, LoS operation is practical necessity due to propagation characteristics. WirelessMAN-SC PHY does not support mobility. This is an adaptive-modulation (QPSK, 16-QAM and 64-QAM) scheme on a single carrier. Both TDD and FDD configurations are supported in order to allow operation in worldwide spectrum allocations [29]. Bandwidth allocation is based on a combination of TDMA and demand assigned multiple access (DAMA). WirelessMAN-SCa PHY – WirelessMAN-SCa (or SC2 as it is alternatively known) is also a single-carrier modulation, defined for the 2–11 GHz band. It is designed for NLoS channels and also uses adaptive modulation. This standard supports “spread BPSK”, BPSK, QPSK, 16-QAM, 64-QAM, and 256-QAM modulations. Both Time- and Frequency-Division Duplex modes are defined. For uplink TDMA is used while for downlink either TDM or TDMA is applied. WirelessMAN-OFDM PHY – This is based on orthogonal frequency division multiplexing (OFDM) with a 256 point transform to support multiple SS in 2–11 GHz frequency band. Access is done by TDMA. The WiMAX Forum has adopted this PHY specification for BWA. Because of employing OFDM and other features like multiple forward error correction method, this is the most suitable candidate to provide fixed support in NLOS environment. Wireless MAN-OFDMA PHY – This PHY specification uses Orthogonal Division Muliple Access (OFDMA) which is an extension of Orthogonal Frequency Division Modulation (OFDM) with at least a single support of specified multipoint transform (2048, 1024, 512 or 128) to provide combined fixed and Mobile BWA. Operation is limited to below 11 GHz licensed band [30]. In this specification, multiple access is provided by addressing a subset of the multiple carriers to individual receivers. WirelessHUMAN – Wireless HUMAN (High-speed Inlicensed Metropolitan Area Network) specification is targeted for license exempt bands below 11 GHz.

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For unlicensed frequency bands, in addition to huge spectrum allocation available for public network access nationwide, any of the air interfaces specified for 2–11 GHz can be used. This specification, however, supports only TDD for duplexing [1]. Unlicensed bands allow experimentation and innovation, attracting significant interest for both academia and industry (manufacturers and service providers). It is, however, subject to various rules and constraints, such as transmitter power (or effective isotropic radiated power) limits. The details on the above PHY air interface specifications follows: Payload – Payload refers to individual units of transmission content that are of interest to some entity at the receiver. Burst – A burst contains payload data and is formed according to the rules specified by the burst profile associated with the burst. The existence of the burst is made known to the receiver through the contents of either the uplink or downlink maps. For the uplink, a burst is a complete unit of transmission that includes a leading preamble, encoded payload, and trailing termination sequence. Burst Set – A burst set is a self-contained transmission entity consisting of a preamble, one or more concatenated bursts, and a trailing termination sequence. For the uplink, burst set is synonymous with burst. Burst Frame – A burst frame contains all information included in a single transmission. The DL and UL sub-frames each hold a burst frame. Burst Profiles – Burst profile contains information about various parameters such as modulation type, FEC, preamble type and guard times. Burst profile is a part of downlink as well as uplink frame. MAC Frame – A MAC frame refers to the fixed bandwidth intervals reserved for data exchange. For TDD, a MAC frame consists of one downlink and one uplink sub-frame, delimited by the transmit transition gap (TTG). For FDD, the MAC frame corresponds to the maximum length of the downlink sub-frame. FDD uplink sub-frames operate concurrently with downlink sub-frames but on a separate (frequency) channel. Downlink Channel Descriptor (DCD) – DCD describes the downlink PHY characteristics of a downlink channel. The DCD is type of medium access control management message and is broadcasted by the BS at periodic intervals. The DCD contains information regarding frame duration codes and downlink burst profiles. Uplink Channel Descriptor (UCD) – UCD describes the downlink PHY characteristics of a uplink channel.UCD is also a type of medium access control management message and is broadcasted periodically by the BS. Downlink Interval Usage Codes (DIUCs) – DIUC is an interval usage code specific to a downlink. An interval usage code identifies a particular burst profile that can be used by a downlink or uplink transmission interval. Thus DIUC is used to identify the burst profile of downlink allocations in DL MAPs. Uplink Interval Usage Codes (UIUCs) – UIUC is an interval usage code specific to an uplink. Downlink MAP (DL MAP) – DL-MAP is type MAC message that defines burst start times for both time division multiplex and time division multiple access (TDMA) for downlink allocations. These allocations are specified in PHY specific

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DL MAP elements. The DL MAP also include information about DIUCs to identify the burst profile. DL_MAP is the only mechanism used in WirelessMAN-SC and WirelessMANSC-a PHYs to describe DL access while in WirelessMAN-OFDM and for WirelessMAN-OFDMA an additional format called downlink frame prefix (DLFP) is also used. Uplink MAP (UL MAP) – UL MAP describes the UL TDMA allocations in which exact time offsets, along with the burst profiles with which the SSs will transmit data is specified. Similar to the DL MAP, UL MAP also include information about UIUCs to identify the burst profile. The UL contention slots also form part of the UL MAP.

2.13 2.13.1

WirelessMAN-SC PHY Overview

WirelessMAN-SC PHY mode of IEEE 802.16-2004 supports operation in the 10–66 GHz frequency band. This PHY specification is designed with a high degree of flexibility in order to allow service providers the ability to optimize system deployments with respect to cell planning, cost, radio capabilities, services and capacity. Both TDD and FDD configurations are allowed for flexible spectrum usage. The FDD mode also supports full-duplex SSs as well as half duplex SSs. Both cases use a burst transmission format, whose framing mechanism supports adaptive burst profiling in which transmission parameters, including the modulation and coding schemes, may be adjusted individually to each SS on a frame-by-frame basis. The FDD case supports full-duplex SSs as well as half duplex SSs, which do not transmit and receive simultaneously. The 802.16 supports adaptive burst profiling in which transmission parameters, including the modulation and coding scheme may be adjusted to each SS on frame by frame basis. The bandwidth allocation, that is, the allocation for channel time is based on combination of time division multiple access (TDMA) and demand– assigned multiple access (DAMA).The uplink channel is divided into a number of time slots. These time slots are assigned on frame by frame basis by the BS MAC. The SS uses these time slots for registration, ranging, contention bandwidth requests and user traffic. The downlink channel is TDM, with the information for each SS multiplexed onto a single stream of data and received by all SSs within the same sector. To support half-duplex FDD SSs, provision is also made for a TDMA portion of the downlink. The downlink PHY includes a Transmission Convergence sub-layer that inserts a pointer byte at the beginning of the payload to help the receiver identify the beginning of a MAC PDU. Data bits coming from the Transmission Convergence sub-layer are randomized, FEC encoded, and mapped to a QPSK, 16-QAM, or 64-QAM (optional) signal constellation.

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The uplink PHY is based upon TDMA burst transmission. Each burst is designed to carry variable-length MAC PDUs. The transmitter randomizes the incoming data, FEC encodes it, and maps the coded bits to a QPSK, 16-QAM (optional), or 64-QAM (optional) constellation.

2.13.2

Duplexing Techniques and PHY Type Parameter Encodings

2.13.2.1

FDD Mode and FDD frame

For FDD operation the uplink and downlink channels are on separate frequencies. The capability of the downlink to be transmitted in bursts facilitates the use of different modulation types and allows the system to simultaneously support full-duplex SSs and half-duplex SSs. The downlink carrier may be continuous. Figure 2.14 shows the basics of the FDD operation. Figure 2.15 presents the half duplex FDD frame while Fig. 2.16 shows the full duplex one. 2.13.2.2

TDD Mode and TDD frame

In the TDD operation, the uplink and downlink transmissions share the same frequency band but are separated in time. A TDD frame has a fixed duration and contains one downlink and one uplink sub-frame. The TDD framing is adaptive, that is, the link capacity allocated to the downlink versus uplink may vary. Figure 2.17 shows the TDD frame structure. Using TDD enables efficient support of asymmetric traffic for easy support of IP-based traffic, channel reciprocity and advanced antenna systems. Hybridautomatic repeat request (H-ARQ) provides added robustness with rapidly

Downlink

f1

Uplink

f2 frame

time Broadcast

Half Duplex SS # 1

Full Duplex Capable SS

Half Duplex SS # 2

Fig. 2.14 FDD frame structure

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Downlink

f1

Uplink

f2 frame

time Half Duplex SS # 1 Half Duplex SS # 2

Fig. 2.15 H-FDD framing

Downlink

f1

Uplink

f2 frame

time Full Duplex Capable SS

Fig. 2.16 Full Duplex framing

n = (Symbol Rate x Frame Duration) / 4 Downlink Subframe

PS 0

Uplink Subframe

PS n – 1

Adaptive

Frame j – 2

Frame j – 1

Fig. 2.17 TDD frame structure

Frame j

Frame j + 1

Frame j + 2

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changing radio path conditions in high mobility scenarios. TDD is less complex than FDD, where uplink and downlink traffic are separated by a guard time.

2.13.3

Frame Structure

The WirelessMAN-SC PHY operates in a framed format. Within each frame are a downlink sub-frame and an uplink sub-frame. The downlink sub-frame begins with information necessary for frame synchronization and control. In the TDD, the downlink sub-frame comes first, followed by the uplink sub-frame. The DL subframe begins with the information necessary for frame synchronisation and control as shown in Fig. 2.18. The downlink frame starts with a frame start preamble used by the PHY for synchronisation and equalization. This is followed by frame control section which is indicated in form of maps. Control section is followed by the TDM data section which is organized in the form of bursts. These burst profiles are organized in decreasing robustness fashion. The burst begins with the QPSK modulation followed by 16QAM and 64QAM. In the FDD case, uplink transmissions occur concurrently with the downlink frame. Supported frame durations allows for three frame durations 0.5, 1, and 2 ms.

Frequency

Uplink Subframe (TDMA)

FDD Downlink Subframe Time

TDD

Downlink Subframe

Uplink Subframe TDMA

Control info Preamble

Fig. 2.18 Frame structure

Maps

Data QPSK Burst

16-QAM Burst

64-QAM Burst

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2.13.4

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Downlink PHY

In a TDD transmission, the BS basically transmits a TDM signal. This TDM signal is a series of individual subscriber stations allocated time slots. The downlink subframe starts with a preamble, which is used for synchronization and equalisation. The frame start preamble is a 32-symbol sequence generated by repeating a 16-symbol sequence. The frame control section is used to pass control information for the channel to all SSs, and this data is not encrypted. The following section is a broadcasting control section that contains the DLMAP and UL-MAP, which specified when physical layer transmissions (modulation and FEC changes) occur within the downlink frame as well as the UL-MAP. The TDM portions are just payloads to be transmitted to SSs which are organized into bursts with different burst profiles and therefore different level of transmission robustness. The bursts are always transmitted in order of decreasing robustness. The DL-MAP portion of the frame control section provides listening SSs with the characteristics of the downlink channel. This information includes: PHY synchronization (i.e., schedule of physical layer transitions to include modulation and FEC changes), a downlink channel descriptor message (DCD), a programmable 48-bit BS identifier, and the number of data elements to follow. Reference [21] The DCD and the BS identifier identify the channel and the BS, respectively, and thus together are useful for situations where a SS is on the border of multiple IEEE 802.16 sectors or cells. For example, with the use of a single FEC type with fixed parameters, data begins with QPSK modulation, followed by 16-QAM, followed by 64-QAM. In the case of TDD, a TTG separates the downlink sub-frame from the uplink sub-frame. The frames in TDMA portions may differ in bandwidth due to the dynamics of bandwidth demand for the variety of services that maybe active. Since the recipient SS is implicitly indicated in the MAC headers rather than in the DL-MAP, SSs listen to all portions of the downlink sub-frame they are capable of receiving. The structure of the downlink sub-frame using TDD is illustrated in Fig. 2.19. The UL-MAP is used to communicate uplink channel access allocations to the SSs. Information provided in the UL-MAP include: Uplink channel identifier, uplink channel descriptor (UCD), number if information elements to map, allocation start time and map information elements. The UCD is used to provide SSs with information regarding the required uplink burst profile. The map information elements message identifies the SS this information applies to by using a connection identifier (CID). This message also provides an uplink interval usage code (UIUC) and offsets that are to be used by the SS to transmit on the uplink. The uplink interval usage code is used to specify the burst profile to be used by the SS on the uplink. The transmit transition gap (TTG) is a gap between the downlink burst and the subsequent uplink burst. This gap allows time for the BS to switch from the transmitter to the receive mode while SSs switch from receive to transmit mode. During this gap, the BS and SS are not transmitting modulated data but simply

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Preamble

TDM Portion Broadcast Control DIUC = 0

TDM DIUC a

TDM DIUC b

TDM DIUC c

Preamble

TTG

DL-MAP

UL-MAP

Fig. 2.19 TDD downlink sub-frame

allowing the BS transmitter carrier to ramp down, the transmit/receive (Tx/Rx) antenna switch to “actuate”, and the BS receiver section to “activate”. After the gap, the BS receiver shall look for the first symbols of uplink burst. This gap is an integer number of PS durations and starts on a PS boundary. The receive transition gap (RTG) is a gap between the uplink burst and the subsequent downlink burst. This gap allows time, for the BS, to switch from receive to transmit mode and SSs to switch from transmit to receive mode. During this gap, the BS and SS are not transmitting modulated data but simply allowing the BS transmitter carrier to ramp up, the Tx/Rx antenna switch to “actuate”, and the SS receiver sections to “activate”. After the gap, the SS receivers shall look for the first symbols of QPSK modulated data in the downlink burst. This gap is an integer number of PS durations and starts on a PS boundary. For FDD case, the structure of the downlink sub-frame is illustrated in Fig. 2.20. As in the TDD case, the downlink sub-frame begins with a Frame Start Preamble followed by a frame control section and a TDM portion organized into bursts transmitted in decreasing order of burst profile robustness. This TDM portion of the downlink sub-frame contains data transmitted to one or more of the following: l l l

Full-duplex SSs Half-duplex SSs scheduled to transmit later in the frame than they receive Half-duplex SSs not scheduled to transmit in this frame

The FDD downlink sub-frame continues with a TDMA portion used to transmit data to any half-duplex SSs scheduled to transmit earlier in the frame than they receive. This allows an individual SS to decode a specific portion of the downlink without the need to decode the entire downlink sub-frame. In the TDMA portion, each burst begins with the Downlink TDMA Burst Preamble for phase

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TDM DIUC c

TDMA DIUC d

TDMA Portion

TDMA DIUC e

TDMA DIUC f

Preamble

TDM DIUC b

Preamble

TDM DIUC a

Preamble

Broadcast Control DIUC = 0

Preamble

Preamble

TDM Portion

Preamble

Burst Start Points

DL-MAP

UL-MAP

Fig. 2.20 FDD downlink sub-frame structure

resynchronization. Bursts in TDMA portion need not be ordered by burst profile robustness. The FDD frame control section includes a map of both the TDM and TDMA bursts. The TDD downlink sub-frame, which inherently contains data transmitted to SSs, transmit later in the frame than they receive, and is identical in structure to the FDD downlink sub-frame for a frame in which no half duplex SSs are scheduled to transmit before they receive.

2.13.4.1

Downlink Channel Encodings

The downlink data sections are used for transmitting data and control messages to the specific SSs. The data are always FEC coded and are transmitted at the current operating modulation of the individual SS. In the TDM portion, data is transmitted in order of decreasing burst profile robustness. For TDMA portion, the data are grouped into separately delineated bursts that need not be in robustness order. The DL-MAP message contains a map stating at which PS the burst profile changes occur. The number of PSs allocated to a particular burst is calculated from the DLMAP, which indicates the starting position of each burst as well as the burst profiles. If n denote the minimum number of PSs required for one FEC codeword of the given burst profile (where n is not necessarily an integer), then, i = kn + j + q, where k is the number of whole FEC code words that fit in the burst, j (not necessarily an integer) is the number of PSs occupied by the largest possible shortened codeword, and q (0  q < 1) is the number of PSs occupied by pad bits inserted at the end of the burst to guarantee that i is an integer.

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In Fixed Codeword Operation, j is always 0. A codeword can end partway through a modulation symbol as well as partway through a PS. When this occurs, the next codeword shall start immediately, with no pad bits inserted. At the end of the burst (i.e., when there is no next codeword), then 4q symbols are added as padding (if required) to complete the PS allocated in the DL-MAP. The number of padding bits in these padding symbols is 4q times the modulation density, where the modulation density is two for QPSK, four for 16-QAM, and six for 64-QAM. Note that padding bits may be required with or without shortening. Either k or j, but not both, may be zero. The number j implies some number of bits b. Assuming that j is nonzero, it shall be large enough such that b is larger than the number of FEC bits, r, added by the FEC scheme for the burst. The number of bits preferably an integral number of bytes) available for user data in the shortened FEC codeword is b–r. Any bits that may be left over from a fractional byte are encoded as binary 1 to ensure compatibility with the choice of 0xFF for pad. A codeword cannot have less than six information bytes. This is illustrated in Fig. 2.21. In the case of TDMA downlink, a burst includes the Downlink TDMA Burst Preamble of length p PSs, and the DL-MAP entry points to its beginning, Fig. 2.22.

2.13.4.2

Downlink Transmission Convergence Sub-layer

The downlink payload is segmented into blocks of data designed to fit into the proper codeword size after the CS pointer byte is added. The payload length may vary,

Number of modulation symbols = 4i

Number of PSs I = y – x = kn + j + q

n

n

FEC Codeword

FEC Codeword

Map entry m starts on PS = x

n

j

q

FEC FEC Codeword Codeword

b-r data bits r redundancy bits

j PSs = b bits

Fig. 2.21 DL-MAP usage with shortened FEC blocks –TDM case

Map entry m +1 starts on PS = y

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Number of modulation symbols = 4i

Number of PSs I = y – x = p + kn + j + q

p

n

n

j

FEC Codeword

FEC Codeword

FEC Codeword

Shortened FEC Codeword

b-r data bits r redundancy bits

Map entry m starts on PS = x

q Remainder q (fraction of a PS) 4q padding symbols

Map entry m + 1 starts on PS = y

j PSs = b bits

Fig. 2.22 DL-MAP usage with shortened FEC blocks –TDMA case

P

MAC PDU that has started in the previous packet

First MAC PDU that starts in this TC packet

Second MAC PDU that starts in the TC packet

Transmission Convergence Sublayer (TC) PDU

P = 1 byte pointer field

Fig. 2.23 Format of the downlink convergence sub-layer PDU

depending on whether shortening of code words is allowed or not for this burst profile. A pointer byte shall be added to each payload segment, as illustrated in Fig. 2.23. The pointer field identifies the byte number in the packet. It indicates either the beginning of the first MAC PDU starts in the packet or the beginning of any stuff bytes that precede the next MAC PDU. For reference, the first byte in the packet is referred to as byte number 1. If no MAC PDU or stuff bytes begin in the CS packet then the pointer byte is set to 0. When no data is available to transmit, a stuff_byte pattern having a value (0xFF) shall be used within the payload, to fill any gaps between the IEEE 802.16 MAC PDUs. This value is chosen as an unused value for the first byte of the IEEE 802.16 MAC PDU, which is designed to never have this value (Fig. 2.23). The downlink PHY coding and modulation for this mode is summarized in the block diagram from Fig. 2.24. The downlink channel supports adaptive burst profiling on the user data portion of the frame. Up to twelve burst profiles can be defined. Since there are optional

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Randomization

FEC Encoder

Preamble Prepend

Baseband Pulse Shaping

Symbol Mapper

Modulator And Physical Interface

To RF Channel

Base Station

From RF Channel

Physical Interface and Burst Demod

Matched Filter and Equalizer

Symbol Demapper

FEC Decoder

Data De-Randomization

SS

Fig. 2.24 Conceptual diagram of the downlink PHY sub-layer

Table 2.6 Selectable FEC code types (From [19]) Code types Outer code 1 Reed-Solomon over Galois field (GF) (256) 2 Reed-Solomon over GF (256) 3 (Optional) Reed-Solomon over GF (256) 4 (Optional) BTC

Inner code None (24,16) Block convolutional code (9,8) Parity check code –

modulation and FEC schemes that can be implemented at the SS, a method for identifying the capability of the BS is required. Randomization is employed to minimize the possibility of transmission of an unmodulated carrier while ensuring adequate numbers of bit transitions to support clock recovery. The stream of downlink packets is randomized by modulo-2 addition of the data with the output of the Pseudo-Random Binary Sequence (PRBS) generator. Selected FEC Code types are presented in Table 2.6.

2.13.4.3

Downlink Modulation

The PHY uses a multilevel modulation scheme to maximize the utilization of the air-link. The modulation constellation can be selected per subscriber based on the quality of the RF channel. In the downlink, the BS supports QPSK and 16-QAM modulation and, optionally, 64-QAM. In changing from one burst profile to another, the BS uses one of two power adjustment rules: maintaining constant constellation peak power (power adjustment rule ¼ 0), or maintaining constant constellation mean power (power adjustment rule ¼ 1). In the former case, corner

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points are transmitted at equal power levels regardless of modulation type, while in the latter the signal is transmitted at equal mean power levels regardless of modulation type. I and Q signals are filtered by square-root raised cosine filters prior to modulation. The excess bandwidth factor is a ¼ 0.25.

2.13.5

Uplink PHY

2.13.5.1

Uplink Sub-frame

The uplink Transmission Convergence sub-layer operation is identical to that of downlink. The structure of the uplink sub-frame used by the SS to transmit to the BS is shown in Fig. 2.25. During the uplink sub-frame, three types of bursts may be transmitted by the SS depending upon the need aroused: l

l

l

Bursts that are transmitted in contention opportunities reserved for Initial Ranging Bursts that are transmitted in contention opportunities defined by Request Intervals reserved for response to multicast and broadcast polls Bursts that are transmitted in intervals defined by Data Grant IEs specifically allocated to individual SSs

Any of these bursts may be present in any uplink sub-frame and may occur in any order and quantity .The scheduler at BS indicates which bursts are present via the UL MAP message. TTG (TDD)

SSTG

Initial Ranging Opportunities (UIUC = 2)

Access Burst

Collision

Request Contention Opps (UIUC = 1)

Access Burst

SS 1 Scheduled Data (UIUC = i )

Bandwidth Request

Fig. 2.25 Uplink sub-frame structure (From [19])

...

Collision

SS N Scheduled Data (UIUC = j )

Bandwidth Request

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The bursts are separated by subscriber station transition gap (SSTGs), which separates transmission of the various SSs during the uplink sub-frame followed by a preamble allowing the BS to synchronize to the new SS. Each uplink burst begins with an uplink preamble. This preamble is based upon a repetition of a + 45 rotated Constant Amplitude Zero Auto-Correlation (CAZAC) sequence. Each Uplink Burst Profile in the Uplink Channel Descriptor (UCD) message includes the following parameters: l l l l l

Modulation type FEC Code Type Last codeword length Preamble Length Randomizer Seed

2.13.5.2

Uplink PHY Sub-layer

The uplink PHY coding and modulation are summarized in the block diagram shown in Fig. 2.26. The uplink modulator implements a randomized, variable modulation which is set by the BS. QPSK is supported, while 16-QAM and 64-QAM are optional. In changing from one burst profile to another, the SS uses one of two power adjustment rules: maintaining constant constellation peak power (power adjustment rule ¼ 0), or maintaining constant constellation mean power (power adjustment rule ¼ 1). In the former case, corner points are transmitted at equal power levels regardless of modulation type, while, in the latter, the signal is transmitted at equal mean power levels regardless of modulation type.

Data

Randomization

FEC Encoder

Preamble Prepend

Symbol Mapper

Baseband Pulse Shaping

Modulator And Physical Interface

To RF Channel

SS

From RF Channel

Physical Interface and Burst Demod

Matched Filter

Symbol Demapper

FEC Decoder

Data De-Randomization

BS

Fig. 2.26 Conceptual block diagram of the uplink PHY (From [19])

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2.13.5.3

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Channel Quality Measurements

Receive Signal Strength Indicator (RSSI) and Carrier-to-interference-plus-noise ratio (CINR) signal quality measurements and associated statistics can aid in such processes as BS selection/assignment and burst adaptive profile selection. As channel behaviour is time-variant, both mean and standard deviation are defined. The process by which RSSI measurements are taken does not necessarily require receiver demodulation lock; for this reason, RSSI measurements offer reasonably reliable channel strength assessments even at low signal levels. On the other hand, although CINR measurements require receiver lock, they provide information on the actual operating condition of the receiver, including interference and noise levels, and signal strength. When collection of RSSI measurements is mandated by the BS, an SS obtains an RSSI measurement from the downlink burst preambles. From a succession of RSSI measurements, the SS derives and updates estimates of the mean and the standard deviation of the RSSI. In the case of CINR, SS obtains CINR measurements.

2.14

WirelessMAN-OFDM PHY

The WirelessMAN-OFDM PHY is based on Orthogonal Frequency Division Multiplexing (OFDM) modulation and is designed for NLOS operation in the frequency bands below 11 GHz. It uses 256- point transform and access is by TDMA. This air interface is mandatory for license exempt bands.

2.14.1

Channel Coding

2.14.1.1

Types and Steps

Channel Coding is an important part of the communication system as it increases both the capacity and the coverage. In order to meet the BER requirements under moderate C/N conditions, channel coding is mandatory. There are two main types of coding schemes: block coding and convolutional coding. Block coding operates on finite length blocks and convolutional code works often in a continuous manner. A combination of these is proposed for the down link. Reed-Solomon forward error code is proposed as the outer code owing to its excellent distance properties and moderate implementation complexity. In the downlink, the inner code is inherent in the TCM modulation. There is no overhead in using TCM as it preserves the signal bandwidth. RS-code is optimal for correcting burst errors that might come from the TCM demodulator. The uplink uses robust modulation and needs just a Reed-Solomon block code.

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Channel coding involves three steps: l l l

Randomization Forward Error Correction (FEC) Interleaving

They are applied in this order at transmission. The inverse operations then performed, in the reverse order, at the receiver side (Fig. 2.27).

2.14.1.2

Randomization

Data randomization is performed independently on each burst for downlink and uplink data. Randomization is done to avoid long sequences of consecutive “ones” or consecutives “zeros”. If the amount of data to transmit does not fit exactly the amount of data allocated, padding of 0xFF (“1” only) is added to the end of the transmission block, for the unused integer bytes. The pseudorandom Binary Sequence (PBRS) generator used for randomisation is shown in Fig. 2.28. Except the preambles, each and every data byte to be transmitted enters sequentially into the randomiser, with the Most Significant Byte (MBS) first. Randomisation is not performed on preambles. Randomiser sequence is applied only to information bits. The bits issued from the randomizer are then applied to the encoder. The randomizer is re-initialized on the downlink, at the start of each frame with the Regular Channel Coding Process Data to be transmitted on the SubChannel

Randomizer

FEC

Bit-Interleaver

Modulation

Symbols to map on the Subchannel

Fig. 2.27 OFDM PHY transmission chain

LSB 1 2

3

4

5

6

7

8

MSB 9 10 11 12 13 14 15

data out data in

Fig. 2.28 PBRS generator used for the data randomization in OFDM and OFDMA PHY (From [19])

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sequence: 1 0 0 1 0 1 0 1 0 0 0 0 0 0 0. The randomizer is not reset at the start of burst #1, but rather at start of subsequent bursts. The frame number used for initialization refers to the frame in which the downlink burst is transmitted.

2.14.1.3

FEC

FEC introduces redundancy in the data before it is transmitted. The redundant data (check symbols) are transmitted with the original data to the receiver. There are three methods of channel coding specified by OFDM PHY: l l l

Reed Solomon concatenated with convolutional coding(RS-CC) Block turbo codes(BTCs) Convolutional turbo codes(CTCs)

An FEC, consisting of the concatenation of a Reed-Solomon outer code and a rate-compatible convolutional inner code, is supported on both uplink and downlink. RS-CC is mandatory, whereas BTC and CTC are optional. More complex design issues are faced for BTC and CTC, although they are able to provide 2–3 dB higher gain.

2.14.2

Concatenated Reed–Solomon-Convolutional Code (RS-CC)

The Reed–Solomon encoding is derived from a systematic RS (N ¼ 255, K ¼ 239, T ¼ 8) code using GF(28), where N is the number of overall bytes after encoding, K is the number of data bytes before encoding and T is the number of data bytes which can be corrected. This code is then shortened and punctured to enable variable block sizes and variable error-correction capability. The code after this is reduced to K’ data bytes. Then, add 239-K’ zero bytes as a prefix. After encoding discard these 239-K’ zero bytes. When a codeword is punctured to permit T’ bytes to be corrected, only the first 2T’ of the total 16 parity bytes is employed. Each RS block is encoded by the binary convolutional encoder, having a native rate of 1/2, and constraint length equal to 7. The encoding is performed by first passing the data in block format through the RS encoder and then passing it through a convolutional encoder. A single 0x00 tail byte is appended to the end of each burst. This tail byte is done after randomization. In the RS encoder, the redundant bits are sent before the input bits, keeping the 0x00 tail byte at the end of the allocation. When the total number of data bits in a burst is not an integer number of bytes, zero pad bits are added after the zero tail bits. The zero pad bits are not randomized. Note that this situation can occur only in subchannelization. In this case, the RS encoding is not employed. Table 2.7 presents the block sizes and the code rates used

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Table 2.7 Mandatory channel coding per modulation Modulation Uncoded block size Coded block size (bytes) (bytes) BPSK 12 24 QPSK 24 48 QPSK 36 48 16-QAM 48 96 16-QAM 72 96 64-QAM 96 144 64-QAM 108 144

Data burst

Overall coding rate 1/2 1/2 3/4 1/2 3/4 2/3 3/4

RS code

CC code rate (12,12,0) 1/2 (32,24,4) 2/3 (40,36,2) 5/6 (64,48,8) 2/3 (80,72,4) 5/6 (108,96,6) 3/4 (120,108,6) 5/6

Tail Byte

RS Parity Bits 2

1

CC Encoder

Fig. 2.29 RS-CC encoding process

for the different modulations and code rates. With 64-QAM (optional for licenseexempt bands) the code is implemented if the modulation is implemented. In the case of BPSK modulation, the RS encoder is bypassed (Fig. 2.29).

2.14.2.1

Block Turbo Codes (BTCs)

Block Turbo Codes (BTC) are defined as an optional FEC for OFDM and OFDMA PHY. The BTC is also optional in WiMAX profiles. In IEEE 802.16, both for OFDM and OFDMA PHY, the BTC is based on the product of two simple component codes, which are binary extended Hamming codes or parity check codes. It should be also noted that the codes are not the same for the two PHYs. Data bit ordering for the composite BTC matrix is defined such that the first bit in the first row is the LSB (Least Significant Byte) and the last data bit in the last data row is the MSB.

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2.14.2.2

103

Interleaving

Interleaving is a technique where sequential data words or packets are spread across several transmitted data bursts. It is used to protect the transmission against long sequences of consecutive errors, which are very difficult to correct. These long sequences of error may affect a lot of bits in a row and can then cause many transmitted burst losses. All encoded data bits are interleaved by a block interleaver with a block size corresponding to the number of coded bits per the allocated subchannels per OFDM symbol, Ncbps. The interleaver is defined by a two step permutation. The first ensures that adjacent coded bits are mapped onto nonadjacent subcarriers. The second permutation insures that adjacent coded bits are mapped alternately onto less or more significant bits of the constellation, thus avoiding long runs of lowly reliable bits. After bit interleaving, the data bits are entered serially to the constellation mapper. BPSK, Gray-mapped QPSK, 16-QAM, and 64-QAM are supported, whereas the support of 64-QAM is optional for license-exempt bands. Pilot subcarriers are inserted into each data burst in order to constitute the Symbol and they are modulated according to their carrier location within the OFDM symbol.

2.14.2.3

Modulation

After bit interleaving, the data bits are entered serially to the constellation mapper. The OFDM PHY mandates BPSK as well as Gray-mapped QPSK, 16-QAM, and 64-QAM as shown in Figure 2.30. The 64-QAM constellation is optional for license-exempt bands. This is to allow use of IEEE 802.11 RF components as they do meet the 64-QAM performance requirements of IEEE 802.16 standard [29].

2.14.2.4

Pilot Modulation

Pilot subcarriers are modulated with a BPSK signal. The values to be used are derived by passing fixed initialization sequences through a PRBS generator with polynomial X11 + X9 + 1 clocked with the OFDM symbol rate. This is done UL as well as Dl separately. The value of the individual pilots in a single OFDM symbol are then defined as being either equal or the negative of the BPSK–modulated PRBS output.

2.14.2.5

Frame Structure

The OFDM PHY supports two different types of Frame Structures based on its two architectures, it supports, PMP and Mesh. The frame structure for PMP is mandatory but for mesh based architectures is optional. The frame durations for both architectures are between 2.5 and 20 ms.

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Q

Q

I

I

BPSK

I

QPSK

16-QAM

Q

I

64-QAM

Fig. 2.30 BPSK, QPSK, 16-QAM, and 64 QAM constellations

2.14.2.6

Point-to-Multipoint

For point-to-Multipoint (PtM) architectures when licensed bands are used, the duplexing method is either FDD or TDD. FDD SSs is also supported for H-FDD. In license exempt bands, the duplexing method used is always TDD as it is provisioned to ensure better coexistence with the existing IEEE 802 standards. The frame interval contains transmissions (PHY PDUs) of BS and SSs, gaps and guard intervals. The OFDM PHY also supports a frame-based transmission. A frame consists of a downlink sub-frame and an uplink sub-frame. A downlink sub-frame consists of only one downlink PHY PDU. An uplink sub-frame consists of contention intervals scheduled for initial ranging and bandwidth request purposes and one or multiple uplink PHY PDUs, each transmitted from a different SS. A downlink PHY PDU starts with a long preamble, which is used for PHY synchronization. The preamble is followed by a FCH burst. The FCH burst is one OFDM symbol long and is transmitted using BPSK ½ with the mandatory coding scheme. The FCH contains DL_Frame_Prefix to specify burst profile and length of one or several downlink bursts immediately following the FCH. A DL-MAP message, if transmitted in the current frame, shall be the first MAC PDU in the burst following the FCH. An UL-MAP message immediately follows either the DL-MAP message (if one is transmitted) or the DLFP. If UCD and DCD messages are transmitted in the frame, they immediately follow the DL-MAP and UL-MAP messages. The FCH is followed by one or multiple downlink bursts, each transmitted with different burst profile. Each downlink burst consists of an integer number of OFDM

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symbols. Location and profile of the first downlink burst is specified in the Downlink Frame Prefix (DLFP). The location and profile of the maximum possible number of subsequent bursts shall also be specified in the DLFP. At least one full DL-MAP must be broadcast in burst #1 within the Lost DL-MAP Interval. Location and profile of other bursts are specified in DL-MAP. Profile is specified either by a 4-bit Rate_ID (for the first DL burst) or by DIUC. The DIUC encoding is defined in the DCD messages. HCS field occupies the last byte of DLFP. If there are unused IEs in DLFP, the first unused IE must have all fields encoded as zeros. The DL Sub-frame may optionally contain an STC zone in which all DL bursts are STC encoded. If an STC zone is present, the last used IE in the DLFP shall have DIUC = 0 and the IE shall contain information on the start time of the STC zone. The STC zone ends at the end of the frame. The STC zone starts from a preamble and an STC encoded FCH-STC burst, which is one symbol with the same payload format. The FCH-STC burst is transmitted at BPSK rate ½. It is followed by one or several STC encoded PHY bursts. The first burst in the STC zone may contain a DLMAP applicable only to the STC zone. If DL-MAP is present, it shall be the first MAC PDU in the payload of the burst. With the OFDM PHY, a PHY burst, either a downlink PHY burst or an uplink PHY burst, consists of an integer number of OFDM symbols, carrying MAC messages, that is, MAC PDUs. To form an integer number of OFDM symbols, unused bytes in the burst payload may be padded by the bytes 0xFF. Then the payload should be randomized, encoded, and modulated using the burst PHY parameters specified by this standard. If an SS does not have any data to be transmitted in an UL allocation, the SS shall transmit an UL PHY burst containing a bandwidth request header, with BR = 0 and its basic CID. If the allocation is large enough, an AAS enabled SS may also provide an AAS Feedback Response (AASFBCK-RSP) message. An SS transmits during the entirety of all of its UL allocations, using the standard padding mechanism to fill allocations if necessary (Fig. 2.31). In each TDD frame, the TTG and RTG is inserted between the downlink and uplink sub-frame and at the end of each frame, respectively, to allow the BS to turn around. In TDD and H-FDD systems, subscriber station allowances must be made by a transmit-receive turnaround gap SSTTG and by a receive-transmit turnaround gap SSRTG. The BS shall not transmit downlink information to a station later than (SSRTG+RTD) before its scheduled uplink allocation, and shall not transmit downlink information to it earlier than (SSTTG-RTD) after the end of scheduled uplink allocation, where RTD denotes Round-Trip Delay. The parameters SSRTG and SSTTG are capabilities provided by the SS to BS upon request during network entry (Fig. 2.32).

2.14.2.7

Mesh

The PMP topology supports both TDD and FDD duplexing modes, but for Mesh only TDD mode is supported. For Mesh mode there is no separate downlink and

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Frame n – 1

Frame n

Frame n + 1

DL subframe

Frame n + 2

UL subframe

Contention slot for Initial ranging

DL PHY PDU

Contention slot for IBW requests

UL PHY PDU from SS#1

One or multiple DL bursts, each with different modulation/coding transmitted inorder of decreasing robustness

Preamble

DLFP

FCH

UL PHY PDU from SS#k One UL burstper UL PHY PDU transmitted in the modulation/coding specific to the source SS

DL burst#1 DL Burst#2

Broadcast messages

Regular MAC PDUs

Preamble

DL Burst#n

MAC Msg N MAC PDU–n

MAC Msg 1 MAC PDU –1

Pad

UL burst

MAC Msg 1 MAC PDU – 1

MAC Msg N MAC PDU–n

Pad

One OFDM sybmol with E.g: DL-MAP, UL-MAP, well-known modulation/ DCD, UCD coding(BPSK rate ½) as defined in Table 2.15

MAC Header 6 bytes

MAC msg payload(optional)

CRC(optional)

MAC Header 6 bytes

MAC msg payload(optional)

CRC(optional)

Fig. 2.31 Example of the OFDM structure with TDD (adapted from [19])

uplink sub-frames as all the stations have the same hierarchy. In addition to the PMP frame structure IEEE 802.16 defines, an optional frame structure to facilitate Mesh networks. The contents of the mesh frame are described below (Fig. 2.33). A Mesh frame consists of a control and data sub-frame. The control sub-frame serves two basic functions. One is the creation and maintenance of cohesion between the different systems, termed “network control”. The other is the coordinated scheduling of data-transfers between systems, termed “schedule control” frames with a network control sub-frame occur periodically, as indicated in the Network Descriptor. All other frames have a schedule control sub-frame. The length of the control sub-frame is fixed and of length OFDM symbols, with indicated in the Network Descriptor.

2.14.2.8

Network Control Sub-frame

During a network control sub-frame, the first seven symbols are allocated for network entry, followed by sets of seven symbols for network configuration. During a schedule control sub-frame, the Network Descriptor indicates how many (MSHDSCH-NUM) Distributed Scheduling messages may occur in the control sub-frame. The first symbols are allocated to transmission bursts containing

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107 time

Frame n – 1

Frame n

Frame n + 1

Frame n + 2

DL subframe

DL PHY PDU

One or multiple DL bursts, each with different modulation/coding transmitted inorder of decreasing robustness

Preamble

FCH

DLFP

One OFDM sybmol with well-known modulation/ coding(BPSK rate ½) as defined in Table 2.15

DL burst#1 DL Burst#2

Broadcast messages

Regular MAC PDUs

DL Burst#n

MAC Msg 1 MAC PDU – 1

MAC Msg N MAC PDU-n

Pad

E.g: DL-MAP, UL-MAP, DCD, UCD

MAC Header 6 bytes

MAC msg payload(optional)

CRC(optional)

UL subframe

Contention slot for Initial ranging

Contention slot for IBW requests

UL PHY PDU from SS#1

Preamble

UL PHY PDU from SS#k

UL burst

MAC Msg 1 MAC PDU – 1

MAC Header 6 bytes

One UL burstper UL PHY PDU transmitted in the modulation/coding specific to the source SS

MAC Msg N MAC PDU – n

MAC msg payload(optional)

Pad

CRC(optional)

Fig. 2.32 OFDM frame structure with FDD (adapted from [19])

MSH-CSCH and MSH-CSCF PDUs, whereas the remainder is allocated to transmission bursts containing MSH-DSCH PDUs. Distributed Scheduling messages (using the long preamble) may further occur in the data sub-frame if not in conflict with the scheduling dictated in the control sub-frame.

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Frame n – 1

Frame n

Frame n + 1

Data subframe

Network Control subframe

Network entry

Networkco nfig

Frame n + 2

Networkco config

PHY tr burs from SS#j

PHY tr burst from SS#k Data subframe

Schedule Control subframe

Central Sched

Central Conf

Dist Sched

PHY tr burs from SS#j

PHY tr burst from SS#k

Network entry

Long preamble

MAC PDU w/ MSH-NENT

Central Conf

Gaurd Symbol

Gaurd Symbol

Gaurd Symbol

Network config

Long preamble

MAC PDU w/ MSH-NCFG

Long preamble

MAC PDU w/ MSH-CSCF

Gaurd Symbol

Central Sched

Gaurd Symbol

Long preamble

MAC PDU w/ MSH-CSCH

Gaurd Symbol

Dist Sched

Long preamble

MAC PDU w/ MSH-DSCH

Gaurd Symbol

Fig. 2.33 Mesh frame structure (adapted from [19])

All transmissions in the control sub-frame are sent by using QPSK-1/2 with the mandatory coding scheme. The data sub-frame is divided into minislots, which are, with possible exception of the last minislot in the frame, of size ceiling [(OFDM symbols per frame – MSH-CTRL-LEN  7)/256]. A scheduled allocation consists of one or more minislots.

2.14.2.9

Control Mechanism: Synchronization

For TDD and FDD realizations, it is recommended (but not required) that all BSs be time synchronized to a common timing signal. In the event of the loss

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of the network timing signal, BSs may continue to operate and automatically resynchronize to the network timing signal when it is recovered. For both FDD and TDD realizations, frequency references derived from the timing reference may be used to control the frequency accuracy of Base-Stations provided that they meet the frequency accuracy requirements.

2.14.2.10

Control Mechanism: Ranging

As a part of control mechanism Ranging is the first process performed by BS to communicate with the SS. There are two types of ranging processes – initial ranging and periodic ranging. Initial ranging, that is, coarse synchronization is done under two conditions: first to initiate registration (or re-registration) of an SS with a BS and, secondly, during transmission on a periodic basis. Initial ranging uses the initial ranging contention-based interval, which requires a long preamble. The periodic ranging uses the regular uplink burst. During registration process, the new subscriber tries to register during the random access channel. If it is successful, then it is entered into a ranging process under control of the BS. The ranging process is cyclic in nature where default time and power parameters are used to initiate the process followed by cycles. These parameters are monitored, measured and stored at the BS, and transmitted to the subscriber unit for use during normal exchange of data. During normal exchange of data, the stored parameters are updated in a periodic manner based on configurable update intervals to ensure that changes in the channel can be accommodated. The update intervals shall vary in a controlled manner on a subscriber unit by subscriber unit basis. Regardless of duplexing type, the appropriate duration of the Initial Ranging slot used for initial system access depends on the intended cell radius. It is mandatory that the initial ranging transmissions use a long preamble and the most robust mandatory burst profile. In case there is need of re-registration the same process of registration is followed. The use of BW by SS to transmit the preamble depends upon whether it is long or subchannelized. The long preamble is transmitted on the entire BW while the subchannelized preamble is transmitted on 1/16 of the BW. But the long preamble and the subchannelized preamble is transmitted using the same total power. Therefore the spectral density of the long preamble is lower by a factor of 16 (about 12 dB) than the power spectral density of the subchannelized preamble. The BS need only detect that energy is sent on a single subchannel and may respond by allocating a single subchannel identifying the SS by the Transmit Opportunity, Frame Number and ranging subchannel in which the transmission was received.

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Control Mechanism: – Initial Ranging in AAS Systems

The above Initial Ranging process does not work if the BS is operating in the AAS mode. A BS supporting the AAS option therefore allocates AAS alert slot in the uplink sub-frame. This is the way AAS SSs that have to initially alert the BS of their presence.

2.14.2.12

Bandwidth Requesting

There may be two types of REQ Regions in a frame. These two types are REQ Region-Full and REQ Region-Focused. In a REQ Region-Full, when subchannelization is not active, each Transmit Opportunity consists of a short preamble and one OFDM symbol using the most robust mandatory burst profile. When subchannelization is active, the allocation is partitioned into Transmission Opportunities (TOs) both in frequency and in time. The width (in subchannels) and length (in OFDM symbols) of each TO is defined in the UCD message defining. The transmission of an SS contains a subchannelized preamble corresponding to the chosen, followed by data OFDM symbols using the most robust mandatory burst profile. In a REQ Region-Focused, a station sends a short code over a Transmit Opportunity that consists of four subcarriers by two OFDM symbols. Each Transmit Opportunity within a frame is indexed by consecutive Transmit Opportunity Indices. The first occurring Transmit Opportunity is indexed 0.

2.14.2.13

Power Control

As with frequency control, a power control algorithm is supported for the uplink channel with both an initial calibration and periodic adjustment procedure without loss of data. The objective of the power control algorithm is to bring the received power density from a given subscriber to a desired level. The received power density is defined as total power received from a given subscriber divided by the number of active subcarriers. When subchannelization is not employed, the number of active subcarriers is equal for all the subscribers and the power control algorithm brings the total received power from a given subscriber to the desired level. The base station should capable be of providing accurate power measurements of the received burst signal. When subchannelization is employed, the SS maintains the same transmitted power density unless the maximum power level is reached.

2.14.2.14

Channel Quality Measurements

Same as the above two PHY specifications, RSSI and CINR are used for signal quality measurement. Implementation of the RSSI and CINR statistics and their

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reports is mandatory. Here, an SS obtains RSSI and CINR measurements from the OFDM downlink preambles, and reports them via REP-RSP messages.

2.15 2.15.1

WirelessMAN-OFDMA PHY Overview

WirelessMAN-OFDMA is among the three specifications defined in IEEE 802.16 family for applications below 11 GHz. The IEEE 802.16e-2005 amendment was developed to extend the 802.16 Air Interface Standard to cover mobile applications. This amendment adopted OFDMA to provide the flexibility to deal with varied usage scenarios and the challenges associated with rapidly moving mobile users in a NLOS environment. IEEE 802.16e includes all the expansion of all three of the lower frequency PHY specifications. This uses orthogonal frequency-division multiple access with a 2048-point transform and is designed for NLOS operation in the frequency bands below 11 GHz. For licensed bands, channel bandwidths allowed is limited to the regulatory provisioned bandwidth divided by any power of 2 no less than 1.0 MHz. In the OFDMA mode, the active subcarriers are divided into subsets of subcarriers; each subset is termed a subchannel. In the downlink, a subchannel may be intended for different (groups of) receivers; in the uplink, a transmitter may be assigned one or more subchannels, several transmitters may transmit simultaneously. The subcarriers forming one subchannel may, but need not to be adjacent. The concept is shown in Fig. 2.34. An OFDMA symbol consists of a number of carriers equal to the size of the Fourier transform. The symbols are constructed from data, pilot, and null carriers: Data carriers – for data transmission Pilot carriers – the magnitude and phase of these carriers are known to the receiver and they are used for channel estimation

Subchannel 1

Guard Band

Subchannel 2

DC Subcarrier

Channel

Subchannel 3

Guard Band

Fig. 2.34 OFDMA frequency description (three channel schematic example) [19]

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Null carriers – there is no transmitted energy on these carriers to enable the signal to naturally decay and prevent leakage of energy into adjacent channels The primitive parameters are the following (Table 2.8): l l l

l

BW: It is the nominal channel bandwidth. Nused: Number of used subcarriers (which includes the DC subcarrier). n: Sampling factor – In conjunction with BW and N used, this parameter determines the subcarrier spacing, and the useful symbol time. This value is set to 8/7 as follows: for channel bandwidths that are a multiple of 1.75 MHz then n = 8/7 else for channel bandwidths that are a multiple of any of 1.25, 1.5, 2 or 2.75 MHz then n = 28/25 else for channel bandwidths not otherwise specified then n = 8/7. G: This is the ratio of CP time to “useful” time.

The 802.16e-2005 standard provides three subchannel allocation alternatives that can be selected based on the usage scenario as follows: l

l

l

Subcarriers can be scattered throughout the frequency channel range. This is referred to as fully used subchannelization or FUSC. Several scattered clusters of subcarriers can be used to form a subchannel. This is referred to as partially used subchannelization or PUSC. Subchannels can be composed of contiguous groups of subcarriers. This is referred to as adaptive modulation and coding or AMC.

Multiple OFDMA modulation modes are supported to accommodate variable channel bandwidths. This scalable architecture is achieved by using different FFT/ IFFT sizes. Table 2.9 shows the relation between the supported channel bandwidths and the FFT size.

Table 2.8 Primitive parameters

Table 2.9 FFT size and supported channel bandwidths

Item BW Nused n G Nfft Fs Df Tb

Value 1.25, 5, 10, 20 8/7, 28/25 1/4, 1/8, 1/16, 1/32 128, 512, 1024, 2048 Floor( n*BW/8000 )*8000 Fs/NFFT = 11.16 kHz 1/Df = 89.6us

Channel bandwidths 1.25 5 10 20

Description Bandwidth # of used subcarriers Sampling factor Guard time ratio FFT size Sampling frequency Frequency spacing Useful symbol time

FFT size 128 512 1024 2048

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2.15.2

Subcarrier Allocation Modes

2.15.2.1

Adjacent Versus Distributed

An OFDMA symbol can be divided into several subchannels by grouping its subcarriers. WirelessMAN-OFDMA, in particular, allows two different grouping methods to realize the subchannelization: distributed and adjacent permutation. These grouping methods are shown in the Fig. 2.35, and their description is as follows: Adjacent Permutation – In this type of permutation a subchannel is formed by grouping a block of contiguous data subcarriers. Adjacent Permutation is suitable for fixed, portable, or low mobility environments. Distributed Permutation – Distributed permutation is implemented as Downlink Full Usage Sub-carriers (DL-FUSC), Downlink Partial Usage Sub-carriers (DLPUSC), Uplink Partial Usage Subcarriers (UL-PUSC), Table 2.10. Subchannels are

User2

User1

Combined OFDMA Signal

SNR

SNR

Combined OFDMA Signal

Adjacent subcarrier allocation (AMC)

Frequency

Distributed subcarrier allocation (FUSC, PUSC)

Frequency

Fig. 2.35 Distributed and adjacent subcarrier allocation

Table 2.10 Comparison of adjacent and distributed subcarrier allocation schemes Parameter Adjacent subcarrier allocation (AMC) Distributed subcarrier allocation (PUSC, FUSC) Gain Subchannelization gain and loading gain Subchannelization gain and benefits of frequency diversity Scheduling Requires advanced scheduler that allocates Simplified scheduler does not subchannels according to channel use info about the channel characteristics Efficiency in Almost no data lost Requires more redundancy multipath (overhead) for forward error channel correction Channel Can be used in stationary channel Can be used in fast-changing channel AAS & MIMO Easier implementation More complicated implementation Usage Fixed, portable, nomadic, pedestrian speed Mobile fast-moving subscribers

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allocated with subcarriers in a pseudorandom way. The subcarriers for a described subchannel in a specific cell will be different from the subcarriers for that same subchannel in another cell. For example sub-carriers in subchannel 1 in cell 1 will be different than the subcarriers in the subchannel 1 in cell number 2. The pseudorandom calculation for the permutations gives an interference averaging by minimizing the bad effects of cell to cell interference.

2.15.2.2

OFDMA Frame

In IEEE 802.16e-2005 air interface, both FDD and TDD are supported. In case of FDD, the uplink and downlink sub-frames are transmitted simultaneously on different carrier frequencies while in the case of TDD, the uplink and downlink sub-frames are transmitted on the same carrier frequency at different times. Figure 2.36 shows the frame structure for TDD. For the FDD mode the frame structure is identical except that the UL and DL sub-frames are multiplexed on different carrier frequencies. For mobile stations, an additional duplexing mode, known as H-FDD (half-duplex FDD) is defined. H-FDD is a basic FDD duplexing scheme with the restriction that the MS cannot transmit and receive at the same time. From a cost and implementation perspective, an H-FDD MS is cheaper and t k+30 k+31 k+33

Rangaing Subchannel

FCH

DL burst #3

UL burst #1

UL burst #2

UL burst #3

DL burst #5

DL burst #2

UL burst #4 DL burst #6 UL burst #5

S+L

TTG

DL subframe

RTG

UL subframe

Fig. 2.36 Example of an OFDMA frame in TDD mode (adapted from [23])

DL-MAP

DL burst #4 Preamble

Preamble

k+17 k+20 k+23 k+26

DL-MAP

FCH

S S+1 S+2

Subchannel logical number

k+1 k+3 k+5 k+7 k+9 k+11k+13 k+15 DL burst #1 (carrying the UL-MAP)

k

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less complex than its FDD counterpart, but the UL and DL peak data rate of, an H-FDD MS are less, owing to its inability to receive and transmit simultaneously. An 802.16e TDD frame is built up by one downlink (DL) sub-frame and one uplink (UL) sub-frame. Each frame in the downlink transmission begins with a preamble followed by a DL transmission period and an UL transmission period. To separate the downlink frame from the uplink one, guard zones are inserted as shown in Fig. 2.36. In the case between the downlink and uplink frame the guard zone is Transmit Transition Gap (TTG) and between the end of the frame and the next frame the guard zone is Receive Transition Gap (RTG). In TDD mode each DL sub-frame and UL sub-frame is divided into various zones, each using a different subcarrier permutation scheme. Some of the zones, such as DL PUSC, are mandatory; other zones, such as FUSC, AMC, UL PUSC, and TUSC, are optional. The relevant information about the starting position and the duration of the various zones being used in a UL and DL sub-frame is provided by control messages in the beginning of each DL sub-frame. The other important sections of the TDD frame are the following: l

l

l

l

Preamble: The first OFDM symbol in the downlink sub-frame is used for transmitting the DL preamble. The preamble can be used for a variety of PHY layer procedures, such as time and frequency synchronization, initial channel estimation, and noise and interference estimation. The subcarriers in the preamble symbol are divided into a group of three carrier sets. The preamble, used for synchronization, is the first OFDM symbol of the frame. Frame Control Header (FCH): The FCH follows the preamble. The FCH is used for carrying system control information, such as the subcarriers used (in case of segmentation), the ranging subchannels, and the length of the DL-MAP message. This information is carried on the DL_Frame_Prefix message contained within the FCH. The FCH is always coded with the BPSK R1/2 mode to ensure maximum robustness and reliable performance, even at the cell edge. It provides the frame configuration information such as MAP message length and coding scheme and usable subchannels. DL-MAP and UL-MAP: The DL-MAP and UL-MAP provide subchannel allocation and other control information for the DL and UL sub-frames, respectively. UL Ranging: The UL ranging subchannel is allocated for mobile stations (MS) to perform closed-loop time, frequency, and power adjustment as well as bandwidth requests.

2.15.2.3

Multiple Subcarrier Allocation Zones

OFDMA PHY supports multiple subcarrier allocation zones (such as PUSC, FUSC, PUSC with all subchannels, optional FUSC, AMC, TUSC1, and TUSC2) within the same frame to enable the possibility of support for and coexistence of different types of SSs. Figure 2.37 shows the OFDMA frame with multiple zones.

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AMC

PUSC

TUSC1

TUSC1

AMC

Optional FUSC

FUSC

(IDL_PermBaseZ)

FUSC

(DL_PermBase Y)

PUSC

(DL_PermBase X)

FCH and DL)

PUSC (first zone contains

Preamble

Optional PUSC

UL subframe

DL subframe

Zone switch IEs in DL-Map

Must appear in every frame May appear in the frame according to mapping

Fig. 2.37 Illustration of the OFDMA frame with multiple zones (adapted from [23])

The switching between zones is performed using an information element included in DL-MAP and UL-MAP. DL and UL sub-frames both start in PUSC mode where groups of subchannels are assigned to different segments by the use of dedicated FCH messages. The PUSC subcarrier allocation zone can be switched to a different type of subcarrier allocation zone through a directive from the PUSC DL-MAP. The PHY parameters such as channel state and interference levels may change from one zone to the next.

2.15.2.4

Time Frequency Mapping

In the OFDMA PHY, the mapping of data to physical subcarriers is performed in two steps. In the first step, data are mapped to one or more data slots on one or more logical subchannels. In the second step, for each data slot, each logical subchannel is then mapped to a number of physical subcarriers. Logical mapping makes use if certain basic terms in its description described below. 1. Slot – Slot is the minimum possible data allocation in the time-frequency domain. It always consists of a single subchannel and two, three or six OFDM symbols depending on the physical mapping. Size of OFDMA slot depends on the OFDMA symbol structure, which varies for uplink and downlink, for FUSC and PUSC, and for the distributed subcarrier permutations and the adjacent subcarrier permutation. l For downlink FUSC using the distributed subcarrier permutation one slot is one subchannel by one OFDMA symbol. l For downlink PUSC using the distributed subcarrier permutation one slot is one subchannel by two OFDMA symbols. l For uplink PUSC using either of the distributed subcarrier permutations one slot is one subchannel by three OFDMA symbols.

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For uplink and downlink using the adjacent subcarrier permutation one slot is one subchannel by one OFDMA symbol. Segment – A Segment is a subdivision of the set of available OFDMA subchannels that may include all available subchannels. One segment is used for deploying a single instance of the MAC. For example, a BS might segment the available subchannels among different sectors. There can be up to three segments where segment 0 must always contain subchannel group 0 and group1, Segment 1 may contain subchannel group 2 and segment 2 contains subchannel group 4. Data Region – In OFDMA, a Data Region is a two-dimensional allocation of a group of contiguous subchannels, in a group of contiguous OFDMA symbols. All the allocations refer to logical subchannels. A two dimensional allocation may be visualized as a rectangle, such as the 4  3 rectangle shown in Fig. 2.38. A data region can be transmitted in the downlink by the BS as a transmission to a SS or group of SSs. Figure 2.39 shows these concepts for 1024-FFT DL PUSC with three segments. Subchannel Group – Subchannel Group is set of contiguous subchannels. The allocations of subchannels to subchannel groups is fixed. Perm Base – It has been separately defined for DL and UL. In DL it is called DL PermBase which is an integer ranging from 0 to 31, which identifies the particular BS segment and is specified by MAC layer. It is set to preamble IDCell in the first zone and determined by the DL-MAP for other zones. For UL, there is a different integer called UL PermBase which ranges from 0 to 69 and is assigned by a management entity. Permutation and Permutation Zone – Permutation is mapping of logical subchannels to physical subcarriers. There are the following mechanisms for permutation: l PUSC (partial usage of subchannels) l FUSC (full usage of subchannels) l

2.

3.

4. 5.

6.

Slot (Symbol Offset)

Subchannel offset

No_subchannels

Fig. 2.38 Example of the data region which defines the OFDMA allocation

No_OFDM_symbols

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Subchannel group index

0

1

2

3

4

k+1 k+2 k+3

k 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

k+4

k+5

k+6 k+7

k+8 k+9

slot

Segment0 Data region

Subchannel index

Segment1

Segment2

Permutation Zone

Fig. 2.39 Schematic indication of logical mapping elements

l l l l l

Optional PUSC Optional FUSC AAS (Adaptive Antenna System) AMC (Adaptive Modulation and Coding) Option FUSC with all subchannels

Permutation Zone is a number of contiguous OFDMA symbols, in the DL or the UL, that use the same permutation formula. The permutation formula describes various configurations of pilot subcarriers, data subcarriers, subchannels, and slots. The DL sub-frame or the UL sub-frame may contain more than one permutation zone. Zones are used to help implement base station functionality such as beamforming, assigning subchannels to different sectors of a single cell, and to define subchannelization that reduces base station to base station interference.

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2.15.2.5

119

Algorithms for OFDMA Data Mapping: Downlink

1. Segment the data after the modulation block into blocks sized to fit into one OFDMA slot. 2. Each slot should span one subchannels in the subchannel axis and one or more OFDMA symbols in the time axis. Map the slots such that the lowest numbered slot occupies the lowest numbered subchannel in the lowest numbered OFDMA symbol. 3. Continue the mapping such that the OFDMA subchannel index is increased. When the edge of the Data Region is reached, continue the mapping from the lowest numbered OFDMA subchannel in the next available symbol.

2.15.2.6

Algorithms for OFDMA Data Mapping: Uplink

The UL mapping consists of two steps. In the first step, the OFDMA slots allocated to each burst are selected. In the second step, the allocated slots are mapped. Details are as follows: Step 1: Allocate OFDMA slots to bursts: 1. Segment the data into blocks sized to fit into one OFDMA slot. 2. Each slot shall span one or more subchannels in the subchannel axis and one or more OFDMA symbols in the time axis. Map the slots such that the lowest numbered slot occupies the lowest numbered subchannel in the lowest numbered OFDMA symbol. 3. Continue the mapping such that the OFDMA symbol index is increased. When the edge of the UL Zone is reached continue the mapping from the lowest numbered OFDMA symbol in the next available subchannel. 4. An UL allocation is created by selecting an integer number of contiguous slots, according to the ordering of steps 1–3. This results in the general Burst structure shown by the gray area in Fig. 2.40. Step 2: Map OFDMA slots within the UL allocation: 1. Map the slots such that the lowest numbered slot occupies the lowest numbered subchannel in the lowest numbered OFDMA symbol. 2. Continue the mapping such that the Subchannel index is increased. When the last subchannel is reached, continue the mapping from the lowest numbered subchannel in the next OFDMA symbol that belongs to the UL allocation. The resulting order is shown by the arrows in Fig. 2.41.

2.15.2.7

Symbol Structure for PUSC

The symbol structure is formed by pilots, data, and zero subcarriers. The symbol is first divided into basic clusters and zero carriers are allocated. Pilots and data

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k+1

k+2

k+3

k+4

k+5

k+6

k+7

k+8

k+9

slot

slot n slot n+1

slot n+12

slot n+11

Data Region

Subchannel number

Fig. 2.40 Example of mapping OFDMA slots to subchannels and symbols in the downlink (in the PUSC mode)

carriers are allocated within each cluster. Pilot positions are marked separately for odd and even OFDM symbol. These subcarriers will be separated from the rest before permutation. For example, consider subcarriers of logical cluster ‘0’ (With Perm Base = 0, it is the sixth physical cluster). These subcarriers are numbered as 0–13. Their positions with respect to the absolute subcarrier index (0–2047) are 268–281. The pilot subcarriers for odd symbols will be ‘4’ and ‘8’ (‘272’ and ‘276’ with respect to absolute subcarrier index). For even OFDM symbols ‘0’ and ‘12’ (‘268’ and ‘280’) will be pilot positions. The rest 12 subcarriers will be used as data subcarriers (Fig. 2.42). Table 2.11 shows the parameters for the symbol structure

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121 Uplink zone OFDMA Symbol Index

k 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

k+1

k+2

slot

n

k+3

k+4

k+5

slot

n+11

k+6

k+7

k+8

k+9

slot n+22

slot n+10

Data Region

Subchannel number

Fig. 2.41 Example of mapping OFDMA slots to subchannels and symbols in the uplink

OFDM symbol

subcarrier

Odd Symbols

Even Symbols

Data Sub-carriers

Fig. 2.42 DL PUSC cluster structure

Pilot Sub-carriers

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Table 2.11 2048 FFT OFDMA downlink subcarrier allocations for PUSC Parameter Value Comments Number of DC subcarriers 1 Index 1024 Number of Guard subcarriers, 184 Left Number of Guard subcarriers, 183 Right Number of used subcarriers 1,681 Number of all subcarriers used within a symbol, (Nused) including all possible allocated pilots and the DC carrier Number of subcarriers per cluster 14 Number of clusters 120 Renumbering sequence 1 Used to renumber clusters before allocation to subchannels: 6, 108, 37, 81, 31, 100, 42, 116, 32, 107, 30, 93, 54, 78, 10, 75, 50, 111, 58, 106, 23, 105, 16, 117, 39, 95, 7, 115, 25, 119, 53, 71, 22, 98, 28, 79, 17, 63, 27, 72, 29, 86, 5, 101, 49, 104, 9, 68, 1, 73, 36, 74, 43, 62, 20, 84, 52, 64, 34, 60, 66, 48, 97, 21, 91, 40, 102, 56, 92, 47, 90, 33, 114, 18, 70, 15, 110, 51, 118, 46, 83, 45, 76, 57, 99, 35, 67, 55, 85, 59, 113, 11, 82, 38, 88, 19, 77, 3, 87, 12, 89, 26, 65, 41, 109, 44, 69, 8, 61, 13, 96, 14, 103, 2, 80, 24, 112, 4, 94, 0 Number of data subcarriers in 24 each symbol per subchannel Number of subchannels 60 Basic permutation sequence 6, 9, 4, 8, 10, 11, 5, 2, 7, 3, 1, 0 12 (for 12 subchannels) Basic permutation sequence 4 7, 4, 0, 2, 1, 5, 3, 6 8 (for 8 subchannels)

2.15.2.8

Downlink Subchannels Subcarrier Allocation in PUSC

The carrier allocation to subchannels is performed by using the following procedure, Table 2.11 (for example 2048-FFT): 1. Divide the subcarriers into the number of clusters (Nclusters) physical clusters containing 14 adjacent subcarriers each (starting from carrier 0). The number of clusters, Nclusters, varies with FFT sizes (e.g., 120 for 2048 FFT or 60 for 1024 FFT). 2. Renumber the physical clusters into logical clusters using the following formula: LogicalCluster ¼ RenumberingSequence  ðfPHY Cluster þ 13  DL PermBasegmod Nclusters Þ (2.6) where DL_PermBase parameter is an integer ranging from 0 to 31. 1. Divide the clusters into six major groups shown in Table 2.12. These groups may be allocated to segments, if a segment is being used, then at least one group shall be allocated to it (by default group 0 is allocated to sector 0, group 2 is allocated to sector 1, and group 4 to is allocated sector 2).

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Table 2.12 Clusters and respective groups

Group Group 0 Group 1 Group 2 Group 4 Group 5 Group 6

123 Clusters 0–23 24–39 40–63 64–79 80–103 104–119

2. Allocate carriers to subchannel in each major group is performed by first allocating the pilot carriers within each cluster, and then taking all remaining data carriers within the symbol. First the six major groups are regrouped into 6 sets of 24 groups, with the pilot tones in each constituent logical cluster excluded. Each of the even numbered major groups (i.e., group 0, 2 and 4) contains 12 logical clusters and each of the odd numbered groups (i.e., groups 1, 3 and 5) contains eight logical clusters, with each cluster carrying 12 data subcarriers and two pilot tones. For the even numbered major groups, each cluster is divided into two groups with six data subcarriers each; for the odd numbered major groups, each cluster is divided into three groups with four data subcarriers each. 3. The subcarriers in each of the 24 groups are mapped into six subchannels or four subchannels using the following equation called permutation formula. subcarrierðk; sÞ ¼ Nsubchannels  nk þ fps ½nk Nsubchannels  þ DL PermBaseg Nsubchannels

ð2:7Þ

where: Subcarrier(k, s) k s Nsubchannels nk ps[j] DL_PermBase

is the subcarrier index of subcarrier k in subchannel s, is the subcarrier-in-subchannel index from the set [0. . .Nsubchannels-1] is the index number of a subchannel, from the set [0. . .Nsubchannels-1], is the number of subchannels in the current Major group = (k + 13 s) mod Nsubcarriers is the series obtained by rotating basic permutation sequence cyclically to the left s times, is an integer ranging from 0 to 31, which is set to preamble IDCell in the first zone and determined by the DL-MAP for other zones.

A comparison of subcarrier allocations in the 1024 FFT OFDMA System is presented in Table 2.13. The comparison is performed among DL PUSC, DL FUSC, UL PUSC and DL/UL AMC. 2.15.2.9

Symbol Structure for FUSC

The symbol structure is constructed using pilots, data, and zero subcarriers. The symbol is first allocated with the appropriate pilots and with zero subcarriers, and then all the remaining subcarriers (Table 2.14) are used as data subcarriers which are later divided into subchannels. There are two variable pilot-sets and two constant pilot-sets. The fixed sets are divided into subset that are used in odd and even symbols respectively. This

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Table 2.13 Subcarrier allocations in the 1024 FFT OFDMA system Parameters DL PUSC DL FUSC UL PUSC Number of DC subcarriers 1 1 1 Number of guard subcarriers, left 92 87 92 Number of guard subcarriers, right 91 86 91 Number of pilot subcarriers 120 82 420/0 Number of data subcarriers 720 768 420/840 Number of subchannels 30 16 35 Number of data subcarriers in each 24 48 12/24 symbol per subchannel Number of clusters 60 Number of subcarriers per cluster 14 Number of tiles 210 Number of subcarriers per tile 4 Number of tiles per subchannel 6 Number of bins Number of subcarriers per bin Number of bins per subchannel

DL/UL AMC 1 80 79 96 768 48 16

96 9 2

Table 2.14 OFDMA downlink subcarrier allocations for FUSC Parameter Value Comments INumber of DC subcarriers 1 Index 1024 Number of guard 160 subcarriers, left Number of guard 159 subcarriers, right Number of used subcarriers, 1,729 Number of all subcarriers used within a symbol, Nused including all possible allocated pilots and the DC carrier Number of data subcarriers 1,536 Number of data subcarriers 48 per subchannel Number of subchannels 32 PermutationBase 3, 18, 2, 8, 16, 10, 11, 15, 26, 22, 6, 9, 27, 20, 25, 1, 29, 7, 21, 5, 28, 31, 23, 17, 4, 24, 0, 13, 12, 19, 14, 30

provides a tradeoff between allocated power and frequency diversity on pilots for channel estimation. Table 2.15 shows the distribution of fixed and variable sets of pilots for 2048 FFT while Tables 2.16 and 2.17 presents the respective distributions for 1024 FFT and 512 FFT, respectively.

2.15.2.10

Downlink Subchannels Subcarrier Allocation in PUSC

The carrier allocation to subchannels is performed using the following procedure, as shown in Fig. 2.43: 1. Divide the subcarriers into the number of physical clusters (Nclusters), containing 14 adjacent subcarriers each (starting from carrier 0). The number

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Table 2.15 2048-FFT OFDMA downlink carrier allocations – FUSC Parameter Value Comments Pilot Subcarrier 71 0,72,144,216,288,360,432,504,576,648,720,792,864, Index: 936,1008,1080,1152,1224,1296,1368,1440,1512,1584, VariableSet #0 1656,48,120,192,264,336,408,480,552,624,696,768, 840,912,984,1056,1128,1200,1272,1344,1416,1488, 1560,1632,24,96,168,240,312,384,456,528,600,672, 744,816,888,960,1032,1104,1176,1248,1320,1392, 1464,1536,1608,1680 Pilot Subcarrier 12 72*(2*n + k) + 9 when k = 0 and n = 0. . ., 5 DC subcarrier shall be Index: included when the pilot subcarrier index is calculated by the ConstantSet #0 equation Pilot Subcarrier 71 36,108,180,252,324,396,468,540,612,684,756, Index: 828,12,84,156,228,300,372,444,516,588,660, VariableSet #1 732,804,60,132,204,276,348,420,492,564,636, 708,780 Pilot Subcarrier 12 72*(2*n + k) + 9 when k = 1 and n = 0. . ., 4 DC subcarrier shall be Index: included when the pilot subcarrier index is calculated by the ConstantSet #1 equation Basic Permutation – 3, 18, 2, 8, 16, 10, 11, 15, 26, 22, 6, 9, 27, 20, 25, 1, 29, 7, 21, 5, 28, Sequence 31, 23, 17, 4, 24, 0, 13, 12, 19, 14, 30

Table 2.16 1024 FFT OFDMA downlink subcarrier allocations – FUSC Parameter Value Comments Pilot Subcarrier Index: 12 0, 24, 48, 72, 96, 120, 144, 168, 192, 216, 240, 264, 288, VariableSet #0 312, 336, 360, 384, 408, 432, 456, 480, 504, 528, 552, 576, 600, 624, 648, 672, 696, 720, 744, 768, 792, 816, 840 Pilot Subcarrier Index: 2 72*(2*n + k) + 9 when k = 0 and n = 0. . ., 5 DC subcarrier shall ConstantSet #0 be included when the pilot subcarrier index is calculated by the equation Pilot Subcarrier Index: 12 36, 108, 180, 252, 324, 396, 468, 540, 612, 684, 756, VariableSet #1 828, 12, 84, 156, 228, 300, 372, 444, 516, 588, 660, 732, 804, 60, 132, 204, 276, 348, 420, 492, 564, 636, 708, 780 Pilot Subcarrier Index: 2 72*(2*n + k) + 9 when k ¼ 1 and n ¼ 0. . . , 4 DC subcarrier ConstantSet #1 shall be included when the pilot subcarrier index is calculated by the equation Basic Permutation – 6, 14, 2, 3, 10, 8, 11, 15, 9, 1, 13, 12, 5, 7, 4, 0 Sequence

of clusters, Nclusters, varies with FFT sizes as mentioned in Tables 2.11 and 2.13. 2. Renumber the physical clusters into logical clusters using the following formula: Logical Cluster ¼ Renumbering SequenceððPhysical ClusterÞ þ 13  DL PermBaseÞ

ð2:8Þ

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Table 2.17 FFT OFDMA downlink subcarrier allocations – FUSC Parameter Value Comments Pilot Subcarrier Index: 18 0, 24, 48, 72, 96, 120, 144, 168, 192, 216, 240, 264, 288, VariableSet #0 312, 336, 360, 384, 408 Pilot Subcarrier Index: 3 72*(2*n + k) + 9 when k ¼ 0 and n ¼ 0. . . , 2 DC subcarrier ConstantSet #0 shall be included when the pilot subcarrier index is calculated by the equation Pilot Subcarrier Index: 18 12, 36, 60, 84, 108, 132, 156, 180, 204, 228, 252, 276, VariableSet #1 300, 324, 348, 372, 396, 420 Pilot Subcarrier Index: 3 72*(2*n + k) + 9 when k ¼ 1 and n ¼ 0. . . , 2 DC subcarrier ConstantSet #1 shall be included when the pilot subcarrier index is calculated by the equation Basic Permutation – 2, 0, 1, 6, 4, 3, 5, 7 Sequence

20 MHz Physical cluster No. ‘0’

184 Guard One cluster Subcarriers 14 Subcarriers

Physical cluster No. ‘1’

Physical cluster No. ‘119’

DC Subcarrier

183 Guard Subcarriers

Total Subcarriers (1440 Data + 240 Pilot + 1 DC) = 1681

Fig. 2.43 Downlink subchannels subcarrier allocation in PUSC

3. Logical clusters of step 2 are grouped together to form six major groups. These groups are numbered from 0 to 5. The allocation algorithm varies with FFT sizes as follows: l FFT size = 2048 – The clusters are divided into six major groups. Group 0 includes clusters 0–23, group 1 includes clusters 24–39, group 2 includes clusters 40–63, group 3 includes clusters 64–79, group 4 includes clusters 80–103, group 5 includes clusters 104–119. These groups may be allocated to segments, if a segment is being used, then at least one group shall be allocated to it (by default group 0 is allocated to sector 0, group 2 is allocated to sector 1, and group 4 to is allocated sector 2). l FFT size = 512 – The clusters are divided into six major groups. Group 0 includes clusters 0–9, group 2 includes clusters 10–19, group 4 includes clusters 20–29. These groups may be allocated to segments, if a segment is being used, then at least one group shall be allocated to it (by default group 0 is allocated to sector 0, group 2 is allocated to sector 1, and group 4 to is allocated sector 2).

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FFT size = 128 – The clusters are divided into six major groups. Group 0 includes clusters 0–1, group 2 includes clusters 2–3, group 4 includes clusters 4–5. These groups may be allocated to segments, if a segment is being used, then at least one group shall be allocated to it (by default group 0 is allocated to sector 0, group 2 is allocated to sector 1, and group 4 to is allocated sector 2). 4. Allocate subcarriers to subchannel in each major group is performed separately for each OFDMA symbol by first allocating the pilot carriers within each cluster, and then taking all remaining data carriers within the symbol and using the Permutation Formula defined in FUSC subcarrier allocation. The parameters vary with FFT sizes as follows: l FFT size = 2048 – Use the parameters from Table 2.15, with basic permutation sequence 12 for even numbered major groups, and basic permutation sequence 8 for odd numbered major groups, to partition the subcarriers into subchannels containing 24 data subcarriers in each symbol. l FFT size = 1024 – Use the parameters from Table 2.16, with basic permutation sequence 6 for even numbered major groups, and basic permutation sequence 4 for odd numbered major groups, to partition the subcarriers into l

2.15.2.11

PUSC UL

One slot of PUSC UL is three OFDM symbols by one subchannel. Out of 2,048, there are 184 left guard subcarriers, 183 right guard subcarriers and one DC subcarrier. There are ‘840 data + 840 pilot’ subcarriers for even numbered OFDM symbols and ‘1680 data + 0 pilot’ for odd numbered OFDM symbols. Figure 2.44 shows how pilots are marked for even numbered OFDM symbols and also it points out the absence of pilot carriers during odd symbol.

2.15.2.12

Adjacent Subcarrier Permutation

OFDMA PHY supports AAS and also a set of second-, third-, and fourth-order transmit diversity options. With the AAS option, the system uses a multipleSymbol 0 Symbol 1 Symbol 2

Fig. 2.44 UL PUSC tile structure

Data Sub - carriers

Pilot Sub - carriers

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antenna transmission to improve the coverage and capacity of the system while minimizing the probability of outage through transmit diversity, beam forming and null steering. An AAS DL Zone begins on the specified symbol boundary and consists of all subchannels until the start of the next Zone or end of frame. The two highest numbered subchannels of the DL frame may be dedicated at the discretion of the BS for the AAS Diversity-Map Zone in PUSC, FUSC, and optional FUSC permutation. It should be noted that AAS Diversity-Map Zone shall is used only with FFT sizes greater than or equal to 512. In the AMC permutation, first and last subchannels of the AAS DL Zone may be dedicated at the discretion of the BS for the AAS Diversity-Map Zone as shown in the Fig. 2.45. When first and the last subchannels are used for Diversity-Map zone, they are not allocated in the normal DL-MAP message but are used to transmit the AAS-DLFP(). In case that the AAS Diversity-Map zone is not included in the AAS zone, these subchannels may be used for ordinary traffic and may be allocated in DL_MAP messages. For all AMC permutations in an AAS zone including the optional AAS Diversity-Map zone, two bin by three symbol tile structure is used. In the AAS zone, the same antenna beam pattern shall be used for all pilot subcarriers and data subcarriers in a given AMC subchannel.

PUSC permutation

DL subframe AAS on FUSC/PUSC permutation

PUSC permutation

FCH

DL subframe AAS on AMC permutation

FCH AAS diversity map zone ( subchannel 0) DL burst #1

DL-MAP

DL-MAP

DL burst #1

DL burst #2

Preamble

Preamble

DL burst #2

DL burst #3

DL burst #3

DL burst #5

AAS diversity map zone

Fig. 2.45 AAS diversity map frame structure

UL-MAP

UL-MAP

DL burst #4

DL burst #4

AAS diversity map zone (subchannel N-1)

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2.15.2.13

129

Adjacent Subcarrier Permutation

In the case of AMC, the basic allocation unit is bin. Bin is the smallest unit in frequency domain for adjacent carrier per-mutation. It is composed of nine contiguous subcarriers. Out of nine, eight are data tones and one is pilot tone as shown in Fig. 2.46. SS may switch from the distributed subcarrier permutation to the adjacent subcarrier permutation, when it changes from non-AAS to AAS-enabled traffic to support Adaptive Antenna System (AAS) adjacent subcarrier user traffic. For AMC, permutation is same for UL and DL. Once switched to the zone of adjacent subcarrier permutation mode in a frame, BS shall continue to transmit/receive data using the adjacent subcarrier permutation mode. The BS shall return to the distributed subcarrier permutation at the beginning of a new DL sub-frame.

2.15.2.14

OFDMA Ranging

In IEEE 802.16e four types of ranging procedure exists: initial ranging, periodic ranging, bandwidth request ranging and handover ranging. Initial and periodic ranging processes are supported to synchronize the SSs with the BS at the initial network entry and also periodically during the normal operation. Bandwidth request mechanism is supported so that SSs can request UL allocations for transmission of data to the BS. Handover ranging is used for ranging against a target BS. The OFDMA PHY specifies a ranging allocation that can be used for ranging as well as bandwidth request. A ranging channel is composed of one or more groups of six adjacent subchannels, where the groups are defined starting from the first subchannel. Optionally, ranging channel may be composed of eight adjacent subchannels using the symbol structure. Users are allowed to collide on this ranging

Pilot Tone

Data Tones

Fig. 2.46 Bin structure in adjacent subcarrier permutation

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channel. To effect a ranging transmission, each user randomly chooses one ranging code from a bank of specified binary codes. These codes are then BPSK modulated onto the subcarriers in the ranging channel, one bit per subcarrier. The initial ranging transmission is used by any SS that wants to synchronize to the system channel for the first time. An initial-ranging transmission is performed during two or four consecutive symbols. The same ranging code is transmitted on the ranging channel during each symbol, with no phase discontinuity between the two symbols. A time-domain illustration of the initial-ranging/handover-ranging transmission is shown in Fig. 2.47. The BS can allocate two consecutive initial-ranging/handover-ranging slots, Fig. 2.48. The SS then transmits the two consecutive initial-ranging/handoverranging codes. The SS can also optionally use two consecutive ranging codes transmitted during a four-OFDM symbol period. This option decreases the probability of failure and increases the ranging capacity to support larger numbers of

time CP

CP

Copy samples

Copy samples

OFDM symbol period

OFDM symbol period

Fig. 2.47 Initial ranging transmissions for OFDMA (adapted from [23])

time

Copy samples CP

Copy samples CP

Code X Copy samples

OFDM symbol period

Code X

Code (X+1)

Code (X+1)

Copy samples

OFDM symbol period

Copy samples

Fig. 2.48 Initial ranging transmission for OFDMA, using two consecutive initial ranging codes

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simultaneous ranging SSs while at the same time it further increases the capability of the system to support larger numbers of synchronization mismatches [35]. For this the starting code should always be multiple of 2.

2.15.2.15

Ranging Codes

The ranging codes are binary pseudo-noise codes produced by the PRBS generator. A set of 256 special pseudo-noise 144 bit-long ranging codes are divided into four groups for Initial Ranging, Periodic Ranging, Bandwidth Requests and Handover Ranging such that the BS can determine the purpose of the received code by the subset to which the code belongs. From the available codes, the first N are for initial ranging, the next M are for periodic ranging, the next L for bandwidth request and the remaining S (S = 144-N-M-L) are for Handover ranging [30, 36].

2.15.2.16

Channel Coding

For OFDMA PHY, channel coding procedures include randomization, FEC encoding, bit interleaving, and modulation. As shown in the Fig. 2.49, the basic block pass the regular coding chain where the first subchannel set the randomization seed, and the data follow the coding chain up to the mapping. The output data from the modulation is mapped onto the block of subchannels allocated for the basic block. Then, it is also mapped on the allocated subchannels.

2.15.2.17

Randomization

Data randomization is performed on all data transmitted on the downlink as well as uplink except the FCH. The randomization is initialized on each FEC block. If the amount of data to transmit does not fit exactly the amount of data allocated, padding of 0xFF (“1” only) shall be added to the end of the transmission block, up to the amount of data allocated. Here, the amount of data allocated means the amount of data that corresponds to the amount of [Ns/R] slots, where Ns is the number of the slots allocated for the data burst and R is the repetition factor used.

Data to in PHY burst

Randomizer

FEC

Bit-Interleaver

Repetition

Modulation

Fig. 2.49 Channel coding process for regular and repetition coding transmission

Mapping to OFDMA subchannels

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Encoding

The encoding block size depends on the number of slots allocated and the modulation specified for the current transmission. Concatenation of a number of slots is performed in order to make larger blocks of coding where it is possible, with the limitation of not exceeding the largest supported block. The OFDMA PHY supports mandatory tail-biting Convolutional Coding and three optional coding schemes. Zero Tailing Convolutional code, Convolutional Turbo code along with HARQ, and Block Turbo code are the optional coding schemes. The tail biting is implemented by initializing the encoders memory with the last data bits of the FEC block being encoded, and the zero tailing is implemented by appending a zero tail byte to the end of each burst. HARQ mitigates the effect of impairments due to channel and external interference by effectively employing time diversity along with incremental transmission of parity codes (subpackets in this case). In the receiver, previously erroneously decoded subpackets and retransmitted subpackets are combined to correctly decode the message. The transmitter decides whether to send additional subpackets, based on ACK/NAK messages received from the receiver.

2.15.2.19

Bit Interleaving

Bit interleaving is done in order to protect the transmission against long sequences of consecutive errors, which are very difficult to correct. Interleaving process is performed on encoded data at the output of FEC. The size of the interleaving block is based on the number of coded bits per encoded block size. The interleaving is performed using a two-step permutation process. The first permutation ensures that adjacent coded bits are mapped onto nonadjacent subcarriers and the second permutation ensures that adjacent coded bits are mapped alternately onto less or more significant bits of the constellation, thus avoiding long runs of lowly reliable bits.

2.15.2.20

Repetition

The Repetition process was added in Channel Coding in IEEE 802.16e standard for PFDMA PHY [24]. Repetition coding is used to further increase signal margin over the modulation and FEC mechanisms. In the case of repetition coding, R = 2, 4, or 6, the number of allocated slots (Ns) will be a whole multiple of the repetition factor R for uplink. For the downlink, the number of the allocated slots (Ns) will be in the range of R  K, R  K + (R1), where K is the number of the required slots before applying the repetition scheme. For example, when the required number of slots before the repetition is 10( = K) and the repetition of R = 6 will be applied for the burst transmission, then the number of the allocated slots (Ns) for the burst can be from 60 slots to 65 slots.

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The binary data that fits into a region that is repetition coded is reduced by a factor R compared to a non-repeated region of the slots with the same size and FEC code type. After FEC and bit-interleaving, the data is segmented into slots, and each group of bits designated to fit in a slot will be repeated R times to form R contiguous slots following the normal slot ordering that is used for data mapping. This repetition scheme applies only to QPSK modulation; it can be applied in all coding schemes except HARQ with CTC.

2.16

Summary and Conclusions

This Chapter covers aspects of OFDM and OFDMA WiMAX physical layer. It started by presenting the historical evolution of OFDM, OFDM fundamentals and the OFDM transmission concept, including details on the serial to parallel converter and the role of the demodulator. The OFDM symbol time structure was presented and ISI and ICI mitigation was discussed together with details on OFDM spectral efficiency and the impact of subchannelisation, which shows the advantages of OFDM. Robustness against narrowband interference, simple equalisation, low cost transmitter, simple receiver, sub-carrier rate adaptation and resistance against selective fading are amongst the advantages of OFDM. The parameters and principles of Scalable OFDMA were also addressed and its usefulness in IEEE 802.16e was highlighted, as it enables that IEEE 802.16e may be backward compatible with FBWA IEEE 802.16-2004. Finally, the IEEE 802.16 PHY layer was described in detail, including aspects of WirelessMAN-SC, WirelessMAN-OFDM, WirelessMAN-OFDMA and WirelessMAN-HUMAN PHYs.

References 1. R.V. Nee, R. Prasad, OFDM for Wireless Multimedia Communications (Artech House, Boston, MA, 2000) 2. M.I. Rahman, S.S. Das, F.H.P. Fitzek, OFDM Based WLAN Systems (Aalborg University, Denmark, Jan 2004). Technical Report R- 4-1002, ISSN 0908-1224, ISBN 87-90834-43-7 3. R.W. Chang, Synthesis of band-limited orthogonal signals for multichannel data transmission. Bell Syst. Tech. J. (Dec 1966) 4. J.L. Holsinger, Digital communication over fixed time continuous channels with memory, with special application to telephone channels, Ph.D. thesis, Massachusetts Institute of Technology, Cambridge, MA, 1964 5. R.G. Gallager, Information Theory and Reliable Communications (Wiley, New York, 1968) 6. B.R. Saltzberg, Performance of an efficient parallel data transmission system. IEEE Trans. Commun. 15(6), 805–811 (1967) 7. S.B. Weinstein, P.M. Ebert, Data transmission of frequency division multiplexing using the discrete frequency transform. IEEE Trans. Commun. COM-19(5), 623–634 (Oct 1971)

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8. R. Peled, A. Ruiz, Frequency domain data transmission using reduced computational complexity algorithms, in Proceeding of the IEEE International Conference on Acoustics, Speech, and Signal Processing, ICASSP ’80 (Denver, CO, USA, 1980), pp. 964–967 9. L.J. Cimini, Analysis and simulation of a digital mobile channel using orthogonal frequency division multiplexing. IEEE Trans. Commun. 33(7), 529–540 (July 1985) 10. S.S. Das, Techniques to enhance spectral efficiency of OFDM Systems, Ph.D. thesis, Aalborg University, Denmark, 2007 11. M.A. Hasan, Performance Evaluation of WiMAX/IEEE 802.16 OFDM Physical Layer, Master’s thesis presentation, Helsinki University, Finland, 2007 12. E.P. Lawrey, Adaptive Techniques for Multiuser OFDM, Ph.D. dissertation, James Cook University, Australia, Dec 2001 13. C.R. Nassar et al., Multi-carrier Technologies for Wireless Communication (Kluwer, Norwell, MA, 2002) 14. M.I. Rahman, S.S. Das, F.H.P. Fitzek, OFDM Based WLAN Systems (Aalborg University, Denmark, 2005). Technical Report R-04-1002; v1.2, 2005 15. H. Rohling et al., Broad-band OFDM Radio transmission for multimedia applications. Proc. IEEE 87(10), 1778–1789 (Oct 1999) 16. J. Geier, Wireless LANs, Implementing High Performance IEEE 802.11 Networks, 2nd ed. (Sams Publishing, Indianapolis, IN, July 2001) 17. D. Matic, OFDM Synchronization and Wideband Power Measurements at 60 GHz for Future Wireless Broadband Multimedia Communications, Ph.D. dissertation, Aalborg University, Denmark, Sept 2001 18. U.S. Jha, Low Complexity Resource Efficient OFDM Based Transceiver Design, Ph.D. dissertation, Aalborg University, Denmark, Sept 2002 19. IEEE 802.16-2004, IEEE Standard for Local and metropolitan area networks – Part 16: Air Interface for Fixed Broadband Wireless Access Systems, June 24, 2004 20. J.H. Scott, The How and Why of COFDM. BBC Research and Development, EBU Technical Review, Winter 1999 21. H. Sari et al., Transmission techniques for digital terrestrial TV broadcasting. IEEE Commun. Mag. 33(2), 100–109 (Feb 1995) 22. H. Rohling, T. May, Comparison of PSK and DPSK Modulation in a Coded OFDM System, in Proceedings of IEEE VTC, Phoenix, Arizona, USA, 1997, pp. 5–7 23. IEEE P802.16e/D9 Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems: Amendment for Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands, IEEE, New York, June 2005 24. IEEE P802.16-2004/Cor1/D3 Corrigendum to IEEE Standard for Local and Metropolitan Area Networks–Part 16: Air Interface for Fixed Broadband Wireless Access Systems, IEEE, New York, 2005 25. Channel Models for Fixed Wireless Applications, IEEE 802.16 Broadband Wireless Access Working Group, http://ieee802.org/16, IEEE, New York, 2003 26. D.C. Cox, 910 MHz Urban mobile radio propagation: multipath characteristics in New York City. IEEE Trans. Commun. com-21(11) (Nov 1973) 27. D.H. Morais, Fixed Broadband Wireless Communications: Principles and Practical Applications, 1st ed. (Prentice Hall, Upper Saddle River, NJ, Jan 2004) 28. H. Yaghoobi, Scalable OFDMA Physical layer in IEEE 802.16 wireless MAN. Intel Technol. J. 8(3) (2004) 29. C. Eklund, R.B. Marks, K.L. Stanwood, S. Wang, IEEE Standard 802.16: A Technical Overview of the WirelessMAN Air Interface for Broadband Wireless Access (June 2002) 30. IEEE Std 802.16e-2005 and IEEE Std 802.162004/Cor 12005 (Amendment and Corrigendum to IEEE Std 802.16-2004), IEEE Standard for Local and metropolitan area networks Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems Amendment 2: Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands and Corrigendum 1 (Feb 2006)

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31. H. Sari, G. Karam, Orthogonal frequency-division multiple access and its application to CATV networks. Eur. Trans. Telecommun. (ETT) 9(6), 507–516 (Nov–Dec 1998) 32. A. Ghosh, D.R. Wolter, J.G. Andrews, R. Chen, Broadband wireless access with WiMax/ 802.16: current performance benchmarks and future potential. IEEE Commun. Mag. 43(2) (Feb 2005) 33. http://en.wikipedia.org/wiki/OFDM#cite_note-4 (March 2010) 34. http://www.umtsforum.com (March 2010) 35. H. Yaghoobi, Scalable OFDMA Physical Layer in IEEE 802.16 WirelessMAN. Intel Communications Group, Intel Corporation, Santa Clara, CA, USA (August 2004) 36. A. Ghost, R. Muhamed, J.G. Andrews, Fundamentals of WiMAX: Understanding Broadband Wireless Networking (Prentice Hall, Upper Saddle River, NJ, 2007)

Chapter 3

Medium Access Control Layer Ramjee Prasad and Fernando J. Velez

Abstract The IEEE 802.16 Medium Access Control (MAC) protocol supports point-to-multipoint (PtM) and mesh broadband very high peak bit rate wireless applications while delivering Quality of Service (QoS) similar to the one of ATM and DOCSIS. The MAC sub-layer, protocol and service data units are described, as well as the missions, functions, connections, addressing and service flows of the Service Specific Convergence and MAC Common Parts Sub-layers. Then, the headers formats, the MAC sub-header, specific payloads and sub-header ordering are analyzed. IEEE 802.16 MAC connections are described and basic, primary and secondary management connections are presented, as well as details on fragmentation, packing and concatenation. The encryption of MAC Packet Data Units and Automatic Repeat Request (ARQ) area also covered, followed by hybrid ARQ. Scheduling algorithms, QoS classes, aspects of bandwidth allocation and request mechanisms are finally addressed, as well as contention resolution mechanisms and network entry issues.

3.1

Introduction

Media Access Control (MAC) layer resides above the PHY layer of the open systems interconnect (OSI) protocol stack. The primary task of the WiMAX MAC layer is to provide an interface between the higher transport layers and the physical layer for controlling the access to the wireless medium. The MAC protocols may use either distributed multiple access techniques or centrally coordinate the access for all devices, or even use a combination of two.

R. Prasad (*) Center for TeleInFrastruktur (CTIF), Aalborg University, Niels Jernes Vej 12, DK-9220 Aalborg Øst, Denmark e-mail: [email protected]

R. Prasad and F.J. Velez, WiMAX Networks, DOI 10.1007/978-90-481-8752-2_3, # Springer ScienceþBusiness Media B.V. 2010

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The IEEE 802.16 MAC protocol was designed for point-to-multipoint (PtM) broadband wireless access applications. But to accommodate the more demanding physical environment and different service requirements MAC supports mesh, rather than only point to multipoint network architectures. Unlike Wi-Fi, WiMAX supports access and bandwidth allocation algorithm to accommodate hundreds of terminals per channel. IEEE 802.16 standard is designed to work with outdoor networks, both in urban as well as rural areas. In order to overcome the errors due to long distance and weather conditions and boost the performance MAC layer adopts adaptive modulation mechanism as well as forward error correction (FEC) codes. The WiMAX MAC is designed from the ground up to support very high peak bit rates while delivering Quality of Service (QoS) similar to that of ATM and DOCSIS. The IEEE 802.16 MAC layer can support bursty data traffic with high peak rate demand while simultaneously supporting streaming video and latency-sensitive voice traffic over the same channel. Strong and good QoS is achieved by using connection-oriented MAC architecture. Different needs for different types of applications is satisfied by the serving BS. The MAC uses a variable-length MPDU and offers a lot of flexibility to allow for their efficient transmission. The remaining of this Chapter is organized as follows. Section 3.2 presents the MAC sub-layer while Section 3.3 presents the MAC Protocol and Service Data Units. Section 3.4 addresses the missions, functions, connections, addressing and service flows for the service specific Convergence Sub-layer. Section 3.5 describes the MAC Common Part Sub-layer while Section 3.6 presents the header formats. Section 3.7 addresses MAC sub-header, special payloads and sub-header ordering Section 3.8 addresses IEEE 802.16 MAC connections. Section 3.9 presents basic, primary and secondary management connections. The details on fragmentation, packing and concatenation are addressed in Section 3.10. Sections 3.11 and 3.12 present the encryption of MAC PDUs and Automatic Repeat Request, respectively. Section 3.13 addresses scheduling and the five QoS classes. Section 3.14 describes the bandwidth allocation and request mechanisms. Section 3.15 presents aspects of contention resolution mechanisms. Section 3.16 presents network entry. Finally, Section 3.17 presents the conclusions.

3.2

MAC Sub-layers

The IEEE 802.16 MAC layer is composed of three sub-layers Service Specific Convergence Sub-layer (CS), MAC Common Part Sub-layer (CPS) and the Security Sub-layer. Each sub-layer has a specific function to perform. Figure 3.1 shows three MAC sub-layers with their respective functions. The Service-Specific Convergence Sub-layer (CS) provides any transformation or mapping of external network data, received through the CS service access point (SAP), into MAC SDUs received by the MAC Common Part Sub-layer (CPS) through the MAC SAP.

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Service Specific Convergence Sublayer

MAC Layer

MAC Common Part Sublayer

PHY Layer

Security Sublayer

Protocol Specific, i.e ATM,Ethernet, Internet Protocol

Packing Fragmentation, ARQ QoS

Authentication, Key Exchange, Encryption

Fig. 3.1 MAC sub-layers

The core part of the IEEE 802.16 MAC is the MAC CPS, as it provides the core MAC functionality of system access, bandwidth allocation, connection establishment, and connection maintenance. Also functions like uplink scheduling, bandwidth request and grant, connection control, and automatic repeat request (ARQ) are also defined. Communication between the CS (Convergence Sub-layer) and the MAC CPS are maintained by MAC Service Access Point (MAC SAP).The four basic actions of communication that is creation of connection, modification of connection, deletion of connection and transport of data over the connection is done at this layer [3]. The MAC also contains a separate security Sublayer providing authentication, secure key exchange, and encryption. Data, PHY control, and statistics are transferred between the MAC CPS and the PHY via the PHY SAP (which is implementation specific). The PHY definition includes multiple specifications, each appropriate to a particular frequency range and application.

3.3

MAC Protocol Data Unit (PDU) and Service Data Unit

MAC Protocol Data Unit (PDU) – A MAC Protocol Data Unit (PDU) is the data unit exchanged between the MAC layers of the BS and associated Subscriber Stations (SSs). A MAC PDU is known as MAC frame. Figure 3.2 illustrates the PDU and SDU in the IEEE 802.16 protocol stack. Layer N addresses Layer N PDU to corresponding Layer N of the peer entity. On the downward direction, PDU is the data unit generated for the next lower layer. On the upward direction, it is the data unit received from the previous lower layer. Service Data Unit (SDU) – SDU’s are data unit exchanged between two adjacent protocol layers. On the downward direction, it is the data unit received from the previous higher layer. While on the upward direction, it is the data unit sent to the next higher layer (see Fig. 3.11). Service Access Point (SAP) – The point in a protocol stack where the services of a lower layer are available to its next higher layer. The role of each of the MAC sub layers is defined the following sections.

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Receiving Entity

Layer N +1

SDU

SDU

PDU

PDU Layer N SAP

Layer N

SDU

SDU layer N functions

PDU

layer N functions

PDU Layer N+1 SAP

Layer N–1

SDU

SDU

PDU

PDU

Fig. 3.2 PDU and SDU in a protocol stack

3.4 3.4.1

Service Specific Convergence Sub-layer (CS) Mission and Functions

The service specific Convergence Sub-layer (CS), often known as CS is the top sublayer of the MAC Layer in IEEE 802.16. The function of CS is to map the traffic coming from upper layer protocols or applications. The CS sits on top of the MAC Common Part Sub-layer (CPS), and its purpose is to make use of the services provided by the latter via appropriate MAC Services Access Points (SAP). This provides scalability to the standard introducing one more degree of freedom because it is just a matter of building the right CS to transport almost any protocol one can think of. In the present version of the IEEE 802.16-2004 standard, two CS specifications are provided as shown in Table 3.1. The first CS specification is the ATM CS. The Asynchronous Transfer Mode (ATM) CS is a logical interface that associates different ATM services with the MAC CPS SAP (Fig. 3.3). The packet CS is used for transport for all packet-based protocols such as Internet Protocol (IP), IPv4, IPv6, Point-to-Point Protocol (PPP), IEEE 802.3 LAN/MAN CSMA/CD Access Method (Ethernet) and, IEEE Std 802.1Q (VLAN). The IP specific part of the Packet CS enables transport of IPv4 and

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Table 3.1 Convergence sublayers of WiMAX (From [4])

141

Value 0 1 2 3 4 5 6 7 8 9

Convergence sub-layer ATM CS Packet CS, IPv4 Packet, IPv6 Packet CS, 802.3/Ethernet Packet CS, 802.1Q VLAN Packet CS, IPv4 over 802.3/Ethernet Packet CS, IPv6 over 802.3/Ethernet Packet CS, IPv4 over 802.1Q VLAN Packet CS, IPv6 over 802.1Q VLAN Packet CS, 802.3 with optional VLAN tags and ROHC header compression 10 Packet CS, 802.3 with optional VLAN tags and ERTCP header compression 11 Packet CS, IPv4 with ROHC header compression 12 Packet CS, IPv6 with ECRTP header compression 13–31 Reserved

ATM Convergence Sublayer CS SAP Service-Specific Convergence Sublayer (CS)

MAC SAP

Packet Convergence Sublayer

Fig. 3.3 ATM and packet convergence sub-layer

IPv6 packets directly over the MAC. However, it should be noted that WiMAX Forum has decided to implement only IP and Ethernet (802.3) CS. The MAC CS accepts higher layer PDUs from the higher layers and transmits them to the MAC CPS where MAC procedures are applied. The Service Specific Convergence Sub-layer (CS) also provides any transformation or mapping of external network data, received through the CS service access point (SAP) into MAC SDUs. This includes classifying external network Service Data Units (SDUs) and associating them to the proper MAC service flow and Connection Identifier (CID). Among other functions of CS is the optional Payload Header Suppression (PHS). As WiMAX is a connection oriented service, most of the information used for routing a packet becomes redundant once the connection is set up, therefore the CS

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also provides a packet header suppression (PHS) mechanism in order to avoid the transmission of redundant information over the link. l

l l l l

Thus, the CS for MAC protocol performs the following functions at the transmitter Receiving the payload protocol PDU from the higher protocol layer Mapping the payload protocol PDUs to the appropriate MAC service flow (SF) Optionally performing Payload Suppression Header (PSH) Delivering the processed packet to the MAC for transmission At the receiver side the reverse actions are taken by the CS which are as follows:

l l

l

Receiving the MAC SDU Restore compressed payload protocol headers (In case, PHS performed at the Transmitter) Deliver the payload protocol PDU to the corresponding higher layers

3.4.2

Connections and Addressing, Connection ID (CID) and Service Flows

3.4.2.1

Concepts

802.16 MAC is connection oriented. Each IEEE 802.16 MAC instance is an SS has a unique 48 bit MAC address [1]. This 48 bit address is used to identify SS during initial registration or authentication as a part of some management messages. The initial ranging process needs to be completed before the SS establishes connectivity and gain access to the network. But this 48 bit MAC address is not carried in every IEEE 802.16 MPDU as in IEEE 802.11. Instead the connection oriented IEEE 802.16 MAC makes primary use of the 16-bit connection identifier to identify all information exchanged between BS and SS, including management and broadcast data. On the basis of the above discussion we define three important terms which are the cornerstones of IEEE 802.16 standard. 1. Connection – A connection is defined as a MAC Level connection between a BS and a SS, or inversely. It is a unidirectional transformation or mapping between the BS and a BS MAC peers for transporting a service flow’s traffic. All traffic is carried on a connection even for a service flow implementing connectionless protocols such as IP. Connections are identified by a connection identifier (CID). The CID can be considered a connection identifier even for nominally connectionless traffic like IP, since it serves as a pointer to destination and context information. 2. Connection ID (CID) – The WiMAX MAC layer is connection oriented and identifies a logical connection between equivalent peers in the MAC layers of a BS and SS by a unidirectional connection identifier called CID. The size of the CID is 16-bit. The use of a 16-bit CID permits a total of 64K connections within each downlink and uplink channel. CID is also the basic ID used in bandwidth

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allocations and bandwidth reservations. CID provides an easy way to differentiate traffic as well as reduces the overhead associated with carrying MAC addresses. CID is used in all MAC level QoS functions such as classifier and QoS scheduler to identify and differentiate traffic in order to maintain service level and fairness between connections. 3. Service Flow (SF) – Service Flows is a MAC transport service. It provides unidirectional transport of packets to UL packets or DL packets. Service Flow is used by the IEEE 802.16 MAC to efficiently support peer connection services such as QoS. A service flow is characterized by a set of QoS Parameters such as latency, jitter, and throughput assurances. In order to standardize operation between the SS and BS, these attributes include details of how the SS requests uplink bandwidth allocations and the expected behaviour of the BS uplink scheduler. CID maps to a service flow identifier (SFID), which defines the Quality of Service (QoS) parameters of the service flow associated with that connection.

3.4.2.2

Classification

Classification is the process by which a MAC SDU is mapped onto a particular connection for transmission between MAC peers [1]. The mapping process associates a MAC SDU with a connection, which also creates an association with the service flow characteristics of that connection. This process facilitates the delivery of MAC SDUs with the appropriate QoS constraints. Classification exists in the uplink as well as downlink. In case of downlink transmission, the classifier is present at the BS and in case of the uplink transmission it is in the SS. The classification process is shown in Figs. 3.4 and 3.5. As

Upper Layer Entity (e.g., bridge, router)

SDU

SDU

SAP

SAP

CID 1 CID 2 Uplink Classifier

Reconstitution (e.g., undo PHS)

…….. CID n {SDU, CID, ,,,}

{SDU, CID, ,,,} BS

SS

SAP

SAP

802.16 MAC CPS

802.16 MAC CPS

Fig. 3.4 Classification and CID mapping (SS to BS)

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Upper Layer Entity (e.g., bridge, router)

SDU

SDU

SAP

SAP CID 1 CID 2

Uplink Classifier

……..

Reconstitution (e.g., undo PHS)

CID n {SDU, CID, ,,,}

{SDU, CID, ,,,} SS

BS

SAP

SAP

802.16 MAC CPS

802.16 MAC CPS

Fig. 3.5 Classification and CID mapping, BS to SS (adapted from [1])

defined in the standard a classifier is a set of matching criteria applied to each packet entering the IEEE Std 802.16 network. It consists of some protocol-specific packet matching criteria (destination IP address, for example), a classifier priority, and a reference to a CID. If a packet matches the specified packet matching criteria, it is then delivered to the SAP for delivery on the connection defined by the CID. Implementation of each specific classification capability (as, for example, IPv4 based classification) is optional. The service flow characteristics of the connection provide the QoS for that packet. Several classifiers may refer to the same service flow. The classifier priority is used for ordering the application of classifiers to packets. Explicit ordering is necessary because the patterns used by classifiers may overlap. The priority need not be unique, but is to be taken within a classifier priority to prevent ambiguity in classification. Downlink classifiers are applied by the BS to packets it is transmitting and uplink classifiers are applied at the SS. In IEEE 802.16 connection is a MAC Level connection between a BS and a MS or inversely. Though the MAC 802.16 is connection oriented, all the connections are virtual. It is a unidirectional transformation or mapping between the BS and a BS MAC peers for transporting a service flow’s traffic. In order to map simultaneously different services and associate varying levels of QoS, all data communications are in the context of a connection. Service flow is provisioned when an SS is installed in the system. After SS registration connections are associated with these service flows to provide a reference for the process of bandwidth request. Thus a connection serves two purposes. One it provides mapping between peer convergence process that utilize the MAC and the second, defines the service flow.

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Fig. 3.6 MSDU format for PCS

MAC SDU

PHSI Optional

Packet PDU

In short, the MAC Layer classifies each application. This classification is an important process because each BS serves a relatively large number of users transmitting different applications simultaneously. Also, classification helps in better link adaptation as it allocates the much needed resources for each application separately. Thus the QoS differentiation, for example, between an email and a voice transmission, is very easy to implement. 3.4.2.3

Packet Convergence Sub-layer

The packet convergence Sublayer is defined for packet-based services such as IP, Ethernet and VLAN. The main purpose of this Sublayer is to classify service data units (SDUs) to the proper MAC connection, enable QoS and bandwidth allocation. Packet Convergence Sub-layer (PCS) also performs important function of payload header suppression (PHS) and reconstruction. PHS enhances air link efficiency. The format of PCS PDU is shown in Fig. 3.6. Packets arriving to the service–specific CS from upper layers are called MAC Service Data Units (SDU).These packets may sometime have large headers, as long as 120 bytes. These headers are often repetitive and prove to be redundant. In PHS, a repetitive portion of the payload headers is suppressed in the MAC SDU by the sending entity and restored by the receiving entity. Implementation of PHS capability is optional. At the uplink, the sending entity is the SS and the receiving entity is the BS. At the downlink, in turn, the sending entity is the BS and the receiving entity is the SS.

3.4.2.4

Packet Header Suppression and Rules

PHS Rules The repetitive (redundant) Packet header suppression is used to avoid the transmission of redundant information over the air link. This helps reduce packet delay, which is essential for maintaining an acceptable delay for applications like VoIP. PHS rules are applied in different ways for the two CS specifications, ATM CS and Packet CS. For the ATM standard again two modes are defined. The VP switched mode (Virtual Path) and the VC switched mode (Virtual Channel). PHS

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rule is applied in the same way on the two modes with the only difference in the payload header size variation after suppression. When the PHS is turned off, no part of the ATM header is suppressed. For the Packet CS mode, when PHS is enabled at MAC connection, each MAC SDU is prefixed with a Packet Header Suppression Index (PHSI) which references the Payload Header Suppression Field (PHSF) to suppress. The PHSI is an 8-bit field and is always added when carrying Ethernet or IP, regardless of whether PHS is enabled for the connection. If PHS is used, the PHSI field indicates which PHS rule is to be applied by the receiver. The sending entity uses classifiers to map packets into a service flow. The classifier uniquely maps packets to its associated PHS Rule. To restore the PHSF the receiving entity uses the CID and the PHSI. Once a PHSF has been assigned to a PHSI, it cannot be changed. To change the value of a PHSF on a service flow, a new PHS rule need to be defined, the old rule is removed from the service flow, and the new rule is added. When a classifier is deleted, any associated PHS rule is also be deleted. PHS has a Payload Header Suppression Valid (PHSV) option to verify the payload header before suppressing it (Fig. 3.7). PHS has also a Payload Header Suppression Mask (PHSM) option which allows some selected bytes not to be suppressed. The PHS with masking is explained in Fig. 3.8. PHSM determines the bytes not to be suppressed. In turn, bytes which are to be suppressed are refereed by PHSF. If PHS verify (PHSV) is used, the CS first compares the bits in the PHSF with the one they are expected to be based on PHS rule. After the verification process is over the bytes corresponding the PHSF are removed and the SDU is appended by the PHSI as provided by the matching rule. But in case if the PHSF of the SDU does not match PHSF of the associated rule, there is no suppression at all and the SDU is appended with PHSI ¼ 0. Thus, PHSM facilitates suppression of header fields that remain static within a higher-layer session for example IP addresses, while enabling transmission of fields that change from packet to packet, for example IP Total Length. Either the sending or the receiving entity specifies the PHSF and the Payload Header Suppression Size (PHSS). It is the responsibility of the higher-layer service entity to generate a PHS Rule that uniquely identifies the suppressed header within the service flow. It is also the responsibility of the higher-layer service entity to guarantee that the byte strings that are being suppressed are constant from packet to packet for the duration of the active service flow.

PHS Operation Figure 3.7 illustrates various steps involved in the PHS operation for WiMAX. A packet is submitted to the packet CS. The SS first applies its list of Classifier rules. If the rule matches it results in an Uplink Service Flow, CID, and a PHS Rule. The PHS Rule provides all the parameters like PHSF, PHSI, PHSM, PHSS, and PHSV (Table 3.2). If PHSV is set or not present, the SS compares the bytes in the packet header with the bytes in the PHSF that are to be suppressed as indicated by the

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Packet arrives from uppper layer entity

PDU arrives from MAC SAP

Classify Packet Retrieve PHSF, PHSI, PHSM, PHSS, PHSV

Identify CID and extract PHSI

Verify?

Retrieve PHSF, PHSM, PHSS

Yes

No

Reconstruct Header

Verify with PHSF together with PHSM

Present Packet to CS SAP Pass Verify? No END

Yes Supress with PHSM Set PHSI to Index

Set PHSI to 0

Prepend PHSI to PDU

Present Packet to MAC SAP

END

Fig. 3.7 PHS operation (adapted from [1])

PHSM. If they match, the SS suppresses all the bytes in the Uplink PHSF except the bytes masked by PHSM. The SS then prefix the PDU with the PHSI and present the entire MAC SDU to the MAC SAP for transport on the uplink. When the MAC PDU is received by the BS from the air interface, the BS MAC layer determines the

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Sender

A

B

C

D

E

PHSM

1

0

1

0

1

PHSF

A’

X

C’

X

E’

B

D

PHSM

1

0

1

0

1

PHSF

A’

X

C’

X

E’

A’

B’

C’

D’

E’

Air Interface

Receiver

= Verify

= Assign

A-E = current header A’-E’ = cached header X = don’t care PHSS = 5

Fig. 3.8 PHS with masking (adapted from [1]) Table 3.2 PHS terms and details

Term PHSI (Identifier) PHSF (Fields)

PHSM (Mask) option PHSS (Size) PHSV (Valid) option

Details To identify the rule The fields to be suppressed because they remain unaltered into transmission from sender to receiver Selects the bytes not to be suppressed Header size before suppressing To verify or not the payload header before suppressing

associated CID by examination of the generic MAC header. The BS MAC layer sends the PDU to the MAC SAP associated with that CID. The receiving packet CS uses the CID and the PHSI to look up PHSF, PHSM, and PHSS. The BS reassembles the packet and then proceeds with normal packet processing. The reassembled packet contains bytes from the PHSF. If verification was enabled, then the PHSF bytes equal the original header bytes. If verification was not enabled, then there is no guarantee that the PHSF bytes match the original header bytes. A similar operation occurs on the downlink. The BS applies its list of Classifiers. A match of the Classifier results in a Downlink Service Flow and a PHS Rule. The PHS Rule provides PHSF, PHSI, PHSM, PHSS, and PHSV. If PHSV is set or not present, the BS verifies the Downlink Suppression Field in the packet with the PHSF. If they match, the BS suppresses all the bytes in the Downlink Suppression Field except the bytes masked by PHSM. The BS then prefixes the PDU with the PHSI and present the entire MAC SDU to the MAC SAP for transport on the downlink. The SS receives the packet based upon the CID Address filtering within the MAC. The SS receives the PDU and then sends it to the CS. The CS then uses the PHSI and CID to lookup PHSF, PHSM, and PHSS. The SS reassembles the packet and then proceeds with normal packet processing. Figure 3.8 demonstrates packet

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suppression and restoration when using PHS masking. Masking allows only bytes that do not change to be suppressed. Note that the PHSF and PHSS span the entire suppression field, included suppressed and unsuppressed bytes.

3.4.2.5

PHS Signalling

PHS requires the creation of the following three objects: 1. Service flow 2. Classifier 3. PHS rule These three objects are created either simultaneously or in separate message flows. PHS Rules are created with DSA or Dynamic Service Change (DSC) messages. The BS defines the PHSI when the PHS Rule is created. PHS rules are deleted with the DSC or Dynamic Service Deletion (DSD) messages. The SS or BS may define the PHSS and PHSF. To change the value of a PHSF on a service flow, a new PHS rule is defined, the old rule is removed from the service flow, and the new rule is added. Figures 3.9 and 3.10 shows the two ways to signal the creation of a PHS rule. It is possible to partially specify a PHS rule (in particular the size of the rule) at the time a service flow is created. As an example, it is likely that when a service flow is first provisioned, the header fields to be suppressed will be known. The values of some of the fields, for example, IP addresses, User Datagram Protocol (UDP) port numbers, etc., may be unknown and would be provided in a subsequent DSC as part of the activation of the service flow (using the “Set PHS Rule” DSC Action). If the PHS rule is being defined in more than one step, each step, whether it is a DSA or DSC message, they contain either the SFID (or reference) and a PHS index to uniquely identify the PHS rule that is being defined.

BS

DSC-REQ

DSC-RSP

DSC-ACK

Fig. 3.9 PHS signalling example, BS initiated

SS Classifier Rule Index +PHSI+PHSS+PHSF

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Fig. 3.10 PHS signalling example, SS initiated

BS

SS Classifier Rule Index +PHSS+PHSF

DSC-REQ

PHSI DSC-RSP

DSC-ACK

3.5 3.5.1

MAC Common Part Sub-layer (MAC CPS) Mission

The Common Part Sub-layer (CPS) forms the second sub-layer of MAC. The CPS forms the core of the MAC protocol and is responsible for: l l l l

System access Bandwidth allocation Connection establishment Maintenance of the connection between the two sides (BS and SS)

CPS is responsible for important functions like frame construction, uplink scheduling, bandwidth request and grant, connection control, and automatic repeat request (ARQ). The CPS includes many procedures for Quality of Service (QoS) management and Radio Resource Management (RRM). Communication between the CS (Convergence Sub-layer) and the MAC CPS are maintained by MAC Service Access Point (MAC SAP). All the four basic actions of communication that is creation of connection, modification of connection, deletion of connection and transport of data over the connection is carried at CPS layer.

3.5.2

MAC Addressing and Connections

Each SS has a 48-bit universal MAC address, as defined in IEEE Std 802.16-2004. This address uniquely defines the air interface of the SS. It is used during the initial ranging process to establish the appropriate connections for an SS. It is also used as part of the authentication process by which the BS and SS each verify the identity of the other. The 802.16 BS is identified by a 48-bit Base Station ID (BSID). Here it should be noted that the BSID is different from the MAC address of the BS. The BSID is used for operator identification.

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In the Mesh mode, along with the 48-bit universal MAC address a 16-bit node identifier (Node ID) is used. When authorized to the network the candidate node receives Node ID upon a request to the Mesh BS. Node ID is the basis for identifying nodes during normal operation. The Node ID is transferred in the Mesh sub-header, which follows the generic MAC header, in both unicast and broadcast messages. As the 802.16 MAC is connection oriented, each and every service is mapped to a connection, and every connection is referenced with 16-bit connection identifier (CID). All services, even connectionless services such as Ethernet and IP, are mapped into a MAC connection. Connections are identified by a 16-bit CID and each connection may have different parameters for bandwidth, security and priority. When a SS is joining the network three CIDs are assigned to it and each one has different QoS requirements used by different management levels: Basic, Primary Management and Secondary Management connections (described in Section).

3.5.3

MAC PDU Format

The maximum length of the MAC PDU is 2,048 bytes. Each standard MAC packet shown in Fig. 3.11 consists of the three components: 1. A fixed length MAC header, which contains frame control information. 2. A variable length payload, which contains information. 3. A Frame Check Sequence (FCS), which contains an IEEE 32-bit cyclic redundancy code (CRC).

LSB

MSB

Payload and Cyclic Redundancy check are optional. They are used only if it SS ask for it in its QoS parameters. Medium access control Packet Data Units (MPDUs) are transmitted in on-air PHY slots [9]. The fixed length headers are of two types, the Generic MAC header and the MAC Header without Payload. Generic MAC Header is the one that is used to transfer almost all the standard MAC Management messages. The second one, MAC Header without Payload, is a header that is sent alone, without a payload. If present, the Payload consists of zero or more sub-headers and zero or more MAC SDUs and/or fragments thereof. The sub-headers may be of six different types described in section (MAC sub-headers, Special payloads and Sub-header Ordering).

Generic MAC Header

Payload (Optional)

6 Bytes

Fig. 3.11 MAC PDU format (adapted from [1])

CRC (Optioanal)

4 Bytes

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The payload information may vary in length, so that a MAC PDU may represent a variable number of bytes. This allows the MAC to tunnel various higher-layer traffic types without knowledge of the formats or bit patterns of those messages. A MAC PDU may contain a Cyclic Redundancy Check (CRC). Implementation of CRC capability is mandatory for SCa, OFDM and OFDMA PHY layers. The maximum length of the MAC PDU is 2,048 bytes, including header, payload, and Cyclic Redundancy Check (CRC).

3.6

MAC Header Formats

3.6.1

Generic MAC Header

Two MAC header formats are defines in IEEE 802.16-2004 and 802.16e standards, Generic MAC Header and MAC Header without payload. For the DL traffic, only one DL MAC header, called generic MAC header is defined. This header begins each MAC PDU containing either MAC management messages or CS data. But for the UL two MAC header formats exist. The first is the generic MAC header that begins each MAC PDU containing either MAC management messages or CS data, in which HT field is set to 0. The second is the MAC header format without payload for which the HT is set to 1. For the latter format, the MAC header is not followed by any MAC PDU payload and CRC. The single-bit Header Type (HT) field distinguishes between the generic MAC header and MAC header without payload. For the generic MAC header the HT field is set to zero and to one for MAC header without payload. The format of generic MAC header is illustrated in Fig. 3.12 and the header fields defined in Table 3.3. The ESF bit in the Generic MAC header indicates that the extended sub-header is present. Using this field, a number of additional sub-headers can be used within a PDU. The extended sub-header is always defined immediately after the Generic MAC header and before all other sub-headers. All extended sub-headers are not encrypted. The Type field in the Generic MAC Header is 6-bit. Each bit has a specific meaning shown in Table 3.4.

3.6.2

MAC Header Without Payload

3.6.2.1

MAC Signalling Header Type I

There are two types of MAC header formats without payload, type I and type II. For MAC frames with this type of header format, the MAC header is not followed by

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Generic MAC Header

0

1

HT(0)

EC

2

3

4

5

TYPE

Payload (Optional)

6

7

8

9

ESF

CI

10

CRC (Optioanal)

11

EKS

12 Rsv

LEN (LSB)

CID (MSB)

CID (LSB)

HCS

13

14

15

LEN (MSB)

Fig. 3.12 Generic MAC header format in detail (adapted from [1])

any MAC PDU payload and CRC. This header format is applicable to UL only. It is of the same size as that of the Generic MAC Header. The IEEE 802.16-2004 standard has Bandwidth Request Header as the header without payload. After the amendment, the IEEE 802.16e standard introduced MAC header without payload as a frame name. Now Bandwidth Request Header is a specific case for MAC header formats without payload. For this MAC header format, there is no payload following the MAC header. The MAC signalling header type I is illustrated in Fig. 3.13. The description of the different assigned bits for MAC signaling header type I is shown in Table 3.5. Table 3.6 describes the 3-bit type field encoding following the EC field.

3.6.2.2

MAC Signalling Header Type II

This type of MAC header is UL specific. There is no payload following the MAC header. The MAC signalling header type II is illustrated in Fig. 3.14. In the type II, the header is changed with regard to type I. MAC signalling header type II is used for some feedbacks specific to OFDMA, MIMO etc. [5].

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Table 3.3 Generic MAC header fields Name Length (bits) Description CI 1 CRC Indicator 1 ¼ CRC is included in the PDU by appending it to the PDU Payload after encryption, if any 0 ¼ No CRC is included EC 1 Indicates whether the payload is encrypted 0 ¼ Payload is not encrypted 1 ¼ Payload is encrypted EKS 2 Encryption Key Sequence. The index of the Traffic Encryption Key (TEK) and Initialization Vector used to encrypt the payload. This field is only meaningful if the EC field is set to 1 HCS 8 8-bit CRC to detect errors in the header Header Check Sequence, generating polynomial D ¼ D8 þ D2 þ D þ 1 HT 1 Header Type, Indicates whether this is a generic or bandwidth request header (set to 0 for such header) LEN 11 Length. The length in bytes of the MAC PDU including the MAC header and the CRC if present Type 6 This field indicates the sub-headers and special payload types present in the message payload ESF 1 Extended sub-header field. If ESF ¼ 0, the extended sub-header is absent. If ESF ¼ 1, the extended sub-header is present and will follow the Generic MAC Header immediately. The ESF is applicable both in the DL and in the UL CID 16 A unidirectional, MAC layer address that identifies a connection to equivalent peers

Table 3.4 Type encodings Type bit #5 most significant bit (MSB) #4

#3

#2 #1 #0 least significant bit (LSB)

Value Mesh sub-header 1 ¼ present, 0 ¼ absent ARQ Feedback Payload 1 ¼ present, 0 ¼ absent Extended Type Indicates whether the present Packing or Fragmentation Subheaders, is Extended, for non ARQ-enabled connections 1 ¼ Extended 0 ¼ not Extended. Applicable to connections where ARQ is not enabled For ARQ-enabled connections, this bit is set to 1 Fragmentation sub-header 1 ¼ present, 0 ¼ absent Packing sub-header 1 ¼ present, 0 ¼ absent Downlink: FAST-FEEDBACK Allocation sub-header Uplink: Grant Management sub-header 1¼ present, 0 ¼ absent

EC = 0 (1)

Medium Access Control Layer HT = 1 (1)

3

Type (3)

155

Header content MSB (11)

Header Content LSB (8)

CID MSB (8)

CID LSB (8)

HCS (8)

Fig. 3.13 MAC signalling header type I format (adapted from [1]) Table 3.5 Fields of the MAC signalling header type I Name Length (bits) Description HT 1 Header Type 1 for the MAC Header without payload EC 1 For MAC header without payload, this bit indicates whether it is Type I or Type II HCS 8 Header check sequence.8-bit CRC to detect errors in the header Header check sequence, generating polynomial D ¼ D8 þ D2 þDþ1 Type 3 This field indicates the type of header without payload types (described in Table 3.6) Header Content 19 Header content Function of the type field value CID 16 A unidirectional, MAC layer address that identifies a connection to equivalent peers

Table 3.6 Type field encodings for MAC signalling header type I

3.7

Type field (3 bits) 000 001 010 011 100 101 110 111

MAC header type (with HT/EC ¼ 0b10) BR incremental BR aggregate PHY channel report BR with UL Tx power report Bandwidth request and CINR report BR with UL sleep control SN Report CQICH allocation request

MAC Sub-headers, Special Payloads and Sub-header Ordering

The presence of sub-headers is indicated by a type field in the Generic MAC header. The following six types of sub-headers may be present:

Type (1)

HT = 1 (1)

R. Prasad and F.J. Velez EC = 1 (1)

156

Header Content MSB (13)

Header Content (16)

Header Content LSB (8)

HCS (8)

Fig. 3.14 MAC signalling header type II format (adapted from [1])

Table 3.7 Classification of sub-headers based on PDU/SDU Per PDU/SDU sub-header Types of sub-headers Per PDU sub-header Fragmentation Grant management sub-header Mesh sub-header FASTFEEDBACK_Allocation Per SDU sub-header Packing

Table 3.8 Sub-header and special payload ordering

1. 2. 3. 4. 5. 6.

Order 1 2 3 4 5 6

Order of the sub-header Inserted Immediately following Generic MAC Header Inserted before each SDU

Sub-header MSH (mesh sub-header) GMSH (Grant management sub-header) FSH (fragmentation sub-header) FFSH (fast-feedback allocation sub-header) PSH (packing sub-header) ARQ special payload

Fragmentation Grant Management Packing Mesh FAST-FEEDBACK allocation ARQ special payload

These sub-headers may be per PDUs or per-SDU sub-headers (shown in Table 3.7) depending upon their function and location they are placed. The perPDU sub-headers (i.e., Mesh, Fragmentation, FASTFEEDBACK_ Allocation, and Grant Management) are inserted in MAC PDUs immediately following the Generic MAC header.

3

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The only per-SDU sub-header is the Packing sub-header. It may be inserted before each MAC SDU if so indicated by the Type field. The Packing and Fragmentation sub-headers are mutually exclusive and are not both present within the same MAC PDU. In case per-PDU sub-header is present it is always preceded by the first per-SDU sub-header. ARQ feedback payload is a special payload, inserted as the first payload after the sub-headers. The ordering of these sub-headers is described sequentially in Table 3.8. Thus if both the Fragmentation sub-header and Grant Management sub-header are indicated, the Grant Management sub-header comes first. If the Mesh subheader is indicated, it is preceded by all other sub-headers. The FAST-FEEDBACK Allocation sub-header always appears as the last per-PDU sub-header.

3.7.1

Significance of Type Field

As shown in the Table 3.9, the type field of the generic MAC header indicates the presence or absence of the sub-headers and more specifically one or all the types of sub-headers present in the MPDU. Type field also specifies order in which the subheaders are placed after the generic MAC header. The use of type field helps to decode the sub-headers correctly whenever multiple sub-headers are present in a single MPDU (Fig. 3.15).

CI (1)

Type (6)

Rsv (1)

HT = 0 (1) EC (1)

Table 3.9 Type encodings Type bit Value #5 most significant bit Mesh sub-header 1 ¼ present, 0 ¼ absent (MSB) #4 ARQ Feedback Payload 1 ¼ present, 0 ¼ absent #3 Extended type Indicates whether the present Packing or Fragmentation Sub-headers, is Extended 1 ¼ Extended 0 ¼ not Extended. Applicable to connections where ARQ is not enabled. #2 Fragmentation sub-header 1 ¼ present, 0 ¼ absent #1 Packing sub-header 1 ¼ present, 0 ¼ absent #0 least significant bit Downlink: FAST-FEEDBACK Allocation sub-header Uplink: Grant (LSB) Management sub-header 1 ¼ present, 0 ¼ absent

Sub-header MAC Header

Fig. 3.15 Significance of type field

CRC-32

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IEEE 802.16 MAC Connections

The 802.16 MAC service is connection oriented. Each connection comes with QoS parameters, is serviced by one of the five scheduling services and may have its own security association. The 16-bit connection identifier (CID) used in MAC PDU (Protocol Data Units), functions as a reference for all connections and is constantly granted bandwidth on demand [1]. There are two types of MAC connection, one is Management connection and the other is Transport connection. The management connections carry only management messages, transport connections carry other traffic, typically user data. SS can have several connections to a BS for different services, like for network management or for data transport. In MAC, all associations use different parameters for priority, bandwidth and security. BS always assigns CID for SS. As soon as a SS joins a network, three different CIDs are allocated to it. Moreover, each CID has separate QoS requirements, which are used by different management connection levels: Primary, Basic and Secondary Management connections. Both basic and primary management connections are created when a Mobile Station (MS)/SS is joined to a BS network. Transport connections can be established on demand. They are used for user traffic flows, unicast or multicast transmission. Additional channels are also reserved by the MAC to send out uplink and downlink schedule. A single CID can carry traffic for many different higher layer sessions.

3.9

Basic, Primary and Secondary Management Connections

All MAC connections for IEEE 802.16 are identified by a 16-bit CID. Some CIDs are set aside for specific purposes such as initial ranging, broadcast and multicast polling. As mentioned before during initialization when a subscriber station enters the network, three types of management connections are established between the SS and the BS (before transport connections can be established). Once all the management connections are established, an SS can set up transport connections. Service flows attached to transport connections can also join multicast groups and so will listen to multicast polling channels that are assigned to those groups. The three types of management connections are described in brief below: l

l

Basic Connection: Basic management connections are established for exchange of short, delay-critical MAC management messages .These connections has a basic CID and uses highest level of QoS. Primary Management connection: The BS MAC and the SS MAC use primary management messages to exchange longer and more delay tolerant MAC management messages. The Primary Management CID is used by these types of connections.

3

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l

Secondary Management Connection: BS and SS use Secondary Management Connection in order to transfer delay tolerant, standards-based messages. These are the Dynamic Host Configuration Protocol (DHCP), Trivial File Transfer Protocol (TFTP), Simple Network Management Protocol (SNMP), etc. These messages are carried on IP datagrams and are thus used for managed SSs.

3.9.1

159

MAC Management Message Format

The Management messages are carried in the Payload of the MAC PDU. All MAC Management messages begin with a Management Message Type field followed by message payload. MAC Management messages on the Basic, Broadcast, and Initial Ranging connections are neither fragmented nor packed. MAC Management messages on the Primary Management Connection may be packed and/or fragmented. For the SCa, OFDM, and OFDMA PHY layers, management messages carried on the Initial Ranging, Broadcast, Broadcast, Basic, and Primary Management connections must have CRC usage enabled. MAC management messages are not carried on Transport Connections. The format of the management message is given in Fig. 3.16. An example of management message payload is shown in Table 3.10. The first part of the payload follows no particular set of encoding rules. In the example, it is string of two bytes containing the management message type and Transaction ID. The rest of the message is defined as TLV-coded information. A TLV encoding consists of three fields or a tuple: Type, Length and Value. For each parameter encoded as a type-length-value (TLV), the first byte identifies the parameter type, the following byte/bytes indicates the length in bytes of the value field and the last is the actual parameter value. The list of 802.16-2004 MAC management messages and the encoding of their management messages type field are shown in the Table 3.11. The 802.16e amendment added some new messages to support mobility given in Table 3.12. The new messages supporting mobility start with ‘MOB’. MAC management messages that have a Type value specified in Table 3.9 as “reserved”, or those not containing all required parameters or containing erroneously encoded parameters, are silently discarded.

Fig. 3.16 MAC management message format

Table 3.10 DSA-REQ message format

Management Message Type

Management Message Payload

Syntax DSA-REQ_Message_Format() { Management Message Type = 11 Transaction ID TLV Encoded Information }

Size

Notes

8 bits 16 bits variable TLV specific

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Table 3.11 List of all IEEE 802.16-2004 MAC management messages (From [1]) Type Message name Message description Connection 0 UCD Uplink channel descriptor Broadcast 1 DCD Downlink channel descriptor Broadcast 2 DL-MAP Downlink access definition Broadcast 3 UL-MAP Uplink access definition Broadcast 4 RNG-REQ Ranging request Initial ranging or basic 5 RNG-RSP Ranging response Initial ranging or basic 6 REG-REQ Registration request Primary management 7 REG-RSP Registration response Primary management 8 reserved 9 PKM-REQ Privacy key management request Primary management 10 PKM-RSP Privacy key management response Primary management 11 DSA-REQ Dynamic service addition request Primary management 12 DSA-RSP Dynamic service addition response Primary management 13 DSA-ACK Dynamic service addition acknowledge Primary management 14 DSC-REQ Dynamic service change request Primary management 15 DSC-RSP Dynamic service change response Primary management 16 DSC-ACK Dynamic service change acknowledge Primary management 17 DSD-REQ Dynamic service deletion request Primary management 18 DSD-RSP Dynamic service deletion response Primary management 19 reserved 20 reserved 21 MCA-REQ Multicast assignment request Primary management 22 MCA-RSP Multicast assignment response Primary management 23 DBPC-REQ Downlink burst profile change request Basic 24 DBPC-RSP Downlink burst profile change response Basic 25 RES-CMD Reset command Basic 28 CLK-CMP SS network clock comparison Broadcast 29 DREG-CMD De/Re-register command Basic 30 DSX-RVD DSx received message Primary management 31 TFTP-CPLT Config file TFTP complete message Primary management 32 TFTP-RSP Config File TFTP complete response Primary management 33 ARQ-Feedback Standalone ARQ feedback Basic 34 ARQ-Discard ARQ discard message Basic 35 ARQ-Reset ARQ reset message Basic 36 REP-REQ Channel measurement report request Basic 37 REP-RSP Channel measurement report response Basic 38 FPC Fast power control Broadcast 39 MSH-NCFG Mesh network configuration Broadcast 40 MSH-NENT Mesh network entry Basic 41 MSH-DSCH Mesh distributed schedule Broadcast 42 MSH-CSCH Mesh centralized schedule Broadcast 43 MSH-CSCF Mesh centralized schedule configuration Broadcast 44 AAS-FBCK-REQ AAS feedback request Basic 45 AAS-FBCK-RSP AAS feedback response Basic 46 AAS_Beam_Select AAS beam select message Basic 47 AAS_BEAM_REQ AAS beam request message Basic 48 AAS_BEAM_RSP AAS beam response message Basic 49 DREG-REQ SS De-registration message Basic

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Table 3.12 List of MAC management messages added by the 802.16e amendment (From [2]) Type Message name Message description Connection 50 MOB_SLP-REQ Sleep request message Basic 51 MOB_SLP-RSP Sleep response message Basic 52 MOB_TRF-IND Traffic indication message Broadcast 53 MOB_NBR-ADV Neighbor advertisement message Broadcast, primary management 54 MOB_SCN-REQ Scanning interval allocation request Basic 55 MOB_SCN-RSP Scanning interval allocation response Basic 56 MOB_BSHO-REQ BS HO request message Basic 57 MOB_MSHO-REQ MS HO request message Basic 58 MOB_BSHO-RSP BS HO response message Basic 59 MOB_HO-IND HO indication message Basic 60 MOB_SCN-REP Scanning result report message Primary management 61 MOB_PAG-ADV BS broadcast paging message Broadcast 62 MBS_MAP MBS MAP message – 63 PMC_REQ Power control mode change request Basic message 64 PMC_RSP Power control mode change response Basic message 65 PRC-LT-CTRL Setup/Tear-down of long-term MIMO Basic precoding 66 MOB_ASC-REP Association result report message Primary management 67–255 Reserved –

3.10 3.10.1

Fragmentation, Packing and Concatenation Fragmentation

To meet the challenges posed by the wireless medium, MAC supports various functions such as data encapsulation, fragmentation and adaptive modulation. The MAC is responsible for encapsulating higher layer packets or SDUs in its own format and delivering it to the peer MAC on another device. But in most cases it is advantageous to fragment a MAC SDU in many MAC PDUs or inversely, to pack more than one MSDU in many PDUs. Fragmentation lowers the risk of losing the whole MSDU instead of losing the part of it. But on the other hand fragmentation also increases the header information need to carried by the channel. Therefore fragmentation is of much interest when the channel is relatively bad or packets too long. Packing is advantageous as the header information or the overhead carried through the channel is low. In Concatenation many PDUs are transmitted in a single transmission. We discuss fragmentation, packing and concatenation in detail in the sections below. Fragmentation is the process by which a MAC SDU is divided into one or more MAC PDUs. There are many reasons for the MAC to fragment a single SDU into multiple fragments before transmission (Fig. 3.17). The idea over here is to allow

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Fragment #1

Generic Fragment MACHeader Sub-Header (6 bytes) (1-2 bytes)

Fragment # 2

MAC SDU Fragment #1

Fragment # n

Generic Fragment MAC Header Sub-Header (6 bytes) (1-2 bytes)

Optional CRC (4 bytes)

MAC SDU Fragment #n

…….

Optional CRC (4 bytes)

MPDU # n MPDU #1

Generic Fragment MAC Header Sub-Header (6 bytes) (1-2 bytes)

MAC SDU Fragment #2

Optional CRC (4 bytes)

MPDU # 2

Fig. 3.17 Fragmentation of MAC SDU in to n MAC PDUs or MAC frames (adapted from [1]) Table 3.13 Fragmentation rules

Fragment First fragment Continuing fragment Last fragment Unfragmented

Fragmentation control (FC) 10 11 01 00

better packing of MAC SDUs into the available OFDM frequency-time resources by using all data sub carriers in each OFDM symbol. Use of fragmentation is optional but encouraged to improve link efficiency. For capacity analysis, it is reasonable to assume that some fraction of the MAC PDUs will be fragmented. Capabilities of fragmentation and reassembly are mandatory. The authority to fragment traffic on a connection is defined when the connection is created by the MAC SAP. Fragmentation may be initiated by a BS for downlink connections and by an SS for uplink connections. Fragments are tagged with their position in their parent SDU in accordance with Table 3.13.

3.10.2

Packing

Packing refers to combining two or more MAC SDUs into a single MAC PDU (Fig. 3.18). Like its converse, fragmentation, this allows better packing of MAC SDUs into the available OFDM frequency-time resources by using all data sub carriers in each OFDM symbol. Use of packing is optional but encouraged to improve link efficiency.

3

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163

Packing with fixed size MAC SDUs (no packing sub-header is needed) MAC SDU 1

HT

MAC SDU 2

......

Fixed size MSDUs, e.g., ATM Cells, on the same connection

MAC SDU k

MAC PDU Payload

CRC

Packing with variable size MAC SDUs (Packing Sub-Header is needed) MAC SDU or seg. 1

HT

PSH

MAC SDU or seg 2

PSH

Variable size MSDUs or MSDU segments, e.g., IP packets, on the same connection

MAC SDU or seg n

......

PSH

CRC

Packing Sub-Header (16 bits)

Fig. 3.18 MAC PDU packing

For capacity analysis, it is reasonable to assume that some fraction of the MAC PDUs will be packed. The variable overhead is an additional three Bytes added to the 802.16 MAC header for each packed SDU. A worst-case assumption is to assume that each MAC PDU includes a one or more sub headers when packing is supported; the exact number depending on the relative sizes of the SDUs and PDU. Both downlink and uplink channels are affected. Normally packing and fragmentation are either both supported or not at all. Since packing and fragmentation are mutually exclusive operations for a given MAC SDU we can conservatively estimate that, on average, one packing sub header will be present in each MAC PDU increasing the total header overhead by three bytes. If packing and fragmentation are not supported then the overhead associated will obviously be higher because the scheduler will have fewer options to size the packets to the bandwidth allocations. This will be particularly true for the uplink where only a single station can use a burst. Depending on the traffic characteristics, this increased overhead can often be larger than the small fractional overhead associated with the packing/fragmentation sub headers.

3.10.3

Concatenation

Per–PDU PHY overhead should be as low as possible to increase the transmission efficiency. This is achieved by a process called Concatenation (Fig. 3.19). In this multiple MPDUs are transmitted in a single PHY burst. In IEEE 802.16 PHY specification an intermediate sub-layer called the transmission CS is specified to

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R. Prasad and F.J. Velez MAC PDU 1

HT

FEC

MAC PDU 2

MAC PDU Payload CRC

FEC block 1

PHY Burst

HT

MAC PDU k ......

MAC PDU Payload CRC

HT

MAC PDU Payload

CRC

...... FEC Block 2

FEC Block 3

FEC block m

OFDM OFDM Preamble symbol symbol 1 2

OFDM symbol n

......

Fig. 3.19 Concatenation of k MAC PDUs into a single PHY burst

Uplink Burst # n

Uplink Burst # n+1

User PDU

Bandwidth Request PDU

Management PDU

CID = 0x02301

CID = 0x0399

CID =0x0EF1 CID = 0x5F3E CID = 0x2555

User PDU

User PDU

Fig. 3.20 Concatenation of user and management MPDUs

efficiently support concatenation. This sub-layer inserts a pointer byte at the beginning of the payload. Figure 3.20 illustrates this concept for an uplink burst transmission. Since each MAC PDU is identified by a unique CID, the receiving MAC entity is able to present the MAC SDU (after reassembling the MAC SDU from one or more received MAC PDUs) to the correct instance of the MAC SAP. MAC Management messages, user data, and bandwidth request MAC PDUs may be concatenated into the same transmission.

3.10.4

CRC Calculation

A service flow may require that a CRC be added to each MAC PDU carrying data for that service flow. In this case, for each MAC PDU with HT = 0, a CRC (as defined in IEEE Std 802.3), is appended to the payload of the MAC PDU; that is, request MAC PDUs are unprotected. The CRC covers the generic MAC header and the Payload of the MAC PDU. The CRC is calculated after encryption; that is, the CRC protects the Generic Header and the ciphered Payload.

Medium Access Control Layer

165 LSB

MSB

3

Generic MAC Header

Payload (Optional)

CRC (Optioanal)

Encrypted portion of the MAC PDU

Fig. 3.21 MAC PDU encryption

3.11

Encryption of MAC PDUs

When transmitting a MAC PDU on a connection that is mapped to an SA, the sender performs encryption and data authentication of the MAC PDU payload as specified by that SA. When receiving a MAC PDU on a connection mapped to an SA, the receiver performs decryption and data authentication of the MAC PDU payload, as specified by that SA. The generic MAC header is not encrypted. The Header contains all the Encryption information (EC Field, encryption key sequence [EKS] Field, and CID) needed to decrypt a Payload at the receiving station. This is illustrated in Fig. 3.21. Encryption of the payload is indicated by the EC bit field. A value of 1 indicates the payload is encrypted and the EKS field contains meaningful data. A value of 0 indicates the payload is not encrypted. Any unencrypted MAC PDU received on a connection mapped to an SA requiring encryption is to be discarded.

3.12 3.12.1

Automatic Repeat Request (ARQ) Error Control

Reliable transfer of information is a critical requirement in the wireless communication. Therefore the wireless system must define a process for handling MPDU errors. The PHY layer supports error correction methods to minimize the number of errors. But at the MAC layer additional error correction methods are necessary as bit errors are inevitable. In order to provide a reliable wireless link, ARQ is introduced in IEEE 802.16 MAC. ARQ is a mechanism by which the receiving end of a connection can request the retransmission of MAC PDU when received with errors. Automatic Repeat Request (ARQ) is one of the most widely used technique for error control in data communication, the other being Forward error correction (FEC). The ARQ method is not basically meant for correcting errors. But whenever the error information of the transmitted DL packets is reported the receiver requests for repeated transmission in the subsequent UL subframe. The erroneous packets will then be retransmitted in the following DL subframe.

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As ARQ is a part of the 802.16 MAC layer it can be enabled on a per-connection basis. The 802.16 specification does not mandate the usage of the ARQ mechanism meaning that it is a provider and a customer specific decision. An algorithm is defined for the Automatic Repeat Request scheme to support reliable delivery of data packets and comprises of following modules: l l l l

Error Detection Feedback Policy Retransmission Strategy Retransmission Unit

3.12.2

ARQ Blocks

An ARQ block is the basic unit of transmission or retransmission for ARQ mechanism. Normally MAC SDU is logically partitioned into blocks of fixed length. In case the length of the SDU is not an integer multiple of the connection’s block size, the final block of the SDU is formed using the SDU bytes remaining after the final full block has been determined.

3.12.2.1

Block Sequence Number (BSN)

Block Sequence Number (BSN) is the sequence number assigned to each ARQ block of SDU. BSN is used for Fragmentation and Packing. Figure 3.22 describes the concept of ARQ blocks and BSNs. ARQ block showed has two consecutive SDUs, SDU#1 and SDU#2 belonging to the same connection. SDU#1 consists of seven blocks starting from BSN 5 and ending at BSN 11. Similarly SDU#2 has five blocks starting from BSN12 and ending at BSN 16.

3.12.2.2

ARQ Block Length

The length of ARQ block is specified by the connection TLV parameter ARQ_ BLOCK_SIZE. Once an SDU is partitioned into a set of blocks, this partitioning remains in effect until all blocks of the SDU are successfully delivered to the receiver, or the SDU is discarded by the transmitter state machine. SDU #2

SDU #1 Frag 0 5

6

Frag 1 7

8

9

Frag 0 10

11

12

13

Frag 1 14

Two consecutive SDUs presented to MAC for the same connection

Fig. 3.22 ARQ blocks

15

16

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167

IEEE 802.16d specification [1] defines an ARQ block size as any value ranging from 1 to 2,040 bytes, the 802.16e specification [2] has limited it to power of two values ranging from 16 to 1,024 bytes, for example, 16, 32, 64 and so on.

3.12.3

ARQ Methodology

The MAC SDUs received are fragmented or packed into required block size. The blocks are then transmitted at the receiver end .These blocks are checked for errors. If the received block is error free, ACK is sent to the transmitter using feedback channel. If the received block is in error, a retransmission request is sent to the transmitter using the feedback channel. The transmitter then retransmits the same block. The ARQ feedback information is sent either as a standalone MAC management message on the appropriate basic management connection, or piggybacked on an existing connection. ARQ feedback cannot be fragmented.

3.12.3.1

ARQ Block Usage and Rearrangement

While retransmitting a PDU, sometimes a connection may face a problem such that an allocated data burst is smaller than the PDU size to be retransmitted. This may happen if the BS scheduler allocates data bursts of different sizes, which is usually the case for rtPS, nrtPS, and BE connections. Suppose, that the BS allocates a data burst of three slots for the BE connection and the latter sends a PDU that spans the whole data burst. If this PDU encounters an error, the connection will retransmit it. But in case, if the BS scheduler allocates later a data bursts of two slots, there is no way to retransmit the original PDU. For such instances, the connection relies upon the retransmission with rearrangement that allows for fragmenting the retransmitted PDU on the ARQ block size boundaries. If there is a sufficiently small ARQ block size, then the connection may construct a smaller PDU. Sets of blocks selected for transmission or retransmission are to be encapsulated into a PDU. A PDU may contain blocks that are transmitted for the first time as well as those being retransmitted. Fragmentation occurs only on ARQ block boundaries. If a PDU is not packed, all the blocks in that PDU must have contiguous block numbers. When a PDU is packed, the sequence of blocks immediately between MAC sub-headers and the sequence of blocks after the last packing sub-header must have contiguous block numbers (shown in the Fig. 3.27). If ARQ is enabled at the connection, Fragmentation and Packing sub-headers contain a BSN, which is the sequence number of the first ARQ block in the sequence of blocks following the sub-header. Generally, it is a matter of transmitter policy to decide whether or not a set of blocks once transmitted as a single PDU should be retransmitted also as a single PDU. Figure 3.23 shows the use of blocks for ARQ transmissions and

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a

SDU #1

SDU #2

Frag 0 5

6

Frag 1 7

8

9

Frag 0 10

11

12

Frag 1

13

14

15

16

Two consecutive SDUs presented to MAC for the same connection

b

PDU #1

Packed PDU #2

Frag 0 of SDU #1 5

5

6

Frag 1 of SDU #1 8

7

8

9

10

Frag 0 of SDU #2 11

12

12

13

14

Original transmission

c

Packed PDU #3 Frag 1 of SDU #1 8

8

9

10

Frag 0 of SDU #2 11

12

12

13

14

Retransmission of PDU #2 without rearrangement

d

PDU #3

Packed PDU #4

Frag 1 of SDU #1

8

8

9

Frag 0 of SDU #2

Frag 2 of SDU #1

10

10

11

12

12

13

14

Retransmission of PDU #2 with rearrangement

Fig. 3.23 ARQ blocks and retransmissions

retransmissions. Two options are presented for retransmission – with and without rearrangements of blocks. Figure 3.23 shows the transmission, loss, and subsequent retransmission of two consecutive SDUs with and without rearrangement. Figure 3.23a shows the construction of two PDUs: l l

PDU#1 consisting of fragment #0 of SDU#1 PDU#2 consisting of fragment #1 of SDU#1 and fragment #0 of SDU#2

We suppose here that PDU#2 did not reach the receiver. Now the ARQ block based approach offers number of possibilities for retransmission of the lost PDU#2. By the time the loss of PDU#2 is detected by the transmitter, fragment #1 of SDU#2 consisting of blocks 15 and 16 had already reached the receiver successfully. Now PDU#2 can be transmitted with no change or rearrangement as new PDU (Fig. 3.23c). Another way of sending the lost PDU is retransmission with a rearrangement where the original PDU#2 is split into separate PDUs, PDU#3 and PDU#4 (Fig. 3.27d). 3.12.3.2

ARQ Feedback Information Element (IE)

ARQ Feedback IE is used by the receiver to provide feedback on successfully received and missing blocks. The format of the IE is shown in the Fig. 3.24. The ARQ feedback IE contains an ACK Type field and also an optional variable size

3

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169

CID (16 bits)

L A S T

ACK Type (2 bits)

BSN (11 Bits)

#ACK Maps (2 bits)

Variable, depending on ACK Type and #ACK Maps

Fig. 3.24 ARQ feedback IE Table 3.14 Acknowledgment types ACK Type Description ACK Type==0x0 BSN value corresponds to the most significant bit of the first 16-bit ARQ ACK map and follows an MSB first approach with the BSN incremented by 1 for each bit in the ARQ ACK map, following through for the subsequent ARQ ACK maps ACK Type==0x1 BSN value indicates that its corresponding block and all blocks with lesser values within the transmission window have been successfully received ACK Type==0x2 Combines the functionality of the previous two acknowledgement types described above ACK Type==0x3 Combines the functionality of type 0x1 with the ability to acknowledge reception of ARQ blocks in terms of block sequences. A block sequence is defined as a set of ARQ blocks with consecutive BSN values. With this option, members of block sequences are identified and associated with the same reception status indication

bitmap to indicate positive or negative acknowledgements. Four different types of acknowledgments are defined to support flexible feedback in Table 3.14. The fields of the ARQ Feedback IE are described below: 1. CID – The CID of the connection for which this feedback is being sent. 2. Last – This bit is used to pack ARQ Feedback IEs to create an ARQ feedback payload. The Last bit is set to zero for all ARQ Feedback IEs, except the last IE in the payload. 3. ACK Type – ACK Type field indicates the type of acknowledgement being send in the feedback IE. Table shows the acknowledgement types and their descriptions. 4. BSN – The BSN value is interpreted differently based on the value of ACK Type described in the table. 5. #ACK MAPs – The value of #ACK MAP plus one represents the total number of 16-bit acknowledgment bitmaps included in this feedback IE.

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6. ACK Maps – The number of acknowledgement MAPs is variable and the acknowledgement type is 0b01 does not have an associated acknowledgement MAP. This acknowledgement MAPs are treated as a bit stream, where the MSB is the MSB of the first acknowledgement Map and LSB is the last LSB of the last acknowledgment MAP. 3.12.3.3

BSN Comparison

ARQ state machines take actions based on comparison of BSNs. After comparing action is based on which is larger or smaller among them. In this context, it is not possible to compare the numeric sequence number values directly to make this determination. Instead, the comparison is made by normalizing the values relative to the appropriate state machine base value and the maximum value of sequence numbers, ARQ_BSN_MODULUS, and then comparing the normalized values. Normalization is based on the BSN value derived below: bsn0 ¼ ½ðbsn  BSN baseÞmod ARQ BSN MODULUS

(3.1)

The base values for the receiver and transmitter state machines are ARQ_TX_ WINDOW_START and ARQ_RX_WINDOW_START, respectively. Table 3.15 shows these ARQ parameters.

3.12.3.4

Transmitter State Machine

In IEEE 802.16 there are four states in which ARQ block may be present (Fig. 3.25): l l l l

Not-sent Outstanding Discarded Waiting for- retransmission

In the beginning, the ARQ block begins as not-sent. After it is sent it becomes outstanding for a period of time termed ARQ_RETRY_TIMEOUT. While a block is in outstanding state, it is either acknowledged and discarded, or transitions to waiting-for-retransmission after ARQ_RETRY_TIMEOUT or NACK. An ARQ block can become waiting-for-retransmission before the ARQ_RETRY_TIMEOUT period expires if it is negatively acknowledged. An ARQ block may also change from waiting-for-retransmission to discarded when an ACK message for it is received or after a timeout ARQ_BLOCK_LIFETIME. The transmitter first handles (transmit or discard) blocks in “waiting-for retransmission” state and only then blocks in “non-sent” state. Blocks in “outstanding” or “discarded” state are not transmitted. When blocks are retransmitted, the block with the lowest BSN is retransmitted first.

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Table 3.15 ARQ Parameters ARQ Parameter ARQ_BSN_MODULUS

Description ARQ_BSN_MODULUS is equal to the number of unique BSN values, i.e., 211. ARQ_WINDOW_SIZE ARQ_WINDOW_SIZE is the maximum number of unacknowledged ARQ blocks at any given time. An ARQ block is unacknowledged if it has been transmitted but no acknowledgment has been received. ARQ_WINDOW_SIZE is less than or equal to half of the ARQ_BSN_MODULUS. ARQ_BLOCK_LIFETIME ARQ_BLOCK_LIFETIME is the maximum time interval an ARQ block is held by the transmitter after the initial transmission of the block has occurred. If the block is successfully transmitted before its lifetime expires this timer is cancelled .But in case, transmission (or subsequent retransmission) of the block is not acknowledged by the receiver before the time limit is reached, the block is discarded. ARQ_BLOCK_SIZE ARQ_BLOCK_SIZE is the length used for partitioning an SDU into a sequence of ARQ blocks prior to transmission. ARQ_RETRY_TIMEOUT ARQ_RETRY_TIMEOUT is the minimum time interval a transmitter waits before retransmission of an unacknowledged block for retransmission. The interval begins when the ARQ block was last transmitted. ARQ_SYNC_LOSS_TIMEOUT This is used to declare loss of synchronisation between the transmitter and the receiver. ARQ_SYNC_LOSS_TIMEOUT is the maximum time interval ARQ_TX_WINDOW_START or ARQ_RX_WINDOW_START is allowed to remain at the same value before declaring a loss of synchronization of the sender and receiver state machines when data transfer is known to be active. The ARQ receiver and transmitter state machines manage independent timers. The transmitter and receiver have their own way of determining whether a connection is actively transferring data. ARQ_RX_PURGE_TIMEOUT ARQ_RX_PURGE_TIMEOUT is the time interval the receiver waits after successful reception of a block that does not result in advancement of ARQ_RX_WINDOW_START, before advancing ARQ_RX_WINDOW_START.

3.12.4

HARQ

Automatic repeat request algorithms are well known in wireless as well as in wireline, networks for retransmitting failed transmissions. The drawback behind using the effective ARQ scheme is the requirement of precise selection of both transmit power and data rate for the retransmissions. If this requirement is not fulfilled the link becomes underutilized or experiences excessive packet errors. In mobile broadband services it is challenging to maintain these optimal settings [8]. Therefore a significantly more robust mechanism called Hybrid ARQ (HARQ) was developed. HARQ is a particularly useful feature when users experience weak or

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ACK

ACK Retransmit

Not sent

Transmit

Waiting for transmission

Outstanding

ACK

ARQ_RETRY_TIMEOUT or NACK

Discarded

Fig. 3.25 ARQ block states at the transmitter MAC PDU (variable length) MAC Header

Payload

MAC PDU (variable length) MAC Header

Payload

CRC

Parity bits

HARQ packet mapped onto PHY burst

Fig. 3.26 Construction of HARQ encoder packet

rapidly changing channel conditions for example when traveling at high speeds, or during hand-off between cells, or at cell edges. The main difference between an ARQ scheme and an HARQ scheme is that HARQ enables fast recovery from transmission errors by storing defective packets and then combining them for subsequent retransmissions of the same packet. Many advanced technologies support HARQ as an important means to improve the robustness of data transmission over the wireless channel [1, 5]. HARQ renders performance improvement due to SNR gain and time diversity achieved by combining previously erroneously decoded packet and retransmitted packet. HARQ is also advantageous to mitigate the effect of channel and interference fluctuation [2]. Hybrid automatic repeat request (HARQ) scheme is optional part of the 802.16 standard MAC and may be only be supported for the OFDMA PHY. HARQ and

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Start

A Await SDU Arrival

Incremental BW request for CIDx

No

Process UL-MAP information elements

Grant for Basic CID?

Yes Process UL-MAP and assign bandwidth to the outstanding requests

No

Timer for aggregate requests expired?

Yes

Unsatisfied requests

Yes Build Incremental Requests

Build Aggregate Requests

No

Send data(and requests)

A Fig. 3.27 SS request/grant flow chart (adapted from [1])

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associated parameters are specified and negotiated using SBC-REQ/RSP messages during initialization network entry or re-entry procedure. The utilization of HARQ is on a per-connection basis, that is, it can be enabled on a per CID basis by using the DSA/DSC messages burst cannot have a mixture of HARQ and non-HARQ traffic. One or more MAC PDUs can be concatenated and an HARQ packet formed by adding a CRC to the PHY burst. Figure 3.24 shows how the HARQ encoder packet is constructed. HARQ scheme is enabled on a CID basis and supports multiple HARQ channels per connection, each of which may have an encoder packet transaction pending. The number of HARQ channels in use is determined by BS. These ARQ channels are distinguished by an HARQ channel identifier (ACID). The ACID for any subpackets can be uniquely identified by the control information carried in the MAPs. For the downlink HARQ, fast ACK/NAK signalling is necessary and therefore a dedicated PHY layer ACK/NAK channel is designed in uplink.

3.12.4.1

Subpacket Generation

Two main variants of HARQ are supported Chase Combining (CC) and Incremental Redundancy (IR). BS may support either CC or IR while SS supports only CC. For IR, the PHY layer will encode the HARQ packet generating several versions of encoded subpackets. Each subpacket is uniquely identified using a subpacket identifier (SPID). For Chase Combining, the PHY layer encodes the HARQ packet generating only one version of the encoded packet. As a result, no SPID is required for Chase Combining. For downlink HARQ operation, the BS will send a version of the encoded HARQ packet. The SS will attempt to decode the encoded packet on this first HARQ attempt. If the decoding succeeds, the SS will send an ACK to the BS. If the decoding fails, the SS will send a NAK to the BS. In response, the BS will send another HARQ attempt. The BS may continue to send HARQ attempts until the SS successfully decodes the packet and sends an acknowledgement.

3.13

Scheduling Control

The wireless medium resources need to be scheduled according to the traffic and QoS requirements. Scheduling control is a mechanism, located in the base station, for managing upstream and downstream packet allocations based on traffic requirements and channel conditions at any given moment. Since data-oriented traffic varies considerably between uplink and downlink, bandwidth allocation, radio resource management and packet assignments needs to be aligned on actual demand.

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175

Scheduling Services

Scheduling services represent the data handling mechanisms supported by the MAC scheduler for data transport on a connection. The purpose of scheduling is to allow each and every user the suitable QoS required for the required application. To ensure meeting the QoS requirements, an efficient scheduling algorithm at the BS will guarantee proper performance, in order to support statistical multiplexing. This demands the Medium Access Control (MAC) protocol to co-ordinate the transmission of multiple traffic flows over it. The scheduling can be divided into downlink and uplink scheduling. The scheduling services in IEEE 802.16 are based on those defined for cable modems in the DOCSIS standard [6, 7]. The QoS is granted on the basis of type of application and service under consideration. For example, a user sending an email needs no real-time data stream alike another user having a Voice over IP(VoIP) application. To provide the service parameters respectively, the traffic management is necessary. The IEEE 802.162004 standard divides all services in four different classes: l l l l

Unsolicited Grant Service (UGS) Real-time Polling Service (rtPS) Non-real-time Polling Service (nrtPS) Best Effort (BE)

The fifth type QoS is added in 802.16e standard: extended real-time Polling Service (ertPS) [2]. UGS, rtPS, nrtPS and BE services are prioritized in decreasing order. Within all these classes of services resources are allocated to manage and satisfy the QoS of higher priority services. Scheduling and types of services are further described in Chapter 4: Quality of Service.

3.14 3.14.1

Bandwidth Allocation and Request Mechanisms Role of SSs

There are several different ways in which subscriber station can inform the base station that it has data to send on the uplink. Most of these methods involve sending a Bandwidth Request Header BRH (described in Chapter 2) for which the subscriber station must first obtain an uplink channel access grant from the base station. Bandwidth allocation and request mechanisms for the IEEE 802.16 is efficient, low-latency and flexible. Requests are made per connection basis to ensure they can be properly used in fairness algorithms in the BS’s UL scheduler. But grants are to the SS, not to the connection. Also there are no explicit acknowledgments sent back to indicate whether a bandwidth request (BW-REQ) message is successfully transmitted or distorted or how much bandwidth the SS is granted. SSs have the

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responsibility to determine that its BW-REQ was corrupted, and then start a contention resolution process. On the other hand, on receiving a grant within the timeout, the SS will stop contention resolution and use the allocated bandwidth for uplink transmission of data packets or to piggyback an additional request if necessary. Furthermore, the SS might know how much bandwidth is awarded by observing the following grant from the BS. Due to different scheduling algorithms at a BS, a grant may be given at any time. During network entry and initialization every SS is assigned up to three dedicated CIDs for the purpose of sending and receiving control messages. These connection pairs are used to allow differentiated levels of QoS to be applied to the different connections carrying MAC management traffic. Increasing (or decreasing) bandwidth requirements is necessary for all services except incompressible constant bit rate UGS connections. The needs of incompressible UGS connections do not change between connection establishment and termination. The requirements of compressible UGS connections, such as channelized T1, may increase or decrease, depending on traffic. Demand Assigned Multiple Access (DAMA) services are given resources on a demand assignment basis, as the need arises. When an SS needs to ask for bandwidth on a connection with BE scheduling service, it sends a message to the BS containing the immediate requirements of the DAMA connection. QoS for the connection was established at connection establishment and is looked up by the BS. UGS service is prohibited from using any contention requests, there is no explicit bandwidth requests issued by SS. The BS must provide fixed size data grants at periodic intervals to the UGS flows. The rtPS and nrtPS flows are polled through the unicast request polling. However, the nrtPS flows receive few request polling opportunities during network congestion and are allowed to use contention requests, while the rtPS flows are polled regardless of network load and frequently enough to meet the delay requirements of the service flows. There are numerous methods by which the SS can get the bandwidth request message to the BS.

3.14.2

Requests

Requests refer to the mechanism that SSs use to indicate to the BS that they need uplink bandwidth allocation. As mentioned above a request may come as a standalone bandwidth request header or it may come as a PiggyBack Request. The capability of Piggyback Request is optional. As the uplink burst profile can change dynamically, all requests for bandwidth is made in terms of the number of bytes needed to carry the MAC header and payload, but not the PHY overhead. The Bandwidth Request message may be transmitted during any uplink allocation, except during any initial ranging interval. Bandwidth Requests are of two types, incremental or aggregate. When the BS receives an incremental Bandwidth Request, it adds the quantity of bandwidth requested to its current perception of the bandwidth needs of the connection.

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In case of aggregate Bandwidth Request, BS replaces its perception of the bandwidth needs of the connection with the quantity of bandwidth requested. The Type field in the bandwidth request header indicates whether the request is incremental or aggregate. Since Piggybacked Bandwidth Requests do not have a type field, Piggybacked Bandwidth Requests is always incremental. The self-correcting nature of the request/grant protocol requires that SSs may periodically use aggregate Bandwidth Requests as a function of the QoS of a service and of the link quality. Due to the possibility of collisions, contention-based Bandwidth Requests are aggregate requests.

3.14.2.1

Piggyback

A piggyback bandwidth request is a method of using a previously granted uplink channel access opportunity to inform the base station that a subscriber station requires another allocation to send pending data. Piggybacked Bandwidth Requests do not have a type field and are always incremental. The advantage behind using piggybacked request is that once a subscriber station obtains uplink channel access it can use the channel for future bandwidth requests without incurring the overhead associated with contention or polling. This is most useful when a subscriber station connection has long consecutive trains of data packets to send.

3.14.3

Grants

Bandwidth grants are addressed to the SS’s Basic CID, not to individual CIDs. Since it is nondeterministic which request is being honoured, when the SS receives a shorter transmission opportunity than expected (scheduler decision, request message lost, etc.), no explicit reason is given. In all cases, based on the latest information received from the BS and the status of the request, the SS may decide to perform backoff and request again or to discard the SDU. An SS may use Request IEs that are broadcast, directed at a multicast polling group it is a member of, or directed at its Basic CID (Fig. 3.25). In all cases, the Request IE burst profile is used, even if the BS is capable of receiving the SS with a more efficient burst profile. To take advantage of a more efficient burst profile, the SS should transmit in an interval defined by a Data Grant IE directed at its Basic CID. Because of this, unicast polling of an SS would normally be done by allocating a Data Grant IE directed at its Basic CID. Also, in a Data Grant IE directed at its Basic CID, the SS may make bandwidth requests for any of its connections. The SS local scheduler decides which connections get the granted bandwidth.

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Polling

The WiMAX standard supports several mechanisms by which an SS can request and obtain uplink bandwidth. Depending on the particular QoS and traffic parameters associated with a service, one or more of these mechanisms may be used by the SS. The BS allocates dedicated or shared resources periodically to each SS, which it can use to request bandwidth. This process is called polling. Polling may be done either individually (unicast) or in groups (multicast). Multicast polling is done when there is insufficient bandwidth to poll each MS individually. When polling is done in multicast, the allocated slot for making bandwidth requests is a shared slot, which every polled MS attempts to use. Polling is a process where the base station periodically allocates part of the uplink channel capacity that is issues a “grant” or “transmit opportunity” in the uplink map to each participating subscriber station that wants to send data. These allocations may be to individual SSs or to groups of SSs. Allocations to groups of connections and/or SSs actually define bandwidth request contention IEs. The allocations are not in the form of an explicit message, but are contained as a series of IEs within the UL-MAP. Polling is done on SS basis. Bandwidth is always requested on a CID basis and bandwidth is allocated on an SS basis. The transmit opportunity itself is the poll, there is no explicit message type. The subscriber stations use the transmit opportunity to send a BRH to request uplink bandwidth. The grants must therefore be at least large enough to send one BRH. Polls may be unicast or multicast or broadcast according to the CID specified in the uplink map transmit opportunity information element. If a poll is multicast or broadcast then one of the contention bandwidth request methods is specified to collect the bandwidth request responses. Unicast polls are directed towards a single CID associated with a single subscriber station. The overhead associated with this method is in the small addition to the size of uplink map. Table 3.16 shows the scheduling services and the poll/grant options available for each. The following sub-clauses define service flow scheduling services for uplink operations.

Table 3.16 Scheduling type UGS rtPS nrtPS

BE ErtPS

Scheduling services and usage rules PiggyBack Bandwidth Polling request stealing Not allowed Not allowed PM bit is used to request a unicast poll for bandwidth needs of non-UGS connections. Allowed Allowed Scheduling only allows unicast polling Allowed Allowed Scheduling may restrict a service flow to unicast polling via the transmission/request policy; otherwise all forms of polling are allowed Allowed Allowed All forms of polling allowed Allowed Allowed All forms of polling allowed

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179

Unicast Polling

The basic intention of unicast polling (Fig. 3.28) is to give the SS a contention-free opportunity to tell the BS that it needs bandwidth for one or more connections. When an SS is polled individually, no explicit message is transmitted to poll the SS. Rather, the SS is allocated, in the UL-MAP, bandwidth sufficient to respond with a Bandwidth (BW) Request. SSs that have an active UGS connection of sufficient bandwidth shall not be polled individually unless they set the PM bit in the header of a packet on the UGS connection. This saves bandwidth over polling all SSs individually. Note that unicast polling would normally be done on a per-SS basis by allocating a Data Grant IE directed at its Basic CID.

3.14.4.2

Multicast and Broadcast Polling

Multicast polling is done when there is insufficient bandwidth to poll each MS individually. When polling is done in multicast, the allocated slot for making bandwidth requests is a shared slot, which every polled MS attempts to use. Multicast polling is one of the mechanisms in 802.16 networks, and achieves better and even guaranteed quality of service with less waste in utilization. When it is used, a group of SSs is added to a multicast polling group and slots are assigned for these SSs to participate on contention resolution process. When polling is done in groups certain CIDs are reserved both for multicast and unicast. As with individual polling, the poll is not an explicit message, but bandwidth allocated in the UL-MAP. The difference is that, rather than associating allocated bandwidth with an SS’s Basic CID, the allocation is to a multicast or broadcast CID.

3.14.4.3

Information Exchange Sequence for Multicast and Broadcast Polling

When the poll is directed at a multicast or broadcast CID, an SS belonging to the polled group may request bandwidth during any request interval allocated to that CID in the UL-MAP by a Request IE. In order to reduce the likelihood of collision with multicast and broadcast polling, only SSs needing bandwidth reply; they shall apply the contention resolution algorithm as defined in Fig. 3.29 to select the slot in which to transmit the initial bandwidth request. Zero-length bandwidth (BW) requests shall not be used in multicast or broadcast Request Intervals. The SS shall assume that the transmission has been unsuccessful if no grant has been received in the number of subsequent UL-MAP messages specified by the parameter Contention-based reservation timeout. Note that, with a frame-based PHY with UL-MAPs occurring at predetermined instants, erroneous UL-MAPs may be counted towards this number. If the re-request is made in a multicast or

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More BW available for individual polling?

No

Yes SSs with expired polling interval?

Yes

Initiate multicast and broadcast polling algorithm

No At SS’s operational burst profile

Setup poll to individual SS and mark as polled.

Yes

Unpolled SSs PM bit set?

No PHY/MAC Control

Preamble

DIUC a Data

DL-MAP

DIUC b Data

DIUC c Data

UL-MAP

Were any individual polls setup?

UL-MAP elements

Yes SS k additional BW allocation

Reg Cont BW Req Slots Slots

SS-1 Data

No

Await individual BW requests in scheduled SS uplink time SS-2 Data

SS-N Data

BW request

BW requests?

No

Yes PHY/MAC Control

Preamble

DIUC a Data

DL-MAP

DIUC b Data

DIUC c Data Use BW allocation algorithm & change uplink subframe map

UL-MAP

UL-MAP elements DONE SS k BW allocation

Fig. 3.28 Unicast polling (adapted from [1])

broadcast opportunity, the SS continues to run the contention resolution algorithm in from Fig. 3.29. Note that the SS is not restricted to issuing the re-request in a multicast or broadcast Request Interval.

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181 Multicast and broadcast polling

Poll next multicast group in MAC Control block

Yes

BW available for multicast polls? No

PHY/MAC Control

DIUC a Data

Preamble

DL-MAP

DIUC b Data

DIUC c Data

BW available for broadcast polls?

UL-MAP Yes UL-MAP elements Place broadcast poll in UL-MAP

Multicast or broadcast poll

Reg Cont BW Req Slots Slots

SS-1 Data

SS-2 Data

SS-N Data

No

Multicast or broadcast polls setup? Yes

Collision

BW Request

PHY/MAC Control

Preamble

DIUC a Data

DL-MAP

SS ID Connection ID Amount

DIUC b Data

DIUC c Data

UL-MAP

UL-MAP elements

Monitor request contention Oppurtunities for BW requests

Valid (noncollision) BW requests?

Yes Use BW allocation algorithm & change uplink subframe map

SS k BW allocation

DONE

Fig. 3.29 Multicast and broadcast polling (adapted from [1])

No

No

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WiMAX defines a contention access and resolution mechanism for the case when more than one MS attempts to use the shared slot. WiMAX defines a contention access and resolution mechanism for the case when more than one MS attempts to use the shared slot. If it already has an allocation for sending traffic, the MS is not polled. Instead, it is allowed to request more bandwidth by (1) transmitting a stand-alone bandwidth request MPDU, (2) sending a bandwidth request using the ranging channel, or (3) piggybacking a bandwidth request on generic MAC packets. 3.14.4.4

PM Bit

In case the piggybacking and BW stealing is exhausted, SS needs to be polled, indicating to the BS that it requires more bandwidth. SSs with currently active UGS connection may set the PM bit (in Grant Management sub-header) to indicate to the BS that they need to be polled to request bandwidth for non-UGS connection (Fig. 3.30). To reduce the bandwidth requirements of individual polling, SSs with active UGS connections need be individually polled only if the PM bit is set (or if the

PM Bit Ugase

Piggybacking & BW Stealing exhausted?

Yes

UGS Packet available?

Yes

No

Fig. 3.30 PM bit usage (adapted from [1])

Set PM = 1 in Grant Management subheader

Done

No

Attempt piggybacking & BW stealing first

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interval of the UGS is too long to satisfy the QoS of the SSs other connections). When the BS detects this request for polling, the process for individual polling is used to satisfy the request. The procedure by which an SS stimulates the BS to poll it is shown in Fig. 3.30. To minimize the risk of the BS missing the PM bit, the SS may set the bit in all UGS MAC Grant Management sub-headers in the uplink scheduling interval.

3.15

Contention Resolution

The contention resolution mechanism is primarily used in Multicast Polling. The 802.16-2004 and 802.16e specifications define the mechanism that is used by the connections in the BE, nrtPS and ertPS classes that are not polled individually. Thus when these connections have some packets in the uplink buffers, and no slots are allocated for them, they must compete with each others to get an allocation. This method is known as the contention resolution mechanism. When an SS wants to enter the contention resolution process, it sets its internal backoff window equal to the backoff start value (2N, N = {0, . . ., 15}) advertised in the UCD message. Then, the SS chooses randomly a number within the window. The SS must then wait for this number of request opportunities before sending a request. If no data grant has been given within a specified interval, the SS considers the request lost. Then, it increases its internal backoff window by a factor of two and chooses a new random number. This process is continued until the internal window of the SS reaches the backoff end value declared in the UCD message. Then, the SS will drop the PDU and start from the beginning with the next PDU. The BS controls assignments on the uplink channel through the UL-MAP messages and determines which mini-slots are subject to collisions. Collisions may occur during Initial Ranging and Request intervals defined by their respective IEs. The potential occurrence of collisions in Request Intervals is dependent on the CID in the respective IE. For simplicity, it refers to the decisions an SS makes. Since an SS can have multiple uplink service flows (each with its own CID), it makes these decisions on a per CID or per service QoS basis. The mandatory method of contention resolution that is supported is based on a truncated binary exponential backoff, with the initial backoff window and the maximum backoff window controlled by the BS. The values are specified as part of the UCD message and represent a power-of-two value. For example, a value of 4 indicates a window between 0 and 15; a value of 10 indicates a window between 0 and 1,023. When an SS has information to send and wants to enter the contention resolution process, it sets its internal backoff window equal to the Request (or Ranging for initial ranging) Backoff Start defined in the UCD message referenced by the UCD Count in the UL-MAP message currently in effect. The SS randomly selects a number within its backoff window. This random value indicates the number of contention transmission opportunities that the SS shall defer before transmitting.

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An SS shall consider only contention transmission opportunities for which this transmission would have been eligible. These are defined by Request IEs (or Initial Ranging IEs for initial ranging) in the UL-MAP messages. Note that each IE may consist of multiple contention transmission opportunities. Using bandwidth requests as an example, consider an SS whose initial backoff window is 0–15 and assume it randomly selects the number 11. The SS must defer a total of 11 contention transmission opportunities. If the first available Request IE is for six requests, the SS does not use this and has five more opportunities to defer. If the next Request IE is for two requests, the SS has three more to defer. If the third Request IE is for eight requests, the SS transmits on the fourth opportunity, after deferring for three more opportunities. After a contention transmission, the SS waits for a Data Grant Burst Type IE in a subsequent map (or waits for a RNG-RSP message for initial ranging). Once received, the contention resolution is complete. The SS shall consider the contention transmission lost if no data grant has been given within T16 (or no response within T3 for initial ranging). The SS shall now increase its backoff window by a factor of two, as long as it is less than the maximum backoff window. The SS shall randomly select a number within its new backoff window and repeat the deferring process described above. This retry process continues until the maximum number (i.e., Request Retries for bandwidth requests and Contention Ranging Retries for initial ranging) of retries has been reached. At this time, for bandwidth requests, the PDU shall be discarded. For initial ranging, proper actions are specified in 6.3.9.5. Note that the maximum number of retries is independent of the initial and maximum backoff windows that are defined by the BS. For bandwidth requests, if the SS receives a unicast Request IE or Data Grant Burst Type IE at any time while deferring for this CID, it shall stop the contention resolution process and use the explicit transmission opportunity. The BS has much flexibility in controlling the contention resolution. At one extreme, the BS may choose to set up the Request (or Ranging) Backoff Start and Request (or Ranging) Backoff End to emulate an Ethernet-style backoff with its associated simplicity and distributed nature as well as its fairness and efficiency issues. This would be done by setting Request (or Ranging) Backoff Start ¼ 0 and Request (or Ranging) Backoff End = 10 in the UCD message. At the other end, the BS may make the Request (or Ranging) Backoff Start and Request (or Ranging) Backoff End identical and frequently update these values in the UCD message so that all SS are using the same, and hopefully optimal, backoff window Transmission opportunities

3.15.1

Transmission Opportunity and Example for ContentionBased Bandwidth Requests

A transmission opportunity is defined as an allocation provided in a UL-MAP or part thereof intended for a group of SSs authorized to transmit bandwidth requests

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185 One Request IE

Transmission Opportunity #1

Transmission Opportunity #2

Preamble B/W Request message (2 minislots) (3 minislots)

Transmission Opportunity #3

SSTG (3 minislots)

Fig. 3.31 Example of request IE containing multiple transmission opportunities

or Initial Ranging requests. This group may include either all SSs having an intention to join the cell or all registered SSs or a multicast polling group. The number of transmission opportunities associated with a particular IE in a map is dependent on the total size of the allocation as well as the size of an individual transmission. The size of an individual transmission opportunity for each type of contention IE is published in each transmitted UCD message. The BS should always allocate bandwidth for contention IEs in integer multiples of these published values. Consider contention-based bandwidth requests for a WirelessMAN-SC system where the PHY protocol has a frame duration of 1 ms, four symbols for each PS, two PSs for each minislot, an uplink preamble of 16 symbols (i.e., 2 minislots), and an SS transition gap (SSTG) of 24 symbols (i.e., 3 minislots).Thus, assuming quadrature phase-shift keying (QPSK) modulation, each transmission opportunity requires eight minislots: three for the SSTG, two for the preamble, and three for the bandwidth request message. This payload requirement would be specified as a value of 16 assigned to the UCD TLV “Bandwidth request opportunity size”. If the BS schedules a Request IE of, for example, 24 minislots, there will be three transmission opportunities within this IE. Details of the three transmission opportunities are shown in Fig. 3.31.

3.16

Network Entry

Each subscriber station or node must follow a list of procedure to be a part of the network and be able to communicate on it the desired BS successfully. The network entry process is divided into the following main phases (Fig. 3.32): 1. 2. 3. 4. 5. 6.

DL channel synchronization Initial ranging Capabilities negotiation Authentication message exchange Registration and IP connectivity stages

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Fig. 3.32 Network entry process and MAC management connections

Initial Ranging

Primary management connection

Basic management connection

Negotiate basic capabilities

Authentication

Registration

Secondary management connection

After the completion of the network entry process, the SS creates one or more service flows to send data to the BS. In case if the network entry process fails, the state machine moves to reset. Figure 3.33 depicts the network entry process.

3.16.1

Downlink Channel Synchronization

When an SS wishes to enter the network, it scans for a channel in the defined frequency list. The SS has non-volatile storage in which the last operational parameters are stored. Therefore the SS first tries to reacquire this downlink channel. If this fails, it scans the possible channels of the downlink frequency band of operation till it finds a valid downlink signal. After the synchronization is done, as given by a PHY Indication, the MAC acquires the channel control parameters for the downlink and then the uplink. The control parameters include DCD and UCD to get information on modulation and other DL and UL parameters as shown in the Fig. 3.31.

3.16.2 l

Initial Ranging

Once the SS has synchronized with the DL channel and received the DL-MAP and UL MAP for a frame, the BS and SS need to adjust timing offset and power parameters in the initialisation phase. This process is called initial ranging.

3

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Scanning & synchronization to the downlink SS scans the possible channels on downlink & synchronises with the BS

2

Obtain downlink and then uplink parameters DL-MAP & DCD (Broadcast CID)

3

Obtain uplink parameters UL-MAP & UCD (Broadcast CID)

4

Initial Ranging RNG-REQ (CID=0) RNG-RSP(CID=0)

5

Basic & Primary Management CID

Negotiate basic capabilities SBC-REQ SBC-RSP

Subscriber Station

6

SS authorization and key exchange PKM-REQ

Base Station

PKM-RSP

7 8 9 10

Establish IP connectivity Get time of the day Transfer operational parameters Establish provisioned connections

Fig. 3.33 Network entry and initialization l

l

l

The process begins by SS sending a ranging request MAC message (RNG-REQ) on the contention based initial ranging interval using the minimum transmission power. If it does not receive a response, the SS sends the ranging request again in a subsequent frame, using higher transmission power. Eventually the SS receives a ranging response. The response either indicates power and timing corrections that the SS must make or indicates success. If the response indicates corrections, the SS makes these corrections and sends another ranging request. If the response indicates success, the SS is ready to send data on the UL. During the initial ranging process SS is allocated its Basic and Primary Management CIDs.

3.16.3

Capabilities Negotiation

After successful completion of initial ranging, the SS sends a capability request message (SBC-REQ) to the BS describing its capabilities in terms of the supported

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modulation levels, coding schemes and rates, and duplexing methods. The BS accepts or denies the SS, based on its capabilities. The BS responds with an SBC-RSP message with the intersection of the SS and the BS capabilities. The SBC-RSP is generated by the BS in response to the received SBC-REQ. If the BS does not recognise an SS capability, it may return this as ‘off’ in the response message.

3.16.4

Authentication

Once the BS has gained the knowledge regarding the capabilities of the SS, it authorises the SS and perform key exchange. The BS authenticates the SS by providing the keying material to enable the ciphering of data. The privacy and key management (PKM) protocol is used to authorize the SS to the BS. The SS first sends the PKM request message (PKM-REQ) along with X.509 certificate of the SS manufacturer. Along with the message a description of the supported cryptographic algorithms is also send to its BS. The BS then validates the identity of the SS, determines the cipher algorithm and protocol that should be used, and sends an authentication response (PKM-RSP) to the SS. The response contains the key material to be used by the SS. The SS periodically perform the authentication and key exchange procedures to refresh its key material.

3.16.5

Registration

After the authentication process is completes, SS is allowed to entry into the network. During the registration process the SS receives its secondary management CID. The SS and BS also negotiate additional operational parameters of the MAC during the registration process. After successful completion of authentication the SS registers with the network. The SS sends a registration request (REG-REQ) message to the BS, and the BS sends a registration response (REG-RSP) to the SS. The registration exchange includes IP version support, SS managed or nonmanaged support, ARQ parameters support, classification option support, CRC support, and flow control. During the initial ranging step basic MAC and primary MAC management connections are established which are not secured. But after the registration process SS receives the secondary management CID and thus a fully secured connection is established. The SS and BS create transport connections using a MAC-create-connection request. A request to create a dynamic transport connection indicates whether MAC-level encryption is required.

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IP Connectivity Stages

At this stage of Network Entry and Initialization process SS acquires an IP address to establish IP connectivity. In case the SS is using mobile IP, SS may secure its address on the secondary management connection using mobile IP. Otherwise, for all SS using IPv4, an IP address is acquired using DHCP [IETF RFC 2131]. If the SS has a configuration file, the DHCP response contains the name of a file that contains further configuration parameters.

The SS and BS need to have the current date and time. The BS and SS maintain the current date and time using the time of the day protocol (IETF RFC868). The SS then downloads operational parameters using TFTP (IETF RFC 1350).

3.16.7

Transport Connection Creation

After completion of registration and the transfer of operational parameters, transport connections are created. For pre-provisioned service flows, the connection creation process is initiated by the BS. The BS sends a dynamic service flow addition request message to the SS and the SS sends a response to confirm the creation of the connection. Connection creation for non-pre-provisioned service flows is initiated by the SS by sending a dynamic service flow addition request message to the BS. The BS responds with a confirmation.

3.17

Summary and Conclusions

This Chapter covered link layer issues, having its main focus on MAC layer. After presenting the MAC sub-layer, the MAC Protocol and Service Data Units were addressed. The missions, functions, connections, addressing and service flows of the Service Specific Convergence Sub-layer were then presented. The specification of MAC Common Part Sub-layer is essential in IEEE 802.16. Its mission was addressed and the details on MAC addressing, connections and PDU format were given. After presenting the header formats, the MAC sub-header, special payloads and sub-header ordering were analyzed. Then, IEEE 802.16 MAC connections were described and basic, primary and secondary management connections were presented. Also the details on fragmentation, packing and concatenation were given. The encryption of MAC PDUs and Automatic Repeat Request were then presented. Appropriate scheduling algorithms are essential in WiMAX. The five QoS classes were described in this context. Finally aspects of the bandwidth allocation and request mechanisms were addressed, as well as contention resolution mechanisms and network entry.

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References 1. IEEE 802.16-2004, IEEE Standard for Local and metropolitan area networks – Part 16: Air Interface for Fixed Broadband Wireless Access Systems (June 24, 2004) 2. Air Interface for Fixed and Mobile Broadband Wireless Access Systems. IEEE P802.16e/D12 (Feb 2005) 3. www.dsns.csie.nctu.edu.tw/course/wireless_sec/2007/report/WiMAX_Security_final.doc 4. A. Ghost, R. Muhamed, J.G. Andrews, Fundamentals of WiMAX: Understanding Broadband Wireless Networking (Prentice Hall, Upper Saddle River, NJ, 2007) 5. M. Yavuz, D. Paranchych, G. Wu, G. Li, W. Krzymien, Performance Improvement of the HDR System due to Hybrid ARQ, in 54th IEEE Vehicular Technology Conference (2001), vol. 4, pp. 2192–2196 6. SCTE DSS 00-05, Data-Over-Cable Service Interface Specification (DOCSIS) SP-RFIv1. 1-I05-000714. Radio Frequency Interface 1.1 Specification (July 2000) 7. IEEE Standard 802.16:A Technical Overview of the WirelessMAN™ Air Interface for Broadband Wireless Access Carl Eklund, Nokia Research Center Roger B. Marks, National Institute of Standards and Technology Kenneth L. Stanwood and Stanley Wang, Ensemble Communications Inc., IEEE 2002 8. http://www.cnct.de/uploads/media/Radio_Mobile_WiMAX_wp.pdf (March 2010) 9. D. Johnston, H. Yaghoobi, Peering into the WiMAX spec: Part 1& Part 2”, Intel Corp. (Jan 2004). www.commsdesign.com/design_corner/showArticle.jhtml?articleID=17500156& 17500163

Chapter 4

Quality of Service Ramjee Prasad and Fernando J. Velez

Abstract The interpretation and definition of service quality and its classes is first presented. While there are four classes of service in Fixed WiMAX (unsolicited granted service, real-time polling service, non-real-time polling service and best effort) in Mobile WiMAX there is an extra class: extend real-time polling service. The Quality of Service (QoS) architecture is presented for the point-to-multipoint (PtM) mode. Packets originated at the SS are classified by the connection classifier based on the connection ID (CID) and are forwarded to the appropriate queue for the communication with the BS. The discussion of details on the architecture includes aspects of UL and DL scheduling. QoS provisioning and the object model for service quality are also discussed. Finally, the authorization module is addressed as well as service flow types and creation.

4.1

Introduction

Quality of Service (QoS) refers to the ability of the network to provide better service to selected network traffic over various technologies. The goal of QoS technologies is to provide priority that is required by some real-time and interactive traffic, while making sure that the traffic on the other paths does not fail. Compared with existing high-speed Internet services, new broadband services, such as interactive television and multimedia telephony, demand different user expectations, such as high service availability, flicker free video quality and smooth voice communication. In order to ensure such a user- centric broadband experience

R. Prasad (*) Center for TeleInFrastruktur (CTIF), Aalborg University, Niels Jernes Vej 12, DK–9220 Aalborg Øst, Denmark e-mail: [email protected]

R. Prasad and F.J. Velez, WiMAX Networks, DOI 10.1007/978-90-481-8752-2_4, # Springer ScienceþBusiness Media B.V. 2010

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becomes a reality, the broadband wireless access networks must meet a number of Quality of Service (QoS) requirements, including guaranteed throughput, and low delay, jitter and packet loss, for such new services in demand. Today in broadband wireless access (BWA) the perception is that as adoption grows, so does the need for guaranteeing QoS. The issue of QoS, therefore, has become a critical area of concern for suppliers of broadband wireless access equipment and their customers. Enforceable QoS is an essential foundation for widespread acceptance of broadband wireless, since it allows for more efficient sharing of the operator’s infrastructure, as demand for capacity increases with subscriber take-up. The recent explosive growth of the Internet has given rise to demands for higher capacity, higher data rate, and more advanced multimedia services to residential and small business customers. The IEEE 802.16 standard is designed to support these demands and specifies the WirelessMAN air interface [1, 2]. IEEE 802.16 can support multiple communication services (data, voice, video) with different QoS requirements. IEEE 802.16 Media Access Control (MAC), which is based on the concepts of connections and service flows, specifies QoS signalling mechanisms (per connection or per station) to support bandwidth requests and bandwidth allocation. However, IEEE 802.16 standard left the QoS based packet scheduling algorithms, that determine the uplink and downlink bandwidth allocation, undefined. Scheduling details are left for the implementation. IEEE 802.16 is designed to accommodate hundreds of different connections per channel. These connections are used for variety of applications and hence need different QoS requirements. The end user applications may be varied in their bandwidth and latency requirements, so 802.16 must be flexible and efficient over a range of different traffic models [3]. This Chapter is organized as follows. Section 4.2 addresses the interpretation and definition of service quality, providing details on the five QoS classes. Section 4.3 presents the QoS architectures for IEEE 802.16 MAC protocol while Section 4.4 addresses QoS provisioning. Section 4.5 describes the object model, including aspects on the attributes, global service flows, the associated connections, class name parameters and service flow creation. Section 4.6 addresses service classes while Section 4.7 presents the authorization module. Sections 4.8 and 4.9 present service flow types and creation, respectively. Finally, Section 4.10 presents the summary and conclusions.

4.2 4.2.1

Interpretation and Definition Technical and Customer-Specific QoS Parameters

In everyday practice, the term quality of service (QoS) is not used in a standard manner. However, if summarization of various approaches is done, two typical QoS features can be recognized [4].

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Differentiation capability – Individual services within a network can be differentiated from one another and treated differently. Allocation of quality parameters – Certain quality parameters generally agreed in advance can be allocated to a service. In the following section we therefore use QoS to mean the possibility of treating individual services in a network and beyond the boundaries of a network differently with regard to service quality.

l

4.2.1.1

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Bandwidth

The bandwidth defines the maximum volume of data per time unit that can be transmitted over a particular network connection. It looks at how much data capacity an application is consuming. It is measured in bits per second (bit/s, bps). Today, bandwidth constitutes the most important quality criterion, particularly in the access area, for differentiating between Internet access solutions. Applications like interactive gaming and VOIP use very little bandwidth, but applications like downloading or streaming multimedia can be very bandwidth heavy.

4.2.1.2

Latency

Latency is a measure of the time it takes for data to make a round trip of the network, and is central for applications that use real-time communications, like voice and video. Delay comprises the length of time that a data package takes from the sender to the recipient and is measured in milliseconds (ms). While the duration of the delay plays no practical role for the quality of traditional Internet services such as downloading of Web pages or sending e-mails, delay does have a crucial influence on service quality in the case of time-critical services. The individual factors that contribute to it are channel propagation delay, serialization delay, channel coding delay, and delays associated with MAC processing. At the network layer, we encounter forwarding and buffering delays, and last at the application layer we have packetization, coding/decoding, and look-ahead delays. For voice if these delays sum to 150 ms or more, the quality is impaired and noticeable by the user. The WiMAX Forum has established guidelines for the maximum amount of latency or delay that would permit these applications to operate acceptably. Actual system latencies, with WiMAX, could be as low as single digits of milliseconds.

4.2.1.3

Jitter

Jitter is caused when packets arrive at different times due to different queuing times or due to the different routes taken by the communications. The maximum

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deviation is measured in milliseconds. A high level of jitter impairs the quality of the connection in the case of time-critical services such as Voice-over-IP or video transmission. One way of combating the impairments caused by jitter is to use a memory buffer. A memory buffer stores early arriving packets, concatenates later arriving packets, and thus smoothes the voice arriving at the receiver.

4.2.1.4

Packet Loss

Packet loss denotes the number of data packets that are lost in transmission from the sender to the receiver. It is measured as the percentage of packets that are lost as a proportion of the total volume of packets. The most frequent causes of packet loss are network overloads which result in individual data packets being rejected by overloaded routers, and technical faults in individual network components or connections.

4.2.2

QoS Classes

The WiMAX QoS Classes are the following (Table 4.1):

4.2.2.1

Unsolicited Grant Service (UGS)

The UGS is designed to support real-time service flows that generate fixed-size data packets on a periodic basis, such as T1/E1 and Voice over IP without silence suppression. For this service BS offers fixed size unsolicited data grants, that is, Table 4.1 QoS classes specifications and their applications QoS category Applications UGS Unsolicited Grant Service VoIP

rtPS Real-Time Packet Service

Streaming audio or video

ErtPS Extended Real-Time Packet Service

Voice with activity detection (VoIP)

nrtPS Non-Real-Time Packet Service

File Transfer Protocol (FTP)

BE Best-Effort Service

Data transfer, web browsing, etc.

QoS specifications Maximum sustained rate l Maximum latency tolerance l Jitter tolerance l Minimum reserved rate l Maximum sustained rate l Maximum latency tolerance l Traffic priority l Minimum reserved rate l Maximum sustained rate l Maximum latency tolerance l Jitter tolerance l Minimum reserved rate l Maximum sustained rate l Traffic priority l Maximum sustained rate l Traffic priority l

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the transmission opportunities on periodic intervals without any explicit request from the SS. This eliminates the overhead and latency of bandwidth requests. In the UGS service, the BS offers a fixed size grants on a real time periodic basis. For UGS SS is prohibited from using any contention request opportunities. As SS does not have to make any explicit bandwidth requests this method eliminates the overhead and latency of SS requests and ensure that grants are available to meet the flow’s real-time needs.

4.2.2.2

Real-Time Polling Service (rtPS)

The rtPS is designed to support real-time uplink service flows that generate transport variable size data packets on a periodic basis, such as moving pictures experts group (MPEG) video. E1/T1 type data services are also supported by rtps. For fixed operators (or WISPs), rtps guarantees E1/T1 data rates to allowing customers to burst higher when extra capacity is available on the network. rtps service offers real-time, periodic, unicast request opportunities, which meet the flow’s real-time needs and allow the SS to specify the size of the desired grant. This service requires more request overhead than UGS, but supports variable grant sizes for optimum data transport efficiency.

4.2.2.3

Non-real-time Polling Service (nrtPS)

The nrtPS is designed to support delay-tolerant data streams consisting of variablesized data packets for which a minimum data rate is required, such as FTP. This service offers unicast polls on a regular basis to ensure assures that the service flow receives request opportunities even during network congestion. The BS grants unicast polls to nrtPS connections on an interval of 1 s or less. The non-real time polling service is almost identical to the real time polling service. The difference is that for nrtps, connections may utilize random access transmit opportunities for sending the bandwidth requests. The mandatory QoS service flow parameters for this scheduling service are Minimum Reserved Traffic Rate, Maximum Sustained Traffic Rate, Traffic Priority, and Request/Transmission Policy. The BE service is designed to support data streams for which no minimum service level is required and therefore may be handled on a space-available basis.

4.2.2.4

Best Effort (BE)

Unlike nrtps, the Best Effort services are defined for applications that do not have any specific delay requirements. For BE the QoS parameters are chosen such that they provide scheduling service to support data streams for which no minimum resources

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allocation are granted. Therefore may be handled on a space-available basis. For BE services there is no QoS guarantee, like the email or the short length FTP. The only difference between nrtps and BE services is that nrtps connections are reserved a minimum amount of bandwidth using the minimum reserved traffic rate parameter. Both the nrtps and BE services request bandwidths by either responding to the broadcast polls from the BS or piggybacking a bandwidth request. 4.2.2.5

Extended rtPS (Ertps)

IEEE 802.16e introduced Extended Real-Time Polling Service (Ertps). Ertps manages traffic rates and transmission policies as well as improving latency and jitter in 802.16e. This is a scheduling mechanism based on the efficiency of both UGS and rtPS. The BS provides unicast grants in an unsolicited manner like in UGS, thus saving the latency of a bandwidth request. The difference between the two is, ertPS allocations are dynamic, while UGS allocations are fixed in size. The Extended rtPS is designed to support real-time service flows that generate variable size data packets on a periodic basis, such as Voice over IP services with silence suppression.

4.3

QoS Architecture for IEEE 802.16 MAC Protocol

As discussed in the earlier chapters, IEEE 802.16 architecture consists of two kinds of entities: Subscriber Stations (SSs) and a Base Station (BS). The communication path between SSs and a BS has two directions: uplink channel (from SS to BS) and downlink channel (from BS to SS). The downlink channel is dedicated for the data flow between the BS to the SSs. This channel is a broadcast channel, while the uplink channel is a shared by SSs. For uplink time-division multiple access (TDMA) is used while for the downlink, channel BS uses a continuous timedivision multiplexing (TDM) scheme [9]. The standard defines two basic operational modes: Point-to-Multipoint (PtM) and the Mesh. On the one hand, In the PtM mode, the network operates with a central BS serving a set of SS within the same antenna sector in a broadcast manner. On the other, in the mesh mode, traffic can be routed through other SSs, that is, the access coordination is distributed among the SSs. Several studies have proposed various QoS differentiation schemes in the PtM mode. Comparatively, for mesh mode, very few schemes are defined and the research is still going on. This Chapter therefore only takes into account the PtM mode. The Quality of Service architecture for IEEE 802.16 PtM mode is shown in Fig. 4.1. In a connection oriented MAC protocol, all data communications, for both transport and control are in the context of unidirectional connections. To start with, when the packets go to the network at the base station from the application layer in the SS, they are classified by the connection classifier based on the connection ID

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Subscriber Station (SS)

Base Station (BS) Connection Request

Applications

Connection Response

Data Traffic

UGS

rtPS

nrtPS

Uplink Packet Scheduling

CID

CID

CID

CID

CID

CID

CID

CID

CID

Connection Classification

Admisssion Control undefined by IEEE 802.16

BM Request Message

Uplink Scheduling for UGS service flows defined by IEEE 802.16

UL-MAP

Uplink Scheduling for rtPS,nrtPS and BE service flows undefined by IEEE 802.16

BE

Packet Scheduler

Data Packets

Fig. 4.1 QoS architecture of IEEE 802.16

(CID) and are forwarded to the appropriate queue. At the SS, the Scheduler will retrieve the packets from the queues and transmit them to the network in the appropriate time slots as defined by the UL-MAP sent by the BS [1]. The application first establishes the connection with the BS as well as the associated service flow (UGS, rtPS, nrtPS, Ertps or BE). BS assigns the connection with a unique CID. The connection classifier classifies the packets based on the CIDs. In order to meet the negotiated QoS requirements the BS station schedules the uplink and the downlink grants at the start of each frame. This is done by the BS scheduler who can anticipate the throughput and latency needs of the uplink traffic. Based on the uplink requests and taking into account the QoS parameters and priorities defined by the scheduling services, the BS scheduler decides the uplink allocations. These allocations are transmitted to the respective SSs through the UL-MAP MAC management message. The UL-MAP is determined by the Uplink Bandwidth Allocation Scheduling module as shown in Fig. 4.1. This module is based on the BW-request messages that report the current queue size of each connection in SS. Figures 4.2 and 4.3 shows the BS scheduler operation for the downlink and the uplink respectively. The Bandwidth request can be transmitted in either of the two modes, contention mode and contention-free mode, which is also called polling. In contention mode, SSs send BW-Request to the BS during the contention period and contention is resolved using back-off resolution. For contention-free mode, BS polls each SS and SSs reply by sending BW request.

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BS

SS

TDM Voice

MAC CS Packet ReConstruct

MAC CPS DL-Traffic Processor CID#1

Data Traffic

MAC CPS

MAC CS

DL-Traffic Processor

Packet Classifier

CID#1 CID#2

VoIP

VoIP

CID#2 DL-MAP Generator

HTTP CID#3

DL-MAP

HTTP CID#3 TFTP

TFTP E-mail

TDM Voice

CID#4

E-mail

CID#4

Fig. 4.2 BS scheduler operation for the downlink

BW-requests using contention or contention free signaling mode

Uplink Scheduler undefined by IEEE 802.16

UL-MAP (multiple IEs)

Fig. 4.3 Uplink scheduler

Contention-free mode is suitable for real time applications. IEEE 802.16 defines the required QoS signalling mechanisms described above such as BW-Request and UL-MAP, but it does not define the Uplink Scheduler, that is the mechanism that determines the IEs in the UL-MAP (described in Chapter 3). Figure 4.1 shows the QoS architecture of IEEE 802.16. Uplink Bandwidth Allocation scheduling resides in the BS to control all the uplink packet transmissions.

4.4

QoS Rovisioning

Quality of Service (QoS) is defined as the performance level of a service offered by the network to the user. QoS service provisioning is defined to achieve more deterministic network behaviour, so that information carried by the network can be better delivered and network resources can be better utilized.

4.4.1

Service Flow

Service flow is one of the most important components of the QoS provisioning and MAC layer. During the provisioning a service flow is classified. Each data packet in

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the network has associated service flow. Also it is possible that many packets can use one service flow. It is a unidirectional, which can be used by BS intended for SS or SS intended for the BS. Each service flow has a 32 bit identifier known as SFID and defined QoS parameter set.

4.4.2

Service Flow Attributes

A service flow is characterized by the following attributes as listed below: l

l

l

l

l

l

Service Flow ID: An SFID is assigned to each existing service flow. The SFID serves as the principal identifier for the service flow between a BS and an SS. A service flow has at least an SFID and an associated direction. CID: The connection ID of the transport connection exists only when the service flow is admitted or active. The relationship between SFID and transport CID, when present, is unique. A single SFID can never be associated with more than one transport CID, and a transport CID is also not associated with more than one SFID. ProvisionedQoSParamSet: This defines a QoS parameter set that is provisioned via means that the standard assumes to be outside of its. The standard states that this could be a part of the network management system. For example, the service class name is an attribute of the ProvisionedQoSParamSet. There are five QoS classes, the fifth having been added by the 802.16e amendment. A set of QoS parameters provided to the MAC, for example by the network management system. AdmittedQoSParamSet: A set of QoS parameters for which the BS and possibly the SS are reserving resources, since the associated service flows have been admitted by the BS. ActiveQoSParamSet: Defines a set of QoS parameters defining the service actually being provided to the service flow. Only an Active service flow may forward packets. Authorization Module: A logical function within the BS that approves or denies every change to QoS Parameters and Classifiers associated with a service flow. It defines an “envelope” that limits the possible values of the AdmittedQoSParamSet and ActiveQoSParamSet.

4.5 4.5.1

Object Model Attributes

The major objects of the IEEE 802.16 QoS model are MAC PDU, Service Flow, Transport, Connection, PHS Rule, Classifier Rule and Service Class. This

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PHS Rule

Classifier rule index Classifier Criteria

PHSI PHSS PHSF PHSM PHSV N

N

1 MAC PDU SFID [Service Class] CID Payload

1 Service Flow

N

1

SFID 1 Direction [CID] [ProvisionedQoSParamset] [AdmittedQoSParamset] [ActiveQoSParamset]

Transport Connection 0,1 Connection ID QoSParameter Set

Service Class Service Class Name QoS Parameter Set

Fig. 4.4 Theory of operation model (adapted from [8])

Table 4.2 QoS object model and respective attributes

Objects of QoS model MAC PDU Service flow Transport connection PHS rule Classifier rule Service class

Respective unique attribute SFID SFID Connection ID PHSI Classifier rule index Service class Name

architecture is represented by named rectangles in Fig. 4.4. Each object has a number of attributes. The attributes which uniquely identifies the object is listed in Table 4.2. There are also optional attributes which are shown in the figure. The service flow is the central concept of the MAC protocol as well as the QoS model. It is uniquely identified by a 32-bit (SFID). Service flows may be in either the uplink or downlink direction. There is a one-to-one mapping between admitted and active service flows (32-bit SFID) and transport connections (16-bit CID). Outgoing user data is submitted to the MAC SAP by a CS process for transmission on the MAC interface. The information delivered to the MAC SAP includes the CID identifying the transport connection across which the information is delivered. The service flow for the connection is mapped to MAC transport connection identified by the CID.

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There exist a relationship among the various objects of the QoS model. This is shown with the associated lines between the respective objects. For example, a service flow may be associated with from 0 to N (many) PDUs but a PDU is associated with exactly one service flow. A Classifier Rule uniquely maps a packet to its transport connection. The Classifier Rule is associated to zero or one PHS Rules. When creating a PHS Rule the associated Classifier Rule Index is used as a reference. A PHS Rule is associated to a single service flow. PHS Rules associated to the same service flow are uniquely identified by their PHSI. The Classifier Rule uniquely maps packets to its associated PHS Rule.

4.5.2

Global Service Flows

In order to facilitate operation across a distributed topology mobile networks require common definitions of service class names and associated AuthorizedQoSParamSets. Global service class names are used support operation in this context. In operation, global service class names are employed as a baseline convention for communicating AuthorizedQoSParamSet or AdmittedQoSParamSet. Global service class names are similar in function to service class names with the exceptions such as: l l l

Global service class name use may not be modified by a BS Global service class names remain consistent among all BS Global service class names are a rules-based naming system whereby the global service class name itself contains referential QoS Parameter codes

4.5.3

Conventions Used for Global Service Class Name

There is a special method to denote the name of Global service class name. Conventions are based on the eight global service class name parameters such that Global service class name is composite name, distributed in eight information fields of format ISBRLSPTR. Each information field placeholder must be an expressed value, obtained from Table 4.3, as part of the name, and may not be omitted.

4.5.4

Global Service Flow Class Name Parameters

1. Uplink/downlink indicator The Uplink/Downlink indicator parameter identifies the defined service flow direction from the originating entity. The value of this parameter can be either 0 or 1 denoting uplink or downlink respectively.

202 Table 4.3 Global service flow class name information field parameters

R. Prasad and F.J. Velez Position Name I S T B R L S P R

Uplink/downlink indicator Maximum sustained traffic rate Traffic indication preference Maximum traffic burst Minimum reserved traffic rate Maximum latency Fixed-length versus variable-length SDU indicator Paging preference Reserved

Size (bits) 1 6 1 6 6 6 1 1 4

2. Maximum sustained traffic rate Maximum sustained traffic rate defines the peak information rate of the service and is expressed in bits per second. This rate pertains to the service data units (SDUs) at the input to the system. Maximum sustained traffic rate parameter does not include transport, protocol, or network overhead such as MAC headers or CRCs, or non-payload session maintenance overhead like SIP, MGCP, H.323 administration, etc. This parameter does not limit the instantaneous rate of the service since this is governed by the physical attributes of the ingress port. The maximum sustained traffic rate field specifies only a bound, not a guarantee that the rate is available. The algorithm for policing this parameter is left to vendor to decide. 3. Traffic indication preference Traffic Indication Preference parameter is a single bit indicator of an SS’s preference for the reception of Traffic Indication messages during sleep mode. When set it indicates that the BS may present Traffic Indication messages to the MS when data SDUs bound for the MS are present while the MS in sleep mode. 4. Maximum traffic burst The Maximum traffic burst is the largest burst expected at the ingress port to be accommodated for the service. Since the physical speed of ingress ports, and the backhaul will in general be greater than the maximum sustained traffic rate parameter for a service, this parameter describes the maximum continuous burst the system should accommodate for the service assuming the service is not currently using any of its available resources. Maximum traffic burst set to zero means no Maximum traffic burst reservation requirement. 5. Minimum reserved traffic rate The Minimum reserved traffic rate parameter specifies the minimum rate, in bits per second, reserved for this service flow. QoS algorithms should be designed to give services their minimum reserved traffic before any services receive bandwidth in excess of their minimum reserved traffic rate. The BS should be able to satisfy bandwidth requests for a connection up to its minimum reserved traffic rate. If less

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bandwidth than its Minimum reserved traffic rate is requested for a connection, the BS may reallocate the excess reserved bandwidth for other purposes. If the Minimum reserved traffic rate is set to zero, it means there is no minimum reserved traffic rate requirement. 6. Maximum latency There is some delay between the reception of a packet at CS of BS or SS and the arrival of the packet to the peer device. Maximum latency is the maximum delay between the receipt of the packet from the network and forwarding it on the air interface. The system is generally designed to minimize latency. This parameter represents a service commitment and is always guaranteed. A value of zero for Maximum latency is interpreted as no commitment. 7. Fixed-length versus variable-length SDU indicator The value of this parameter specifies whether the SDUs on the service flow are fixed-length(like ATM cells) or variable-length(IP packets).This parameter is usually meaningful for QoS in the case of UGS type connections. 8. Paging preference This parameter is a single bit indicator of an MS’s preference for the reception of paging advisory messages during idle mode. When set, it indicates that the BS may present paging advisory messages or other indicative messages to the MS when data SDUs bound for the MS are present while the MS is in Idle Mode.

4.5.5

Service Flow Creation

Service flows may be created, changed or deleted. This is accomplished through a series of MAC management messages described in Table 4.4. The above series of MAC management messages referred to as DSA, DSC and DSD are responsible for creation, modification and deletion of service flows, respectively (Fig. 4.5). There is no service flow in the Null state. In the operational state, there is a service flow, with assigned SFID. A service flow makes a transition whenever DSx messaging occurs and remains operational. Multiple state machines, one for each service flow, may be active as multiple service flow can exist simultaneously. Only those state machines are affected by the DSx messages that match the SFID and/or Transaction ID. HMAC Table 4.4 Management messages

Management message type Action Dynamic Service Change(DSC) Changes existing service flows Dynamic Service Delete(DSD) Deletes existing service flows Dynamic Service Activate Creates a new service flow (DSA)

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DSD DSC

DSA Null

Operational

Fig. 4.5 Dynamic service flow overview [5]

Digest on all DSx messages is verified by both the SS and BS before being processed. Messages that fail are discarded.

4.6

Service Classes

Service classes are identifiers for a specific set of QoS parameter set values. They perform two functions: l

l

Allows operators to move the burden of configuring service flows from the provisioning server to the BS. As operators provision the SS with Service Class Name, they are able to modify the implementation of a given service to local circumstances without changing SS provisioning. It also allows higher-layer protocols to create a service flow by its Service Class Name. Service classes also identify the service characteristics of a service flow to external systems such as billing system or customer service system. Operators always ensure that the service class names are unique within an area serviced by the same operation support system (OSS).

At the time the BS successfully admits the service flow, the Service Class Name is “expanded” to its defined set of parameters. This is done through BS-originated messages: DSA-REQ, DSC-REQ, DSA-RSP, and DSC-RSP. The BS includes a service flow encoding that contains the Service Class Name and the QoS Parameter Set for the Service Class. In an admission or activation request, when a Service Class name is given it is possible that the returned QoS Parameter Set may change from activation to activation. This can happen because of administrative changes to the Service Class’s QoS Parameter Set at the BS. If the definition of a Service Class Name is changed at the BS (by modifying associated QoS Parameter Set) there is no effect on the QoS Parameters of existing service flows associated with that Service Class. A BS may initiate DSC transactions to existing service flows that reference the Service Class Name to affect the changed Service Class definition. If the SS uses the Service Class Name to specify the Admitted QoS Parameter Set, the expanded set of TLV encodings of the service flow is returned to the SS in the response message (DSA-RSP or DSC-RSP).

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The use of the Service Class Name later in the activation request may fail if the definition of the Service Class Name has changed, and the new required resources are not available. Thus, the SS should explicitly request the expanded set of TLVs from the response message in its later activation request.

4.7 4.7.1

Authorization Module Concept

Authorization Module approves any change to the service flow QoS Parameters. A new service flow is created and QoS parameter set of an existing service flow is changed. This includes every DSA-REQ message to create a new service flow and every DSC-REQ message to change a QoS Parameter Set of an existing service flow. Such changes include requesting an admission control decision like setting the AdmittedQoSParamSet. Requesting activation of a service flow by setting the ActiveQoSParamSet is approved by authorization module. Reduction of requests regarding the resources to be admitted or activated are also checked by the module. There are two types of authorization modules: l l

Static authorization model Dynamic authorization model

4.7.2

Static Authorization Model

In the static authorization model, the authorization module stores the provisioned status of all “deferred” service flows. Admission and activation requests are permitted for these provisioned service flows, as long as the Admitted QoS Parameter Set is a subset of the Provisioned QoS Parameter Set, and the Active QoS Parameter Set is a subset of the Admitted QoS Parameter Set. In case there is a request to change the Provisioned QoS Parameter Set, it is refused. Requests to create new dynamic service flows (this defines a static system where all possible services are defined in the initial configuration of each SS).

4.7.3

Dynamic Authorization Model

In the dynamic authorization model, the authorization module also communicates through a separate interface to an independent policy server. This policy server may provide the authorization module with advance notice of upcoming admission and

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activation requests. It specifies the proper authorization action to be taken on those requests. Admission and activation requests from an SS are then checked by the Authorization Module to ensure that the ActiveQoSParamSet being requested is a subset of the set provided by the policy server. Admission and activation requests from an SS signalled in advance by the external policy server are permitted. Admission and activation requests from an SS that are not pre-signalled by the external policy server may result in a real-time query to the policy server or may be refused. Prior to initial connection setup, the BS shall retrieve the Provisioned QoS Set for an SS. This is handed to the Authorization Module within the BS. The BS shall be capable of caching the Provisioned QoS Parameter Set and shall be able to use this information to authorize dynamic flows that are a subset of the Provisioned QoS Parameter Set. The BS should implement mechanisms for overriding this automated approval process (such as described in the dynamic authorization model). For example, it could: l l

l

Deny all requests whether or not they have been preprovisioned. Define an internal table with a richer policy mechanism but seeded by the Provisioned QoS Set. Refer all requests to an external policy server.

4.8 4.8.1

Service Flow Types Provisioned Service Flow

The standard defines three types of service flows: l l l

Provisioned service flow Admitted service flow Active service flow

Provisioned service flow is provisioned but not immediately activated (Fig. 4.6). Therefore it is also called “deferred” service flow. It is provisioned through the network management system. SS can use DSC messages to change provisioned service flow to admitted service flow or activated service flow. This is done by passing the SFID and the associated QoS Parameter Sets to the BS in the DSC-REQ message. If authorized and resources are available, the BS responds by mapping the service flow to a CID. Similarly, the BS can also choose to activate a service flow by passing the SFID as well as the CID and the associated QoS Parameter Sets to the SS in the DSCREQ message. Such a provisioned service flow can be activated and deactivated many times through DSC exchanges. The original SFID is always used when reactivating the service flow.

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AuthoriseQoSParamSet=ProvisionedQoSParamSet (SFID) AdmittedQoSParamSet (SFID & Active CID) ActiveQoSParamSet (SFID & Active CID)

Fig. 4.6 Provisioned authorization model “envelopes” (adapted from [6])

4.8.2

Admitted Service Flow

Admitted service flow can be created by using two types of authorization models: provisioned authorization model and dynamic authorization model. It can be created either by BS or by SS. Provisioned authorization model supports two phase activation model. BS first admits resources for a service flow in response to SS’s DSC-REQ message. By doing so it ensures that resources required by service flow are available, once admitted service flow is established. QoS parameter set of admitted service flow should always be subset of provisioned service flow. In dynamic authorization model service flow can be created dynamically by using DSA message which will be discussed later on.

4.8.3

Active Service Flow

Active service flows can be created by using provisioned authorization model or dynamic authorization model. It can be created by either BS or SS. BS reserves resources for active service flow. QoS parameter set of active service flow should be a subset of admitted service flow. In two phase activation model, as discussed earlier, BS reserves resources for admitted service flow, then SS sends active QoS parameter set to base station in DSC message. In the dynamic authorization

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AuthoriseQoSParamSet=ProvisionedQoSPara mSet (SFID) AdmittedQoSParamSet (SFID & Active CID) ActiveQoSParamSet (SFID & Active CID)

Fig. 4.7 Dynamic authorization model “envelopes” (adapted from [6])

model, SS can dynamically create active service flow by using DSA message that contains active QoS parameter set (Fig. 4.7). Once active service flow is authorized and established BS can transmit data over connection if it is downlink active service flow or SS can transmit data over connection if it is uplink service flow. Dynamic service flow has either null state or normal state. In null state no service flow exits that matches the SFID or transaction ID of transaction message. To move service flow from null state to normal state a DSA message is used. Service flow has an assigned SFID once service flow exits. In normal state it can be changed many times using DSC messages. Service flow goes back to null state when DSD message is used.

4.9 4.9.1

Service Flow Creation Three-Way Handshaking Protocol

In general, in IEEE 802.16, service flows are pre-provisioned. Service flows setup is initiated by the BS during SS initialization. During provisioning, service flow is instantiated, gets a service flow ID and a “provisioned” type. Service flows can be dynamically created while being initiated either by the BS (mandatory capability) or SS (optional capability). The SS typically initiates service flows only if there is a dynamically signalled connection, such as a switched virtual connection (SVC) from an ATM network. The establishment of service flows is performed via a three-way handshaking protocol in which the request for service flow establishment is responded to and the response acknowledged. In addition to dynamic

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service establishment, IEEE 802.16 also supports dynamic service changes in which service flow parameters are renegotiated. Like dynamic service flow establishment, service flow changes also follow a similar three-way handshaking protocol.

4.9.2

Dynamic Service Flow Creation

Creation of a service flow can be initiated by either BS (mandatory) or SS (optional).

4.9.2.1

Dynamic Service Flow Creation: SS Initiated

When the SS wants to create a new service flow (Fig. 4.8) it first checks whether the resources are available. If the resources are present the SS sends DSA-REQ with service flow reference(s) and QoS parameter set(s) to BS. A DSA-REQ from an SS contains QoS Parameter set marked either for admission-only or for admission and activation. After receiving the DSA-REQ, BS responds with DSA-RSP indicating acceptance or rejection. When the rejection is caused by presence of non-supported parameter of non-supported value the specific parameter may be included into DSA-RSP. BS than checks integrity of message and sends DSA-RVD message to SS. BS also verifies the following points: l l

Whether SS is authorized for service(s). And if yes are the resources available. BS creates SFID(s). BS then maps service flow to CID if it is an uplink admission request and if it is an uplink activation request then it enables reception of data over new service flow. DSA-R

EQ

D

SS

DSX-RV

P

DSA-RS

Fig. 4.8 DSA message flow – SS-initiated

DSA-A

CK

BS

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Fig. 4.9 DSA message flow – BS-initiated Q

SS

DSA-RE

BS

DSA-R

SP

K

DSA-AC

BS sends DSA-RSP message to SS. If it is activation request then SS enables transmission/reception of data over new uplink/downlink service flow(s). SS sends DSA-ACK message to BS. BS enables transmission of data over new downlink service flow(s) if it is an activation request.

4.9.2.2

Dynamic Service Flow Creation: BS Initiated

BS can create one uplink and one downlink service flow (or only one of them) (Fig. 4.9) in DSA-REQ message. It sends QoS parameter set(s) of service flow(s) and SFID in message. BS first checks whether SS needs new service flow(s) or not then it checks whether SS is authorized for service flow(s) and also checks availability of resources for service(s). BS creates SFID(s) for either one uplink or one downlink Service flow. BS maps the service flow on CID if it is an admission request. BS sends DSA-REQ and set timer T7. SS checks whether it can support service(s). SS enables reception of data over new service flow(s) if it is activation request. SS sends DSA-RSP to BS. BS stops timer T7 and enables transmission of data over new service flow if it is downlink activation request or enables reception of data over new service flow if it is uplink activation request. BS sends DSA-ACK to SS. SS enables transmission of data over new service flow if it is uplink activation request.

4.9.3

Dynamic Service Flow Modification and Deletion

It is used to change provisioned service flow into admitted service flow and admitted service flow to active service flow. It is also used to change the QoS parameter set of admitted service flow and active service flow. If DSC message contains no QoS parameter set then the admitted and active QoS parameter set for a service flow are set to null, and service flow is admitted. If DSC message contains only admitted QoS

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parameter set then service flow’s admitted QoS parameter set is modified and it is deactivated. If DSC message contains admitted and active QoS parameter set than first admitted QoS parameter set of service flow are modified than it is checked whether active QoS parameter set is subset of admitted QoS parameter set of service flow, if it is then the active QoS parameter set of service flow is replaced with active QoS parameter set present in DSC message. DSC message can be initiated either by BS or SS. If BS has initiated a DSC message and SS has also initiated DSC message then SS has to abort its DSC message. Similarly, if SS has initiated DSC message and BS has also initiated DSC message then BS aborts the DSC message of SS.

4.9.3.1

SS Initiated

If SS need to change the service flow it sends modified QoS parameter set in DSCREQ to BS and set timer T7 and T14. BS checks the integrity of message and sends DSC-RVD to SS. SS stops timer T14. BS then checks availability of resources and modifies the service flow. BS then increases the bandwidth of channel if necessary and sends DSC-RSP to SS. SS stop timer T7 and modifies the service flow. SS changes the bandwidth of payload and sends DSC-ACK to BS. BS decreases the bandwidth of channel if necessary. Dynamic service change diagram is similar to Fig. 4.8 in which instead of DSA we have DSC sequence.

4.9.3.2

BS Initiated

If BS wants to modify the service flow then first it checks whether it can support the modification. BS sends DSC-REQ to SS and sets timer T7. SS after receiving message checks availability of resources then modifies the service flow. SS decreases the bandwidth of the payload if necessary. SS sends DSC-RSP to BS. BS changes channel bandwidth and sends DSCACK to SS. SS increases the bandwidth of payload if necessary. The dynamic service change diagram for message flow is similar to the one from Fig. 4.9 but instead of DSA messages there is a DSC message sequence.

4.9.3.3

Dynamic Service Deletion

To delete a service flow a DSD message is used. At a time only one service flow can be deleted using message. Resources reserved for service flow are released after deletion. SS has to reregister itself if management related service flow is deleted. If the provisioned service flow is deleted then it can only be used by SS if it re-register itself.

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SS Initiated

If SS does not need a service flow then it deletes it and sends DSD-REQ to BS. BS first verifies that SS is owner of service flow, then deletes it and sends DSD-RSP message to SS.

4.9.3.5

BS Initiated

If BS does not need service flow anymore then it deletes the service flow and checks which SS is associated with service flow. Then, BS sends a DSD-REQ to it. SS deletes the service flow and sends DSD-RSP to BS. 4.9.3.6

Comparison

When compared to other last mile technologies such as Cable, WiMAX’s built in PHY and MAC provisions are better able to support QoS. It is not possible to do reservations of bandwidth on cable networks, and it is hard to commit to certain bit rates for enterprise customers. In cable, each video channel is given a fixed amount of bandwidth which cannot be made available for other purposes. This has advantages in that, there are no issues like jitter or insufficient bandwidth and this is the reason we can expect excellent video quality on cable connections. But things got more complex when cable operators started to offer broadband data. The operators assigned only certain fixed channels for data, and access was contention-based which meant that it was not possible to offer any kind of QoS or SLAs. And as far as voice is concerned, cable operators initially offered circuit-switched voice, but now most have migrated to VoIP wherein voice is allocated channels that are separate from data. Table 4.5 lists the various QoS advantages and disadvantages of technologies competing with WiMAX. DSL service providers can do voice communications well – both circuitswitched as well as VoIP, since their traditional business was in offering toll-quality voice. But the story for data over DSL is not as rosy. Though the last mile to the consumer is a dedicated connection, and even the backhaul is usually on the Table 4.5 QoS advantages and disadvantages of competing technologies Technology QoS Advantages/Disadvantages IEEE 802.11 Contention based MAC, requires acknowledgments which cause overhead, latency, timeouts. Uses time slots; fixed channel size. 3G Not an ‘All IP’ solution; IP QoS has to be mapped onto circuit-switching layer. Mapping point may be far away, causing queuing and scheduling inefficiencies. Most of the parameters are fixed, not adaptive. IEEE 802.16 Connection-oriented protocol, provides service flows; Grant based MAC allows centralized control and eliminated overhead and delay of acknowledgments; flexible and efficient QoS is supported by OFDM, FEC and adaptive modulation.

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provider’s ATM network, once past the central office the data goes over the Internet. At this point, the transmission can degrade to Best-Effort. And as far as video-over-DSL is concerned, the earlier DSL technologies did not have sufficient bandwidth, and that’s why DSL providers partnered with satellite entities for the video portion of the triple-play.

4.9.3.7

3G

In 3G, support for QoS is more limited. It uses priority-based technique to support various classes of services. Therefore in 3G, higher priority traffic may completely starve lower priority traffic during periods of high usage [5]. 3G is also not all IP solution, but IP is overlaid on the underlying circuitswitched layer. Therefore with 3G, IP QoS control must be mapped onto the circuit switching layer .The mapping point in the core can be far away from the delivery point, creating queuing and scheduling inefficiencies. At the PHY layer, 3G does not offer OFDM and adaptive modulation .HSDPA technology includes Hybrid ARQ(HARQ) to allow it to dynamically adjust to network conditions somewhat, but lacks the flexibility as WiMAX does. At a service level, 3G does support different classes such as Background Class, Conversational Class, Interactive Class, and Streaming Class through priority based methods. QoS capabilities in 3G wireless are more limited than those in Mobile WIMAX.

4.9.3.8

Wi-Fi

IEEE 802.11 wireless LAN (Wi-Fi) is one of the most deployed wireless technologies all over the world. Its main characteristics are simplicity, flexibility and cost effectiveness. This technology provides people with a ubiquitous communication. Users now require to receive high-speed video, audio, voice and Web services even when they are moving in offices or travelling around campus. However, multimedia applications demand quality of service (QoS) support such as guaranteed bandwidth, delay, jitter and error rate. Guaranteeing QoS requirements in 802.11 WLAN is very challenging as the standard provide the QoS unaware functions of its MAC layer and the noisy and variable PHY layer characteristics. In the revised versions of IEEE 802.11 standard, QoS capabilities is endowed. With the new standard 802.11e – the MAC layer will be changed to allow priority mechanisms for say voice or video but note: the QoS guarantees will still only be statistical. Basically only traffic (not locations) can be prioritized, and higher priority traffic is assigned shorter deferral times, so it has a greater chance of grabbing the next opportunity to transmit. Voice and network control traffic are given the highest priority followed by video, Best-Effort data, and background data. Moreover, Wi-Fi’s QoS operates on a distributed architecture where the operation of the MAC is coordinated between Access Points and Subscriber Stations (SS), while WIMAX operates on a centralized architecture which allows the base station

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to have complete control of all the SSs in its network. Another disadvantage that Wi-Fi QoS suffers is that the MAC uses acknowledgements which results in delays and overhead. In addition, the channel size is fixed, unlike in WIMAX where the channel size is changeable.

4.10

Summary and Conclusions

This Chapter starts by presenting the interpretation and definition of service quality and its classes. While there are four classes of service in Fixed WiMAX (unsolicited granted service, real-time polling service, non-real-time polling service and best effort) in Mobile WiMAX there is an extra class: extend real-time polling service. The IEEE 802.16 standard defines the point-to-multipoint (PtM) and mesh modes of operation but this Chapter only considers the former. The QoS architecture was presented for the PtM mode. Packets originated at the SS are classified by the connection classifier based on the connection ID (CID) and are forwarded to the appropriate queue for the communication with the BS. The discussion of details on the architecture includes aspects of UL and DL scheduling. QoS provisioning and the object model for service quality were also discussed. Finally, the authorization module was addressed as well as service flow types and creation.

References 1. A. Ghosh, D. Wolter, J. Andrews, R. Chen, Broadband wireless access with WiMax/802.16: current performance benchmarks and future potential. IEEE Commun. Mag. 43(2), 131 (Feb 2005) 2. W. Zhao, D. Olshefski, H. Schulzrinne, Internet Quality of Service: An Overview (Columbia University, New York, 2000) 3. K. Wongthavarawat, A. Ganz, Packet scheduling for QoS support in IEEE 802.16 broadband wireless access systems, in Military Communications Conference, IEEE 2003 4. IEEE Standard for Local and metropolitan area networks-Part 16: Air Interface for Fixed Broadband Wireless Access Systems-Amendment 2: Medium Access Control Modification and Additional Physical Layer Specifications for 2–11 GHz. IEEE Standard 802.16a-2003 5. Mobile WiMAX – Part II: A Comparative Analysis, WiMAX Forum (2006) 6. IEEE Std 802.16-2004 (Revision of lEEE Std 802.16-2001): IEEE Standard for Local and Metropolitan Area Networks Part 16: Air Interface for Fixed Broadband Wireless Access Systems 7. C. Eklund, R.B. Marks, K.L. Stanwood, S. Wag, IEEE Standard 802.16: A Technical Overview of the WirelessMAN Air Interface for Broadband Wireless 8. IEEE, IEEE Standard for Local and Metropolitan Area Networks – Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems, Amendment 2: Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands, IEEE 802.16e-2005, The Institute of Electrical and Electronics Engineers, New York, USA, Feb 2006 9. GuoSong Chu, Deng Wang, Shunliang Mei, A QoS architecture for the MAC protocol of IEEE 802.16 BWA system. Communications, Circuits and Systems and West Sino Expositions, IEEE 2002

Chapter 5

Security Sublayer Ramjee Prasad and Fernando J. Velez

Abstract This Chapter starts by addressing aspects of the security architecture for IEEE 802.16, including its functions, secure encapsulation of MPDUs, encryption algorithms, data encryption methodologies (with DES in CBC mode, AES in CCM mode and the ones for IEEE 802.11e). Then, the authentication protocol (RSA and PKM EAP) is addressed and the PKM protocol presents. After describing the PKM protocol MAC management messages, addresses key management is discussed. The network aspects of security are finally presented, including a description of RADIUS and Extensible Authentication Protocol (EAP).

5.1

Introduction

The exploding growth of wireless networks recently has raised several security issues. As the wireless networks are less secured due to the lack of physical infrastructure special attention should be paid to security aspects. With the increasing popularity of the broadband internet wireless networking market is thriving. WiMAX is the emerging broadband wireless metropolitan area network (WMAN) technology for the future. As the security part of the IEEE 802.11 standard was developed after its initial release, it has many security vulnerabilities and threats. In IEEE 802.16, however, security has been considered as the main issue during the design of the protocol but some issues still need to be solved on threats, risk and vulnerability in real situations. For secure communications, privacy and confidentiality are fundamental issues. Secured communication provides resistance to interception and eavesdropping. Message authentication provides integrity of the message and sender authentication, R. Prasad (*) Center for TeleInFrastruktur (CTIF), Aalborg University, Niels Jernes Vej 12, DK–9220 Aalborg Øst, Denmark e-mail: [email protected]

R. Prasad and F.J. Velez, WiMAX Networks, DOI 10.1007/978-90-481-8752-2_5, # Springer ScienceþBusiness Media B.V. 2010

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corresponding to the security attacks of message modification and impersonation. Anti-replay detects and disregards any message that is a replay of a previous message. Non-repudiation is against denial and fabrication. Access control prevents unauthorized access of the resources. IEEE 802.16, the standard for wireless metropolitan area networks (WMAN), incorporates a pre-existing standard called Data Over Cable Service Interface Specifications (DOCSIS), which was designed for cable networks not wireless networks [1]. As DOCSIS was designed for cable networks not wireless networks, IEEE 802.16 security failed to protect the IEEE 802.16 link [2] and had significant changes in its Privacy and Key Management (PKM) protocol, with the latest IEEE 802.16e-2005 standard [3]. Many of the security goals discussed in this chapter are based on [4, 5] but also addressing wireless networks. Security provides subscribers with privacy across the fixed broadband wireless network. The entire security aspects of IEEE 802.16 are in the privacy sub-layer. The function of this sub-layer is to provide access control and the confidentiality of the data link. The Security sub-layer provides subscribers with privacy, authentication, or confidentiality across the broadband wireless network by applying cryptographic transforms to MPDUs carried across connections between SS and BS. In addition, the security sub-layer provides operators with strong protection from theft of service. The BS is also responsible for the protection against the unauthorized access to these data transport services. This is done by securing the associated service flows across the network. The Security sublayer employs an authenticated client/server key management protocol in which the BS, the server, controls distribution of keying material to client SS. Additionally, the basic security mechanisms are strengthened by adding digital-certificate-based SS device-authentication to the key management protocol. The remaining of this Chapter is organized as follows. Section 5.2 addresses aspects of the security architecture for IEEE 802.16, including its functions, secure encapsulation of MPDUs, encryption algorithms, data encryption methodologies (with DES in CBC mode, AES in CCM mode and the ones for IEEE 802.11e). Section 5.3 presents the authentication protocol (RSA and PKM EAP) while Section 5.4 describes the PKM protocol. Section 5.5 presents the PKM protocol MAC management messages while Section 5.6 addresses key management. The network aspects of security are presented in Section 5.7, including RADIUS and Extensible Authentication Protocol (EAP). Finally, conclusions are drawn in Section 5.8.

5.2 5.2.1

Security Architecture for IEEE 802.16 Architecture and Functions

Security is handled at multiple layers of the wireless network OSI model. Each layer handles a complimentary aspect of security.

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For IEEE 802.16 the specified security sub-layer only deals with the Data Link Layer. Network Layer security measures protect the network from malicious attacks achieved through the use of firewalls and AAA servers. The Transport and Application layers provide additional security measures as deemed appropriate by the network operator, application service providers (ASPs) or end users themselves. To start with the description of the security sub-layer we first define the protocol stack for the system security components as shown in Fig. 5.1 The Security Sub-layer involves two main protocols. Table 5.1 lists the two protocols and their functions. Their missions are the following: 1. An encapsulation protocol for encrypting packet data across the BWA network. This protocol defines: (a) A set of supported cryptographic suites, that is, pairings of data encryption and authentication algorithms (b) The rules for applying those algorithms to a MAC PDU payload 2. A key management protocol (PKM) providing the secure distribution of keying data from BS to SS. The SS and BS synchronize keying data through this key management protocol. In addition, the BS uses the protocol to enforce conditional access to network services.

EAP method EAP RSA-based authentication

Authorisation /SA EAP encapsulation/ control decapsulation PKM control management

Traffic data encryption/authentication processing

Control message Message Processing authentication processing PHY SAP

Scope of IEEE 802.16 specifications Scope of recommendations (Out of scope)

Fig. 5.1 Security architecture for IEEE 802.16 (adapted from [3]) Table 5.1 Security protocol and their functions Protocol Protocol function Encapsulation Protocol Encrypt packet data across the BWA Privacy and Key Management Provide secret distribution of keying data from BS to SS and Protocol(PKM) enabling BS to impose conditional access to network services

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During capability negotiations, if the SS specifies that it does not support IEEE 802.16 security, the step of authorization and key exchange is skipped by the BS. The BS, if provisioned so, considers the SS authenticated. Otherwise, the SS is not recognized and therefore is not served. Neither key exchange nor data encryption is performed.

5.2.2

Secure Encapsulation of MPDUs

Encryption services are defined as a set of capabilities within the MAC Security Sub-layer. MAC Header information specific to encryption is allocated in the generic MAC header format. Encryption is applied to the MAC PDU payload when required by the selected cipher suite. The generic MAC header is not encrypted. All MAC management messages are sent in the clear to facilitate registration, ranging, and normal operation of the MAC.

5.2.3

Encryption Algorithms

Cryptography is the art or science of keeping messages secret. Cryptography deals with all aspects of secure messaging, authentication, digital signatures, electronic money, and other applications. This sub-clause specifies the cryptographic algorithms and key sizes used by the PKM protocol. All SS/MS and BS implementations support the method of packet data encryption. IEEE 802.16 has used many different types of algorithms. These algorithms are used for securing ciphering key exchange as well as for encryption of transport data. The encryption algorithms applied in IEEE 802.16 are the following: 1. Rivest Shamir Adleman (RSA) – RSA is an algorithm for public-key cryptography. It was the first algorithm known to be suitable for signing as well as encryption, and one of the first great advances in public key cryptography [6]. It is used to encrypt the authorization reply message using the SS public key. RSA is also used for the encryption of the traffic encryption keys when these are transmitted from the BS to the SS 2. Data Encryption Standard (DES) – The DES and 3-DES are shared method for encrypting information selected as an official Federal Information Processing Standard (FIPS) [6, 7]. DES and 3-DES are used for key encryption as well as traffic data encryption. It is mandatory for the IEEE 802.16 standard 3. Advanced Encryption Standard (AES) – The AES algorithm is a shared (secret) key encryption [8] algorithm. The AES algorithm may be used for traffic data encryption and can also be used for the encryption of the traffic encryption keys

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4. Hashed Message Authentication Code (HMAC) & Cipher -based Message Authentication Code (CMAC) – The HMAC and CMAC are used to protect both a message’s integrity as well as its authenticity [9–11]. IEEE 802.16 standard includes the use of HMAC for message authentication and integrity control. CMAC is used in IEEE 802.16e as an alternative to HMAC

5.2.4

Data Encryption Methods

As defined in the standard only the payload part of the MPDU is encrypted, not the generic MAC header. The generic MAC header is always sent in the clear text. Also the Basic and primary MAC management messages are not encrypted. The Encryption Control (EC) bit in the generic MAC header indicated whether the MAC PDU payload is encrypted or not. The IEEE 802.16-2004 uses the most popular data encryption algorithms for the encryption of MAC PDU payloads: DES-CBC and AES-CCM.

5.2.4.1

Data Encryption with DES in CBC Mode

If the data encryption algorithm identifier in the cryptographic suite of an SA equals 0x01, data on connections associated with that SA uses the CBC mode of the Data Encryption Standard (DES) algorithm to encrypt the MAC PDU payloads [7, 13, 14], Fig. 5.2. The CBC IV is calculated in different ways for uplink and downlink.

GMH (6 bytes)

Optional CRC (4bytes)

Plaintext payload

IV from security association state IV

DES-CBC algorithm

PHY synch field from frame header

Ciphered data block

Fig. 5.2 DES algorithm in CBC mode (adapted from [3])

Key

TEK from security association state

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For the downlink CBC mode is initialized with the exclusive-or (XOR) of the IV parameter included in the TEK keying information, and the content of the PHY synchronization field (right justified) of the latest DL-MAP as shown in Fig. 5.2 In the uplink, the CBC is initialized with the XOR of the IV parameter included in the TEK keying information, and the Frame Number of the frame where the relevant UL-MAP was transmitted

There are some drawbacks of using the DES algorithm. The level of security provided by DES algorithm in CBC mode is not so strong. Besides, there is no MPDU authentication, which is a considerable weakness on wireless media. The cipher chain which is initialized can be sometimes predicated making the privacy a serious threat.

5.2.4.2

Data Encryption with AES in CCM Mode

When the weaker security provided by the DES algorithm is a concern advanced encryption standard (AES) is the solution to replace it. The AES algorithm is 128 bit key encryption. It is more secure than the DES but is more complex and little slower than DES. In IEEE 802.16, AES is included in its counter with CBC-MAC (CCM) mode [15]. When the data encryption algorithm identifier in the cryptographic suite of an SA equals 0x02, data on connections associated with that SA use the CCM mode of the Advanced Encryption Standard (AES) algorithm to encrypt the MAC PDU payloads. Figure 5.3 shows the AES-CCM generated payload. Table 5.2 presents the cryptographic suites used in IEEE 802.16. The PDU payload is pre-pended with a 4-byte PN (Packet Number). This PN is not encrypted. The LSB is transmitted first and then the MSB.

Payload before encryption L bytes

plaintext payload

Payload after encryption L + 12 bytes 4 bytes

PN

8 bytes

ciphertext payload

Fig. 5.3 Encrypted payload format in AES-CCM mode

Ciphertext message authentication code

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Table 5.2 Cryptographic suites used in IEEE 802.16-2004 and IEEE 802.16e IEEE 802.16-2004 IEEE 802.16e Data Encryption/Decryption 56 bit CBC-Mode DES 56 bit CBC-Mode DES 128 bit CCM-Mode AES 128 bit CCM-Mode AES 128 bit CBC-Mode AES 128 bit CTR-Mode AES Data Authentication Not Supported 128 bit CCM-Mode AES Key Generation Not defined Dot16KDF Key Encryption/Decryption 128 bit EDE-Mode 3-DES 128 bit EDE-Mode 3-DES 1024 bit RSA 1024 bit RSA 128 bit ECB-Mode AES 128 bit ECB-Mode AES 128 bit ECB-Mode AES

• X.509 certification • RSA authorization • 56 bit DES-CBC and 128 bit AES-CCM encryption • HMAC message integrity protection • Authorization state machine and TEK state machine

Security features of IEEE 802.16d

+

• EAP authentication • mutual authentication • CMAC message integrity protection • Key hierarchy • Secure key establishment • Multicast security • Mobility support

=

IEEE 802.16e Securiy

New added features

Fig. 5.4 IEEE 802.16d and IEEE 802.16e security features

The plaintext PDU is encrypted and authenticated using the active TEK, according to the CCM specification. This includes appending an 8-byte ICV (Integrity Check Value) to the end of the payload and encrypting both the plaintext payload and the appended ICV. The cipher text Message Authentication Code is transmitted such that byte index 0 is transmitted first and byte index 7 is transmitted last (i.e., LSB First). This processing yields a payload that is 12 bytes longer than the plaintext payload.

5.2.4.3

Data Encryption Methods for IEEE 802.16e

AES is most widely and the recommended algorithm of 802.16e security sub-layer, Fig. 5.4. This is because it can perform stronger protection from theft of service and data across broadband wireless mobile network. Besides, CCM-Mode and ECB-Mode AES algorithm, IEEE 802.16e supports three more AES algorithms. They are CBC-Mode AES, CTR-Mode AES and AESKey-Wrap. AES KeyWrap is a 128-bit key. The AES wrap algorithm accepts both a cipher text and integrity check value. The decryption algorithm returns a plaintext key and the integrity check value.

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Key Management Protocol

PKM protocol is used by the SS to obtain authorization and traffic keying material from the BS, and to support periodic reauthorization and key refresh. The key management protocol uses X.509 digital certificates (IETF RFC 3280), the RSA public-key encryption algorithm [PKCS #1], and strong encryption algorithms, to perform key exchanges between SS and BS. The PKM protocol shown in Fig. 5.5 enables for both mutual authentication and unilateral authentication (e.g., where the BS authenticates SS, but not vice versa). It also supports periodic reauthentication/reauthorization and key refresh. The key management protocol uses either EAP, or X.509 digital certificates, together with RSA public-key encryption algorithm or a sequence starting with RSA authentication and followed by EAP authentication [20]. It uses strong encryption algorithms to perform key exchanges between an SS and BS. The terms used in PKM protocol authorization messages are presented in Table 5.3. The PKM’s authentication protocol establishes a shared secret (called an Authorization Key [AK]) between the SS and the BS. Once a shared AK is established between the Bs and the SS, the shared secret is then used to secure subsequent PKM

Message 1: Authentication Information Message SS ® BS: Certificate (Manufacturer (SS)) Message 2: Authorization Request SS ® BS: Certificate (SS) | Capabilities | SAID Message 3: Authorization Reply BS ® SS: RSA-Encrypt (PubKey(SS), AK) | Lifetime | SeqNo |SAIDList

Fig. 5.5 PKM authorization protocol Table 5.3 Terms used in PKM protocol authorization messages Term Description Cert(Manufacturer(SS)) An X.509 certificate identifying SS’s manufacturer Cert(SS) An X.509 certificate with the SS public key Capabilities SS-supported authentication and data encryption algorithms SAID The secure link between SS and BS (the connection ID) RSA-Encrypt(k, a) Instruction to RSA-OAEP encrypt its second argument a under the key k PubKey(SS) The SS’s public key, as reported in Cert(SS) AK Authorization key Lifetime A 32-bit unsigned number giving the number of seconds before AK expires SeqNo A 4-bit value for AK SAIDList A list of SA descriptors, each including an SAID, the SA type – primary, static, or dynamic – and the SA cipher suite

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exchanges of TEKs. This two-tiered mechanism for key distribution enables to refresh TEKs without incurring the overhead of computation-intensive operations. A BS authenticates a client SS during the initial authorization exchange. Each SS presents its credentials, which will be a unique X.509 digital certificate issued by the SS’s manufacturer (in the case of RSA authentication) or a operator-specified credential (in the case of EAP-based authentication). The BS associates an SS’s authenticated identity to a paying subscriber, and hence to the data services that subscriber is authorized to access. Thus, with the AK exchange, the BS determines the authenticated identity of a client SS and the services (i.e., specific TEKs) the SS is authorized to access. Since the BS authenticates the SS, it may protect against an attacker employing a cloned SS, masquerading as a legitimate subscriber’s SS. The traffic-key management portion of the PKM protocol adheres to a client/ server model, where the SS (a PKM “client”) requests keying material, and the BS (a PKM “server”) responds to those requests, ensuring that individual SS clients receive only keying material for which they are authorized. The PKM protocol uses MAC management messaging, that is, PKM-REQ and PKM-RSP messages. The PKM protocol is defined in detail in Section 5.4.

5.3

Authentication Protocol

An SS uses the PKM protocol to obtain authorization and traffic keying material from the BS, and to support periodic reauthorization and key refresh. PKM supports two distinct authentication protocol mechanisms: 1. RSA protocol [PKCS #1 v2.1 with SHA-1(FIPS 186-2)] support is mandatory in PKMv1 and optional in PKMv2 2. Extensible Authentication Protocol is optional unless specifically required

5.3.1

RSA Authentication

The PKM RSA authentication protocol uses X.509 digital certificates, the RSA public key encryption algorithm that binds public RSA encryption keys to MAC addresses of SSs. A BS authenticates a client SS during the initial authorization exchange. Each SS carries a unique X.509 digital certificate issued by the SS’s manufacturer. The digital certificate contains the SS’s Public Key and SS MAC address. When requesting an AK, an SS presents its digital certificate to the BS. The BS verifies the digital certificate, and then uses the verified Public Key to encrypt an AK, which the BS then sends back to the requesting SS.

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All SSs using RSA authentication either have factory-installed RSA private/ public key pairs or provide an internal algorithm to generate such key pairs dynamically. If an SS relies on an internal algorithm to generate its RSA key pair, the SS generates the key pair prior to its first AK exchange, described in Section 5.2.1. All SSs with factory-installed RSA key pairs also have factoryinstalled X.509 certificates. All SSs that rely on internal algorithms to generate an RSA key pair shall support a mechanism for installing a manufacturer- issued X.509 certificate following key generation.

5.3.2

PKM EAP Authentication

PKM EAP Authentication uses Extensible Authentication Protocol in conjunction with an operator-selected EAP Method. The EAP method will use a particular kind of credential – such as an X.509 certificate in the case of EAP-TLS, or a Subscriber Identity Module in the case of EAP-SIM. During re-authentication, the EAP transfer messages are protected with an HMAC/CMAC tuple. The BS and SS must discard unprotected EAP transfer messages, or EAP transfer messages with invalid HMAC/CMAC digests during re-authentication.

5.4

PKM Protocol

The PKM authorization protocol distributes an authorization token to an authorized SS. It is the protocol that makes the BS to identify the SS. The authorization protocol consists of three steps: two messages send from SS to BS and then one message send from the BS to the SS. The SS uses the PKM protocol to obtain authorization and traffic keying material from the BS, and to support periodic reauthorization and key refresh. The key management protocol uses the following entities: l l l

X.509 digital certificates The RSA public-key encryption algorithm [PKCS #1] The strong encryption algorithms to perform key exchanges between SS and BS

There are two Privacy Key Management Protocols supported in IEEE Standard 802.16e. PKM version 1 and PKM version 2 more enhanced features such as new key hierarchy, AES-CMAC, AES-key-wraps and MBS.

5.5

PKM Protocol MAC Management Messages

PKM employs two MAC management message types: PKM Request (PKM-REQ) and PKM Response (PKM-RSP), Table 5.4.

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Table 5.4 PKM MAC management messages Type Value Message name 9 PKM-REQ 10 PKM-RSP

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Message description Privacy Key Management Request [SS -> BS] Privacy Key Management Response [BS -> SS]

Management Message Type Code PKM Identifier (8 bits) (8 bits) (=9,for PKM-REQ)

TLV encoded Information

Fig. 5.6 PKM-REQ MAC management format

Management Message Type Code PKM Identifier (8 bits) (8 bits) (=10,for PKM-RSP)

TLV encoded Information

Fig. 5.7 PKM-RSP MAC management format

These MAC management message types distinguish between PKM requests (SS-to-BS) and PKM responses (BS-to-SS) as follows: 1. PKM Request (PKM-REQ) – The PKM-REQ message is sent from the SS to the BS, Fig. 5.6. It encapsulates one PKM message in its message payload. 2. PKM Response (PKM-RSP) – The PKM-RSP message is sent from the BS to SS, Fig. 5.7. It encapsulates one PKM message in its message payload. Each message encapsulates one PKM message in the Management Message Payload The X.509 certificates The X.509 certificates are used to identify the communicating parties. The IEEE 802.16 standard states that 802.16-compliant SSs must use X.509 Version 3 certificate formats, providing a public key infrastructure used for secure authentication. Each SS carries a unique X.509 digital certificate issued by the SS manufacturer, known as the SS X.509 certificate. This certificate is issued and signed by a Certification Authority (CA) and installed by the manufacturer. The digital certificate contains the SS RSA public key and the MAC address of the SS. IEEE 802.16 requires the X.509 certificate to come up with the following fields [1, 11]: l

l l l l l

The X.509 certificate version is always set to v3 when used in the 802.16 standard Certificate serial number Certificate issuer’s signature algorithm Public Key Cryptography Standard 1, that is, RSA encryption with SHA1 hashing Certificate issuer Certificate validity period

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Certificate subject, that is, the certificate holder’s identity, which, if the subject is the SS, includes the station’s MAC address Subject’s public key, which provides the certificate holder’s public key, identifies how the public key is used, and is restricted to RSA encryption Signature algorithm, which is identical to the certificate issuer’s signature algorithm Issuer’s signature, which is the digital signature of the Abstract Syntax

The standard works with two types of certificate: manufacturer and SS ones. It does not refer to BS certificates. Manufacturer certificates are used to identify the manufacturer of an IEEE 802.16 device. It could either be self-signed or issued by a third party. SS certificates are used for a single SS to be identified and its MAC address is present in the subject field. Manufacturers usually issue and sign the SS certificates. Then, BS is using the manufacturer’s public key and verifies the SS certificate through PKI. Table 5.5 shows the IEEE 802.16 encryption keys. Figure 5.8 presents the privacy and key management protocol. Table 5.6 presents the terms used in a PKM protocol message exchange. Table 5.5 IEEE 802.16 encryption keys Encryption Key Notation Number of bits Authorization AK 160 Key Key Encryption KEK 128 Key Traffic TEK 128 Encryption Key HMAC Key for HMAC_KEY_D 160 the Downlink HMAC Key for HMAC_KEY_U 160 the Uplink HMAC Key for HMAC_KEY_S 160 the Uplink

Generated Description by BS Authentication of an SS by its BS BS, SS BS

3DES key used for the encryption of the TEK Used for encrypting data traffic

Used for authenticating messages in the downlink direction. Used for authenticating messages in the uplink direction Used for authenticating messages in the Mesh mode

Message 1: BS ® SS: SeqNo | SAID | HMAC(1) Message 2: Key Request SS ® BS: SeqNo | SAID | HMAC(2) Message 3: Key Reply BS ® SS: SeqNo | SAID | OldTEK | NewTEK | HMAC(3)

Fig. 5.8 Privacy and key management protocol

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Table 5.6 Terms used in a PKM protocol message exchange Term Description SeqNo The AK used for the exchange SAID The ID of the data SA being created or rekeyed HMAC(1) The HMAC-SHA1 digest of SeqNo | SAID under AK’s downlink HMAC key HMAC(2) The HMAC-SHA1 digest of SeqNo | SAID under AK’s uplink HMAC key OldTEK The previous-generation TEK’s initialisation vector, remaining lifetime (in seconds), and sequence number for the data SA specified by SAID (the TEK sequence number is a 2-bit quantity) NewTEK The next TEK’s initialisation vector, lifetime (in seconds), and sequence number for the data SA specified by SAID (the TEK sequence number is 1 greater, modulo 4, than the OldTEK sequence number) HMAC(3) The HMAC-SHA1 digest of SeqNo | SAID | OldTEK | NewTEK under AK’s downlink HMAC key

5.5.1

PKM Version 1

5.5.1.1

Security Associations

A Security Association (SA) is defined as the set of security information a BS and one or more of its client SSs share in order to support secure communications across the WiMAX access network. Three types of SAs have been defined, Primary, Static, and Dynamic. Each SS establishes a primary security association during the SS initialization process. Static SAs are provisioned within the BS. Dynamic SAs are created and destroyed in real time in response to the initiation and termination of specific service flows. Both Static and Dynamic SAs may be shared by multiple SSs. Each SS can have several service flows on the go and can therefore have multiple dynamic SAs. The BS always makes sure that the assigned SAs are compatible with the service types the SS is authorized to access. SA is identified by SAID, which contains Cryptographic suite (i.e., encryption algorithm) and Security Info (i.e., key, IV). The basic and primary management connections do not have SAs. The secondary management connection can have an optional SA. Transport connections always have SAs. An SA’s shared information includes the Cryptographic Suite employed within the SA. The shared information may include TEKs and Initialization Vectors. The exact content of the SA is dependent on the SA’s Cryptographic Suite. When SS establishes an exclusive Primary SA with its BS, the SAID for SS is equal to the Basic CID of that SS. Using the PKM protocol, an SS requests from its BS an SA’s keying material. An SA’s keying material (e.g., Data Encryption Standard (DES) key and CBC Initialization Vector) has a limited lifetime. When the BS delivers SA keying material to an SS, it also provides the SS with that material’s remaining lifetime.

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Fig. 5.9 PKMv1 protocol

Authorisation Protocol (AK Generation)

AK

KEK ( Derived from AK

Privacy & Key Management (TEK Generation )

TEKs

It is the responsibility of the SS to request new keying material from the BS before the set of keying material that the SS currently holds expires at the BS. In certain Cryptographic Suites, key lifetime may be limited by the exhaustion rate of a number space, for example, the Packet Number (PN) in AES-CCM mode. In this case, the key ends either at the expiry of the key lifetime or the exhaustion of the number space, whichever is earliest. Note that in this case, security is not determined by the key lifetime (Fig. 5.9).

5.5.1.2

SS Authorization and AK Exchange Overview

During the process of SS authorization the BS performs following steps: l l

l l

Authenticating a client SS’s identity Establishing a shared AK by RSA, from which a key encryption key (KEK) and message authentication keys are derived Providing the authenticated SS with the SAIDs Providing the SS with properties of primary and static SAs the SS is authorized to obtain keying information for

After achieving the initial authorization, SS needs to periodically reauthorize with the BS. The process of reauthorization is also managed by the SS’s Authorization state machine. TEK state machines manage the refreshing of TEKs. Authorization via RSA authentication protocol An SS begins authorization by sending an Authentication Information message to its BS. The Authentication Information message contains the SS manufacturer’s X.509 certificate, issued either by the manufacturer itself or by an external authority. The Authentication Information message is strictly informative, that is, the BS may choose to ignore it. However, it does provide a mechanism for a BS to learn the manufacturer certificates of its client SS.

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SS

BS Authorisation Request (SS Certificate, Security Capabilities, SAID)

Verify SS Certificate

AK (128bits) Generation Authorisation Reply (AK, Key Lifetime, selected security suite, AK sequence number)

AK (128bits) Generation

AK (128bits) Generation Key lifetime = 1-70 days

Fig. 5.10 SS authorization using AK

The SS sends an Authorization Request message to its BS immediately after sending the Authentication Information message. This is a request for an AK, as well as for the SAIDs identifying any Static Security SAs the SS is authorized to participate in. The Authorization Request includes: 1. A manufacturer-issued X.509 certificate 2. A description of the cryptographic algorithms the requesting SS supports: SS’s cryptographic capabilities are presented to the BS as a list of cryptographic suite identifiers, each indicating a particular pairing of packet data encryption and packet data authentication algorithms the SS supports 3. The SS’s Basic CID: the Basic CID is the first static CID the BS assigns to an SS during initial ranging – the primary SAID is equal to the Basic CID In response to an Authorization Request message, a BS validates the requesting SS’s identity, determines the encryption algorithm and protocol support it shares with the SS, activates an AK for the SS, Fig. 5.10, encrypts it with the SS’s public key, and sends it back to the SS in an Authorization Reply message. The authorization reply includes the following components: l l

l l

An AK encrypted with the SS’s public key A 4-bit key sequence number, used to distinguish between successive generations of AKs A key lifetime The identities (i.e., the SAIDs) and properties of the single primary and zero or more static SAs the SS is authorized to obtain keying information for

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Authorization Reply identifies only Primary SA and Static SAs, not Dynamic ones. Before responding to the SS Authorization Request, the BS cross verifies whether the SS is authorized for basic unicast services and other provisioned services. This is done through X.509 certificate. AK is refreshed periodically by reissuing an Authorization Request to the BS. Reauthorization is identical to authorization with the exception that the SS does not send Authentication Information messages during reauthorization cycles. To avoid service interruptions during reauthorization, successive generations of the SS’s AKs have overlapping lifetimes. Therefore provision is made that both the SS and BS are capable of supporting up to two simultaneously active AKs during these transition periods. The protected services a BS makes available to a client SS can depend upon the particular cryptographic suites SS and BS share support for.

5.5.1.3

TEK Exchange

After the SS authentication procedure has been done, the AK is used to derive KEK and HMAC key. TEK is then generated by BS randomly. The TEK is the key actually used to encrypt data traffic exchanged between the BS and SS. A key exchange message is authenticated by HMAC-SHA1 to provide message integrity and AK confirmation. Two TEKs are used to encrypt data. The first one is used as the current operational key and the second one is used when the current TEK key expires.

TEK Exchange: for PtM Topology Upon achieving authorization, an SS starts a separate TEK state machine for each of the SAIDs (or per SA) identified in the Authorization Reply message. Each TEK state machine operating within the SS is responsible for managing the keying material associated with its respective SAID. TEK state machines periodically send Key Request messages to the BS, requesting a refresh of keying material for their respective SAIDs. The BS responds to a Key Request with a Key Reply message, containing the BS’s active keying material for a specific SAID, Fig. 5.11. The TEK is encrypted using appropriate KEK derived from the AK. Note that at all times the BS maintains two active sets of keying material per SAID. The lifetimes of the two generations overlap such that each generation becomes active halfway through the life of its predecessor and expires halfway through the life of its successor. A BS includes in its Key Replies both of an SAID’s active generations of keying material. The Key Reply provides the requesting SS, in addition to the TEK and CBC initialization vector (IV), the remaining lifetime of each of the two sets of keying material. The receiving SS uses these remaining lifetimes to estimate when the BS will invalidate a particular TEK, and therefore when to schedule future Key

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SS

BS

AK (128bits)

AK (128bits)

KEK (128bits)

KEK (128bits) HMAC-Key(160bits)

HMAC-Key(160bits) TEK Key Request (AK Sequence Number, SAID, HMAC-SHA1)

TEK (128bits) Generation

TEK Key Reply (AK Sequence Number, SAID, HMAC-SHA1, Encrypted TEK, TEK key lifetime)

TEK TEK(128bits) (128bits)

TEK (128bits)

Key lifetime = 30mins to 7 days

Fig. 5.11 Data key exchange and TEK generation

Requests such that the SS requests and receives new keying material (before the BS expires the keying material the SS currently holds). The operation of the TEK state machine’s Key Request scheduling algorithm, combined with the BS’s regimen for updating and using an SAID’s keying material, ensures that the SS will be able to continually exchange encrypted traffic with the BS. A TEK state machine remains active as long as: l

l

The SS is authorized to operate in the BS’s security domain, that is, it has a valid AK The SS is authorized to participate in that particular SA, that is, the BS continues to provide fresh keying material during re key cycles

The parent Authorization state machine stops all of its child TEK state machines when the SS receives from the BS an Authorization Reject during a reauthorization cycle. Individual TEK state machines can be started or stopped during a reauthorization cycle if an SS’s Static SAID authorizations changed between successive re-authorizations. Communication between Authorization and TEK state machines occurs through the passing of events and protocol messaging. The Authorization state machine generates events (i.e., Stop, Authorized, Authorization Pending, and Authorization Complete ones) that are targeted at its child TEK state machines. TEK state machines do not target events at their parent Authorization state machine. The

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TEK state machine affects the Authorization state machine indirectly through the messaging a BS sends in response to an SS’s requests: a BS may respond to a TEK machine’s Key Requests with a failure response (i.e., Authorization Invalid message) to be handled by the Authorization state machine.

TEK Exchange: For Mesh Mode Upon achieving authorization, a Node starts for each Neighbour a separate TEK state machine for each of the SAIDs identified in the Authorization Reply message. Each TEK state machine operating within the Node is responsible for managing the keying material associated with its respective SAID. The Node is responsible for maintaining the TEKs between itself and all nodes it initiates TEK exchange with. Its TEK state machines periodically send Key Request messages to the Neighbours of the node, requesting a refresh of keying material for their respective SAIDs. The Neighbour replies to a Key Request with a Key Reply message, containing the BS’s active keying material for a specific SAID. The TEK in the Key Reply is encrypted, using the node’s public key found in the SS-Certificate attribute. The node maintains two active sets of keying material per SAID per neighbour at all times. The lifetimes of the two generations overlap such that each generation becomes active halfway through the life of its predecessor and expires halfway through the life of its successor. A neighbour includes in its Key Replies both of an SAID’s active generations of keying material. The Key Reply provides the requesting Node, in addition to the TEK, the remaining lifetime of each of the two sets of keying material. The receiving Node uses these remaining lifetimes to estimate when the Neighbour invalidates a particular TEK, and therefore when to schedule future Key Requests. The transmit regime between the initiating Node and the Neighbour one provides for seamless key transition.

State Machines for Key Exchange The request, generation and distribution of the encryption keys are complex processes that involve many states, messages, events, parameters and actions. State machine diagrams make this process simplified and systematic. Many different state machines are needed to describe the generation and distribution of the encryption keys. In the next section we describe the state machines for AK and TEK.

Authorization State Machine The Authorization state machine consists of six states and eight distinct events (including receipt of messages) that can trigger state transitions, Fig. 5.12. The

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Start

Auth Reject Wait

Silent

Auth Reject/

Communication Establised Auth Info,Auth Request

Perm Auth Reject/ Auth Reject / [TEK] stop

Auth Wait

Timeout/Auth Info, Auth Request Auth Reply/ [TEK] Authorised

Authorised

Perm Auth Reject / [TEK] stop

Reauth/ Auth Request

Auth Invalid / [TEK] Auth Pend

Auth Invalid/Auth Request, [TEK] Auth Pend Auth Grace Timeout/ Auth Request

Auth Replyo/ [TEK] Authorised,[TEK] Auth Comp,[TEK]Stop

Reauth Wait

Timeout /Auth Request

Fig. 5.12 Authorization state machine flow diagram

Authorization finite state machine (FSM) is presented below in a graphical format, as a state flow model and in a tabular format, as a state transition matrix. The state flow diagram depicts the protocol messages transmitted and internal events generated for each of the model’s state transitions; however, the diagram does not indicate additional internal actions, such as the clearing or starting of timers that accompany the specific state transitions. Accompanying the state transition matrix is a detailed description of the specific actions accompanying each state transition; the state transition matrix shall be used as the definitive specification of protocol actions associated with each state transition. The legends from Table 5.7 apply to the Authorization State Machine flow. The Authorization state transition matrix presented in Table 5.7 lists the six Authorization machine states in the topmost row and the eight Authorization machine events (includes message receipts) in the leftmost column. Any cell within the matrix represents a specific combination of state and event, with the next state (the state transitioned to) displayed within the cell. For example, cell 4-B represents the receipt of an Authorization Reply (Auth Reply) message when in the Authorize Wait (Auth Wait) state. Within cell 4-B is the name of the next state, “Authorized”. Thus, when an SS’s Authorization state machine is in the Auth Wait state and an Auth Reply message is received, the Authorization state machine will transition to the Authorized state. A shaded cell within the state transition matrix implies that either the specific event cannot or should not occur within that state. If the event does occur, the state machine should ignore it. For example, if an Auth Reply message arrives when in the Authorized state, that message should be ignored. The SS may, however, in response to an improper event, log its occurrence, generate an SNMP event, or take some other vendor-defined action. These actions,

234 Table 5.7 Authorization FSM state transition matrix State (A) (B) (C) Event or Rcvd Start Auth Wait Authorized Message (1) Communication Auth Wait Established (2) Auth Reject Auth Reject Wait (3) Perm Auth Silent Reject (4) Auth Reply Authorized (5) Timeout Auth Wait (6) Auth Grace Timeout (7) Auth Invalid (8) Reauth

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(D) (E) Reauth Wait Auth Reject Wait

(F) Silent

Auth Reject Wait Silent Authorized Reauth Wait Start Reauth Wait Reauth Wait Reauth Wait Reauth Wait

however, are not specified within the context of the Authorization state machine, which simply ignores improper events. The description of the FSM states, messages, events and parameters follows [12]: 1. States (a) Start – This is the initial state of the FSM. No resources are assigned to or used by the FSM in this state, for example, all timers are off, and no processing is scheduled. (b) Authorize Wait (Auth Wait) – The SS has received the “Communication Established” event indicating that it has completed basic capabilities negotiation with the BS. In response to receiving the event, the SS has sent both an Authentication Information and an Auth Request message to the BS and is waiting for the reply. (c) Authorized – The SS has received an Auth Reply message that contains a list of valid SAIDs for this SS. At this point, the SS has a valid AK and SAID list. Transition into this state triggers the creation of one TEK FSM for each of the SS’s privacy-enabled SAIDs. (d) Reauthorize Wait (Reauth Wait) – The SS has an outstanding reauthorization request. The SS was either about to expire (see Authorization Grace Time in Table 343) its current authorization or received an indication (an Authorization Invalid message from the BS) that its authorization is no longer valid. The SS sent an Auth Request message to the BS and is waiting for a response. (e) Authorize Reject Wait (Auth Reject Wait) – The SS received an Authorization Reject (Auth Reject) message in response to its last Auth Request. The Auth Reject’s error code indicated the error was not of a permanent nature. In response to receiving this reject message, the SS set a timer and transitioned to the Auth Reject Wait state. The SS remains in this state until the timer expires.

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(f) Silent – The SS received an Auth Reject message in response to its last Auth Request. The Auth Reject’s error code indicated the error was of a permanent nature. This triggers a transition to the Silent state, where the SS is not permitted to pass subscriber traffic. The SS shall, however, respond to management messages from the BS issuing the Perm Auth Reject. 2. Messages (a) Authorization Request (Auth Request) – Request an AK and list of authorized SAIDs. It is sent from SS to BS. (b) Authorization Reply (Auth Reply) – Receive an AK and list of authorized, static SAIDs. Sent from BS to SS. The AK is encrypted with the SS’s public key; (c) Authorization Reject (Auth Reject) – Attempt to authorize was rejected. Sent from the BS to the SS. (d) Authorization Invalid (Auth Invalid) – The BS may send an Authorization Invalid message to a client SS as follows: l l

An unsolicited indication or A response to a message received from that SS

In either case, the Auth Invalid message instructs the receiving SS to re-authorize with its BS. The BS responds to a Key Request with an Auth Invalid message if (1) the BS does not recognize the SS as being authorized (i.e., no valid AK associated with SS) or (2) verification of the Key Request’s keyed message digest (in HMAC-Digest attribute) failed. Note that the Authorization Invalid event, referenced in both the state flow diagram and the state transition matrix, signifies either the receipt of an Auth Invalid message or an internally generated event. (e) Authentication Information (Auth Info) – The Auth Info message contains the SS manufacturer’s X.509 Certificate, issued by an external authority. The Auth Info message is strictly an informative message the SS sends to the BS; with it, a BS may dynamically learn the manufacturer certificate of client SS. Alternatively, a BS may require out-of-band configuration of its list of manufacturer certificates. 3. Events (a) Communication Established – The Authorization state machine generates this event upon entering the Start state if the MAC has completed basic capabilities negotiation. If the basic capabilities negotiation is not complete, the SS sends a Communication Established event to the Authorization FSM upon completing basic capabilities negotiation. The Communication Established event triggers the SS to begin the process of getting its AK and TEKs. (b) Timeout – A retransmission or wait timer timed out. Generally a request is resent. (c) Authorization Grace Timeout (Auth Grace Timeout) – The Authorization Grace timer timed out. This timer fires a configurable amount of time (the Authorization Grace Time) before the current authorization is supposed

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to expire, signalling the SS to reauthorize before its authorization actually expires. The Authorization Grace Time takes the default value or may be specified in a configuration setting within the Auth Reply message. (d) Reauthorize (Reauth) – SS’s set of authorized static SAIDs may have changed. This event is generated in response to an SNMP set and meant to trigger a reauthorization cycle. (e) Authorization Invalid (Auth Invalid) – This event is internally generated by the SS when there is a failure authenticating a Key Reply or Key Reject message, or externally generated by the receipt of an Auth Invalid message, sent from the BS to the SS. A BS responds to a Key Request with an Auth Invalid if verification of the request’s message authentication code fails. Both cases indicate BS and SS have lost AK synchronization. A BS may also send to an SS an unsolicited Auth Invalid message, forcing an Auth Invalid event. (f) Permanent Authorization Reject (Perm Auth Reject) – The SS receives an Auth Reject in response to an Auth Request. The error code in the Auth Reject indicates the error is of a permanent nature. What is interpreted as a permanent error is subject to administrative control within the BS. Auth Request processing errors that can be interpreted as permanent error conditions include the following: l

l l l

l

Unknown manufacturer (do not have CA certificate of the issuer of the SS Certificate) Invalid signature on SS certificate ASN.1 parsing failure Inconsistencies between data in the certificate and data in accompanying PKM data attributes Incompatible security capabilities

When an SS receives an Auth Reject indicating a permanent failure condition, the Authorization State machine moves into a Silent state, where the SS is not permitted to pass subscriber traffic. The SS shall, however, respond to management messages from the BS issuing the Perm Auth Reject. The SS shall also issue an SNMP Trap upon entering the Silent state. (g) Authorization Reject (Auth Reject) – The SS receives an Auth Reject in response to an Auth Request. The error code in the Auth Reject does not indicate the failure was due to a permanent error condition. As a result, the SS’s Authorization state machine shall set a wait timer and transition into the Auth Reject Wait State. The SS shall remain in this state until the timer expires, at which time it shall reattempt authorization. (h) Authorization Complete (Auth Comp) – Sent by the Authorization FSM to a TEK FSM in the Operational Reauthorize Wait (Op Reauth Wait) or Rekey Reauthorize Wait (Rekey Reauth Wait) states to clear the wait state begun by a TEK FSM Authorization Pending event.

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4. Parameters All configuration parameter values take the default values from Table 5.7 or may be specified in the Auth Reply message. (a) Authorize Wait Timeout (Auth Wait Timeout) – Timeout period between sending Authorization Request messages from Auth Wait state. (b) Authorization Grace Timeout (Auth Grace Timeout) – Amount of time before authorization is scheduled to expire that the SS starts reauthorization. (c) Authorize Reject Wait Timeout (Auth Reject Wait Timeout) – Amount of time an SS’s Authorization FSM remains in the Auth Reject Wait state before transitioning to the Start state.

5.5.1.4

TEK State Machine

The TEK state machine consists of six states and nine events (including receipt of messages) that can trigger state transitions. Like the Authorization state machine, the TEK state machine is presented in both a state flow diagram and a state transition matrix. As was the case for the Authorization state machine, the state transition matrix shall be used as the definitive specification of protocol actions associated with each state transition. Shaded states (Operational, Rekey Wait, and Rekey Reauthorize Wait) have valid keying material and encrypted traffic can be passed. The Authorization state machine starts an independent TEK state machine for each of its authorized SAIDs. The BS maintains two active TEKs per SAID. The BS includes in its Key Replies both of these TEKs, along with their remaining lifetimes. The BS encrypts downlink traffic with the older of its two TEKs and decrypts uplink traffic with either the older or newer TEK, depending upon which of the two keys the SS was using at the time. The SS encrypts uplink traffic with the newer of its two TEKs and decrypts downlink traffic with either the older or newer TEK, depending upon which of the two keys the BS was using at the time. Through operation of a TEK state machine, the SS attempts to keep its copies of an SAID’s TEKs synchronized with those of its BS. A TEK state machine issues Key Requests to refresh copies of its SAID’s keying material soon after the scheduled expiration time of the older of its two TEKs and before the expiration of its newer TEK. To accommodate for SS/BS clock skew and other system processing and transmission delays, the SS schedules its Key Requests a configurable number of seconds before the newer TEK’s estimated expiration in the BS. With the receipt of the Key Reply, the SS shall always update its records with the TEK Parameters from both TEKs contained in the Key Reply message. The SS’s scheduling of its key refreshes in conjunction with its management of an SA’s active TEKs. The six states in TEK state machine are Start, Op Wait, Op Reauth Wait, Operational, Rekey Wait, and Rekey Reauth Wait, Table 5.8. Their description follows:

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Table 5.8 Table Authorization FSM state transition matrix State Event or (A) (B) (C) (D) Rcvd Message Start Op Wait Op Reauth Op Wait (1) Stop (2) Authorized Op Wait (3) Auth Pend

(4) Auth Comp (5) TEK Invalid (6) Timeout (7) TEK Refresh Timeout (8) Key Reply (9) Key Reject

Start

Start

Start

Op Reauth Wait

(E) Rekey Wait Start

(F) Rekey Reauth Wait Start

Rekey Reauth Wait Op Wait Op Wait

Op Wait

Op Wait

Rekey Wait Op Reauth Wait

Rekey Wait Rekey Wait

Operational Start

Operational Start

1. Start – This is the initial state of the FSM. No resources are assigned to or used by the FSM in this state – for example, all timers are off, and no processing is scheduled. 2. Operational Wait (Op Wait) – The TEK state machine has sent its initial request (Key Request) for its SAID’s keying material (TEK and CBC initialization vector), and is waiting for a reply from the BS. 3. Operational Reauthorize Wait (Op Reauth Wait) – The wait state the TEK state machine is placed in if it does not have valid keying material while the Authorization state machine is in the middle of a reauthorization cycle. 4. Operational – The SS has valid keying material for the associated SAID. 5. Rekey Wait – The TEK Refresh Timer has expired and the SS has requested a key update for this SAID. Note that the newer of its two TEKs has not expired and can still be used for both encrypting and decrypting data traffic. 6. Rekey Reauthorize Wait (Rekey Reauth Wait) – The wait state the TEK state machine is placed in if the TEK state machine has valid traffic keying material, has an outstanding request for the latest keying material, and the Authorization state machine initiates a reauthorization cycle.

5.5.1.5

TEK Exchange Overview for PtM Topology

If the SS and BS decide “No authorization”, as their authorization policy, the SS and BS shall perform neither SA-TEK handshake nor Key Request/Key Reply

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handshake. In this case, target SAID value, which may be included in DSA-REQ/ RSP messages, shall be Null SAID. Upon achieving authorization, an SS starts a separate TEK state machine for each of the SAIDs identified in the Authorization Reply or PKMv2 SA-TEK-RSP message, if data traffic encryption is provisioned for one or more service flows. Each TEK state machine operating within the SS is responsible for managing the keying material associated with its respective SAID. TEK state machines periodically send Key Request messages to the BS, requesting a refresh of keying material for their respective SAIDs. The BS responds to a Key Request with a Key Reply message, containing the BS’s active keying material for a specific SAID. TEKs and KEKs may be either 64 bits or 128 bits long. SAs employing any ciphersuite with a basic block size of 128 bits shall use 128-bit TEKs and KEKs. Otherwise 64-bit TEKs and KEKs shall be used. The name TEK-64 is used to denote a 64-bit TEK and TEK-128 is used to denote a 128-bit TEK. Similarly, KEK-64 is used to denote a 64-bit KEK and KEK-128 is used to denote a 128-bit KEK. For SAs using a ciphersuite employing DES-CBC, the TEK in the Key Reply is triple DES (3-DES) (encrypt-decrypt-encrypt or EDE mode) encrypted, using a two-key, 3-DES KEK derived from the AK. For SAs using a ciphersuite employing 128 bits keys, such as AES-CCM mode, the TEK in the key Reply is AES encrypted using a 128-bit key derived from the AK and a 128-bit block size. Note that at all times the BS maintains two diversity sets of keying material per SAID. The lifetimes of the two generations overlap such that each generation becomes active halfway through the life of it predecessor and expires halfway through the life of its successor. A BS includes in its Key Replies both of an SAID’s active generations of keying material. For SAs using a ciphersuite employing CBC mode encryption the Key Reply provides the requesting SS, in addition to the TEK and CBC initialization vector, the remaining lifetime of each of the two sets of keying material. For SAs using a ciphersuite employing AES-CCM mode, the Key Reply provides the requesting SS, in addition to the TEK, the remaining lifetime of each of the two sets of keying material. The receiving SS uses these remaining lifetimes to estimate when the BS will invalidate a particular TEK, and therefore when to schedule future Key Requests such that the SS requests and receives new keying material (before the BS expires the keying material the SS currently holds). For AES-CCM mode, when more than half the available PN numbers in the 31-bit PN number space are exhausted, the SS shall schedule a future Key Request in the same fashion as if the key lifetime was approaching expiry. The operation of the TEK state machine’s Key Request scheduling algorithm, combined with the BS’s regimen for updating and using an SAID’s keying materia ensures that the SS will be able to continually exchange encrypted traffic with the BS (Table 5.9).

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Table 5.9 Different keys used in IEEE 802.16 Key Generated Used for by Authentication BS Generating KEKs Calculating Key (AK) HMAC digests Verifying received HMAC digests Key Encryption BS, SS Encrypting TEK for Key (KEK) transmission (BS) Decrypting TEK for use (SS) BS Encrypting data traffic Traffic Encryption Key (TEK)

5.6

Lifetime

Algorithm

1–70 days

3-DES SHA-1

Same as AK

3-DES

30 min to 7 days

DES CBC

Key Management

Key management is handled by the authorisation and TEK state machines in the SS. The authorization SA has a 60-bit authorization key (AK) and uses a 4-bit quantity to identify the AK. It uses an X.509 certificate to identify SS. The default lifetime of AK is 7 days and it could be set from 1 to 70 days.

5.6.1

Authorisation Key (AK) Management

The BS is responsible for maintaining keying information for all SAs. This section describes a mechanism for synchronizing this keying information between the BS and its client SS. After an SS completes basic capabilities negotiation with the BS, it sends an Authorisation Request (Auth Request) message. When the BS receives an unauthorised SS request it initiates the activation of a new AK. This is send through the Authorisation Reply message. This AK remains active until it expires according to its predefined AK Lifetime which is a BS system configuration parameter. In case the SS fails to reauthorize before the expiration of its current AK, the BS does not hold active AKs for the SS and SS is declared as unauthorized. The BS therefore removes all associated TEKs from its keying tables for such an unauthorized SS. Using AK transition period the BS is always prepared to send an AK to an SS upon request. The SS is responsible for requesting authorisation with its BS and maintaining an active AK. An SS refreshes its AK by reissuing an Authorisation Request to the BS. Two simultaneous AKs for different clients are handled by the BS. The BS has two active AKs during an AK transition period; the two active keys have overlapping lifetimes. An AK transition period begins when the BS receives an Auth

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Request message from an SS and the BS has a single active AK for that SS as shown in the figure. In response to this Auth Request, the BS activates a second AK. This AK has a key sequence number one larger than that of the existing AK and is sent back to the requesting SS along with Auth Reply message. The active lifetime of the second AK is set by the BS as the remaining lifetime of the first AK plus the predefined AK Lifetime. The second AK therefore remains active for one AK Lifetime beyond the expiration of the first, “older” key. The key transition period ends with the expiration of the older key. As long as the BS is holding two active AKs and is in the midst of an SS’s AK transition period, it responses to Auth Request messages with the newer of the two active keys. When the older key expires, Auth Request triggers the activation of a new AK, and the start of a new key transition period.

5.6.1.1

BS Usage of AK

The BS uses keying material derived from the SS’s AK for the following: l l

l

Verifying the HMAC-Digests in Key Request messages received from that SS Calculating the HMAC-Digests it writes into Key Reply, Key Reject, and TEK Invalid messages sent to that SS Encrypting the TEK in the Key Reply messages it sends to that SS

HMAC_KEY_U derived from one of the SS’s active AKs is used to verify the HMAC-Digest in Key Request messages received from the SS. The AK Key Sequence Number accompanying each Key Request message allows the BS to determine which HMAC_KEY_U was used to authenticate the message. If the AK Key Sequence Number indicates the newer of the two AKs, the BS shall identify this as an implicit acknowledgment that the SS has obtained the newer of the SS’s two active AKs. BS shall use an HMAC_KEY_D derived from the active AK selected above when calculating HMAC-Digests in Key Reply, Key Reject, and TEK Invalid message. When sending Key Reply, Key Reject, or TEK Invalid messages within a key transition period, if the newer key has been implicitly acknowledged, the BS shall use the newer of the two active AKs. If the newer key has not been implicitly acknowledged, the BS shall use the older of the two active AKs to derive the KEK and the HMAC_KEY_D. The BS shall use a KEK derived from an active AK when encrypting the TEK in the Key Reply messages. The right-hand side of Fig. 5.13 shows the BS’s policy regarding its use of AKs, where the shaded portion of an AK’s lifetime indicates the time period during which that AK shall be used to derive the HMAC_KEY_U, HMAC_KEY_D, and KEK. For calculating the HMAC-Digest in the HMAC Tuple attribute, the BS shall use the HMAC_KEY_U and HMAC_KEY_D derived from one of the active AKs. For signing messages, if the newer AK has been implicitly acknowledged, the BS shall

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BS Authenticat

ion Informat ion Authorizatio n Request

K 0}

n Reply {A

Authorizatio

Authorizatio

x

n Request

AK0 Active Lifetime AK Grace time

AK0 Lifetime

K 1}

n Reply {A

Authorizatio

a

Key Reque

st {AK } 1 b c

y AK1 Active Lifetime

Authorizatio n Request Authorizatio n (re)Reque st

AK1 Lifetime d

K 2}

n Reply {A Authorizatio

AK Grace time

e

Key Reque

st {AK } 2 f AK2 Lifetime

AK2 Active Lifetime

switch over point AK used to en/decrypt TEK

Fig. 5.13 AK management in BS and SS (adapted from [3])

use the newer of the two active AKs to derive the HMAC_KEY_D. If the newer key has not been implicitly acknowledged, the BS shall use the older of the two active AKs to derive the HMAC_KEY_D. The HMAC Key Sequence Number in the HMAC Tuple, equal to the AK’s sequence number from which the HMAC_KEY_D was derived, enables the SS to correctly determine which HMAC_KEY_D was used for message authentication.

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When receiving messages containing the HMAC Tuple attribute, the BS shall use the HMAC_KEY_U indicated by the HMAC Key Sequence Number to authenticate the messages.

5.6.1.2

TEK Lifetime

The BS maintains two sets of active TEKs (and their associated Initialization Vectors, or IVs) per SAID, corresponding to two successive generations of keying material. The two generations of TEKs shall have overlapping lifetimes determined by TEK Lifetime, a predefined BS system configuration parameter. The newer TEK shall have a key sequence number one greater (modulo 4) than that of the older TEK. Each TEK becomes active halfway through the lifetime of its predecessor and expires halfway through the lifetime of its successor. Once a TEK’s lifetime expires, the TEK becomes inactive and shall no longer be used. The Key Reply messages sent by a BS contain TEK parameters for the two active TEKs. The TEKs’ active lifetimes that a BS reports in a Key Reply message shall reflect, as accurately as an implementation permits, the remaining lifetimes of these TEKs at the time the Key Reply message is sent. 5.6.1.3

BS Usage of TEK

The BS transitions between the two active TEKs differently, depending on whether the TEK is used for downlink or uplink traffic. For each of its SAIDs, the BS shall transition between active TEKs according to the following rules: l

l

At expiration of the older TEK, the BS shall immediately transition to using the newer TEK for encryption. The uplink transition period begins from the time the BS sends the newer TEK in a Key Reply message and concludes once the older TEK expires.

It is the responsibility of the SS to update its keys in a timely fashion; the BS shall transition to a new downlink encryption key regardless of whether a client SS has retrieved a copy of that TEK. The BS uses the two active TEKs differently, depending on whether the TEK is used for downlink or uplink traffic. For each of its SAIDs, the BS shall use the two active TEKs according to the following rules: l

l

The BS shall use the older of the two active TEKs for encrypting downlink traffic. The BS shall be able to decrypt uplink traffic using either the older or newer TEK.

Note that the BS encrypts with a given TEK for only the second half of that TEK’s total lifetime. The BS is able, however, to decrypt with a TEK for the TEK’s entire lifetime.

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Node Re-Authorization in Mesh Mode During Normal Operation

When re-authorizing with the network, the re-authorizing node shall tunnel the authorization messages.

5.6.2

SS Key Usage

For sustaining authorisation the SS is responsible for maintaining an active AK with its BS. An SS uses its two most recently obtained AKs according to the following manner.

5.6.2.1

SS Reauthorization

AKs are refreshed regularly as they have a limited lifetime. An SS refreshes its AK by reissuing an Auth Request to the BS. The Authorization State Machine manages the scheduling of Auth Requests for refreshing AKs. An SS’s Authorization state machine schedules the beginning of reauthorization a configurable duration of time, the Authorization Grace Time, before the SS’s latest AK is scheduled to expire. The Authorization Grace Time is configured to provide an SS with an authorization retry period that is sufficiently long to allow for system delays and provide adequate time for the SS to successfully complete an Authorization exchange before the expiration of its most current AK.

5.6.2.2

SS Usage of AK

An SS shall use the HMAC_KEY_U derived from the newer of its two most recent AKs when calculating the HMAC-Digests it attaches to Key Request messages. The SS shall be able to use the HMAC_KEY_D derived from either of its two most recent AKs to authenticate Key Reply, Key Reject, and TEK Reject messages. The SS shall be able to decrypt an encrypted TEK in a Key Reply message with the KEK derived from either of its two most recent AKs. The SS shall use the accompanying AK Key Sequence Number to determine which set of keying material to use. The left-hand side of Fig. 5.14 illustrates an SS’s maintenance and usage of its AKs, where the shaded portion of an AK’s lifetime indicates the time period during which that AK shall be used to decrypt TEKs. Even though it is not part of the message exchange, Fig. 5.14 also shows the implicit acknowledgment of the reception of a new AK via the transmission of a Key Request message using the key sequence of the new AK. An SS shall use the HMAC_KEY_U derived from the newer of its two most recent AKs when calculating the HMAC-Digests of the HMAC Tuple attribute.

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SS

BS

Key Request

EK0,TEK1}

Key Reply {T

TEK0 Active Lifetime

TEK0 Active Lifetime TEK1 Active Lifetime

TEK1 Active Lifetime

Key Reques

t

TEK Grace Time

EK0,TEK1}

Key Reply {T

TEK2 Active Lifetime

TEK2 Active Lifetime

TEK Grace time

TEK3 Active TEK Lifetime Grace time TEK0 Active Lifetime

Key Req

uest

Key (re)

Request TEK3 Active Lifetime

EK0,TEK1}

Key Reply {T

Key Request Key Reply {TEK0,TEK1}

TEK0 Active Lifetime TEK1 Active Lifetime

Switch over point TEK used for encryption

Fig. 5.14 TEK management in BS and SS (adapted from [3])

5.6.2.3

SS Usage of TEK

An SS shall be capable of maintaining two successive sets of traffic keying material per authorized SAID. Through operation of its TEK state machines, an SS shall request a new set of traffic keying material a configurable amount of time, the TEK Grace Time [see points (x) and (y) in Figure 134], before the SS’s latest TEK is scheduled to expire.

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For each of its authorized SAIDs, the SS: l l

Shall use the newer of its two TEKs to encrypt uplink traffic Shall be able to decrypt downlink traffic encrypted with either of the TEKs

The left-hand side of Fig. 5.14 illustrates the SS’s maintenance and usage of an SA’s TEKs, where the shaded portion of a TEK’s lifetime indicates the time period during which that TEK shall be used to encrypt MAC PDU payloads.

5.6.3

PKM Version 2

The PKMv1 supports only the device authentication and had many critical drawbacks. Therefore IEEE 802.16e released the second version of Privacy and Key Management (PKM) protocol called PKMv2. PKMv2 aims to fix the bugs in the former version PKMv1.The new released version of the PKM protocol provides mechanisms for the double user/device authentication. It has many security features like message authentication codes, key ids, certificates, etc. The IEEE 802.16e-2005 standard supports PKMv2 which allows for three types of authentication: l l l

RSA based authentication EAP based authentication (optional) RSA based authentication followed by EAP authentication

Compared to PKMV1 which only supported RSA for Authentication/Authorisation, PKMv2 supports EAP also. The PKMv2 comprises of two main parts, an Authentication/Authorization protocol to establish a shared Authorization Key (AK), and a 3-Way Security Association (SA) Traffic Encryption Key (TEK) Handshake. As shown in the Fig. 5.15, the first part of the PKMv2 protocol an Authorization Key (AK) is generated using RSA or EAP or both. After that, each party (SS as well as BS generates a Key Encryption Key (KEK) using their AKs. KEKs are used in AK Generation is established using Either EAP or RSA or both

AK also KEKs and H-C/MAC keys are derived from AK

PKMv2 SA-TEK 3-Way Handshake

TEKs

Fig. 5.15 PKMv2 protocol

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encrypting and distributing Traffic Encryption Keys (TEK), TEKs can be taken as session keys, while AK/KEK are long term keys. The important part of PKMv2 is the SA-TEK 3-Way Handshake. Through SATEK 3-Way Handshake SS (here MS, used interchangeably in the entire text) and BS exchange TEKs. In the handshake, TEKs are encrypted by KEKs. The EAP protocol can support a large set of methods, such as EAP-TLS, EAP-AKA and EAP-TTLS. PKMv2 uses a slightly different key hierarchy. This is due to the fact that two authentication systems are used one based on RSA and the other on EAP. TEKs are derived in the same way as in PKMv1 except that their names are different. The RSA-generated key is called pre-primary AK (pre-PAK) and the one generated through EAP based authentication is called Master Session Key(MSK) The general procedure to derive Authentication Key (AK) depends on authentication scheme used as listed below: l

If RSA-based authorization then AK = Dot16KDF (PAK, SS MAC address|BSID|PAK|“AK”,160)

l

If EAP-based authorization then AK = Dot16KDF (PMK, SS MAC address|BSID|“AK”, 160)

l

If RSA-based and EAP-based authorization then, AK=Dot16KDF (PAK xor PMK, SS MAC address|BSID|PAK|“AK”,160)

l

If EAP-in-EAP then, AK = Dot16KDF (PMK xor PMK2, SS MAC address | BSID | “AK”, 160) Table 5.10 presents a summary of the comparisons between PKMv1 and PKMv2.

5.7

Network Aspects of Security

Access control mechanism ensures that only valid users are allowed access to the network. Figure 5.16 shows a typical access control architecture. Table 5.10 Comparison of PKMv1 and PKMv2 PKMv1 Authentication direction Unilateral Authentication method RSA based TEK encryption 3DES, AES, RSA Authentication object Keys involved in authorization Data encryption Data integrity

MS/SS AK No encryption, DES, AES-CCM No MAC, HMAC

PKMv2 Bilateral RSA based, EAP based 3DES, AES, RSA AES-ECB/ KEY-WRAP MS/SS, BS RSA based: Pre-PAK,AK EAP based: MSK, PMK, AK No encryption, DES, 3DES, AES-CCM/CBC/CTR No MAC, HMAC/CMAC

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EAP

WiMAX Link

AAA-RADIUS/DIAMETER

user1

user2

Authenticator (Network Access Server)

IP cloud

Authentication Server

user3

Fig. 5.16 Access control architecture and authentication

The authentication is based on a three-party model: the supplicant, which requires access; the authenticator, which grants access; and the authentication server, which gives permission. Thus the three elements make an access control mechanism: l

l l

User/Client/Supplicant – The party in the authentication process that will provide its identity, and evidence for it and, as a result, will be authenticated. This party may also be referred to as the authenticating user, or the client. Authenticator – is the party that controls the access gate. Authentication server – is the entity that validates client credentials and determines if the client should be allowed access. The authenticator itself does not know whether an entity can be allowed access, it’s the authentication server who decides it.

5.7.1

Radius

Remote Authentication Dial-In User Service (RADIUS) is widely used standard for communication between the authenticator and authentication server. It has client/ server architecture and utilizes UDP messages .The authentication server is also the RADIUS server whereas the authenticator acts as RADIUS client. RADIUS is an IETF standard [17, 18]. In addition to authentication, RADIUS also supports authorization and accounting functions [18]. The authentication, authorization and accounting functions are collectively referred to as AAA functions. IETF has also developed a new standard for AAA functions named as DIAMETER [19] which tries to overcome the deficiencies in RADIUS. DIAMETER has higher reliability, security, and roaming support compared to RADIUS [18].

5.7.2

Extensible Authentication Protocol (EAP)

EAP is flexible framework defined by IETF (RFC 3748) which allows complex authentication protocols to be exchanged between the authenticator and the end user [16], Fig. 5.16.

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EAP was introduced which can offer an authentication scheme to prevent the above mentioned problems. It integrates different authentication methods to match the nature of the communication channel. These methods are advised by IEEE including EAP-PKM, EAP-MD5, EAP-OTP, EAP-GTC, EAP-TLS, EAP-SIM and EAP-AKA. In mobile WiMAX, authentication is achieved using one of several possible EAP methods. Table 5.11 presents a list of the Wireless network security concerns and their solutions for WIMAX. Table 5.12 presents the difference between the security aspects in IEEE 802.16d and 802.16e. Table 5.11 Wireless network security concerns and their solutions for WIMAX Concern for Security Concern Purpose Implementation of the stakeholder respective security concern in IEEE 802.16 Network User Privacy Protect from interception RSA encryption, EAP-TLS, concern and eavesdropping PKM protocol Message Provides integrity of the X.509 Authentication message and sender authentication RSA encryption, EAP-TLS, Data Integrity Protect user data from PKM protocol being tampered in transit Access to services Allow only the user with X.509, EAP the right credentials service access Correct accounting Accuracy and efficiency AAA architecture of accounting User authentication Is the user who he says X.509, EAP-TTLS Network he is? Operator Concerns Device Is the device the correct X.509, EAP-TTLS authentication device? RSA, EAP, PKMv2 Authorization Is the user authorized to protocol receive a particular service? Access control Is the user authorized to RSA, EAP, PKMv2 receive this service? protocol Correct accounting Accuracy and efficiency AAA architecture of accounting

Table 5.12 Difference between IEEE 802.16d and 802.16e IEEE 802.16d PKM version PKM v1 Supported Mode Unicast Authorization method X.509 cert Authentication Unilateral Security algorithms RSA/DES/3DES/AES

IEEE 802.16e PKM v1/PKM v2 Unicast/Multicast/Broadcast X.509 cert/EAP Mutual/Unilateral RSA/DES/3DES/AES

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Conclusions

This Chapter starts by addressing aspects of the security architecture for IEEE 802.16, including its functions, secure encapsulation of MPDUs, encryption algorithms, data encryption methodologies (with DES in CBC mode, AES in CCM mode and the ones for IEEE 802.11e). Then, the authentication protocol (RSA and PKM EAP) was addressed and the PKM protocol presents. After describing the PKM protocol MAC management messages, addresses key management was discussed. The network aspects of security were finally presented, including RADIUS and Extensible Authentication Protocol (EAP).

References 1. C. Eklund, R.B. Marks, K.L. Stanwood, S. Wang, IEEE Standard 802.16: A Technical Overview of the WirelessMAN Air Interface for Broadband Wireless Access (June 2002) 2. D. Johnston, J. Walker, Overview of IEEE 802.16 security. IEEE Secur. Privacy Mag. 2(3), 40–48 (2004) 3. IEEE Std 802.16e-2005, 2006. Standard for Local and metropolitan area networks Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems Amendment 2: Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands and Corrigendum 1, IEEE, New York, USA 4. K. Pahlavan, P. Krishnamurthy, Principles of Wireless Networks: A unified Approach (Pearson Education, Prentice Hall PTR, Upper Saddle River, NJ, 2002) 5. W. Stalling, Cryptography and Network Security: Principles and Practices, 3rd edn. (Pearson Education, Prentice Hall PTR, Upper Saddle River, NJ, 2003) 6. PKCS#1 v2.0,RSA Cryptography Standard, RSA Laboratories (Oct 1998) 7. National Technical Information Service (NTIS), FIPS 46-3, Data Encryption Standard (DES) (Oct 1999). http://www.ntis.gov/ 8. National Technical Information Service (NTIS), FIPS 197, Advanced Encryption Standard (AES) (Nov 2001) 9. National Technical Information Service (NTIS), FIPS 198, The key Hash Message Authentication Code (HMAC) (Mar 2002) 10. H. Krawczyk, M. Bellare, R. Canetti, IETF RFC. HMAC: Keyed-Hashing for Message Authentication (Feb 1997) 11. J.H. Song et al., IETF RFC 4493. The AES-CMAC Algorithm (June 2006) 12. IEEE 802.16 Broadband Wireless Access Working Group. Mapping of authentication Rejection from PKMv1 to PKMv2, IEEE (April 2008). http://www.ieee802.org/16/maint/ 13. FIPS 74, Guidelines for Implementing and Using the NBS Data Encryption Standard (Apr 1981) 14. FIPS 81, DES Modes of Operation (Dec 1980) 15. IETF RFC 3610, Counter with CBC-MAC (CCM) (D. Whiting et al., Sept 2003) 16. M. Barbeau, WiMax/802.16 Threat Analysis, School of Computer Science, Carleton University, Ottawa, Canada (October 2005) 17. C. Rigney et al., Remote dial-in user service (RADIUS). IETF RFC 2865 (June 2000) 18. A. Ghost, R. Muhamed, J.G. Andrews, Fundamentals of WiMAX: Understanding Broadband Wireless Networking (Prentice Hall, Upper Saddle River, NJ, 2007) 19. P. Calhoun et al., Diameter in use. IETF RFC 3588 (Sept 2003) 20. S. Xu, M. Matthews, C.-T. Huang, Security issues in privacy and key management protocols of IEEE 802.16, in Proceedings of the 44th ACM Southeast Conference (ACMSE 2006) (Mar 2006)

Chapter 6

Mobility Management Architecture for WiMAX Networks Susana Sargento, Pedro Neves, Ricardo Matos, Marı´lia Curado, Bruno Sousa, Kostas Pentikousis, and Giada Landi

Abstract Although WiMAX, based on the IEEE 802.16 family of standards, has emerged as one of the major candidates for next generation networks, it is also clear that in the near future, the combination of several technologies will be required. In this sense, the support of mobility in heterogeneous environments, addressing broadband wireless, is one of the main requirements in next generation networks. This chapter presents an architecture based on the recently standardized IEEE 802.21 framework, integrating both mobility and Quality of Service (QoS) mechanisms, and accommodating different wired and wireless technologies, such as WiMAX, Wi-Fi, DVB, and UMTS. This architecture supports seamless mobility in broadband wireless access (BWA) networks, and thus, it is suitable for next generation network environments. The results, obtained through real experimentation of the implemented architecture through an advanced mobility scenario using a real WiMAX testbed, show that the architecture is able to provide QoS under dynamic scenarios, with fast integrated QoS and mobility signaling.

Abbreviations AAA AC AF AIP AP ASN ASN-GW

Authentication, Authorization and Accounting Admission Control Application Function All-IP Access Point Access Service Network ASN-Gateway

S. Sargento (*) Institute of Telecommunications, University of Aveiro, Campus Universita´rio de Santiago, 3810193 Aveiro, Portugal e-mail: [email protected]

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Best Effort Base Station Broadband Wireless Access Connection Identifier Commercial-of-the-Shelf Common Part Sublayer Convergence Sublayer Connectivity Service Controller Connectivity Service Network Dynamic Host Configuration Protocol Domain Name Service Extended real time Polling Service Foreign Agent Fast Base Station Switching Fast Handovers for MIP Generic Adapter General Internet Signaling Transport Generic Link State Monitor Home Agent Handover Hard Handover IDentifier IP Multimedia Subsystem Internet Protocol Link Lower Controller Link-specific Information Monitor Physical Medium Access Control Macro Diversity Handover Media Independent Command Service Media Independent Event Service Media Independent Handover Media Independent Handover Function Media Independent Handover User Media Independent Information Service Mobile IP Mobility Management Mobile Node Message Routing Information Mobile Station Network Control and Management System Next Generation Network Network Reference Model Non-real-time Polling Service

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Next Steps in Signaling NSIS Signaling Layer Protocol Network Working Group Proxy MIP Point of Attachment Point of Service QoS Node Entity Quality of Service QoS SPECification Resource Controller Resource Management Function Reference Point Redline Specific Adapter real time Polling Service Service Access Point Session Description Protocol Service Data Units Service Flow Service Flow Management Soft Handover Session Initiation Protocol Simple Network Management Protocol Subscriber Station Transmission Control Protocol Trivial File Transfer Protocol User Datagram Protocol Unsolicited Grant Service WEIRD Agent WiMAX Extension to Isolated Research Data networks Worldwide Interoperability for Microwave Access

Introduction

Broadband Wireless Access (BWA) technologies are expected to play a central role in Next Generation Networks (NGN) [1, 2]. WiMAX [3], based on the IEEE 802.16 family of standards [4, 5], is one such technology that has the potential to form the foundation upon which operators will deliver ubiquitous Internet access in the near future, greatly benefiting from existing and future infrastructures. One of the central concerns in the emerging telecommunications environment is the support for seamless mobility while taking advantage of different access networks, some of which are already in use, others, such as WiMAX, will soon be deployed.

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There are several proposals for fast and seamless mobility management between different access networks. IEEE has been working on the 802.21 draft standard [6] to enable Media Independent Handovers (MIH). IEEE 802.21 defines an abstract framework which delivers link layer information to the higher layers, in an effort to optimize handovers between heterogeneous media. We could argue that IEEE 802.21 aspires to harmonize mobility management processes, irrespective of the underlying technologies, considering that proper communication and interfaces are presented to the link layers. Although the work within the IEEE 802.21 working group is already in an advanced stage, the framework needs to be integrated with specific technologies, since each one has its particular mobility control procedures. Moreover, seamless mobility requires the active support of Quality of Service (QoS) related mechanisms in the handover process, guaranteeing that resources are reserved in the target access network before mobility management operations are completed. In other words, we cannot dissociate mobility management and QoS processes. This chapter presents mobility architecture with integrated QoS support, based on IEEE 802.21. The proposed architecture can accommodate different wired and wireless technologies, such as WiMAX, Wi-Fi, DVB, and UMTS. The way mobility management processes are intertwined with QoS mechanisms in order to support seamless mobility over heterogeneous networks is described. More specifically, we explain how QoS mechanisms based on the Next Steps in Signaling (NSIS) protocol family [7–9] can be integrated with IEEE 802.21 concepts. Finally, a prototype implementation of the proposed architecture is presented and results from its empirical evaluation on a state-of-the-art testbed using commercial off-the-shelf (COTS) WiMAX equipment are provided. By using a real demonstrator, with a WiMAX backhaul, we measured the processing time for each module involved in the handover process while discussing the obtained results. This chapter is organized as follows. Section 6.2 reviews the current state of the art in WIMAX mobility management architectures, reporting on recent advances in standardization for a, such as IEEE, WiMAX Forum and IETF. Section 6.3 introduces the proposed mobility-QoS integrated architecture, its elements and functionalities, taking as a use case the architecture developed within the WEIRD project [10]. Section 6.4 briefly describes how this architecture was implemented and Section 6.5 presents the testbed and the performed tests, and analyzes the obtained results as well. Finally, Section 6.6 concludes this chapter with providing interesting topics for future work in this area.

6.2

WiMAX Architecture

This section starts by describing the overall WiMAX architecture standardized by the WiMAX Forum, typically referred to as the WiMAX Network Reference Model (NRM). Then, we succinctly summarize the salient characteristics of IEEE 802.16 [4, 5, 11], the MAC and PHY layers used in WiMAX networks, emphasizing on the

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data, control and management planes, as well as on mobility management procedures for mobile WiMAX. This section concludes with an introduction to the recently finalized IEEE 802.21 standard [6], which aims at optimizing mobility management procedures for handover scenarios, including networks based on IEEE 802.16, such as WiMAX.

6.2.1

The WiMAX Forum Network Reference Model

IEEE 802.16 defines a broadband wireless access technology for metropolitan area networks (MANs), supporting both fixed and mobile terminals, as defined in the IEEE 802.16-2004 [4] and IEEE 802.16e-2005 [5] standards, respectively. IEEE 802.16 specifies the air interface, including the MAC and the PHY layers. Nevertheless, it does deal with the radio access network functionalities. The standardization of the WiMAX access network is part of the WiMAX Forum. In particular, the WiMAX Forum Network Working Group (NWG), which is currently defining a high-performance All-IP (AIP) end-to-end network architecture to support fixed, nomadic, portable, and mobile users [3]. Besides defining an end-to-end IP framework, the WiMAX Forum also aims to ensure full interoperability between Base Stations (BSs) and Subscriber Stations (SSs)/Mobile Stations (MSs) from different WiMAX vendors. The WiMAX Forum introduced an architecture based on IEEE 802.16 by defining the NRM. The NRM, illustrated in Fig. 7.1, is a logical representation of the WiMAX network architecture, based on a set of functional entities and standardized interfaces, known as Reference Points (RPs). Table 6.1 summarizes the WIMAX NRM Reference Points. By implementing the WiMAX NRM, multiple

Table 6.1 WiMAX NRM reference points Reference Description Point R1 Interface between the MS and the BS: implements the IEEE 802.16e-2005 air interface. R2 Logical interface between the MS and the CSN: used for AAA, IP host configuration, and mobility management. R3 Interface between ASN and CSN: supports AAA, policy enforcement and mobility management; implements the tunnel between ASN and CSN. R4 Interface between ASN and ASN: used for MS mobility across ASNs. R5 Interface between CSN and CSN: used for internetworking between the home and visited networks. R6 Interface between BS and ASN-GW: implements intra-ASN tunnels; used for control plane signaling. R7 Interface between data and control plane in the ASN-GW: used for coordination between data and control plane in ASN-GW. R8 Interface between BS and BS: used for fast and seamless handovers.

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Fig. 6.1 The WiMAX forum network reference model

implementation options for a given functional entity are allowed, maintaining interoperability through the adoption and use of RPs R1-R8. As shown in Fig. 6.1, the WiMAX NRM defines three functional entities, namely, the Connectivity Service Network (CSN), the Access Service Network (ASN) and the MS. The MS is also referred to as the terminal equipment, and is responsible for establishing radio connectivity with the BS (via the R1 reference point). The ASN provides the connectivity between the MS and the IP backbone. The ASN is generally composed of several BSs connected to one or several ASNGateways (ASN-GW). The ASN-GW is the gateway for the ASN, aggregating all BSs’ information towards the CSN. The ASN is responsible for a set of important functionalities to provide radio connectivity to WiMAX subscribers, such as network discovery and selection, radio resource management, multicast and broadcast control, intra-ASN mobility, accounting, admission control, and Quality of Service. Furthermore, the ASN also performs relay functions to the CSN for IP connectivity establishment. Finally, the CSN complements the ASN by providing IP connectivity-related services. For example, the CSN operates Dynamic Host Configuration Protocol (DHCP), Domain Name Service (DNS) and Authentication, Authorization, and Accounting (AAA) servers, and oversees mobility management procedures.

6.2.2

The IEEE 802.16 Reference Model

Since IEEE 802.16 is a connection-oriented technology, all data transfers require the prior establishment of dedicated connections between the BS and the SS/MS. As detailed in [4], a connection, which is identified by a 16 bit Connection Identifier (CID), is a unidirectional mapping between the BS and the SS/MS MAC layer for

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Fig. 6.2 IEEE 802.16 reference model (Data, control and management planes)

transporting the traffic of the corresponding service flow. During the SS/MS initialization process, three pairs of management connections (basic, primary and secondary) are established between the BS and the SS/MS, reflecting distinct QoS levels. The basic connection is used to transfer short, time-critical MAC management messages. The primary management connection transports longer, more delay-tolerant management messages. The secondary management connection is used to transfer delay-tolerant, standard-based management messages such as DHCP, Trivial File Transfer Protocol (TFTP) and Simple Network Management Protocol (SNMP). Moreover, a broadcast connection is configured by default to transmit MAC management messages to all receivers. Besides the aforementioned management connections, a multicast polling connection is also established so the SS/MS joins multicast polling groups and requests additional bandwidth. Finally, to satisfy the contracted services, transport connections are allocated to convey data packets in the air interface. As illustrated in Fig. 6.2, the MAC layer is divided in three sublayers, namely, the Service Specific Convergence Sublayer (CS), the MAC Common Part Sublayer (CPS) and the Security Sublayer. The CS is the first sublayer of the MAC layer, accepting higher layer MAC Service Data Units (SDUs) through the CS Service Access Point (SAP) and classifying them to the appropriate connection. The classifier is based on a set of matching criteria applied to each individual packet, consisting of specific protocol fields (e.g. IPv4/v6, Ethernet, Virtual Local Area Networks – VLAN, TCP/UDP ports), a classifier priority and a reference to a CID (see Fig. 6.2). Downlink classification is made at the BS whereas uplink classifiers are located in the SS/MS. When the classification process concludes, packets are delivered to the MAC Common Part Sublayer (MAC CPS) through the MAC Service Access Point (MAC SAP).

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The MAC CPS is responsible for the core MAC functions, such as system access, bandwidth request and allocation mechanisms, connection establishment, contention resolution, and QoS management. QoS is catered for by associating each packet traversing the air interface with a service flow, as identified by the CID. According to IEEE 802.16-2004 [4], a service flow is a unidirectional flow of packets with a specific set of QoS parameters, such as latency, jitter, throughput and scheduling service. The scheduling service allows the IEEE 802.16 system to define transmission ordering and scheduling on the air interface, as well as how the SS/MS requests uplink bandwidth allocations. Five scheduling services are supported by IEEE 802.16: Unsolicited Grant Service (UGS), real time Polling Service (rtPS), extended real time Polling Service (ertPS) (only for IEEE 802.16e-2005 [5]), non real time Polling Service (nrtPS) and Best Effort (BE). Table 6.2 describes each one of the mentioned scheduling services. The Security Sublayer is the third and last sublayer from the MAC layer. This sublayer provides authentication and data encryption functions. The IEEE 802.16g-2007 [11] standard has been defined to efficiently integrate the IEEE 802.16 system with the higher layer control and management functionalities (see right-hand side of Fig. 6.2). In particular, 802.16g specifies the Network Control and Management System (NCMS) abstraction, which represents the higher

Table 6.2 IEEE 802.16 scheduling services Scheduling Target services service UGS Support real-time service flows that generate fixed size data packets on a periodic basis, such as VoIP.

rtPS

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Support real-time service flows that generate variable size data packets on a periodic basis, such as MPEG video or streaming video. Support real-time service flows that generate variable size data packets on a periodic basis, such as VoIP with silence suppression. Instead of providing fixed allocations such as UGS, ertPS provides dynamic allocations. Support non-real-time service flows that require variable size data grants on a regular (but not strictly periodic) basis, such as high bandwidth FTP. Support service flows where no throughput or delay guarantees.

QoS parameters Maximum Sustained Traffic Rate (equal to the Minimum Reserved Traffic Rate) Maximum Latency Tolerated Jitter Request/Transmission Policy Maximum Sustained Traffic Rate Minimum Reserved Traffic Rate Maximum Latency Request/Transmission Policy Maximum Sustained Traffic Rate Minimum Reserved Traffic Rate Maximum Latency Request/Transmission Policy

Minimum Reserved Traffic Rate Maximum Sustained Traffic Rate Traffic Priority Request/Transmission Policy Maximum Sustained Traffic Rate Traffic Priority Request/Transmission Policy

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layers entities (e.g. QoS and/or mobility management functions) that interoperate with the IEEE 802.16 system. Furthermore, the Control Service Access Point (C-SAP) and the Management Service Access Point (M-SAP) establish communication between an IEEE 802.16based system and NCMS entity(ies) for control and management purposes, respectively. The Management SAP (M-SAP) is used for less time-sensitive management plane primitives, such as system configuration, monitoring statistics, notifications, triggers and multi-mode interface management. Besides, the Control SAP (C-SAP) is used for more time sensitive control plane primitives, including handover, mobility management, security context management, radio resources management, subscriber and session management, and Media Independent Handover Function (MIHF) [6] services.

6.2.3

Mobility Management in WiMAX

Hard Handover (HHO) and Soft Handover (SHO) methods are supported by mobile WiMAX, defined in IEEE 802.16e. In the HHO method or “break-before-make” approach, the serving network link is broken before the handover execution is triggered and the target link is established. With respect to the SHO method or “make-before-break” approach, the target link is prepared and established before the serving network link is broken and the handover is executed. Although the SHO method provides continuous connectivity for the MS, it is much more complex and requires backbone communication between the serving and the target access technologies. In mobile WiMAX, two types of SHO are optionally supported, namely, the Fast Base Station Switching (FBSS) and the Macro Diversity Handover (MDHO). In the FBSS handover case, the MS is able to rapidly switch between several Base Stations without completing the entire network entry procedure. In the MDHO mode, the MS has simultaneous communication links with several Base Stations, enabling a fast handover to occur with minimum traffic degradation. Both mobile and network initiated handovers are supported in mobile WiMAX. For the former case (mobile initiated handover), the MS is responsible to trigger the handover initiation process, whereas for the network initiated handover scenario, the serving BS is in charge of triggering the mobility procedures. In order to provide a brief explanation about the handover procedures in Mobile WiMAX, we will present the example of a mobile initiated handover between BSs located in the same ASN (intra-ASN handover), as illustrated in Fig. 6.3. Before proceeding with the intra-ASN handover example, it is important to clarify that IEEE 802.16e-2005 [5] only defines the air interface procedures, including the MAC management messages that are exchanged between the Base Station and the MS. All the communication procedures in the backbone network are not covered by IEEE 802.16e-2005 itself. To overcome this gap, the WiMAX Forum has specified a network protocol [3] to establish the communication in the backbone network between the serving,

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Fig. 6.3 WiMAX intra-ASN mobile initiated handover

candidate and target Base Stations (reference point R8, illustrated in Fig. 6.3), as well as between the Base Stations and the ASN-GWs (reference point R6, also illustrated in Fig. 6.3). The intra-ASN handover scenario shown in Fig. 6.3 is composed of both IEEE 802.16e-2005 [5] MAC management messages (R1 reference point) and WiMAX Forum backbone messages (in this case, the R8 reference point). Initially, the MS is connected to the serving BS and receives the Mobility Neighbor Advertisement (MOB-NBR-ADV) MAC management message from the serving BS (Fig. 6.1), indicating that a WiMAX BS is available in the surrounding area. As a consequence, the MS triggers the handover preparation phase and sends the Mobility Mobile Station Handover Request (MOB-MSHO-REQ) MAC management message to the serving BS (Fig. 6.2) with a list of the candidate BSs for the handover. Thereafter, the serving BS sends a Handover Request (HO-REQ) backbone message to the candidate BSs (:3), Fig. 6.2, including the required QoS parameters to satisfy the MS currently running services. The candidate BSs reply with a Handover Response (HO-RESP) backbone message to the serving BS via the R8 reference point (:4), indicating whether the required QoS resources are available or not. The serving BS collects all responses and sends a Mobility Base Station Handover Response (MOB-BSHO-RESP) MAC management message to the MS (:5) with the list of recommended candidate BSs. Finally, the mobility decision algorithm of the MS selects the target BS (from the provided list of candidate BSs) and notifies the serving BS about the handover execution using the Mobility Handover Indication (MOB-HO-IND) MAC management message (:6). Finally,

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the serving BS notifies the target BS that the MS will execute handover using the Handover Confirm (HO-CNF) backbone message (:7).

6.2.4

IEEE 802.21 Media Independent Handover Overview

The recently finalized IEEE 802.21 standard [6] aims to optimize the mobility management procedures in heterogeneous access environments. Towards this aim, it defines a Media Independent Handover (MIH) framework, which provides standardized interfaces between the access technologies and the mobility protocols from the higher layers in the protocol stack. The envisaged heterogeneous environment is illustrated in Fig. 6.4. A multi-operator, multi-technology network employing WiMAX, Wi-Fi and 3GPP UMTS/LTE is shown, including the IEEE 802.21 Point of Attachment (PoA) and Point of Service (PoS). PoA is the access technology attachment point, whereas PoS is the MIH entity that communicates with the multimode terminal. IEEE 802.21 introduces a new entity called MIH Function (MIHF) which hides the specificities of different link layer technologies from the higher layer mobility entities. Several higher layer entities, known as MIH Users (MIHUs) can take advantage of the MIH framework, including mobility management protocols, Non-PoS ¬ ® PoS MN ¬ ® PoS

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such as Fast Mobile IPv6 (FMIPv6) [12], Proxy Mobile IPv6 (PMIPv6) [13] and Session Initiation Protocol (SIP) [14], as well as the other mobility decision algorithms. In order to detect, prepare and execute the handovers, the MIH platform provides three services: l

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The following section introduces a QoS-aware mobility management architecture that capitalizes on IEEE 802.21 for inter-technology handovers for WiMAX networks.

6.3

QoS-Aware Mobility Management: A Use Case for the WEIRD System

The WEIRD overall architecture follows the WiMAX Forum NRM [3] and is illustrated in Fig. 6.6. The WiMAX resources dynamic control is handled by the coordinated action of the control plane modules located in the MS and in the ASN Gateway, while the CSN control plane manages the interaction between the WiMAX access network and the core network. Finally, the application servers and the AAA server are situated in the CSN as recommended by the WiMAX Forum. Quality of Service and mobility are managed in a coordinated way at the control plane level through the inter-communication and the combined processing of the

Fig. 6.6 WEIRD architecture

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Connectivity Service Controller (CSC) modules, located in each segment of the NRM, and their interaction with the physical layer and the application layer. It is worthwhile to highlight that QoS and mobility management are strictly correlated and interdependent in WiMAX networks. QoS in WiMAX links is supported by a connection-oriented approach. Each WiMAX connection is associated with a set of downlink or uplink Service Flows characterized by a specific profile that defines both the scheduling class and the QoS parameters (bandwidth, priority, latency, jitter). In this architecture, each application session is associated with a set of endto-end flows with a QoS description based on the traffic type and application requirements. Two main issues must be considered in order to ensure the same QoS level along the full end-to-end path, including the WiMAX access segment, and independently of user mobility. Firstly, the end-to-end path can include several domains, like Diffserv or Intserv domains, supporting heterogeneous underlying network technologies and QoS guarantees, with different parameters and detail levels. The uniformity of the QoS level in this scenario, even with the bounds imposed by the different technologies, can be obtained using a multi-domain QoS signaling protocol, like QoS NSIS Signaling Layer Protocol (NSLP) [9] and mapping the QoS description in a set of specific parameters as defined by the QoS metric supported in each domain [15]. The QoS parameters carried in the QSPEC (QoS specification) are opaque to the QoS NSLP and are defined in the QoS model of the specific network technology, so that they can be interpreted only by the Resource Management Functions (RMF) of the NSIS peers located in each domain. In case of multi-domain path, the NSIS node located at the ingress of each domain is in charge of the translation between the received QSPEC and the internal QSPEC. This QSPEC is based on the QoS parameters supported by the underlying technology of the specific domain, and it can be easily understood by the RMF of each internal NSIS node. Figure 6.7 shows an example with a scenario including a WiMAX access network and a Diffserv domain in the core network. The QSPEC Wimax domain

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Fig. 6.7 Multi-domain QoS NSLP signaling

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carried in the QoS NSLP messages follows the Diffserv QoS model in the Diffserv domain and the WiMAX QoS model in the WiMAX domain. In particular, at the WiMAX access domain, the QoS description is based on a set of Service Flows characterized by the scheduling class and the WiMAX QoS parameters which are more suitable for the current session. These Service Flows are reserved and activated during the session setup phase using the network-initiated procedure defined as mandatory in the IEEE 802.16 d/e specifications [4, 5]. In this case, the Service Flow creation is initiated by the BS and controlled by the corresponding ASN-GW. With respect to mobility, the user must be able to move between different access networks. The mobility management architecture must be able to support not only handover between WiMAX BSs (located in the same ASN or in different ASNs), but also handover between different access technologies, like Wi-Fi and WiMAX networks. A further scenario, presented in detail in Section 6.3.2, is an intertechnology handover between Ethernet and Wi-Fi with the WiMAX network as the backhaul access technology. All these types of handovers must be transparent for the user and the same QoS level must be maintained during the entire length of the active sessions involved in the handover, if this handover is authorized through the user contracts. Therefore, QoS and mobility need to be managed together and independently on the specific link layer technology, through an interaction between the control plane and the lower layers of the involved access technologies. Notifications about the current link status can be processed by the Mobility Manager modules at the MS, ASN and CSN, in order to manage handovers through procedures that are completely transparent for the application layer. In particular, handover management in WiMAX networks involves the automatic reconfiguration of the wireless links through a “make-before-break” approach: the “make” phase includes the creation and the activation of new Service Flows in the segment between target SS and target BS, and the “break” phase includes the deletion of the preexistent Service Flows on the old wireless link. While this procedure can be controlled entirely by the ASN-GW in case of serving and target BS located in the same ASN, if the user moves between two different ASNs, the global handover management must be coordinated at the CSN level and the two ASN-GWs are just in charge of the resource control in the related WiMAX segments.

6.3.1

Integrated QoS and Mobility Management

As discussed earlier, the twofold interaction between the control plane and the application plane, on the one hand, and between the control plane and the transport plane, on the other, is of great importance. While the former allows the acquisition of the application QoS requirements for the resource control during the session setup and tear-down phases, the latter enables the control plane to modify the resource allocation during the handover.

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During the session setup phases, the CSCs interact with the service layer in order to retrieve information from the applications, regarding the traffic type and the required QoS parameters. In particular, two different approaches can be adopted to support both legacy and IP Multimedia Subsystem (IMS), like applications based on the Session Initiation Protocol and Session Description Protocol (SIP/SDP) [14, 16] signaling. As shown in Fig. 6.8, in the first case [17], the QoS signaling follows the host-initiated approach. The CSC located at the MS (CSC_MS) communicates with a module, called WEIRD Agent (WA), in charge of obtaining parameters such as required bandwidth, maximum latency and jitter from the applications. CSC_MS coordinates end-to-end QoS signaling, using the NSIS framework, translating the application QoS requirements to a QSPEC adopted in the WiMAX NSIS model [15] and initiating the end-to-end signaling towards the ASN, the CSN and the core network. In the case of IMS-like applications (Fig. 6.9), the QoS signaling follows the network-initiated approach and it is strictly connected to the application layer SIP/SDP signaling [14, 16]. The SIP Proxy located at the CSN intercepts the SIP signaling between the SIP User Agents and extracts the session description from the SDP messages. The QoS parameters are forwarded to the CSC located at the ASN (CSC_ASN), through a set of Diameter [18] messages describing the media flows included in the sessions, where they are translated into WiMAX parameters. In this case the QoS NSIS signaling follows the edge-to-edge model since it is initiated and controlled by the CSC_ASN. For both legacy and IMS-like applications, WiMAX resource reservations are handled by the ASN-GW through the interaction of the CSC with the lower planes. In particular, at the link layer level the Resource Control (RC) module manages all

Fig. 6.8 Host-initiated QoS signaling and resource reservation

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Fig. 6.9 QoS signaling and resource reservation for IMS-like applications

the WiMAX technology related functionalities, like Service Flow creation, modification and deletion, enforcing the QoS decisions on the WiMAX system through a set of technology dependent adapters [19]. Mobility management is based on the MIP protocol [20] and the IEEE 802.21 [6] framework that enables MIH defining an abstract layer for the unified interaction between the upper layer entities, called MIHU, and lower layer entities based on different technologies through a common interface. Figure 6.5 illustrates the abstractions introduced by IEEE 802.21. In the architecture (see Fig. 6.6), the mobility management framework includes several instances of the MIHF, located at each segment of the NRM. MIHF hides all technology dependent messages and procedures from the MIHUs exposing only a set of standardized interfaces that can be used to exchange common messages like events, commands or notifications among local or remote MIHUs and Link Layer Controllers (LLC). In the specific architecture, the following SAP are used to manage the handovers in the architecture: l l

MIH_LINK_SAP between the lower layers and the MIHF MIH_SAP between the MIHF and the MIHUs

MIHF also handles the exchange of the MIH protocol messages between remote MIHUs and LLCs providing three different services: MIES, MICS and MIIS. The MIH Events originate from the LLC and include information about the link layer, for example, the respective link status. The MIH Commands originate at the MIHUs and are used to convey the handover decisions. The transport of the MIH protocol messages between remote MIHF peers is supported by the NSIS framework through the Media Independent Handover NSLP (MIH NSLP), proposed by

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the authors in [21], and Generic Transport Internet Signaling (GIST) protocol [8]. The MIH NSLP was developed as an extension to the NSIS framework in order to transport the MIH protocol messages. There are two main reasons to sustain this approach. First, the IEEE 802.21 proposed standard does not specify any protocol for message exchange, providing only the requirements for such protocol, namely, security and reliability. Second, QoS signaling, which is tightly coupled with mobility, is performed through the QoS-NSLP. In this context, the use of the NSIS framework to support both QoS and mobility process becomes the natural choice, since it fulfills the requirements for MIH message exchange between remote entities. As previously referred, the mobility management architecture, illustrated in Fig. 6.10, includes a Mobility Manager (MM) instance, acting as a MIHU and strictly connected with the related CSC, located on each NRM segment (MS, ASNGW, CSN), and a LLC located on the MS. The LLC is in charge of monitoring the link condition (signal level for Wi-Fi and WiMAX links, connected/disconnected cable for Ethernet). In case of link status variation, the related MIH Event is created and sent to the local MIHF through the MIH_LINK_SAP. Here, it is delivered to the registered MIHUs, both local and remote MMs, through the MIH_SAP. The MIH Events are used by the MM to update their internal status and detect new imminent handovers. In this case, the MM located at the MS searches for the availability of a new target link to be established and requests a new resource reservation to the associated CSC. The entire procedure is performed jointly by the CSC and the MM. While the MM manages the link status and is able to take decisions about the handover executions, the CSC handles the sessions at the control plane and controls the resources for the associated traffic flows. Following

Fig. 6.10 Mobility management architecture

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the approaches used for resource control in the session setup and tear-down phases, the handover procedure and the wireless link reconfiguration are controlled by the MM located at the MS for host-initiated sessions and by the MM located at the ASN for IMS-like applications. When a mobile node moves between different ASNs, the entire procedure is controlled by the MM located at the CSN, which takes the final handover decision. However, the actual resource reservation is still performed by the CSC_ASN. Handover decisions are finally notified to the lower layers using the MIH Commands delivered to the LLC.

6.3.2

QoS-Aware Inter-technology Handovers for WiMAX

This subsection presents the sample scenario for inter-technology QoS-aware mobility, designed, implemented and deployed in the WEIRD project. It involves a vertical handover between Ethernet and Wi-Fi with WiMAX as the backhaul access technology, as shown in Fig. 6.11. A laptop with two different network interfaces (Ethernet and Wi-Fi) plays the role of the MS and it is initially connected via Ethernet cable to a LAN backhauled by an IEEE802.16d Subscriber Station (SS), the serving SS. When the user moves from its desk, it unplugs the cable and the laptop is connected through the Access Point to the Wi-Fi network, backhauled by another IEEE 802.16d SS, the target SS. The two SSs are located in the same ASN and can be connected to the same BS or to different BSs controlled by the same ASN-GW following the intra-ASN WiMAX mobility model. In our prototype, some applications are running on the laptop while it is connected via the Ethernet segment. The corresponding sessions are activated with the associated resources reserved along the end-to-end path. In particular, a set of WiMAX Service Flows has been activated between the serving SS and the Home Network

IEEE 802.16d SS - 1 Serving SS

MS Ethernet Connection

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IEEE 802.16d SS - 2 Target SS

Fig. 6.11 Inter-technology mobility scenario

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associated BS during the session setup phase when the applications have been initialized. Each current Service Flow is characterized by the WiMAX parameters and the scheduling class more suitable for the QoS requirements of the active services. When the user moves to the Wi-Fi network, the same QoS level must be assured for each running application, so new Service Flows must be created and activated in the WiMAX segment between the target SS and the associated BS. This mobility scenario includes both intra-technology and inter-technology handover: the inter-technology handover involves the Ethernet and the Wi-Fi technology, but since they are backhauled by two different WiMAX SS when the MS moves, an intra-technology handover from the serving WiMAX SS to the target WiMAX SS must be performed. Figure 6.12 presents the handover signaling diagram applied to legacy applications, characterized by host-initiated sessions, for the scenario described in the previous paragraph. When the user starts a legacy application, the resource reservation procedure is triggered by the WEIRD Agent and the end-to-end QoS NSIS signaling is initiated as described in Section 6.3.1. As a result, a set of Service Flows are created at the ASN between the serving SS and the connected BS in order to assure the required

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Fig. 6.12 Signaling diagram for QoS-aware handover

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QoS. It should be noted that the path including the Ethernet connection is automatically selected by the CSC located at the ASN, since the Wi-Fi connection is configured with a lower priority value and the network connected through SS#1 is considered the home network. At the beginning of the handover process, two Link_Up events are triggered by the LLC in order to notify the MIHF that both the Ethernet and the Wi-Fi connections are available. This event is forwarded to the registered MMs, in particular to the local MM (located at the MS) and to the remote MM (located at ASN and CSN), using MIH NSLP messages. Since for legacy applications the handover procedures are managed by the local MM, the MMs located on the other NRM entities and the related signaling are not shown in Fig. 6.12 and will not be further considered. When the Link_Up messages are received, the MM updates the internal state machine about the available network connections and is able to select the connection to be used for new sessions. The user can interact with the LLC in order to unplug the Ethernet cable and move to the Wi-Fi connection. The LLC detects that the Ethernet connection is going down and sends a Link_Going_Down event to the MIHF located at the MS that forwards it to the registered MMs. The MM at the MS internal state machine is updated again and, as consequence, an imminent handover is detected. The handover preparation phase is triggered in order to reserve the new resources before the Ethernet cable is unplugged. The MM at the MS selects the Wi-Fi link as the network connection to be used after the handover according to the current status of the internal machine and notifies this decision to the CSC at the MS. Here a new NSIS QoS signaling is triggered to update the resource reservation for the existing sessions and create new Service Flows (target SFs) in the segment between Home Agent (HA) located in the ASN-GW and the selected Foreign Agent (FA). The NSIS response message notifies the CSC at the MS that resources have been allocated between the target SS and BS and that they can be used by the data traffic flows after the handover. At this point the MS can move from the home network to the foreign network where it will be able to maintain the same level of QoS, so the MM at the MS can start the handover execution procedure through the MIH Link_Action command. When the user unplugs the Ethernet cable from the laptop, the Wi-Fi network interface starts the MIP registration with the FA, and the MIP tunnel between the FA and the HA at the ASN is established. Data traffic is carried through the Wi-Fi link and is mapped to the new Service Flows between the target SS and BS on the WiMAX link, ensuring the QoS level originally required by the active applications. The resources previously allocated between the serving SS and BS are released during the handover completion phase. When the Ethernet cable is unplugged, the LLC sends a Link_Down event, forwarded by the MIHF located at the MS to its MM. The CSC at the MS, as responsible of the dynamic control of sessions and resources, is in charge of handling the deletion of the old Service Flows for the existing sessions and initiates the related NSIS QoS signaling towards the CSC at the ASN.

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Implementation

In this section, we take a closer look at the design and implementation of the components developed in order to demonstrate the feasibility of the mobility management architecture introduced in the previous section. More specifically, we present the MIHF module implemented, as well as the LLC, NSIS framework (regarding QoS signalling and MIH transport mechanisms), and at last, we present the details of the implementation of CSC, with its own MM.

6.4.1

MIHF Framework

The MIHF, located at the MS and ASN, is the central unit of the IEEE 802.21 architecture. It provides communication with lower layers through MIH_LINK_ SAP, with upper layers through MIH_SAP, and with remote MIHFs through MIH_NET_SAP, using the MIH protocol. Its implementation follows a set of steps, which are necessary for the proper integration with the architecture. Figure 6.13 shows the main features of the MIHF entity implemented. As can be seen, initially it is required to configure all the topology of the network with the important information of different units. Then, the creation of communication means (sockets) with all modules is performed. Each MIHF provides a set of

LLC

MIH_LINK_SAP

Configure the topology; Create sockets;

Listen Sockets

MIH Users

MIH_SAP

Receive message

Identify the message

Remote MIHFs

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Fig. 6.13 MIHF implementation overview diagram

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events (Link_Up, Link_Down and Link_Going_Down), commands (Link_Action), information services (MIH_Get_Information) and elements of control (MIH_Register and MIH_Subscribe). After the MIHU has subscribed to the services provided by the MIHF, it will become associated with these services. Then, the MIHF is able to receive any message from MIHUs, LLCs or remote MIHFs, and will have the adequate behaviour depending on the message received. The main functions that must be performed by MIHF are the following: l

l

l

Interaction with Link Layer Controller: MIHF must have the ability to receive events from the LLCs, process these messages, identify the associated event and forward it to the MIHUs (local or remote) that subscribe it. Interaction with Media Independent Handover User: MIHF must have the ability to receive messages coming from MIHUs who want to register or subscribe its events. The registration or the subscription may be requested by a local MIHU or by a remote MIHU. Moreover, MIHF must generate and submit their response to these requests. Overall interaction: Additionally to the direct interactions specified above, MIHF must also have the ability to receive the MIH_Link_Action.request and send the respective answer to all MIHUs or LLCs who signed to this type of command.

6.4.2

Link Layer Controller

The aim of the LLC is to implement a link information collector independent of the specific hardware, vendor, or GNU/Linux kernel. For this, Linux natively provides convenient ways for application layer software to gather link specific information from the kernel and directly from network device drivers without modifications to both of them. LLC, illustrated in Fig. 6.14, constantly monitors the network link states and, based on this information, it provides events through an Event Trigger module to the registered MIHF. For simplicity, in the examined scenario, LLC provides only Link_Up, Link_Down and synthetically generated Link_Going_Down

MIHF TCP Event Trigger

Generic Link State Monitor

Link-specific Information Monitor

Kernel

Fig. 6.14 Schematic of LLC

802.3 Initiate

802.11

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events. The monitored link types are Ethernet (IEEE 802.3) and Wi-Fi (IEEE 802.11). Link states are identified in the Generic Link State Monitor (GLSM) by observing the operation status of access network interfaces. After each link is operationally up and its link type has been identified, GLSM initiates the Link-specific Information Monitor (LSIM) which acquires link-specific information. For instance, LSIM can obtain Access Point information for Wi-Fi accesses. This information is gathered using ioctl system calls. Since the Link_Up message content, specified in IEEE 802.21, optionally includes the MAC address of an access router (gateway) assigned to the link, LSIM also verifies and monitors the connectivity with the access router. In this study, LLC is configured to trigger a Link_Up event only if a mobile node has L2 connection with both the AP and the assigned access router.

6.4.3

NSIS: QoS and MIH Transport

The NSIS framework includes different software modules, namely MIH NSLP for the transport of MIH messages, QoS NSLP to accomplish QoS signalling, and GIST, which acts as the transport layer. Figure 6.15 shows the different modules of the NSIS framework and their interconnections. All NSIS modules employ TCP/IP sockets for their communication. Also the interface with upper layers, such as MIHF and applications is based on TCP/IP sockets. The MIH NSLP module implements different functionalities to achieve the MIH message transport between remote MIHF entities. The processing of MIH messages, including message parsing, enqueueing and mapping, is one of the first operations performed by the MIH NSLP. The mapping process corresponds to a map between a destination ID determined by the MIHF, to an IP address, which is required by GIST. The instructions for the delivery process, such as the type of transport required (assured delivery) and the destination address, are included in the Message Routing Information (MRI) object. Such instructions are fundamental for MIH User MIHF

Application

MIH NSLP

QoS NSLP

GIST

Fig. 6.15 NSIS framework decomposition

NSIS

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the operation of GIST. Therefore, at this second stage, the serialization of MRI is performed. These operations are executed in the nodes initiating the MIH messages, namely the Mobile Station. Afterwards, the destination nodes or the nodes intercepting such messages perform the reverse operations. For instance, the MIH NSLP installed on the ASN node performs deserialization of the messages received from GIST, in order to obtain the MIH payload. QoS NSLP, as a NSLP for QoS signalling, performs operations similar to the ones described above for the MIH NSLP, such as serialization and deserialization of MRI. Nevertheless, besides some functional similarity, the QoS NSLP module implements other more complex operations, such as soft-state management. State maintenance is performed within specific messages and it is used to maintain sessions that are active and that require resources. In the architecture presented, QoS NSLP northbound interface is the CSC. GIST, as the transport layer of the NSIS framework, is the foundation for the proper message signalling, both in terms of QoS and MIH functionalities. GIST can work using unreliable and reliable modes of operation. For instance, if the MRI object specifies the need for reliable transport, GIST will establish message associations between peer entities. Being a generic transport protocol, GIST has the capacity to support a NSLP for different purposes, such as the MIH NSLP and QoS NSLP described above.

6.4.4

MM and CSC

As described in Section 6.3, each segment of the WiMAX network (MS, ASN and CSN) is managed by a CSC, with its own MM. In the architecture, the role of the CSCs is to coordinate the WiMAX network control plane. In particular, the main functions of the Connectivity Service Controller are the following: l l

l

l

Manage sessions with the associated QoS signalling mechanisms. Coordinate authorization procedures in cooperation with the Diameter (AAA) server [18]. Manage WiMAX resources, which are dynamically created, activated, updated, and deleted during the session setup and tear-down. Control the resource update during the handover phases following the “makebefore-break” model. This reconfiguration is coordinated together with the MMs that handle all mobility-related procedures, monitoring the status of the network connections of the controlled MSs and making handover decisions.

The high-level flow chart of the dynamic session management and the corresponding control of the WiMAX resources is illustrated in Fig. 6.16. WiMAX resources are firstly created and activated during the session setup. The first step of the handover towards a foreign network is triggered by the LLC. At this stage, the LLC issues a Link_Going_Down message and then new WiMAX Service Flows are created in the target wireless segment. The end of the

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Fig. 6.16 Session and resource dynamic control

New Session ® Activate Resources Link Going Down ® Create target SFs ACTIVE SESSION

HO MAKE

Link Down ® Remove serving SFs Session Termination ® Remove existing resources

Session Termination ® Remove existing resources END

handover execution is signalled by the Link_Down message. Then, the old WiMAX resources between serving SS and BS are released. Finally, during the tear-down phase, all the existing Service Flows associated to the session are removed.

6.4.5

QoS Signalling and Resource Reservation

This section describes the procedures for QoS signalling and resource reservation for legacy and SIP-based applications. CSC at the MS is the main coordinator for legacy applications that follow the host-initiated model for QoS signalling. In this case, the CSC at the MS acts as the NSIS signalling initiator and creates the first QSPEC, translating the application requirements (as received from the WEIRD Agent) in a set of parameters based on the WiMAX QoS model [15]. In this scenario, the ASN at the GW is a generic QoS NSIS node located inside a WiMAX domain on the end-to-end path, and the CSC at the ASN acts as a local RMF: it receives requests from the NSIS layer and, if authorized, allocates the resources in the WiMAX link through the RC. In case of SIP-based applications based on the SIP/SDP protocol, networkinitiated QoS signalling is adopted. The CSC at the ASN is the main coordinator for both the WiMAX resource reservation and the edge-to-edge NSIS signalling through the CSN and the core network. The media flow description included in the SDP messages is retrieved by the Application Function (AF) located on the SIP Proxy of the CSN and transferred to the CSC at the ASN through Diameter messages. Here, resources are allocated and activated on the WiMAX link following the two-phase activation model defined by the IEEE802.16d/e specification.

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During the first phase of the SIP call, a set of provisioned SFs is created with the maximum level of QoS required by the codecs specified in the SDP messages. At the end of the SIP negotiation phase, the SFs are activated with the QoS parameters corresponding to the audio/video codecs agreed by the two SIP clients. The mechanism for resource allocation on the WiMAX link follows the same network-initiated model for both legacy and SIP-based applications, and it is entirely managed by the CSC_ASN at the ASN-GW. The procedure consists of the following steps: l

l

l

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Mapping between the QoS parameters included in NSIS or SDP messages and a set of WiMAX Service Flows QoS authorization through an interaction between the CSC at the ASN and the Diameter AAA server located in the CSN Admission Control (AC) for the ASN segment resources, including the WiMAX SFs Interaction between the CSC at the ASN and the RC in order to create and activate the SFs

6.4.6

Mobility

The management of the handovers and the corresponding resource updating follow the same approach of the resource reservation control during the session setup and teardown phases. In case of legacy applications, characterized by host-initiated sessions, all handover procedures are handled by the joint action of CSC and MM both at the MS, while all the processing is controlled by the CSC and MM at the ASN for SIP-based applications. In particular, the MM handles the status of the network connections of the corresponding MS through the events received from the local MIHF module and detects imminent handovers, taking active decisions and triggering the resource updating. This reconfiguration is controlled by the CSC, which is able to retrieve from its internal state all required information about the running sessions involved in the planned handover and, in particular, the WiMAX resources associated to the active data traffic flows that must be re-allocated. In this section, we present in detail the handover procedure introduced in Sections 6.3.1 and 6.3.2. This scenario is characterized by an inter-technology handover between Ethernet and Wi-Fi, with WiMAX as the backhaul access technology. Legacy applications with host-initiated sessions are considered, therefore all handover procedures are handled by the MM at the MS. The status of the MS network connections is handled by a mobility manager submodule, called Node Manager (NM), and is updated whenever a new MIHF message is received from the local MIHF module. The network interface information managed by the NM is shown in Table 6.3. The Network Interface ID is the unique identifier associated to the network interface, while the Network Interface Type defines the network technology. In this scenario only Ethernet and Wi-Fi technologies are considered. However, other types of network interfaces can be

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S. Sargento et al. Table 6.3 Network interface information handled by the node manager Network interfaces information Network Interface ID Network Interface Type (ETH/Wi-Fi) MAC Address IP Address Priority (0/1) Status (Up/Going-Down/Down) Active (True/False) With traffic (True/False)

START Ethernet: UP T Wi-Fi: UP

Ethernet MIH Link Going Down ® NSIS HO Make Request

NSIS HO Make Response ® Ethernet MIH Link Action Command

Wi-Fi MIH Link UP ® null Ethernet: UP T Wi-Fi: D

Ethernet: GD Wi-Fi: UP T Ethernet MIH Link Down ® NSIS HO Break Request

NSIS HO Break Response ® null Ethernet: UP T Wi-Fi: D

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Wi-Fi MIH Link Down ® NSIS HO Break Request Ethernet: UP T Wi-Fi: GD NSIS HO Make Response ® Wi-Fi MIH Link Action Command Ethernet: UP WiFi: GD T

Ethernet: GD T Wi-Fi: UP

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Ethernet MIH Link Up ® null Ethernet: UP Wi-Fi: UP T

Fig. 6.17 MM at the MS finite state machine transitions

specified if supported by the MS device. The Status field includes an enumerated value (Up/Going-Down/Down) that describes the current status of the network interface as notified by the received MIHF messages. In order to decide which connection is active when more network interfaces are “UP”, the integer value of the Priority field is considered. This value is commonly configured with “0” for Ethernet (higher priority) and with “1” for Wi-Fi (lower priority). As a consequence, when both the interfaces are “UP”, the Boolean Active field is true for the Ethernet connection. Finally, the Boolean “With traffic” field is adopted to mark the network connection that is currently used to carry data traffic flows. Figure 6.17 shows the finite state machine for a MM handling two network connections: Ethernet with higher priority and Wi-Fi with lower priority. Each state describes the current status of the network interfaces: up (UP), going-down (GD) or down (D). The network connection which is currently used to carry data traffic is marked with the “T” flag. The right side of the figure shows the handover procedure from the Ethernet to the Wi-Fi connection, while the left side shows the handover from the Wi-Fi to the Ethernet connection.

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Resource updating for mobility follows the “make-before-break” approach and is completely transparent to the application layer. When the MM receives a new MIHF Link_Going_Down message for a connection that is currently carrying data traffic, it initiates the procedures for resource reconfiguration. As a result, the CSC at the MS sends an NSIS request to the CSC at the ASN with the Handover Make command. In its turn, the CSC at the ASN creates a set of new Service Flows on the target segment. At the end of the resource allocation process, the MM sends a MIHF Link_Action message to the MIHF so that the handover procedure can proceed. The MIHF Link_Down message announces the end of the handover procedure and the availability of the new L3 connection at the end of the Mobile IP (MIP) registration. Resources between serving SS and BS are released through the NSIS request with the Handover Break command, and data traffic is mapped on the Service Flows over the WiMAX link between target SS and BS. The handover management has been designed in order to minimize the amount of WiMAX resource reconfiguration procedures: if in a given instant the Wi-Fi network connection with lower priority is carrying data flows and the Ethernet interface with higher priority comes back to the “UP” status, the traffic of the existing sessions is maintained on the first interface. The MM only triggers the resource reconfiguration if a Wi-Fi interface Link_Going_Down message is received.

6.5

Testbed Evaluation

This section describes the empirical evaluation of the proposed mobility management architecture prototype. The experimental scenario was depicted in Fig. 6.11. The testbed includes modules that implement the CSN, ASN and MS functionalities. Under the ASN, we install a real, commercial-of-the-shelf (COTS) WiMAX BS directly connected to the ASN-GW. Two WiMAX SSs are connected to the BS creating a Point-to-Multipoint topology. The MS can be connected to SS1 by Ethernet and to SS2 by Wi-Fi. The video server is located in the CSN and the video client in the MS. To carry out the handover between Ethernet and Wi-Fi, we use MIPv4. Since the beginning, we already know that MIPv4 has inherent latency problems because of the packet tunnelling between the Home Agent and the Foreign Agent. However, we use it as demonstrator because of its simplicity. Due to MIPv4 we have to define the Home Network and the Home Agent, the Foreign Network and the Foreign Agent, and the Mobile Node. Table 6.4 shows the testbed components. The goal of this testbed is to evaluate the effectiveness of WiMAX technology in a mobility scenario (handover between Ethernet and Wi-Fi, backhauled by WiMAX), regarding QoS reservation in WiMAX links and user’s authentication mechanisms. Initially the MS is connected to Ethernet. Therefore, it is necessary to reserve in the BS-SS1 WiMAX link, two Service Flows (one uplink and one downlink) with an allocated bandwidth of 512 Kb/s, to handle a video stream.

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Desktops MS’s Laptop

Frequency band Channel bandwidth PHY WiMAX Downlink ratio Uplink & downlink modulation for SSs BS-SSs distances Ubuntu 8.04 (Linux) Ubuntu 8.04 (Linux)

3.5 GHz 7 MHz 16d, OFDM 56/44 64QAM 15 m

Table 6.5 Architecture modules involved in the scenario for the testbed Module Description VLC Client and Server Application CSC_MS Connectivity Server Controller located on the MS Link Layer Controller (LLC) Monitoring the state of MS Network Interfaces WEIRD Agent (WA) Resource Reservation provisioning for Legacy Applications MIHF MIH Function (subset of the IEEE 802.21 specification) NSIS framework NSIS Signalling Generic Adapter Service Flow management Redline equipment Specific Adapter Resource Controller (RC) Control the Resource Reservation on the ASN Gateway AAA Server Authentication, Authorization and Accounting Administration Console Control Plane Monitoring CSC_ASN Connectivity Service Controller located on the ASN Gateway CSC_CSN Connectivity Service Controller located on the CSN MIP (Home Agent, Foreign Agent enabling the Mobile IP protocol Agent, Mobile Node)

While the user is watching a video received through the concatenated WiMAX/ Ethernet link, he/she decides to unplug the Ethernet cable and connect to the Wi-Fi AP. This automatically triggers a vertical handover procedure between Ethernet and Wi-Fi, which will initiate the Service Flows reservation in the BS-SS2 WiMAX link. After this process, the user performs the handover and can continue to watch the video by the composed WiMAX/Wi-Fi link, experiencing the same videoquality. A brief summary of the architecture modules involved in the scenario and their main functionalities is provided in Table 6.5. The performance of the proposed mobility architecture is addressed in the remainder of this section. After a brief overview of the overall handover process, the procedures to provide QoS-aware mobility are analyzed evaluating the internal processing times of the involved modules and the communication times between remote entities for both QoS and MIHF signalling. We repeated each measurement run ten times and report for the median value of the obtained times.

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Handover Process Overview

As discussed in Section 6.3, the handover process follows the “make-before-break” model and consists of three main sequential phases: handover preparation, handover execution and handover conclusion. The first step includes all the procedures to configure the target segment, while during the handover execution the data path towards the foreign network is established. Finally, existing resources on the old path are removed during the handover conclusion phase. In order to ensure the same level of QoS for the active applications when the user moves to the foreign network, the configuration of the target resources during the handover preparation requires the coordination between the entities handling mobility (Mobility Manager) and session control (CSC), as well as the exchange of NSIS messages between MS and ASN for the creation of new Service Flows. Similar procedures have been adopted during the handover conclusion to delete the old resources. The resource reconfiguration phase (handover preparation) is based on IEEE 802.21 technology. It enables to provide QoS-aware mobility and have no impact on the handover execution phase, which is based on MIPv4 [20], and includes the creation of the MIP tunnel between the Foreign Agent and the Home Agent, located in the ASN-GW. Table 6.6 shows the duration of the three handover phases: 736 ms for the handover preparation, 4,199 ms for the handover execution and 655 ms for the handover conclusion. It is important to highlight that the most critical values from the user’s point of view are the handover preparation and the handover execution times since they can lead to some interruptions to the data flows and a consequent degradation of the QoS at the application level. On the other hand, the handover conclusion is completely transparent and has no consequence on the QoS perceived by the user. The handover execution is measured as the time interval between the instant when the Ethernet interface stops receiving the video streaming and the moment when the Wi-Fi interface starts receiving it. The higher value of the handover execution time is due to the MIPv4 and the problems associated with the routing of the packets to the Care-of-Address of the MS. It is known that MIPv6 has improvements relatively to MIPv4, including among others, the redundancy of Foreign Agent entities in the network as the mobile host itself can handle the Foreign Agent functionalities, a native solution for the triangle routing, dynamic address auto-configuration also for Care-of-Addresses and improved security. Nevertheless, for simplicity reasons, and since our focus was in the IEEE 802.21 and QoS integration, MIPv4 was used in this demonstrator. Table 6.6 Handover processing time Handover phase Time (ms) Preparation 736 Execution 4,199 Conclusion 655

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Mobility Manager Initialization

The initialization phase allows the system to be configured with all the required information about the WiMAX network topology and the available network connections for the controlled mobile nodes. While the location of the BSs and their connections with the ASN can be statically configured, other data like the configuration of fixed IEEE 802.16d SS and MS must be dynamically updated. Moreover, when a new device joins the network, there is the need to notify the MMs of the WiMAX network about the status of the network connections between the fixed SS and the connected mobile nodes. During the start-up procedure, the LLC of the MS sends an Ethernet Link_Up event and a Wi-Fi Link_Up event to the MIHF at the MS, and here the messages are forwarded to the registered MMs. Since MIHF at the MS receives the events until it forwards them to the MM at the MS, it takes nearly 215 ms to process the events. The processing time is approximately 4 ms at the MM at the MS and 5 ms at the MM at the ASN, including the updating of the internal status for both network interfaces of the mobile node.

6.5.3

Resource Reconfiguration During HO Preparation and Conclusion

During the handover preparation phase, the resources on the WiMAX/Wi-Fi link are allocated to support the handover of the MS from the home network to the foreign network. A set of service flows is created and activated on the WiMAX link between the target SS and BS, in order to support the media flows of the active video streaming. After the handover execution, during the conclusion phase, the resources reserved in the WiMAX/Ethernet link are released so that they can be available for future connections (consequently, the service flows allocated between the serving SS and BS are also deleted). Figure 6.18 shows the full processing time for handover preparation and conclusion phases in case of mobile-initiated handovers. In both cases the main component is the duration of the NSIS bidirectional communication between the MS and the ASN-GW (87% for handover preparation and 94% for handover conclusion). The MM and CSC at the MS and the CSC at the ASN processing time are detailed in Fig. 6.19 for the handover preparation and the handover conclusion phases. The MS processing time (nearly 70 ms for the handover preparation and 25 ms for the handover conclusion) is due to the CSC at the MS module, where the MM acts as the coordinator of the entire handover procedure. During the first step of the handover preparation, the MM updates the internal state machine with the current status of the MS Ethernet connection and triggers the handover, while the CSC

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ASN Processing Time + Cross Layer MS Processing Time MS<->ASN Communication

800 700

Time (ms)

600 500 400 300 200 100 0 HO Preparation

HO Conclusion

Fig. 6.18 Processing and communication time for mobile-initiated handover

100 90 80 Time (ms)

70

CSC/MM@MS - Session update and Link Action

60 50

CSC_ASN - Target resources creation

40 30 20 10

CSC_MS - Session update CSC_MS - Target resources computation

CSC_ASN - Old resources deletion CSC_MS - Old resources retrieving

MM@MS - Ho make triggering

0 HO Preparation

MM@MS - HO break triggering

HO Conclusion

Fig. 6.19 Processing time for HO preparation and conclusion

retrieves the QoS requirements of the stored sessions and computes the new resources to be allocated in the target link for each of them. The corresponding NSIS QSPEC is sent to the NSIS module to initiate the signalling to the CSC at the ASN through the WiMAX link. The processing time for this first step is approximately 37 ms (13 ms for the MM and 24 for the CSC). In the last step of the handover preparation, when the new resource reservation has been notified by the NSIS response, the CSC at the MS updates the status of the stored sessions, while the MM sends the Link_Action message to the MIHF module, with a total processing time of nearly 33 ms. The conclusion phase is very similar for the first step

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when the deletion of the old Service Flow is triggered, while the last step is characterized by a lower processing time since it does not include the exchange of a MIHF command. The processing time at the ASN-GW includes both the processing of the CSC at the ASN and the cross-layer modules. It is approximately 25 ms for the handover preparation and 15 ms for the handover conclusion). These modules do not take any active handover decision, since they are only in charge of the WiMAX resources reconfiguration for the active sessions, as specified in the received QSPEC. In particular, during the handover preparation phase the new Service Flows are allocated and activated in the WiMAX segment towards the target SS, while during the handover conclusion the Service Flows are deleted over the serving WiMAX link. NSIS communication time between the MN and the ASN is the highest for both handover preparation and conclusion phases. This is due to the NSIS processing time, namely the message association performed by GIST between the first nodes on the preparation phase and changes due to the mobility which affect the NSIS framework as stated in [22]. Besides, all the signalling between the MS and ASN QoS NSIS Entities (QNE) nodes crosses WiMAX links, on which the message delay is approximately 30 ms. With respect to the MIHF at the MS, during the handover preparation phase the processing time to forward the Link_Going_Down event received from the LLC is nearly 215 ms (as we can see in Fig. 6.20). The MIHF processing time at the MS, after receiving the Link_Action from the MM and before sending the message to the LLC, is 145 ms. During the handover conclusion phase, the MIHF at the MS takes approximately 215 ms to process the Link_Down event received from the LLC. It is noticeable that the internal processing time of the MIHF is much smaller than in the CSC modules both in the MS and ASN. The MIHF, when properly configured and initialized, just has to forward events and commands to the MIHUs and LLCs.

LD_Eth

Case of Study

LGD_Eth LU_WiFi LU_Eth LA LD_Eth

MIHF_ASN

LGD_Eth LU_WiFi LU_Eth

MIHF_MS (remote communication)

LD_Eth LGD_Eth

MIHF_MS (local communication)

LU_WiFi LU_Eth

0

50

100

150

200

250 Time (us)

Fig. 6.20 MIHF processing time

300

350

400

450

500

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Finally, the communication time between the MIHF and the CSC is around 750 ms on each direction.

6.5.4

MIH Transport Mechanism

As stated before, the MIH transport mechanism relies on the NSIS communication facilities, namely GIST, to guarantee the transport of messages, and MIH NSLP, to instruct GIST on the delivery process. The processing time of GIST includes the parsing of MIH messages received from the MIH NSLP, the forwarding to the next peer, and the refresh mechanisms to keep the associations. Since the MS acts as the initiator, GIST has a higher processing time when compared with the ASN. This observation is due to the decision process on the transport protocol (UDP or TCP), as well as on the message association mechanism required by GIST. On the ASN side, the GIST processing time is nearly 7.5 ms. Table 6.7 depicts the processing time of MIH NSLP which includes different processes in the MS and the ASN. At the MS, the MIH NSLP processes the messages received by the MIHF (MIH messages to be transported to a remote MIHF), and due to the messages received, the MIH NSLP instructs GIST on the delivery process through the MRI serialization. The MIH Processing at the MS takes approximately 25 ms and includes the parsing of MIH messages, in order to map the destination ID to an IP address (required by the forwarding process of GIST). The MRI Serialization at the MS side lasts nearly 15 ms. At the ASN side, the MIH NSLP processes the messages received from GIST and performs the necessary processing to deliver the MIH messages to the remote MIHF. This process takes around 7.5 ms. All these values are small and do not compromise the handover efficiency. In a remote communication, when MIHF at the MS forwards the events sent by LLC, the MIHF processing time is nearly 310 ms. These results stem from the fact that MIHF receives the event until it forwards them to the NSIS at the MS in order to make a remote communication between the MIHF both at the MS and ASN. Then, when the MIHF at the ASN receives the MIH messages from NSIS (also at the ASN), it has a processing time of nearly 300/400 ms, in order to forward them to CSC (as we can see in Fig. 6.20). The results presented in this section have shown the processing times of the architecture modules involved in the different phases of the vertical handover between Ethernet and Wi-Fi links, detailing the cost associated with the mechanisms to achieve a “make-before-break” approach. Table 6.7 MIH NSLP processing time Phase MIH Processing MRI_Serialization Receive Processing

Time (ms) 25.88 15.23 8.08

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Conclusions

As mobile communication becomes widespread over a wide set of wireless technologies, there is the need for mechanisms that support seamless inter-technology handovers. Moreover, given the user requirements for next generation applications, inter-technology handover mechanisms must be developed while maintaining adequate levels of quality of service. This chapter has presented a solution that addresses this twofold problem based on a QoS-enabled architecture for mobility management in WiMAX networks. Mobility management in heterogeneous environments, with inter-technology handovers, can be substantially improved by the use of a unifying framework such as the Media Independent Handover, described in IEEE802.21. With such an approach, the details of the underlying technologies become transparent to the upper layers, allowing a smoother support of vertical handovers. Seamless handovers call for a “make-before-break” solution, where resources are reserved in the target network before the connection to the serving network is broken. In the mobility management architecture described in this chapter, the IEEE 802.21 Media Independent Handover standard was integrated with the Next Steps in Signalling framework for achieving quality of service signalling in the inter-technology mobility scenario. The chapter introduced a use case developed in the context of the WEIRD project. Implementation aspects about the integration of the Media Independent Handover standard with the Next Steps in Signalling framework within the mobility management architecture were also detailed. The results obtained from an empirical evaluation of a prototype implementation of the proposed architecture of the main mobility and quality of service mechanisms indicate that the solutions presented in this chapter are able to seamlessly integrated these two worlds of QoS and mobility management in a media independent way. Acknowledgment Part of this work was conducted within the framework of the IST Sixth Framework Programme Integrated Project WEIRD (IST-034622), which was partially funded by the Commission of the European Union. Study sponsors had no role in study design, data collection and analysis, interpretation, or writing the book chapter. The views expressed do not necessarily represent the views of the authors’ employers, the WEIRD project, or the Commission of the European Union. We thank our colleagues from all partners in WEIRD project for fruitful discussions.

References 1. ITU-T, General Principles and General Reference Model for Next Generation Networks. Recommendation Y2011 (Oct 2004) 2. ITU-T, General Overview of NGN. Recommendation Y.2001 (Dec 2004) 3. WiMAX Forum, WiMAX End-to-End Network Systems Architecture Stage 2-3: Architecture Tenets, Reference Model and Reference Points, Release 1, Version 1.2 (Jan 2008)

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4. IEEE 802.16 WG, IEEE Standard for Local and Metropolitan Area Networks. Part 16: Air Interface for Fixed Broadband Wireless Access Systems. IEEE Standard 802.16-2004 (Oct 2004) 5. IEEE 802.16 WG, Amendment to IEEE Standard for Local and Metropolitan Area Networks. Part 16: Air Interface for Fixed Broadband Wireless Access Systems – Physical and Medium Access Control Layer for Combined Fixed and Mobile Operation in Licensed Bands. IEEE Standard 802.16e-2005 (Dec 2005) 6. IEEE 802.21 WG, IEEE Draft Standard for Local and Metropolitan Area Networks: Media Independent Handover Services. IEEE P802.21/D10.0 (Apr 2008) 7. R. Hancock, G. Karagiannis, J. Loughney, S. Van den Bosch, Next Steps in Signaling (NSIS): Framework, IETF RFC 4080 (June 2005) 8. H. Schulzrinne, R. Hancock, GIST: General Internet Signalling Transport, IETF NSIS WG Internet-Draft (July 2008) 9. J. Manner, G. Karagiannis, NSLP for Quality-of-Service Signaling, IETF NSIS WG InternetDraft (Feb 2008) 10. G. Martufi, M. Katz, P. Neves, M. Curado, M. Castrucci, P. Simoes, E. Piri, K. Pentikousis, Extending WiMAX to new scenarios: Key results on system architecture and testbeds of the WEIRD project, in Proceedings of the Second European Symposium on Mobile Media (EUMOB) (Oulu, Finland, July 2008) 11. IEEE 802.16 WG, IEEE Standard for Local and Metropolitan Area Networks: Part 16: Air Interface for Fixed Broadband Wireless Access Systems; Amendment 3: Management Plane Procedures and Services. IEEE Standard. 802.16g-2007 (Dec 2007) 12. R. Koodli, Fast Handovers for Mobile IPv6, IETF RFC 4068 (July 2005) 13. S. Gundavelli, K. Leung, V. Devarapalli, K. Chowdhury, B. Patil, Proxy Mobile IPv6, IETF RFC 5213 (Aug 2008) 14. J. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J. Peterson, R. Sparks, M. Handley, E. Schooler et al., SIP: Session Initiation Protocol, IETF RFC 3261 (June 2002) 15. N. Ciulli, G. Landi, M. Curado, G. Leao, T. Bohnert, F. Mitrano, C. Nardini, G. Tamea, A QoS model based on NSIS signalling applied to IEEE 802.16 networks, in 2nd IEEE International Broadband Wireless Access Workshop (Las Vegas, Nevada, USA, Jan 2008) 16. M. Handley, V. Jacobson, C. Perkins, et al., SDP: Session Description Protocol, IETF RFC 4566 (July 2006) 17. M. Castrucci, I. Marchetti, C. Nardini, N. Ciulli, G. Landi, An architecture for the QoS management in a WiMAX network – Analysis and design, in International Conference on Late Advances in Networks (Paris, France, Dec 2007) 18. P. Calhoun, J. Loughney, E. Guttman, G. Zorn, J. Arkko, Diameter Base Protocol, IETF RFC 3588 (Sept 2003) 19. P. Neves, T. Nissil€a, T. Pereira, I. Harjula, J. Monteiro, K. Pentikousis, S. Sargento, F. Fontes, A vendor-independent resource control framework for WiMAX, in Proc. 13th IEEE Symposium on Computers and Communications (ISCC) (Marrakech, Morocco, July 2008), pp. 899–906 20. C. Perkins, IP Mobility Support, IETF RFC 2002 (Oct 1996) 21. L. Cordeiro, M. Curado, P. Neves, S. Sargento, G. Landi, X. Fu, Media Independent Handover Network Signaling Layer Protocol (MIH NSLP), IETF NSIS WG Internet-Draft (Feb 2008) 22. T. Sanda, X. Fu, S. Feong, J. Manner, H. Tschofening, Applicability Statement of NSIS protocols in Mobile Environments, IETF NSIS WG Internet-Draft (July 2008)

Chapter 7

Radio Resource Management in WiMAX Networks Ljupcˇo Jorguseski and Ramjee Prasad

Abstract This chapter presents the general Radio Resource Management (RRM) problem in wireless access networks and gives performance evaluations for different downlink resource (sub-carrier) allocation algorithms in WiMAX TDD systems based on OFDMA wireless access. This is particularly important in downlink due to the traffic asymmetry and due to the information availability at the base station regarding the quality requirements for a particular user. The comparative performance analysis of the different resource allocation algorithms is using the average cell/user throughput and user throughput versus distance from the reference base station as performance metrics. For the comparative performance evaluation, we have resorted to MATLAB simulations. Additionally, a semi-analytical approach is proposed for the downlink throughput performance estimation of the algorithms that do not rely on the channel quality information feedback from the mobile users. The analysis shows that Proportional Fair and Soft partitioning/re-use algorithms are good candidates for downlink resource allocation in WiMAX TDD systems and that the proposed semi-analytical approach accurately estimates the throughput performance of the reuse schemes.

7.1

Introduction

This chapter addresses the radio resource management (RRM) in OFDMA based cellular networks such as WiMAX. One of the major RRM task is the allocation of the time-frequency resource units for the different users in a way that user specific quality thresholds are satisfied and at the same time the overall throughput of the system is maximized. This is particularly important in downlink due to the traffic L. Jorguseski (*) TNO Information and Communication Technology, Department – Access Network Technologies, Postbus 5050, 2600 GB, Delft, The Netherlands e-mail: [email protected]

R. Prasad and F.J. Velez, WiMAX Networks, DOI 10.1007/978-90-481-8752-2_7, # Springer ScienceþBusiness Media B.V. 2010

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asymmetry and due to the information availability at the base station regarding the quality requirements for particular user. This chapter also presents simulation and semi-analytical approaches for estimating WiMAX throughput performance. The chapter is organized as follows. Section 7.2 presents a general definition of the RRM problem for a cellular system. The definition of resource units (RUs) is presented in Section 7.3. The different downlink RU allocation algorithms investigated in this chapter are presented in Section 7.4. The simulation and semianalytical approach for evaluating WiMAX system performance are presented in Sections 7.5 and 7.6, respectively. The chapter is finalized with the conclusions and recommendations in Section 7.7.

7.2

General Radio Resource Management (RRM) Problem Definition

Let us assume a WiMAX cellular network with M active mobiles in the service area denoted with M = {1, 2, . . . M}. Denote with B = {1, 2, . . . B} the set of all base stations (BSs) used to provide the necessary cellular coverage. The radio propagation link between each pair BS and mobile subscriber can be characterized with the link gain gi,j, where i ¼ 1, 2, . . ., B represents the index of the BS and j ¼ 1, 2, . . . M denotes the index of the mobile user. The link gains gi,j include all propagation phenomena such as path-loss, shadowing, and multi-path fading. This is schematically presented in Fig. 7.1. The radio link gain g links the received power level Prx at the input of the receiver with the transmitted power Ptx at the output of the transmitter as follows: Prx ¼ Gt Gr gPtx 1

2 g21 g1M

B gB1

g22

g12

g2M

gB2 gBM

g11

1

(7.1)

2

M

Fig. 7.1 Schematic view of the radio link gains in a wireless cellular network

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Here, Gt and Gr are the transmitter and receiver antenna gains, respectively. In order to describe the instantaneous radio conditions in the cellular system under investigation we can use the link gain matrix G that is defined as: 0

g11 g12 ::: g1M

1

B g g ::: g C B 21 22 2M C G¼B C @ :::: A

(7.2)

gB1 gB2 ::: gBM The gain matrix G is dynamic; the dimension M is changing depending on the number of active mobile users and each element gij changes with the mobile’s movement. Note that in general we have different gain matrix G for uplink and downlink (e.g. if different frequency bands are used for uplink and downlink). The elements of this matrix are describing the individual radio link gains between the pairs BS and mobile subscriber. Assume that each BS from the set B has a limited set of waveforms C that can be allocated to the mobile users and C ¼ {1, 2, . . .C} is the numbered set of these waveforms. Note that with a waveform we refer to the combination of: l l

l

Modulation scheme such as BPSK, QPSK, 16QAM, etc. [1]. Channel coding such as convolutional coding [2], turbo coding [3], etc. with a certain coding rate. Multiple access specific signal form such as the combination of time-slot(s) and frequency in TD/FDMA system (e.g. GSM, GPRS or EDGE), channelisation/ spreading code in DS-CDMA systems (e.g. UMTS), or a set of sub-carriers in the OFDM signal in WiMAX and E-UTRAN wireless cellular systems.

The radio resource management problem can be defined as follows. Taking into account the link gain matrix G as presented in Section 7.2 the RRM algorithms in the given wireless cellular system handle the following assignments: l l l

Assign one or more access point from the set B. Assign uplink and downlink waveform from the set C. Assign transmitting power for the BS and for the mobile.

These assignments should be such that the following quality requirements in uplink and downlink are satisfied: ul SINRul i;j  gj

(7.3)

dl SINRdl i;j  gj

(7.4)

dl Here, gul j and gj are the quality targets for the individual users in uplink and downlink, respectively. Note here that the uplink and downlink quality requirements for the SINR can be derived from the link-level evaluations of the particular

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radio bearer and depend on the desired communication service (e.g. voice, video, web-browsing, etc.), radio propagation characteristics, and the transmission/ reception algorithms implemented at the BS and the user terminal. Radio resource management (RRM) aims at optimal “management” or (realtime) “allocation” of the available radio resources among the currently active users given the radio network infrastructure and its capacity. The optimal management in the context of RRM is governed by the QoS levels that the wireless operator provides to its customers and operator’s policies. The operator’s policies are driven by the operator’s business plan. This requires a complex and dynamic interaction between the different RRM algorithms (e.g. admission/congestion control, radio link adaptation, scheduling, handover, etc.) in the network to achieve the desired QoS levels according to the operator’s policy, given the current system conditions. These interactions between the RRM algorithms should jointly facilitate the overall optimization goal. The RRM algorithm usually aims at the optimization of an objective function given the quality related conditions (7.3) and (7.4). The objective functions can relate to the desired policy by the operator. Here are few examples for the operator policies: l

l

l

l

Serve as many users as possible: the RRM algorithms would aim at maximizing the number of concurrently active users given the target conditions (7.3) and (7.4). Maximizes the total achieved throughput in downlink and uplink: the RRM algorithm assignments would optimize the total sector throughput in downlink and uplink given the conditions (7.3) and (7.4). Minimize the downlink and uplink interference: the RRM algorithm assignments would minimize the used power in downlink and uplink (especially interesting for interference limited systems). The likelihood that the user throughput is lower than a minimum level Rmin should be lower than 5%. The RRM algorithm assignments would then aim at optimizing the assignments in such a way that the uplink/downlink throughput per user is higher than the pre-defined threshold Rmin with sufficient probability.

The RRM algorithms take also the responsibility for an efficient utilization of the available radio spectrum. The efficient usage is of crucial importance because radio spectrum is a scarce and costly resource. Measures must be taken to ensure this effectiveness, and this is handled at two stages – network planning and during network operation via RRM functions. Usually the extended set of (advanced) RRM functions is implemented at the BS. This is because the BS can perform and gather measurements that are used as input for the RRM functions and they additionally require significant processing. At new session set-up or handover request the admission control decides whether to admit the user to the BS. The admission/rejection decision is based on interaction with the load/congestion control, in order to assess the current load conditions, and with the scheduling and link adaptation in order to assess the achievable throughputs. The load control function monitors the interference and the current load in the BS and takes appropriate

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actions (e.g. orders the admission control to not admit any new users) to resolve overload/congestion situations. The power and rate assignments are executed by the e.g. packet scheduling and radio link adaptation functions in order to satisfy the different QoS requirements for the new and ongoing sessions. These functions also interact with the admission/load control algorithms in order to adjust the scheduling order or the link adaptation. In the following, these important RRM algorithms are briefly explained.

7.3

Radio Resource Definition in WiMAX

In WiMAX system, OFDM transmission is scalable. The scalability can be made by changing the size of FFT and consequently the number of sub-carriers. The supported FFT sizes are 128, 512, 1024, and 2048, but only 512 and 1024 are mandatory for Mobile WiMAX. The 802.16e PHY supports Time Division Duplex (TDD), Full and Half Frequency Division Duplex (FDD) operations. However, the initial release of mobile WiMAX only includes TDD. Figure 7.2 shows the OFDMA frame structure for a TDD implementation. The data is configured into frame of 48 OFDM symbols. Each frame is divided into downlink (DL) and uplink (UL) sub-frames separated by Transmit/Receive and Receive/Transmit Transition Gaps (TTG and RTG). Each DL sub-frame starts with a preamble followed by the Frame Control Header (FCH), the DL-MAP, and the UL-MAP. In the DL, sub-channels may be assigned for different users. Frame duration is 5 ms. Each frame consists of 37 data symbols and 11 overhead symbols.

Fig. 7.2 WiMAX OFDMA frame structure

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The 37 data symbols can be partitioned between the uplink and downlink according to a certain ratio, for example DL versus UL ratio of 28:9. For the RRM algorithm evaluations in this chapter the WiMAX TDD resource model consists of 35 OFDM symbols (28 data symbols and 7 overhead symbols)/DL sub-frame [5], and 840 useful sub-carriers/OFDMA symbol [4]. These 840 sub-carriers are organized into 30 RUs (28 sub-carriers/RU) [4]. There are two types of sub-carrier permutations for sub-channelization: diversity and contiguous [4]. The diversity permutation draws sub-carriers pseudo randomly to form a sub-channel such as FUSC (Fully Used Sub-carrier), PUSC (Partially Used Sub-carrier), and additional optional permutations. It minimizes the probability of using the same sub-carrier in adjacent cells or sectors. The contiguous permutation groups a block of contiguous sub-carriers to form a sub-channel such as AMC. The channel estimation in this case is easier than in the case of diversity permutation.

7.4

Downlink RRM Algorithms for WiMAX Systems

In a WiMAX cellular OFDMA system we have two-dimensional Frequency-Time (F-T) resource as presented in Fig. 7.3. In the frequency domain we have N subcarriers labeled f1 to fN. In the time domain we have OFDM symbols with duration Ts, grouped in Transmission Time Intervals (TTIs). The system allocates a set of sub-carriers per TTI (or multiple of TTIs) to a particular user that is referred to as Resource Unit (RU). Note that one or more RUs can be allocated to a particular user. This is indicated with the colored shaded areas in Fig. 7.3 with the assumption that the RU is allocated per TTI, each TTI contains eight OFDM symbols, and there are K resource units with different number of

Fig. 7.3 Downlink time-frequency resource in OFDMA cellular system; Ts is the OFDM symbol duration; TTI is the transmission time interval; gray shaded area is one OFDM symbol; different color per RU designates different user

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sub-carriers per RU. The AMC scheme allocates one modulation and coding scheme for the whole RU and this is done per TTI (or multiple TTIs) basis. Denote with ‘m’ an arbitrary user in a WiMAX cellular system presented is communicating with ‘b’-th base station (b ¼ 1, 2, . . ., NB), sector ‘s’ (s ¼ 1, 2, 3) and has been allocated RU ‘r’ (r ¼ 1, 2, . . ., K). Then the signal-to-interference and noise ratio (SINR) for the allocated RU can be calculated as: SINRm;b;s ðrÞ ¼

PRU b;s ðrÞgm;b;s ðrÞ NB P 3 P i¼1 j¼1

PRU b;s ðrÞ gm;i;j ðrÞ

RU ¼ kTWRU Nth

PRU i;j ðrÞgm;i;j ðrÞ

þ

; j 6¼ s if i ¼ b RU Nth

is transmission power of the r-th RU from the ‘b’-th base station, and sector ‘s’ is the radio link gain (path-loss, shadowing, multi-path fading, and antenna gain) between user ‘m’ and sector ‘j’ from base station ‘i’ and for the resource unit ’r’. The dependency on the RU index is due to the frequency selective multi-path fading. is the thermal noise level for the RU, calculated from the Boltzman constant, receiver temperature, and RU bandwidth

The achievable bit-rate Rm,b,s(r) given the allocated RU ‘r‘ with bandwidth ‘Br’ depends on the allocated bandwidth and the achievable SINRm,b,s(r) that is Rm,b, s(r) ¼ f(Br, SINRm,b,s(r)). The RU allocation algorithm aims at finding the optimum solution according to a certain optimization criteria such as for example minimize the total downlink power, maximize the total downlink throughput in the system, etc. This optimization should be done given the conditions that all users achieve their minimum throughput requirement, the total power per base station does not exceed the physical maximum and that each RU is allocated to not more than a single user: ( min P

Total

¼

NB X 3 X

PTotal i;j

¼

i¼1 j¼1

NB X 3 X K X

) PRU r;i;j

i¼1 j¼1 r¼1

or ( max RTotal ¼

NB X 3 X

Ri;j ¼

i¼1 j¼1

Rm ¼

Mi;j X NB X 3 K X X i¼1 j¼1

K X

!) gm;r Rm;i;j ðrÞ

s.t:

m¼1 r¼1

gm;r Rm;i;j ðrÞrRmin m

(7.5)

r¼1

PTotal i;j bPmax

(7.6)

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gm;r b1; 8r ¼ 1; :::; K

(7.7)

m¼1

Mi;j gm;r RU ¼ kTWRU Nth

is the number of users active in base station ‘i’ and sector ‘j’. is the integer variable equal to 1 if r-th resource unit is allocated to the m-th user; otherwise it is zero. is the thermal noise level for the RU, calculated from the Boltzman constant, receiver temperature, and RU bandwidth

Condition (7.5) ensures that the minimum QoS level (e.g. user bit rate) for the m-th user is satisfied. Condition (7.6) ensures that the physical limit for the total transmitted power per sector is not exceeded. Condition (7.7) ensures that only one user per RU has been allocated. It the optimization problem presented above we have a non-linear dependency between the allocated power and the achievable RU throughput that is Rm,b,s(r) ¼ f(Br, SINRm,b,s(r)). This non-linear dependency (usually logarithmic) results in a non-linear optimization problem. Additional complexity is the integer character of the allocation variables gm,r making the optimization problem mixed with real and integer variables. In order to avoid complex optimization solving of the RU allocation problem in the following sections several heuristic/practical downlink RU allocation algorithms are proposed.

7.4.1

Reuse-One

All available RUs can be allocated in a random fashion in each sector with reuse one. More than one users can be randomly selected for each RU. This is the simplest form of allocating the sub-carriers to different users and is considered as a reference case. Note that a user is allocated one or more RUs and that some users might not get any RU allocated.

7.4.2

Reuse-Three

The number of available resource units NRU is divided in three disjoint sets, which are consequently used in different sectors as presented in Fig. 7.4. Within one sector the users are allocated to RUs of this sector randomly as it is the case with the reuse-one. The division of sub-carriers into NRU total number of RUs is done in a continuous way in the frequency domain as presented in Fig. 7.5.

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Fig. 7.4 Sub-carrier reuse three 2 2

3

1 3

2

1

2 1

2 1

3

3

2

Node-B

1 3

2 1

1 3

3

Target cell

1

NRU – 5

4

NRU – 2

Sector 1

f 2

NRU – 4

5

NRU – 1

Sector 2

3

6

NRU – 3

f NRU

Sector 3

f

Fig. 7.5 Sub-carrier divisions per RU for different sectors in frequency domain – reuse three

7.4.3

Soft Re-Use

All available sub-carriers are used in each sector as in case of Reuse-one, but the power allocated to sub-carriers is not equal as presented in Fig. 7.6. The number of sub-carriers with Pedge (dark color) is one third of the total number of sub-carriers, hence, the rest (2/3) will have power Pclose (light color). The users are classified into “close” (close to the cell center) and “edge” (close to the cell edge) by comparing the user’s average geometry Gavg with a pre-defined threshold Gth : Gavg ¼

NRU 1 X GðrÞ NRU r¼1

GðrÞ is the average geometry per RU and is given by: . PRU r;b;s Lb;s ; where j 6¼ s if i ¼ b GðrÞ ¼ N N . cell P sec tor P RU RU Pr;i;j Li;j þ Nth i¼1 j¼1

(7.8)

(7.9)

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is the allocated transmission power to the rth RU from the bth base station PRU r;b;s and sector s. Li,j is the propagation loss including path loss, shadowing, antenna gain between user and the ith base station and sector j. RU is the thermal noise level for RU. Nth All users with Gavg b Gth are “edge” users, and users with Gavg > Gth are “close” users. All RUs are allocated with Pclose to close users and Pedge to edge users in the random fashion. A soft re-use named “re-use partitioning” presented in Fig. 7.7 is supported in WiMAX system. The user close to a base station can operate with all available sub-channels. In case of an edge user, each sector can operate with a fraction of all available

1

NRU – 5

4

NRU – 2

Sector 1

f 2

NRU – 4

5

NRU – 1

Sector 2

3

6

NRU – 3

f NRU

Sector 3

f

Fig. 7.6 Soft reuse – ‘edge’ sub-carriers (dark color) have higher power than ‘close’ sub-carriers (light color) NRU – 5

1 4

5

NRU

6

Sector 1

f

NRU – 4

2 4

5

NRU

6

Sector 2

f

NRU – 3

3 4

5

6

NRU

Sector 3

f

Fig. 7.7 Sub-carrier division in re-use partitioning in WiMAX system

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sub-channels [6], for example, a fraction of 1/3 as in our model. The WiMAX case shows that the full load frequency reuse one is kept for “close” users to maximize spectrum efficiency, whereas fractional frequency reuse is used for “edge” users to improve their throughput as well as mitigate inter-cell interference among users.

7.4.4

Maximum C/I

In this case it is assumed that CQI information is available at the downlink subcarrier allocation algorithm at the NodeB as reported per RU from each mobile. This radio channel quality information is used in the allocation decision as illustrated in Fig. 7.8. Assume that the three different curves in Fig. 7.8 represent the normalized radio channel realization (i.e. the multi-path frequency selective power profile) for three different users.1 The maximum C/I sub-carrier allocation algorithm allocates the RUs Normalized − Pedestrian A 2.5 User 1 User 2 User 3

Power per subcarrier

2

1.5

1

0.5

0 0

50

100

150

200

250

300

350

400

450

500

Subcarrier number

Fig. 7.8 The maximum C/I based sub-carrier allocation algorithm for three users (512 subcarriers)

It is normalized in a sense that all users have average sub-carrier power E[P(k)] ¼ 1 over all subcarriers. 1

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to the user that has the best radio channel conditions for that particular RU. This is illustrated in Fig. 7.8 with the different thickness of the curves. Note that all the subcarriers (RUs) between one and 48 and 123 and 251 are allocated to User 1 (thick solid line). Similarly, all sub-carriers where the channel conditions are the best for User 2 (User 3) marked with dot-dashed (dashed) line and allocated to this user. Note that User 3 will be allocated only a small part of the subcarriers between 49 and 122. This is due to the bad radio-conditions for User 3 with respect to the other two users. This means that users in bad radio conditions in this algorithm will “starve” for resources.

7.4.5

Proportional Fair (PF)

The PF scheduler calculates the ratio of the feasible rate to the average throughput for each user. The user with maximum ratio will be selected for transmission at the next coming time slot. In time slot t, the feasible rate of user k is Rk(t) and its average throughput is denoted by . Then user k* with maximum is served in time slot t. And the average throughput of each user is updated by [7]: 8  1  1 > > > 1  RðtÞ þ Rk ðtÞ <  tc k tc   Rðt þ 1Þ ¼  > 1 k > > 1 RðtÞ : tc k

k ¼ k (7.10) k 6¼ k

where tc is the time constant for the moving average.

7.5

Simulation Evaluation of Downlink Sub-Carrier Allocation Algorithms

For the performance evaluation of the different sub-carrier allocation algorithms we have used the system scenario with 19 three-sectored base stations as presented in Fig. 7.4. We have generated from ten to 30 users per sector in the three sectors of the central base station in order to avoid edge effects. We have assumed that all RUs are occupied in the surrounding base stations. A crucial modeling step is how to decide from the SINR calculated on the system level per RU the corresponding throughput (or BLER). Note that the BLER versus SINR performance is usually determined via link-level simulations with AWGN channels. Consequently, the appropriate modulation and coding scheme can be assigned that gives the maximum throughput for a given BLER target (e.g. BLER ¼ 10%). In this chapter we use the Effective Exponential SIR Mapping (EESM) approach [8], which is presented in Fig. 7.9. The EESM is especially applicable to the case of low/medium Doppler, that is when the channel can be assumed to be constant during a Transmission Time

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Link level

System level

SIReff (G ; h) BLEPAWGN

BLEP (G ; h)

Mapping funct. SIReff ( . )

G,h

- Determine short-termaveraged Geometry - Generate instantanoeus channel

Link adaptation, Scheduling, ARQ, etc.

Throughput

Fig. 7.9 Effective Exponential SIR Mapping (EESM) methodology in OFDMA [8]

Interval (TTI). In the case of high Doppler (when the channel cannot be assumed to be constant over the TTI) the EESM cannot be applied as straightforwardly as for the case of low/medium Doppler. The reason is that, in this case, the effective SIR cannot be assumed to be constant during the TTI. Thus, a more complex mapping function may be needed for accurate performance estimation. The EESM works as follows: l

l

l

l

On system level, a UE exists within the simulated deployment. Based on the UE position, a short-time-average geometry G is calculated as the ratio between the desired signal level originated from the reference sector and the interference level originated from the surrounding cells. The geometry G includes the effect of distance-dependent path-loss, shadowing, and thermal noise. For each UE and each TTI, an instantaneous channel-impulse response hðtÞ is generated according to the average channel-delay profile e.g. Pedestrian B, Pedestrian A, etc. Based on the geometry G and the instantaneous channel-impulse response hðtÞ an effective SIR is calculated and used in the link-level evaluations. From the link-level simulations with AWGN channel the corresponding BLER is determined for a particular modulation and coding scheme, which in turn is used for the system level evaluations (see Fig. 7.9).

The link level results [9] (Tables 3.1–3.4) are used for the mapping between the effective SINR and the block error rate (BLER) for each AMC combination. Note here that these link level results were found as most appropriate publicly available results at the time of writing of the thesis. The link level performance depends heavily on the physical layer transmission and reception algorithms (e.g. MIMO techniques, interference cancellation techniques, etc.), radio channel knowledge (e.g. ideal or non-ideal channel estimation or feedback), etc. Therefore, the absolute performance results for the downlink throughput in the WiMAX system presented in this chapter have to be comprehended by having these reference link level results in mind. The interested reader should be aware that the absolute downlink throughput performance of WiMAX presented in this chapter will change if other reference link level

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results are considered. However, the relative performance trends between the different allocation algorithms should still hold even if other link level results are used. The performance evaluation of the different downlink resource allocation schemes was done by MATLAB simulations. The wireless cellular system was modeled with one central three-sectored site surrounded with two tiers of interfering three-sector sites. The simulations were done for different number of users per sector randomly placed in the central site with uniform spatial distribution. The users are assumed continuously active in downlink (i.e. the full buffer approach). The geometry thresholds of 8 dB and 14 dB for the Soft Reuse and Partitioning Reuse allocation algorithms were used, respectively. These values were selected by trial simulations as a best compromise between satisfactory average sector throughput and reasonable throughput for cell edge users, as shown in Table 7.1, Figs. 7.10 and 7.11. Table 7.1 The sensitivity of geometry threshold Allocation algorithms Average sector throughput (Mbps) 2.9269 Gth1 ¼ 0 dB 2.5448 Gth2 ¼ 0 dB 6.1217 Gth1 ¼ 8 dB(selected) 5.9526 Gth2 ¼ 14 dB(selected) 8.6212 Gth1 ¼ 15 dB 7.1100 Gth2 ¼ 20 dB

Cell edge throughput (at 0.475 km) (Mbps) 0.0411 0.0398 0.0534 0.0632 0.0451 0.0509

Note: Gth1 and Gth2 are geometry threshold for Soft Reuse and Partitioning Reuse, respectively

Normalized User Throughput [bit/s/Hz]

Sensitivity of Geometry Threshold for Soft Reuse; Pedestrian B; WiMAX Gthr1 = 0 dB Gthr1 = 15 dB Gthr1 = 8 dB (selected)

0.2 0.18 0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

Distance [km]

Fig. 7.10 WiMAX user throughput versus distance for soft reuse, 30 users/sector

0.5

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Normalized User Throughput [bit/s/Hz]

Sensitivity of Geometry Threshold for Partitioning Reuse; Pedestrian B; WiMAX Gthr2 = 0 dB Gthr2 = 20 dB Gthr2 = 14 dB (selected)

0.2 0.18 0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0

0

0.05

0.1

0.15

0.2 0.25 0.3 Distance [km]

0.35

0.4

0.45

0.5

Fig. 7.11 WiMAX user throughput versus distance for partitioning reuse, 30 users/sector

Although the selected geometry thresholds do not give us the maximum average sector throughput they perform better than the other geometry thresholds in terms of throughput for cell edge users. From Fig. 7.10 it can seen that at distances further than 0.275 km the selected geometry threshold outperforms the other in terms of user throughput versus distance. The other important system parameters are presented in Table 7.2. The normalized average sector and user throughput for WiMAX is presented in Figs. 7.12 and 7.13, respectively. The normalization is done with the system bandwidth. Note that the vertical bars presented in these figures are the 95% confidence intervals. It can be observed that the maximum C/I resource allocation algorithm has the best performance regarding the average sector and user throughput. This is because the RUs are allocated always to the user that has the best channel conditions at the moment of allocation. The Proportional Fair, Soft Re-use and Reuse-Partitioning have similar performance with regard to the average sector/user throughput. However, in a practical implementation it is expected that the proportional fair algorithm will perform better as it uses the channel quality feedback from the UEs and tries to achieve fairness by weighting the achieved throughput in the previous allocations. The soft reuse schemes in this study were already ‘optimized’ for this uniform spatial distribution of the end users by selecting an appropriate geometry threshold for deciding if the UE is ‘close’ or at the ‘cell edge’. In practice this could be difficult to achieve on the fly for different spatial distributions of the UEs. The reuse three has the worst performance as it uses only one third of the available bandwidth.

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Table 7.2 The main system parameters for the simulations

Parameter fcarrier (GHz) fsampling (MHz) Bandwidth (MHz) Frame length (ms) Nr. OFDM sym. Cell radius (km) Total sub-carriers Used sub-carriers fspacing (KHz) Guard time (s) Symbol dur. (s) Number of RUs Total DL power (W) DL modulation Coding rates Antenna gain Antenna FTB ratio Link-level interf. Nth (dBm/Hz) ssh (dB) Shadow corr.

WiMAX 2.5 11.2 10 5 48 per frame 0.5 1,024 840 10.9375 11.43e-06 102.86e-06 30 40 QPSK, 16/64 QAM 1/2, 2/3, 3/4, 5/6 16 dBi 25 dB EESM 174 8.9 0.5

Average Sector Throughput vs Number of Users; Pedestrian B; WiMAX

Normalized Sector Throughput [bit/s/Hz]

1.6

1.4 Re-use 1 Re-use 3 Soft re-use Maximum C/I Proportional Fair Soft partitioning

1.2

1

0.8

0.6

0.4

0.2

5

10

15 20 Number of Users per Sector

Fig. 7.12 WiMAX sector throughputs with 95% confidence intervals

25

30

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Average User Throughput vs Number of Users; Pedestrian B; WiMAX 0.16 Re-use 1 Re-use 3 Soft re-use Maximum C/I Proportional Fair Soft partitioning

Normalized User Throughput [bit/s/Hz]

0.14 0.12 0.1 0.08 0.06 0.04 0.02 0

5

10

15

20

25

30

Number of Users per Sector

Fig. 7.13 WiMAX User throughputs with 95% confidence intervals

The reuse one has better performance than the reuse three and its performance can be improved by either differentiation between close and edge users (e.g. soft reuse or reuse partitioning) or implementing channel aware resource allocation (e.g. proportional fair or maximum C/I). Another important performance measure is the dependence of the average user throughput versus the distance from the reference cell, as presented in Fig. 7.14. From the enlargement of Fig. 7.14 we can see that the drawback of the maximum C/I algorithm is that it discriminates users near the cell edge. Especially, the users at the cell edge (e.g. distances larger than 0.45 km) are starved for resources and have a rather low downlink throughput. The proportional fair algorithm has the best performance with regard to the user throughput versus distance as it makes the trade-off between the current channel conditions and previously experienced throughputs.

7.6

Semi-analytical Evaluation of Downlink Sub-carrier Allocation Algorithms

This section proposes an effective analytical framework to estimate the average sector throughput, user throughput, and user throughput versus distance for the resource allocation algorithms not relying on channel quality feedback that is Reuse

306

L. Jorguseski and R. Prasad Normalized User Throughput vs Distance; Pedestrian B; WiMAX 0.5

Re-use 1 Re-use 3 Soft re-use Maximum C/I Proportional Fair Soft partitioning

Normalized User Throughput [bit/s/Hz]

0.45 0.4 0.35 0.3

0.025

0.25

0.02

0.2

0.015 0.01

0.15

0.005

0.1

0 0.3

0.35

0.4

0.45

0.05 0

0

0.05

0.1

0.15

0.2 0.25 0.3 Distance [km]

0.35

0.4

0.45

0.5

Fig. 7.14 WiMAX user throughput versus distance for 30 users per sector

One, Reuse Three, and Soft reuse. The investigated WiMAX cellular system is presented in Fig. 7.4 with the following assumptions: l l l l

The cells are circular with radius R. Users are uniformly distributed over the whole target cell. No frequency selective multi-path fading.2 No shadowing effects in the propagation loss.

Let B ¼ {B1, B2, . . ., BQ} be a set of Resource Units (RUs) within the transmission bandwidth. Each RU consists of M¼28 for WiMAX. Average sector throughput of the qth RU is given by: p

Z 2 ZR Rq ¼

Rq ðr; yÞf ðr; yÞrdrdy p6

(7.11)

0

2 Note that in the simulation studies in Section 7.5 the frequency selective multi-path is taken into account in order to show the performance gain of Proportional Fair and Maximum C/I allocation algorithms. These algorithms utilize the frequency selectivity of the radio channel in the allocation of the resource units. However, the frequency selective multi-path is not considered in the semianalytical approach because the focus is first on the Reuse-One, Reuse-Three and Soft Reuse algorithms that do not utilize the frequency selectivity of the radio channel for the allocation decisions. This is left for further study.

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f(r, y) is the probability density function of user’s location (r, y) Rq(r, y) is the achievable throughput per RU if allocated to a user on location (r, y) Because we have assumed that users are uniformly distributed, hence f(r, y) is a constant and has to satisfy the following condition: Zymax Zrmax f ðr; yÞrdrdy ¼ 1 ymin

(7.12)

rmin

After solving the double integration (7.12), we get: f ðr; yÞ ¼ 

2  2 2 rmax  rmin ðymax  ymin Þ

(7.13)

Rq(r, y) is a function from effective SIR i.e. Rq(r, y) ¼ f(SIReffq(r, y)) [8]: ! M g ðr;yÞ 1 X  mb SIReffq ðr; yÞ ¼ b ln e (7.14) M m¼1 gm(r, y) is the Signal-to-Interference-and-Noise Ratio (SINR) of user at position (r, y) over sub-carrier m and given by:  gm ðr; yÞ ¼ PðmÞGq ðr; yÞ

 N RD N þ Np NSD =NST

(7.15)

We have assumed no frequency selective multi-path fading which means that P(m) ¼ 1 for all sub-carriers. For a UE located at a position (r, y) in the target cell, the average geometry of user at position (r, y) over qth RU Gq(r, y) is defined as the ratio of the total received power from the reference (desired) sector to the total aggregate power of all interfering sector (7.9):

Gq ðr; yÞ ¼

. PRU q;b;s Lb;s ðr; yÞ 19 P 3 P i¼1 j¼1

PRU q;i;j =Li;j ðr; yÞ

þ

with j 6¼ s if i ¼ b

(7.16)

RU Nth

The propagation loss consists of two factors: l

l

The distance based path loss. For WiMAX with 2.5 GHz operating frequency the distance based path loss can be calculated as [10] PLi(r, y) ¼ 130.18þ37.6Di(r, y). Here, Di(r, y) is the distance between user at position (r, y) and ith base station (km). When the distance between user and the base station is smaller than 0.03 km the path loss is set to 70 dB. The antenna gain has e beam pattern as defined in [8, 10]. For angle y (relative the boresight direction), the antenna has gain:

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"



GðyÞ ¼ Gmax þ max 12

y

#

2

y3dB

; GFB

(7.17)

y 3dB is the 3dB beam width Gmax is the maximum antenna gain (boresight direction); Gmax = 16 dBi GFB is the front-to-back ratio; GFB = 25 dB In case of adaptive modulation and coding (AMC) the Rq(r, y) can be approximated by the sigmoid function as presented in Fig. 7.15: The sigmoid function has the following form: Rq ðr, yÞ ¼

Rmax 1 þ eabSIReff q ðr;yÞ

(7.18)

Rmax is the maximum transmission rate of AMCs per RU a, b are the fitting parameters (e.g. least square estimates fitting) The fitting parameters can be determined by, for example, least square estimate fitting of the sigmoid function to the link-level results Tables 3.1–3.4 in [9] for WiMAX. This is why the approach is labeled as semi-analytical. Replacing (7.18) in (7.12) and by using (7.14) and (7.15) we have average throughput of q-th RU per sector as follows: p

Z 2 ZR Rq ¼ p6 p 2

Z ZR p6

0

1þe

(7.19)

R  max 



¼

0

Rmax f ðr; yÞrdrdy abSIR effq ðr;yÞÞ ð 1þe

ab10log10 Gq ðr;yÞ



N NþNp

RD NSD =NST

 f ðr; yÞrdrdy

Throughput (Mbps)

16QAM

16QAM 1/2 QPSK 2/3 QPSK 1/3

S1

S2

S3

SIReff

Fig. 7.15 Approximation of the average user throughput per RU as a function of the effective SIR

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Fig. 7.16 Division of the integration area according to the path loss calculation

A2 0.03 0

A1

The propagation loss is calculated based on two parts (smaller and larger than 0.03 km) as presented in Fig. 7.16. Hence, the average sector throughput of q-th RU is given by: p

Z 2 Z0:03 Rq ¼ A1 p6

0

Rmax f1 ðr; yÞrdrdy abSIR effq ðr;yÞÞ ð 1þe

p

Z 2 ZR þ A2 p6 0:03

Rmax f2 ðr; yÞrdrdy abSIR effq ðr;yÞÞ ð 1þe

(7.20)

A1, A2 are the ratios of the inner and the outer area to the whole sector area, respectively f1(r, y), f2(r, y) are the PDFs (7.12) of user’s location in the two integration parts. The average sector throughput is calculated as summation of the RU throughput as calculated in over the whole set Bq of available RUs. For calculating the average user throughput given the distance from the reference base station we can divide the covered cell area in concentric rings. The inner circle of the l-th ring is on distance rl while the outer circle in on distance rl+1, where the ring width is equal to rl + 1  rl as Fig. 7.17 and depends on the desired granularity for the throughput versus distance calculation. Nu is the number of users per sector. 0 1 ymax Zrlþ1 Z B Q 1 XB C Rq ðr; yÞf ðr; yÞrdrdyA Rðrl Þ ¼ @ Nu q¼1 0

rl

ymin

Z BQ 1 X B ¼ @ Nu q¼1

p 2

p6

1

Zrlþ1 rl

 1þe

R  max

ab10log10 Gq ðr;yÞð

Þ

RD N NþNp NSD =NST

 f ðr; yÞrdrdyC A (7.21)

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Fig. 7.17 The illustration of the user throughput versus distance calculation

R r1+1 r1

0

7.6.1

Comparison of Semi-analytical and Simulation Results

In order to compare the performance estimation of the semi-analytical approach with the simulation results the same simulation set-up is used as in Section 7.5 except for the following adjustments: l

l

The effect of shadowing and frequency selective multi-path fading were excluded from the simulations. Only the Reuse One, Reuse Three, and Soft Reuse algorithms were simulated for the WiMAX system that is the algorithms that do not rely on channel quality feedback information.

Due to the three-sector base stations and the corresponding antenna pattern in the investigated OFDMA cellular system the contour of the integrations for calculating the average sector and user throughput versus distance according has to be determined. For this purpose coverage only simulations were used to determine the angles and distances where the coverage is provided from the reference base station as illustrated in Fig. 7.18. These coverage only simulations were needed also to determine the integration contours for the Soft Reuse algorithm, depending on the selected geometry threshold of 8 dB (see Section 7.4.3). The goal is to determine the angles and distances where users are classified as “close” and “edge” as illustrated in Fig. 7.19 The semi-analytical and simulation results in term of average sector throughput and user throughput versus distance are presented in Table 7.3 and Fig. 7.20. Note that the relative errors are with regard to simulation results without the shadowing and frequency selective multi-path fading effects. From Table 7.3, we can see that the semi-analytical results of average sector throughput are approximately equal to the simulation results with relative error up to 3.7%. Additionally, the semi-analytical curves for average user throughput versus distance are quite close to simulation curves in Fig. 7.20. The existing relative errors as well as the slight deviation of semi-analytical curves and simulation curves can be explained by the accuracy of least squares fitting method used to find the

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Radio Resource Management in WiMAX Networks

Fig. 7.18 The illustration of investigated parts of the sector

pi/2 rad

311

1.51 rad 1.45 rad 1.33 rad 0.64 rad 0.6 rad 0.76 rad

0.46 rad 0.4 rad 0.28 rad

– 0.28 rad – 0.40 rad 0.44 km – 0.46 rad 0.46 km 0.47 km – pi/6 rad 0.49 km

p/2

Fig. 7.19 The classification of “close” users and “edge” users

p/3 “edge” users 0.25 km

0

0.3 km “close” users

– p/6

Table 7.3 Semi-analytical and simulation results of normalized sector throughput Allocation algorithm Semi-analytical (bit/s/Hz) Simulation (bit/s/Hz) Relative errors (%) Reuse one 0.5739 0.5688 0.90 Reuse three 0.5127 0.5139 0.23 Soft reuse 0.9533 0.9900 3.7

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L. Jorguseski and R. Prasad Average User Throughput vs Distance; WiMAX

Normalized User Throughput [bit/s/Hz]

0.12

Reuse One - Simulation Reuse One - Semi-analytical Reuse Three - Simulation Reuse Three - Semi-analytical Soft Reuse - Simulation Soft Reuse - Semi-analytical

0.1

0.08

0.06

0.04

0.02

0

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

Distance [km]

Fig. 7.20 User throughput versus distance of semi-analytical and simulation results, 30 users/ sector, WiMAX

sigmoid function for the user throughput and effective SIR per RU and possible errors in the determination of the integration contours in Figs. 7.18 and 7.19 due to the finite granularity of the location estimations. In summary, the semi-analytical results are reliable when compared with simulation results without shadowing and frequency selective multi-path fading for the sub-carrier allocation algorithms Reuse One, Reuse Three, and Soft Reuse. The semi-analytical approach is valuable because it saves excessive time for calculating the average sector/user throughput and user throughput versus distance in OFDMA cellular systems. For example, for each point on the graphs presented in this section the semi-analytical approach needed few minutes compared with the simulation time (on a standard PC) of more than one day for 30 users/sector.

7.7

Conclusions and Recommendations

In this chapter four different sub-carrier allocation algorithms with low complexity are evaluated for WiMAX cellular systems with respect to the average sector/user throughput, and the average user throughput versus distance from the reference base station. The simulation analysis presented in this chapter has shown that the maximum C/I based allocation algorithm has the best performance with regard to the average sector and user throughput. However, it is highly unfair for the users on locations further

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away (e.g. roughly 0.3 km) from the reference base station because they are “starving” for resources resulting in the lowest user throughput when compared with the other sub-carrier allocation algorithms. The proportional fair sub-carrier allocation algorithm mitigates this unfairness and has significantly more even distribution of the downlink throughput for different distances from the reference base station when compared to the maximum C/I algorithm. It clearly outperforms all other algorithms for distances roughly larger than 0.25 km from the reference base station. For example, at the sector edge the user throughput for the proportional fair algorithm is roughly doubled when compared to the Reuse One (i.e. the reference case). The soft-reuse allocation algorithms have similar sector and user throughput when compared to the proportional fair allocation algorithm. However, the user throughput at cell edge is lower when compared with the proportional fair algorithm. The Reuse One and Reuse Three sub-carrier allocation algorithms have the worse downlink throughput performance when compared to the other sub-carrier allocation algorithms. This is the result of purely random allocation of the RUs to different users and, in case of Reuse Three, using only a portion of the available bandwidth. From this relative throughput performance comparison of the different subcarrier allocation algorithms it can be concluded that proportional fair sub-carrier allocation algorithm is recommended for an OFDMA cellular system as it has relatively high sector/user throughput and has a fair distribution of the user throughput versus the distance from the reference base station. The semi-analytical approach for the downlink throughput evaluation of Reuse One, Reuse Three, and Soft Reuse sub-carrier allocation algorithms has shown reasonable accuracy when compared with simulation results without the effects of shadowing and frequency selective multi-path fading. The relative error for the average sector/user throughput was up to 3.7% for WiMAX. The low relative error and drastically reduced processing time (minutes versus days) make this semianalytical approach very useful for practical use. It is recommended to evaluate in more detail the power allocation per RU for the Soft Reuse algorithm and the division of the total amount of RUs into a block of resources available either for the “close” or “edge” users. The more detailed investigation should include a “dynamic” allocation of the number of RUs with higher power (intended for the “edge” users) depending on the amount of “edge” users in the sector. Regarding the semi-analytical approach it is recommended to include the effect of shadowing and frequency selective multi-path fading in the model and investigate the accuracy of the approach by comparing the semi-analytical results with simulations of the maximum C/I and proportional fair sub-carrier allocation algorithms.

References 1. J.G. Proakis, Digital Communications – Second Edition (McGraw-Hill, New York, 1989). ISBN 0-07-050937-9 2. C. Lee, L.H.C. Lee, Convolutional Coding: Fundamentals and Applications (Artech House, Boston, MA, 1997)

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3. L. Hanzo, T.H. Liew, B.L. Yeap, Turbo Coding, Turbo Equalisation and Space-time Coding for Transmission Over Fading Channels (Wiley, New York, July 2002) 4. WiMAX Forum, Mobile WiMAX – Part I: A Technical Overview and Performance Evaluation (Aug 2006) 5. WiMAX Forum, Mobile WiMAX – Part II: A Comparative Analysis (Aug 2006) 6. L. Jorguseski, R. Prasad, Downlink resource allocation in beyond 3G OFDMA cellular systems, in 18th Annual IEEE International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC’07), Athens, Greece, 3–7 September 2007 7. J.-G. Choi, S. Bahk, Cell throughput analysis of the proportional fair scheduling policy, in Proceedings of NETWORKING 2004, Athens, Greece, May 2004 8. 3GPP TR 25.892, Feasibility Study for Orthogonal Frequency Division Multiplexing (OFDM) for UTRAN enhancements, V 6.0.0 (June 2004) 9. IEEE 802.16 Broadband Wireless Access Working Group. Draft IEEE 802.16m Evaluation Methodology (14 Dec 2007) 10. WiMAX forum, WiMAX system evaluation methodology, Version 2.0 (15 Dec 2007)

Chapter 8

Radio and Network Planning Fernando J. Velez, Pedro Sebastia˜o, Rui Costa, Daniel Robalo, Cla´udio Comissa´rio, Anto´nio Rodrigues, and A. Hamid Aghvami

Abstract This chapter starts by presenting the Stanford University Interim (SUI) and modified Friis propagation models. Although the SUI model is being recommended for WiMAX, the comparison between the model and experimental results show that, in our environment, at 3.5 GHz, the modified Friis model with g = 3 fits better the measurement values. From the analyses of the signal-to-noise-plusinterference ratio, SNIR, interference-to-noise ratio and reuse pattern, it is found that both noise and interference present a strong limitation to the performance of fixed WiMAX, mainly for higher order modulation and coding schemes (MCSs). In general terms, the use of sectorization in fixed WiMAX enables to reduce the reuse pattern while considering sub-channelisation allows for improvement on the coverage. The reduction of the reuse pattern directly corresponds to an increase in the system capacity but the improvement in the coverage range (through subchannelisation) can also allow for an improvement in UL system capacity, as adaptive MCS are used. Two different approaches are considered for graphical cellular planning, and the district of Covilha˜ is considered as a case study. On the one hand, one considered a GIS based WiMAX planning tool conceived by considering coverage issues, frequency reuse, and the impact of the different classes of service. On the other, WinpropTM is used as it distinguishes among different MCS in the graphical presentation of the results. Both tools consider the information coming from the digital terrain profile. The GIS functionalities allow for appropriately adjusting azimuth and tilt of antennas. This cellular planning exercises confirm the results of theoretical analysis, where different crowns are achieved for the coverage with each MCS (corresponding to a given range of values for SNIR), for the maximum physical throughput, and for the “best server” cells. The frequency radio resources should be considered as the most valuable resource

F.J. Velez (*) Instituto de Telecomunicac¸o˜es-DEM, Universidade da Beira Interior, Calc¸ada Fonte do Lameiro, 6201-001, Covilha˜, Portugal e-mail: [email protected]

R. Prasad and F.J. Velez, WiMAX Networks, DOI 10.1007/978-90-481-8752-2_8, # Springer ScienceþBusiness Media B.V. 2010

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during the planning of wireless broadband access networks. As a rule, spectral efficiency needs to be optimized by using several advanced techniques, corresponding to an optimization from the cost-benefit point of view.

8.1

Introduction

The present context of frequency spectrum management worldwide, as well as the need for making broadband access flexible for users, creates opportunities for the entrance of new operators and offer diversification of innovative access technologies. As Worldwide Interoperability for Microwave Access (WiMAX) enables the support of mobile broadband Internet services in outdoor (and even in indoor, for the lower frequency bands) with high coverage ranges and user mobility support. It allows the exchange of truly wide and broadband multimedia content, and support simultaneously all-Internet Protocol (IP) voice, data, streaming, image and video multi-rate communications. The goal of cellular coverage is to provide access to mobile users in a given region, called cell, while guaranteeing the quality of the received signal in both directions, Uplink (UL) and Downlink (DL), even for the users at the cell edge. As resources, for example, frequency channels, need to be reused in different geographical zones (but not in close proximity), the impact of interference among co-channel cells needs to be evaluated also in both directions. In WiMAX, as in Wideband Code Division Multiple Access (WCDMA) and High Speed Downlink Packet Access (HSDPA), the ideal situation would be to reuse the channels in every cell, that is, to deploy systems with a frequency reuse pattern, K, equal to one, which would be achieved by means of Pseudo Random Mapping (PRM) of sub-carriers where Orthogonal Frequency Division Multiple Access (OFDMA) is used. However, due to heavy interference in frequency reuse deployment, users at cell edge may suffer from low connection quality since these improvements may not be available in some versions of the standard, or may simply reduce but not eliminate the interference. In the context of WiMAX planning, research on the variation of the carrier-tonoise-plus-interference ratio (CNIR) with different system parameters is therefore of paramount importance. As there are limitations in both links, UL and DL, techniques such as sub-channelisation need to be applied to reduce the impact of the noise on the link performance. However, only mobile WiMAX will allow for sub-channelisation in the DL while fixed WiMAX only allows for it in the UL, and may cause a degradation of performance (mainly owing to the extra noise caused by the largest bandwidth). For cellular planning purposes, the UL and DL CNIRs from/at the wireless Subscriber Station (SS) are very important parameters. From a detailed analysis of its variation with the coverage and reuse distances for different modulation and coding schemes (MCS), an evaluation of the possible reuse patterns can be performed.

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If Frequency Division Duplexing (FDD) is used, in fixed WiMAX, worst-case situations occur in the DL when the Base Station (BS) of the central cell transmits to the most distant SS, located at the cell edge, whilst receiving interference from the BS of the six co-channel cells of each ring of interference (Fig. 8.1). In the UL, the worst-case situation occurs when the SS is transmitting to the BS from the cell boundary while interfering mobiles are at the interfering cells edge (in the region closest to the central cell) (Fig. 8.2). When sectorization is considered the number of interfering cells is decreased, and system capacity increases. Usage scenarios will be enabled by using innovative terminals, similar to PDAs or Tablet PCs, which will combine voice with other type of services, including image and video. One example can be the communication of real-time image from an actual fire site to the fire department. In Summer time, in the south of Europe, simultaneous fires in forests are a persistent calamity, and authorities lack access to real-time fire information in order to coordinate fire brigades. Another good example is the surveillance of commercial streets by using real-time video. For demonstration, a network was deployed in the city of Covilha˜, Portugal, by using IEEE 802.16-2004 BreezeMAX Alvarion equipment with 3.5 MHz channels at 3.5 GHz [1], as indicated in Table 8.1 (where supported data rates are presented). Later, by using the IEEE 802.16e standard [2], it will be possible to support true mobility. Different received power levels correspond to different net physical (PHY) bit rates, and to different modulation and coding schemes (MCSs), as shown in Table 8.2 (for the Alvarion BreezeMAX 3.5 MHz equipment). This Point-to-Multipoint (PtM) network is the basic tool for our research inbroadband mobile access, mobile IP, and always best connected WiMAX scenarios, including the possibility of performing extensive field trials in the FDD mode. In the initial phase of WiMAX deployment, the operators experience is limited, and measurement based cellular planning procedures, extracted from the experimental

D+R D

D–R

Fig. 8.1 Co-channel interference in the worst-case for the DL

D+R

R D D–R

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Fig. 8.2 Co-channel interference in the worst-case for the UL

D– R D–R

D –R

R

D–R

Table 8.1 Total data rates for IEEE 802.16-2004

Bandwidth (MHz) 3.5 5.0 7.0 10.0 20.0

Table 8.2 Correspondence among modulations, sensitivity, and net PHY rate

Modulation & coding BPSK 1/2 BPSK 3/4 QPSK 1/2 QPSK 3/4 QAM 16 1/2 QAM 16 3/4 QAM 64 2/3 QAM 64 3/4

QPSK 3.3 4.6 6.5 9.3 18.7

D–R D–R

Data rate (Mbps) 16-QAM 6.5 9.3 13.1 18.7 37.5

Net PHY bit rate (Mbps) 1.41 2.12 2.82 4.23 5.64 8.47 11.29 12.27

64-QAM 9.8 13.9 19.6 28.0 56.2

Sensitivity (dBm) 100 98 97 94 91 88 83 82

networks and prototypes, are fundamental at for the validation of the proposed planning algorithms. A Geographic Information Systems (GIS) based planning tool was developed for the purpose of helping in the process of design WIMAX coverage and frequency reuse. It includes the propagation models, the co-channel interference computation aspects, as well as the services and applications details. However, it does not fully includes a detailed analysis of the consequences of using different MCS, and a

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comparison with a commercially available planning tool, as WinpropTM [3] was justified. This specific functionality of WinpropTM allows for helping to verify the impact of the improvement strategies, as sub-channelisation and sectorization. Different operation “modes” and the information coming from the digital terrain profiles will be considered in the context of specific cellular planning exercises. The structure of this Chapter is as follows. Section 8.2 presents the point-tomulti-point propagation measurements and models, namely the modified Friis and the Stanford University Interim (SUI) models. Section 8.3 addresses aspects of cellular planning. It starts by discussing the limitations of a simplified analysis, and then a comparison of the results for the interference-to-noise ratio and the achievable reuse pattern is performed. The variation of the CNIR with co-channel reuse factor is used as a basis to compute the supported PHY throughput for different cases (by considering the absence and presence of sub-channelisation and of sectorization). Section 8.4 presents results obtained by using two wireless planning tool platforms, one developed by ourselves while the other one is commercially available. The framework and scenarios are analysed, the functionalities and potentials of the tools are discussed, and planning results are given for different environments as well. Finally, in Section 8.5 conclusions are made as well as suggestions for further work.

8.2 8.2.1

Propagation Models SUI Versus Modified Friis Model

In Non Line-of-Sight (NLoS) channel conditions, signals may undergo scattering, diffraction, polarization changes and reflection impairments, which affect their level and phase at the receiver. Usually these impairments are not important if there is Line-of-Sight (LoS) between the transmitter and the receiver. For outdoor environments, obstacles, such as building materials, foliage and clutter, also contribute to increase path loss [4, 5], and the SUI outdoor propagation model is especially relevant [4]. It will be considered together with the modified Friis model. Over the years, various models have been developed to characterize Radio Frequency (RF) environments and allow for the prediction of the RF signal strengths. These empirical models are used to predict large-scale coverage for radio communications systems in cellular applications and provide estimates for path loss (PL) by considering the distance between the transmitter and receiver, terrain factors, antenna height, and cellular frequencies. Nevertheless, according to [4] none of these approaches address the needs of broadband fixed wireless adequately. To overcome this limitation, AT&T developed an empirical wireless model that has been validated against deployed fixed wireless systems which yielded results comparable to other models and experiments. This model was the

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basis of an industry-accepted model, and is being used by the standardization bodies, such as in the IEEE 802.16. The adoption of the AT&T wireless PL model by IEEE is referred as “Channel Models for Fixed Wireless Applications” in [5]. The AT&T wireless PL model includes, as parameters, antenna heights, carrier frequency and types of terrain [4]. Apart from the modified Friis model (where the propagation exponent g instead of taking a value of 2 is replaced by a different empirical value), one possible solution for the Wireless Planning Tool (WPT) is therefore the SUI model, which is an extension of the earlier work of AT&T propagation model [4]. The SUI model uses three basic terrain types: l l l

Category A – Hilly/moderate-to-heavy tree density Category B – Hilly/light tree density or flat/moderate-to-heavy tree density Category C – Flat/light tree density

These terrain categories provide a simple method to estimate more accurately the PL of the RF channel in an NLoS situation. Being statistical in nature, the model is able to represent the range of PLs experienced within an actual RF link. SUI models were explored for the design, development, and testing of WiMAX links in six different scenarios, SUI-1 to SUI-6 [6]. By using these propagation models (both modified Friis and SUI ones), it is then possible to predict more accurately the coverage probability achieved within a base station site sector. These models do not replace detailed site planning (and site surveying), but can provide an estimate before actual planning. Besides, it is very important to perform RF planning activities to adequately evaluate specific environment factors, co-channel interference, actual clutter and terrain effects. This model allows several frequencies and SSs heights. The path loss is given (in dB) by [7] PLðdÞ ¼ PLðd0 Þ þ 10  g  logðd=d0 Þ þ Xf þ Xh þ S;

(8.1)

with the following parameters PLðd0 Þ½dB ¼ 20  logð4pd0 =lÞ;

(8.2)

g ¼ a  b  hb þ c=hb ;

(8.3)

and

where d is the distance between the BS and a given point, in meter, d0 ¼ 100 m, l ¼ c=f is the wave length, c ¼ 3  108 ms1 , f is the carrier frequency, hb is the BS height above ground, in meter (10 < hb < 80 m), and a, b, and c are parameters which are chosen according to three environments, represented by A, B or C, Table 8.3. The terms Xf and Xh are correction factors for frequency and SS antenna height above the ground, respectively.

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Table 8.3 Values for the parameters in the SUI model

321 Model constant a b c

A 4.6 0.0075 12.6

Terrain type B 4.0 0.0065 17.1

C 3.6 0.0050 20

These correction factors are defined as
 Xf ¼ 6:0  log f=2000 ;

(8.4)

and
 8 < 10:8  log hm= ; for terrain types A and B 2:0
 ; Xh ¼ : 20:0  log hm= 2:0 ; for terrain type C

(8.5)

where f is the carrier frequency, in MHz, and hm is the receiver height above the ground, in meter. The term S is a lognormal-distributed random variable with zero mean and standard deviation sS, with typical values from 8.2 to 10.6 dB, depending on the type of terrain [7]. This term takes shadow fading originated by trees and structures into account [7]. The average received power is given byPRðdÞ ¼ PE  PLðdÞ, where PE is the average transmission power and PLðdÞ is the average path loss (attenuation factor). In the context of other commercially available cellular planning tools, models with high complexity can be used, namely, the NLoS dominant ray path loss one [7, 8]. However, in order to obtain the most efficient cellular planning tools it is important to compare these models with the simplest ones, for example, the modified Friis and SUI ones, and validate them against experimental results.

8.2.2

Experimental Results

Figure 8.3 presents some of the PtM Alvarion WiMAX equipment used in the experimental setup installed on the roof top of the Health Sciences Faculty (HSF) of University of Beira Interior, Covilha˜, near the Hospital. They are a BreezeMAX 3000 OFDM micro BS and self-installable Alvarion BreezeMAX Customer Premise Equipments (CPEs) operating at 3.5 GHz, an omnidirectional antenna, and the Outdoor Unit (ODU). The appropriate Ethernet and RF cables were also used, as well as a Global Positioning System (GPS) device, a 12–240 V power inverter (to feed the CPE), and a portable PC, used as a terminal and running a File Transfer

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Fig. 8.3 IEEE 802.16-2004 PtM equipment operating at the 3.5 GHz band

30 25

~550 m 20 15 10

500 m

5

Fig. 8.4 LoS regions and measurements of SNR[dB] for the DL at 3.5 GHz

Protocol (FTP) application, the BreezeCONFIG software, and a tool for acquiring GPS positions. In the HSF backhaul network, there was an FTP server, and a Dynamic Host Configuration Protocol (DHCP) server, for automatically assigning an IP address to the users’ CPEs. The BS antenna gain is 10 dBi (360 azimuth, 8 elevation, vertical polarization). The SS antenna is a beam switching array of six 9 dBi, 60 antennas, integrated into the CPE. Field trials were performed in the suburban area of Covilha˜, in a zone with approximately 2.80  1.55 km2, and initial results for signal-to-noise ratio (SNR) and the throughput were obtained at the SSs (or CPEs) that roam around the suburban area surrounding the HSF. The dynamic range of the CPE was found to be adequate. There is a direct correspondence between the SNR values from Fig. 8.4, the MCSs, and the achieved data rate, for example, 6 Mbps for 16-QAM. The BreezeMAX duplexing frequency range is 3,499.5–3,553.5 MHz and 3,550–3,600 MHz for downlink (DL), and 3,399.5–3,453.5 MHz, and 3,450–3,500 MHz for uplink (UL) [9]. In these particular field tests, our ODU was operating at 3,551.75 MHz (DL), and 3,451.75 MHz (UL), and with a transmitter power of 28 dBm. NLoS regions, obtained with ArcGIS, are also represented

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80 70 60

C/N [dB]

50

C/N= – 8.259log(d ) + 25.417

40 30 20 10 0 –10 –20

0

0.2

0.4

0.6

0.8 d [km]

1

1.2

1.4

Friis (g = 2)

Friis g = 3)

Friis (g = 4)

Measured

SUI (type A)

SUI (type B)

SUI (type C)

Trendline

1.6

Fig. 8.5 Trend curve for the measured SNR in the locations around HSF: comparison between the SUI and the modified Friis models

in the background, in green, in Fig. 8.4. At distances far from the base station, the experimental regions with reasonable signal quality coincide basically with the LoS regions. However, for distances up to 550 m even NLoS areas near the boundary between LoS and NLoS areas can be covered. Another important issue is the comparison between the results for the curve fitting of SNR and the curves obtained from the application of the propagation models (SUI model and modified Friis equation), as depicted in Fig. 8.5, for distances up to 1.6 km. Within the modified Friis model different propagation environments are modelled by different propagation exponents, g, which vary from g ¼ 2, corresponding to free space conditions, for example, rural areas, to g ¼ 3, in urban areas (no shadowing), and g ¼ 4, in shadowed urban areas [10]. For the SUI model, one considers hm ¼ 2 m, hb ¼ 13.3 m and sS ¼ 8.8 dB. For both models, a total antenna gain (transmitter plus receiver) of 19 dBi, a transmitter power of 28 dBm, a bandwidth of 3.5 MHz, and a noise factor of 3 dB were assumed. To understand the results, an analysis of the terrain profile around the BS location at HSF is required. While at Southeast (SE) of the BS the terrain is flat, at Northwest (NW) it is continuously hilly, with increasing altitudes. The first coverage circular zone, with a radius of 550 m from the BS, is part of the suburban region of Covilha˜, with a moderate building density. The second coverage zone (or crown), for distances larger than 550 m, corresponds to a rural area (and the small airport) at Southeast, and to a dense urban area at NW. However, this dense urban area corresponds to zones predominantly in LoS with the BS as the terrain height continuously increases from the BS to this zone. At SE, the zones up to a distance of 550 m are predominantly in non-LoS owing to the shadowing effect of the HSF roof. However, at NW of the BS, this crown is

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C/ N [dB]

32

C/N = – 32.72log(d) + 15.86

26

20

14 0.25

0.3

0.35

0.4

0.45

0.5

d [km] Friis ( g = 3) SUI-B

Measured SUI-C

SUI-A Trendline

Fig. 8.6 Analysis of the measured SNR for distances in the interval [275, 475] m: comparison between the SUI and the modified Friis models

predominantly in LoS (as for higher distances), as the terrain height increases. For distances larger than 550 m measurements were taken mostly at locations with LoS coverage. A curve fitting approach was used to interpret the measurement results from Fig. 8.5 (in dB). The coefficient 8.259 for log(d) corresponds to a very low power decay rate. If the modified Friis equation is considered, the experimental results take values similar with the curve for g ¼ 4 for distance in the interval (60, 150 m), similar to the ones from the curve for g ¼ 3 for distances in the interval (300, 500 m). Then, for larger coverage distances, values correspond to modified Friis equation propagation exponents between 2 and 3. It seems that the results consecutively correspond to (1) shadowed urban areas, (2) urban areas (with no shadowing), and (3) approximately free space, which is partially true if we consider the actual terrain. Despite the fact that the use of the SUI model is being recommended for WiMAX, the comparison of the experimental results with the SUI model is harder since they only coincide for distances in the interval (275, 475 m). In order to clarify this issue, Fig. 8.6 presents a partial analysis of the results for C/N in this interval, where a different trendline is obtained, and only the modified Friis equation curve for g ¼ 3 is considered for comparison, as it approximately follows the experimental trendline for the results with a difference of circa 2.5 dB (which can be caused by the penetration loss due to the placement of the SS antenna in the rear seat of the car during the measurements). If this difference of 2.5 dB was subtracted from results for modified Friis equation with g ¼ 3, the curves would be almost coincident. This was confirmed by the reduction of the Mean Square Error (MSE) from 4.917 to 0.113.

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Without this correction factor, while the distance to the BS increases the trend line consecutively crosses the curves for SUI-A, SUI-B, and SUI-C, that is, the curves for (a) hilly/moderate-to-heavy tree density, (b) hilly/light tree density or flat/moderate-to-heavy tree density, and (c) flat/light tree density, respectively. The experimental results cross the three curves of the SUI model but a good correspondence was only found for the SUI-B and SUI-C, as the MSE are 1.564 and 1.617, respectively. For the SUI-A curve, the MSE was 4.657. However, if we apply the correction factor of 2.5 dB (as for the modified Friis equation) the results for the SUI-A and SUI-B models would be much worst (MSE of 19.227 and 9.247, respectively). Only the curve for the SUI-C would still offer an almost acceptable correspondence (with an MSE of 4.808). Results from field trials show that, at 3.5 GHz, the propagation at distances higher than 550 m is mainly in LoS; hence, a need is identified of using lower frequency bands to achieve the objective of having appropriate NLoS propagation within WiMAX networks. Another important result at this band is the appropriateness of the modified Friis propagation model for this band. Despite the use of the SUI model is recommended for WiMAX, in these experiments at 3.5 GHz, for distances in the interval (275, 475 m), the experimental results fit quite well with the modified Friis equation with #  3, which corresponds to urban areas (with no shadowing), although the SUI-C model can also be a solution.

8.3 8.3.1

Cellular Planning Limitations of a Simplified Analysis

In order to achieve an efficient use of the radio frequency spectrum, it is important to choose a frequency reuse scheme that leads to coverage guarantee, and improved system capacity whilst minimising the interference. If FDD is used, an analytical approach may be followed in fixed WiMAX (IEEE 802.16-2004) to solve coverage and frequency reuse problems. Traditionally, several text books decouple the analysis of the carrier-to-noise ratio aspects from the analysis of the carrier-to-interference ones. This way, interference is not considered in the coverage problem while noise is not considered when addressing the frequency reuse. On the one hand, not considering the interference in the coverage problem means that the maximum coverage distance is obtained without allowing for extra margin for the interference, which is a critical limitation for the dimensioning process of a cellular system. On the other hand, the absence of noise in the interference analysis is unrealistic, as noise is always present in communications. As there would be limitations arising from an independent analysis, cellular planning has to consider simultaneously carrier-to-noise and carrier-to-interference constraints. Improvement techniques as sub-channelisation and sectorization, will be addressed to improve coverage and avoid interference.

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Signal-to-Noise-Plus-Interference Ratio

This Section addresses aspects related to the analysis of the cell coverage distance (or cell radius), R, the co-channel reuse factor, rcc, the ratio between the reuse and the coverage distances, the reuse pattern, K, for several levels of IEEE 802.16 modulation and coding schemes. The conclusions to be extracted facilitates an adequate choice of the reuse pattern and an efficient frequency planning. If one considers the interference-to-noise ratio, defined by M ¼ I=N ;

(8.6)

and the equation for the carrier-to-noise-plus-interference ratio (CNIR) to be used in the dimensioning process is C ¼ ðN þ I Þ

  C ; N min

(8.7)

Equation (8.7) can therefore be re-written in the two following ways   C ð1 þ MÞ; N min

(8.8)

    C 1 þ M1 : N min

(8.9)

C ¼ N and C ¼ I

In (8.7) one is using the model for CNIR from [11] while assuming that the weights for noise and interference are the same. From Eq. (8.8) one obtain the following equation for the interference-to-noise ratio MðRÞ ¼

ðCðRÞ=N Þ  1; ðC=N Þmin

(8.10)

where C(R) ¼ PR(R) is computed by applying the modified Friis formula with g ¼ 3, the hypothesis followed in this Section for urban environments. This value for the propagation exponent results from the experimental results in Covilha˜, Portugal. Values of M(R) are proportional to the interference still tolerable for a given coverage distance R while (still) agreeing with the quality requirements for a given MCS.

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With a hexagonal cell topology, in the DL (Fig. 8.1) as the distance associated with interference is D, that is, the reuse distance itself, the carrier-to-interference ratio can be given by C 1 rcc g ; ¼  6 I 2ðrcc þ 1Þg þ 2rcc g þ 2ðrcc  1Þg

(8.11)

where rcc is the co-channel reuse factor, given by rcc ¼ D=R:

(8.12)

The approximate expression in (8.11) is very useful in practice. For the UL (Fig. 8.2) the carrier-to-interference ratio is given by C ðrcc  1Þg : ¼ 6 I

(8.13)

By replacing (8.11) into (8.9), it is therefore possible to obtain the following equation for the reuse factor in the DL rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
 ffi g C 1 : rcc ¼ 6  ð1 þ M Þ  =N min

(8.14)

For the UL, in turn, by replacing (8.13) into (8.9), one obtain the following equation rcc ¼

rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
 ffi g þ 1: 6  ð1 þ M1 Þ  C=N min

(8.15)

It is worthwhile to note that, for hexagonal reuse geometries, the reuse pattern is given by K¼

rcc 2 : 3

(8.16)

As a horizontal asymptote arises in the analysis of the curves of rcc as a function of the coverage distance, R, it is important to present the mathematical details associated to it. To compute the horizontal asymptote in the chart of rcc(R), one has to consider that R ! 0. From (8.10), if R ! 0 then M ! +1, and M1 ! 0. On the one hand, for the DL, in the limit, one obtains rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
 ffi g C : lim rcc ¼ 6  =N

R!0

min

(8.17)

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On the other, for the UL, also in the limit, one obtains rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
 ffi g þ 1: lim rcc ¼ 6  C=N R!0

min

(8.18)

By considering (8.16), it is straightforward to conclude that, for each value for the propagation exponent, the reuse pattern, K, only depends on the MCS through the value of the corresponding minimum carrier-to-noise ratio, as well as on the cellular interference geometry, either UL or DL. While the asymptotic reuse factor is associated with the upper bound for system capacity, the maximum coverage distance is associated with the carrier-to-interference-plus-noise ratio at the cell boundary when the interference is null. Since the interference-to-noise ratio, M, represents the interference that can still be tolerated for a given R, in the limit, the maximum coverage distance for which no extra interference is tolerated is obtained when I(R) ! 0, that is, when M(R) ! 0 (meaning that M[dB] ! 1). Hence, the vertical asymptotes for the M(R) and rcc(R) charts is Rasymptote ¼ RM!0 :

(8.19)

It is obtained by solving the following equation MðRÞ ¼

ðCðRÞ=N Þ  1 ¼ 0; ðC=N Þmin

(8.20)

or, in a simplified way
 CðRÞ= ¼ C= N min : N

(8.21)

By comparing this equation (valid only when M ! 0) with Equation (8.8), one concludes that only considering the carrier-to-noise ratio to determine the coverage distance, R, is inadequate in systems where interference is relevant, as Equation (8.21) corresponds to a null interference-to-noise ratio, M. If a cellular system was dimensioned this way there would not be an extra margin for interference, represented by M ¼ I/N. Finally, it is a worth noting that, for a given propagation exponent, the maximum coverage distance corresponding to the vertical asymptote, Rasymptote, depends not only on the MCS but also on the noise power, N. This is the reason why the reduction of the noise power through sub-channelisation, that is, through the reduction of the RF bandwidth, is so important.

8.3.3

Interference-to-Noise Ratio and Reuse Pattern

By using (8.10), one obtains the chart for the interference-to-noise ratio without sub-channelisation from Fig. 8.7, which is valid both for the UL and DL. The considered propagation exponent for the modified Friis model is g ¼ 3.

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50

BPSK3/4 QPSK1/2

40

QPSK3/4

30

16QAM1/2

M [dB]

16QAM3/4

20

64QAM2/3 64QAM3/4

10 0 –10 –20 0

1000

2000

3000 R [m]

4000

5000

6000

Fig. 8.7 Interference-to-noise ratio without sub-channelisation

Table 8.4 Values for the vertical asymptote without sub-channelisation

Level 1 2 3 4 5 6 7 8

MCS BPSK 1/2 BPSK 3/4 QPSK 1/2 QPSK 3/4 16-QAM 1/2 16-QAM 3/4 64-QAM 2/3 64-QAM 3/4

Rasymptote (m) 5,814.86 4,911.41 4,548.55 3,783.32 2,936.79 2,368.86 1,638.85 1,494.65

The modified Friis propagation model with g ¼ 3, transmitter power Pt ¼ 2 dBW, and transmitter and receiver antenna gains Gt ¼ 17 dBi and Gr ¼ 9 dBi, respectively, were assumed. Note that transmitter antenna gain is 7 dB higher than the value considered in Section 8.2.2. The radio frequency bandwidth, the noise figure and the frequency were brf ¼ 3.5 MHz, Nf ¼ 3 [dB], and f ¼ 3.5 GHz, respectively. Table 8.4 presents the corresponding values for the vertical asymptote without sub-channelisation, Rasymptote. It is observed a relevant decrease of the values for the vertical asymptote (maximum coverage distance) as the MCS level increases, which is compatible with the lowest values for SNRmin. By applying (8.14) and (8.16) to the DL one obtains the charts for rcc(R) and K (R) from Figs. 8.8 and 8.9, respectively. By using a reuse pattern K ¼ 7 it is possible to use a maximum MCS level of 4, that is, QPSK , for R b 2.7 km, and a maximum MCS level of 5, that is, 16-QAM ½, for coverage distances lower than 1.2 km. Figure 8.10 presents the results for the UL, which are worst since they correspond to higher values for the reuse pattern. In the UL without sub-channelisation, for a reuse pattern K ¼ 7, only a low order MCS is achievable, that is, QPSK , up to a coverage distance of 2 km. It is not possible to use 16-QAM ½, as it was in the DL.

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BPSK1/2 BPSK3/4 QPSK1/2 QPSK3/4 16QAM1/2 16QAM3/4 64QAM2/3 64QAM3/4

12 10 rcc

8 6 4 2 0 0

1000

2000

3000 R [m]

4000

5000

6000

Fig. 8.8 Reuse co-channel factor as a function of the coverage distance with MCS level as a parameter, in the DL without sub-channelisation

40 BPSK1/2 BPSK3/4

35

QPSK1/2

30

QPSK3/4 16QAM1/2

K

25

16QAM3/4 64QAM2/3 64QAM3/4

20 15 10 5 0 0

1000

2000

3000 R [m]

4000

5000

6000

Fig. 8.9 Reuse pattern as a function of the coverage distance with MCS level as a parameter, in the DL without sub-channelisation

It is therefore important to address techniques for the improvement of system capacity and coverage range. As sub-channelisation in the IEEE 802.16-2004 UL is an optional feature, one explored its impact on the achieved MCS. Differently from the mobile version of WiMAX, IEEE 802.16-2004, based on Orthogonal Frequency division Multiplexing Physical (OFDM-PHY), does not support sub-channelisation in the DL. For the UL, the use of sub-channelisation limits the SS transmissions to 1/16 of the bandwidth assigned to the communication through the BS. The standard defines 16 sub-channels, and 1, 2, 4, 8 or all sets of sub-channels can be assigned to a SS, and each subscriber may use a different MCS in a more permanent way as far he/she is using a different sub-channel.

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40 BPSK1/2 BPSK3/4 QPSK1/2 QPSK3/4 16QAM1/2 16QAM3/4 64QAM2/3 64QAM3/4

35 30

K

25 20 15 10 5 0 0

1000

2000

3000 R [m]

4000

5000

6000

Fig. 8.10 Reuse pattern as a function of the coverage distance with MCS level as a parameter, in the UL without sub-channelisation

50

BPSK1/2 BPSK3/4 QPSK1/2 QPSK3/4 16QAM1/2 16QAM3/4 64QAM2/3 64QAM3/4

40

M [dB]

30 20 10 0 –10 –20 0

1000

2000

3000 R [m]

4000

5000

6000

Fig. 8.11 Interference-to-noise ratio with sub-channelisation (valid for both links)

Nevertheless, in the DL, as the MCS can be chosen at burst level, there is also the flexibility of using different MCS by different users (even without sub-channelisation), as they use different consecutive bursts within a frame. By using (8.10) and (8.15) one obtains the charts for M(R) and K(R) from Figs. 8.11 and 8.12, respectively. Table 8.5 presents the new values for the vertical asymptotes, which are clearly higher than the ones without sub-channelisation (more than twice the value). In this case, with 16 sub-channels, the variation of the noise power is 10log(1/16) ¼ 12 dB, providing an enhancement of 12 dB in the link budget. By comparing the evolution of K(R) from Fig. 8.12 with the case without sub-channelisation there is no decrease in the reuse pattern; as a consequence, there is no direct increase in system capacity for the lowest values of R (only the achievable coverage distances are increased). For K ¼ 7, the achievable

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BPSK1/2 BPSK3/4 QPSK1/2 QPSK3/4 16QAM1/2 16QAM3/4 64QAM2/3 64QAM3/4

35 30

K

25 20 15 10 5 0 0

1000

2000

3000 R [m]

4000

5000

6000

Fig. 8.12 Reuse co-channel pattern as a function of the coverage distance with MCS level as a parameter, in the UL with sub-channelisation

Table 8.5 Values for the vertical asymptote with subchannelisation

Level 1 2 3 4 5 6 7 8

MCS BPSK 1/2 BPSK 3/4 QPSK 1/2 QPSK 3/4 16-QAM 1/2 16-QAM 3/4 64-QAM 2/3 64-QAM 3/4

Rasymptote (m) 14,652.51 12,375.98 11,461.63 9,533.36 7,400.25 5,969.16 4,129.65 3,766.28

MCS is QPSK . However, the achievable coverage distance increases from 2 to 5 km, approximately. It is a worth noting that, in this case, the QPSK ½ MCS may be used up to a coverage distance of 6 km. In order to achieve higher system capacity the use of sectorization is suggested. The use of 120 sectorial BS antennas is adopted, that is, one proposes the use of trisectorial antennas. By inverting both members of (8.9) while using the formula for C/I from [12], one obtains ½ðrcc þ 0:7Þg þ ðrcc  0:22Þg  

1 ¼ 0; ð1 þ M1 Þ  ðC=N Þmin

(8.22)

which is valid both for UL and DL. The minimum reuse factor required for such a tri-sectorial system may be obtained by solving this equation in order to rcc while obtaining the reuse pattern through the use of (8.16). Note that, for the omnidirectional case, the usual assumptions for interference coming from six sources of interference were used in the computations. Although one only have considered

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25

BPSK1/2 BPSK3/4 QPSK1/2 QPSK3/4 16QAM1/2 16QAM3/4 64QAM2/3 64QAM3/4

20

K

15 10 5 0 0

1000

2000

3000 R [m]

4000

5000

6000

Fig. 8.13 Reuse pattern as a function of the coverage distance with MCS level as a parameter, in the UL with sectorisation but without sub-channelisation

one ring of interference some care would be needed if lower propagation exponents were used [11, 13]. Figure 8.13 presents the chart for the variation of the reuse pattern, K, with the coverage distance. As no sub-channelisation is considered in this case, the vertical asymptotes are the ones from Table 8.4. It is observed that, with sectorization, a clear improvement is obtained in the reuse pattern results in comparison with the ones previously presented, as reuse patterns suffer an important reduction. For K ¼ 7 it is now possible to consider level 6 MCS, that is, 16-QAM 3/4, up to R  1.5 km, overcoming the level 5 MCS without sectorization. While 16-QAM 3/4 can be used for coverage distances up to 1.5 km, 16-QAM ½ may be used up to R  2.2 km. With the QPSK ½ and QPSK 3/4 MCSs it is possible to achieve K ¼ 7 for coverage distances up to approximately 4.1 and 3.3 km, respectively. The use of sub-channelisation increases the coverage distance while the use of sectorization increases the achievable system capacity (through the decrease of the reuse pattern). It is therefore worthwhile to explore the simultaneous use of subchannelisation and sectorization. Figure 8.14 presents the variation of the reuse pattern with the cell coverage distance for this new case, only possible in the UL for fixed WiMAX. Larger coverage distances are possible together with lower reuse distances. With K ¼ 7, it is possible to achieve the 16-QAM 3/4 MCS (level 6) up to R ¼ 4.3 km, while the achievable MCS is 16-QAM ½ MCS (level 5) up to a coverage distance of 6.0 km. In this case, with K ¼ 3, lower order MCSs, for example, BPSK ½, BPSK 3/4, QPSK ½, or QPSK 3/4, are perfectly achieved up to coverage distances larger than 6.0 km. The reduction of the reuse pattern directly corresponds to an increase in system capacity (but not in the cellular coverage). However, it indirectly contributes to an

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BPSK1/2 BPSK3/4 QPSK1/2 QPSK3/4 16QAM1/2 16QAM3/4 64QAM2/3 64QAM3/4

K

20

15

10

5

0 0

1000

2000

3000 R [m]

4000

5000

6000

Fig. 8.14 Reuse pattern as a function of the coverage distance with MCS level as a parameter, for the UL, with the use of sectorisation and sub-channelisation

increase in system capacity as higher level MCSs are made available into outer cell coverage rings through the use of adaptive MCSs. One issue that is left for further study is the dependence of these results on the propagation exponent, g. For example, if the propagation exponent decreases the value of the coverage distance asymptote will increase but the asymptotic value for the reuse factor, rcc, will also increase, corresponding to a reduction on the supported system capacity by each MCS.

8.3.4

CNIR and Supported Throughput

To better understand the changes caused by sub-channelisation (16 sub-channels) and sectorization it is worthwhile to plot the CNIR curves as a function of the reuse factor, rcc, with R as a parameter. To produce these curves the power of the carrier is obtained by computing the power received by an SS at a distance R from the BS while the computation of the interference depends on the UL and DL configuration, and on the use of sectorization as well. It can be computed, for a fixed R, by making the same considerations for the reuse as assumed for Equations (8.11), (8.13) and (8.22). Although IEEE 802.16-2004 cannot use sub-channelisation in the DL, one important comparison is between absence and presence of sub-channelisation in the UL. Another important case is the simultaneous use of sub-channelisation and sectorization. From these charts, considering C/N thresholds for each MCS, that is, (C/N)min, it is straightforward to obtain the achievable physical cell throughput, not considering the mixture of services and applications and the corresponding “multiplexing” characteristics. These charts allow for exploring what the achievable CNIR and

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throughput are for a given reuse pattern, K. As, for hexagonal cells, K ¼ 7 corresponds to a reuse factor rcc ¼ 4.58 this value is considered as a goal. We are aware that, for the cases where sub-channelisation is considered in Fixed WiMAX, the approach we follow for CNIR does not cope with per sub-channel equivalent SINR (or CNIR) computations. These computations can be performed accounting either for exponential effective SINR mapping (EESM), effective code rate map (ECRM), or mean instantaneous capacity (MIC), and may be applied in the future to improve the relevance of the CNIR curves through the use of one of these compression techniques. Figure 8.15 shows CNIR as a function of rcc with R as a parameter for the UL while Fig. 8.16 presents the corresponding variation of the achievable physical throughput with rcc for each MCS.

25

R = 250m R = 500m

20 C/(N + I) [dB]

R = 1000m R = 1500m

15

R = 2000m

10

R = 3000m R = 4500m

5

R = 5000m

0 –5 –10 0

2

4

6

8

10

rcc

Fig. 8.15 CNIR as a function of rcc with R as a parameter, in the UL, no sub-channelisation

12

R = 250m R = 500m

Rb [Mbps]

10

R = 1000m R = 1500m

8

R = 2000m R = 3000m

6

R = 4500m R = 5000m

4 2 0 0

2

4

6

8

10

rcc

Fig. 8.16 Physical throughput as a function of rcc with R as a parameter, in the UL, no subchannelisation

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It is clear that for rcc ¼ 4.58 values of CNIR are always lower than 8.9 dB while for coverage distances larger than 2 km it decreases drastically. As a consequence, for rcc ¼ 4.58, the achievable physical throughput is very low (Rb ¼ 2.82 Mbps maximum) compared with the maximum achievable, that is, 12.27 Mbps, Fig. 8.16. For the DL the results are better, Fig. 8.17, and PHY throughput of 4.23 Mbps is achieved for distances up to 2 km. Figures 8.18 and 8.19 present the results for CNIR and Rb as a function of rcc, in the UL with sub-channelisation. Improvements are only evident for the longest coverage distances, that is, with sub-channelisation the main improvement is on the coverage. If sectorization is applied alone then the values for CNIR at rcc ¼ 4.58 will be higher. However, a truly improvement for coverage distances up to 3 km (not only 2 km anymore) requires both sectorization and sub-channelisation for the UL, as CNIR exceeds 15 dB, as shown in Figs. 8.20 and 8.21. 14

R = 250m

12

R = 500m R = 1000m

Rb [Mbps]

10

R =1500m R = 2000m

8

R = 3000m R = 4500m

6

R = 5000m

4 2 0 0

2

4

6

8

10

rcc

Fig. 8.17 Physical throughput as a function of rcc with R as a parameter, in the DL 25

R = 250m R = 500m

C/(N + I) [dB]

20

R = 1000m

15

R = 1500m

10

R = 3000m

R = 2000m R = 4500m R = 5000m

5 0 –5 –10 0

2

4

6

8

10

rcc

Fig. 8.18 CNIR as a function of rcc, with R as a parameter, in the UL with sub-channelisation

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12 R = 250m

10

R = 500m

Rb [Mbps]

R = 1000m

8

R = 1500m R = 2000m

6

R = 3000m R = 4500m

4

R = 5000m

2 0 0

2

4

6

8

10

rcc

Fig. 8.19 Supported throughput as a function of rcc, with R as a parameter, in the UL with subchannelisation

30 25

C/(N + I) [dB]

20 15 R = 250m R = 500m R = 1000m

10 5

R = 1500m R = 2000m R = 3000m R = 4500m R = 5000m

0 –5 –10 0

2

4

6

8

10

rcc

Fig. 8.20 CNIR as a function of rcc, with R as a parameter, in the UL with sub-channelisation and sectorization

This leads to a clear confirmation of the need for the simultaneous use of both improvement techniques. Improvements in the analysis can be obtained with the assessment of the supported throughput, Rb, as a function of the distance within a cell when the coverage distance (or cell radius) takes a given value, for example, 2 or 3 km. As, for a fixed rcc, larger coverage distances imply coverage limitations but less interference, it is important to compare the achievable maximum throughput for a given reuse pattern, for example, K ¼ 7, for each value of the distance, d (from the BS to an SS) and each MCS, for different Rs. In the omnidirectional case, while the power of the received carrier is computed for a distance d, the distances assumed for the computation of co-channel

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R = 250m R = 500m R = 1000m R = 1500m R = 2000m R = 3000m R = 4500m R = 5000m

12 Rb [Mbps]

10 8 6 4 2 0 0

2

4

6

8

10

rcc

Fig. 8.21 Physical throughput as a function of rcc, with R as a parameter, in the UL with subchannelisation and sectorization

14 R = 3km

Rb [Mbps]

12

R = 2km

10 8 6 4 2 0

0

500

1000

1500 d [m]

2000

2500

3000

Fig. 8.22 Maximum achievable physical throughput as a function of d for R ¼ 2 and 3 km, in the DL in the absence of sub-channelisation and sectorization (K ¼ 7)

interference are maintained, that is, rcc  (R  1) in the UL and rcc  R in the DL. In the tri-sectorial case, the power of the received carrier is also computed for a distance d, whilst considering the following equation for co-channel interference d g C= ¼ g I ðr  R þ 0:7  dÞ þ ðr  R  0:22  d Þg ; cc cc

(8.23)

Figure 8.22 shows the maximum achievable physical throughput as a function of d for K ¼ 7 for the DL, in the absence of sub-channelisation and sectorization, while Fig. 8.23 presents the case of UL, and achieved results are worst. Figure 8.24 shows the same type of results in the presence of sub-channelisation but without sectorization while Fig. 8.25 presents results in the absence of subchannelisation and with sectorization. For a fixed K, with the use of sectorization

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14 R = 3km

Rb [Mbps]

12

R = 2km

10 8 6 4 2 0

0

500

1000

1500 d [m]

2000

2500

3000

Fig. 8.23 Maximum achievable physical throughput as a function of d for R ¼ 2 and 3 km, in the UL in the absence of sub-channelisation and sectorization (K ¼ 7)

14 R = 3km

Rb [Mbps]

12

R = 2km

10 8 6 4 2 0

0

500

1000

1500 d [m]

2000

2500

3000

Fig. 8.24 Maximum achievable physical throughput as a function of d for R ¼ 2 and 3 km, in the UL, with sub-channelisation but without sectorization (K ¼ 7) 14 R = 3km

12

R = 2km

Rb [Mbps]

10 8 6 4 2 0 0

500

1000

1500 d [m]

2000

2500

3000

Fig. 8.25 Maximum achievable physical throughput as a function of d for R ¼ 2 and 3 km, in the UL, without sub-channelisation but with sectorization (K ¼ 7)

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(tri-sectorial 120 antennas) it is visible a clear increase on the distances where the highest throughputs are achievable. Figure 8.26 presents the case with the simultaneous use of sub-channelisation and sectorization (tri-sectorial 120 antennas). Tables 8.6 through 8.8 present a summary of the values of the maximum distances up which the different MCS may be used (and the respective values of the physical throughput). By using these values for the distance, it is possible to obtain the area of the coverage rings where each MCS is supported in the absence of sectorization, Tables 8.9 and 8.10 (for R ¼ 2 and 3 km, respectively), and with sectorization, Tables 8.11 and 8.12 (in the presence or absence of sub-channelisation, respectively). If one assumes a uniform distribution of users, the area of the coverage rings represents the percentage of use for each MCS. For a fixed K, the use of sub-channelisation improves the coverage slightly but only sectorization clearly improves the results for the achievable physical throughput. Furthermore, the simultaneous use of sub-channelisation and sectorization clearly benefits the possibility of using the highest level MCSs for larger coverage distances (compared with the cases of absence of sub-channelisation and sectorization). 14 R = 3km

12

R = 2km

Rb [Mbps]

10 8 6 4 2 0

0

500

1000

1500 d [m]

2000

2500

3000

Fig. 8.26 Maximum achievable physical throughput as a function of d for R ¼ 2 and 3 km, in the UL, with sub-channelisation and sectorization (K ¼ 7)

Table 8.6 Achievable distance, d, versus supported physical throughput and MCS, for R = 2 and 3 km in the absence of sub-channelisation and sectorization Rb (Mbps) MCS d (m) R ¼ 2 km R ¼ 3 km DL UL DL UL 12.27 64-QAM 910 750 1,185 1,030 11.29 64-QAM 2/3 995 820 1,295 1,130 8.47 16-QAM 1,420 1,190 1,865 1,635 5.64 16-QAM ½ 1,740 1,475 2,295 2,025 4.23 QPSK 2,000 1,900 2,920 2,610 2.82 QPSK ½ – 2,000 3,000 3,000

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Table 8.7 Achievable distance, d, versus supported physical throughput and MCS, for R = 2 and 3km in the presence of sub-channelisation but no sectorization Rb (Mbps) MCS d (m) R ¼ 2 km R ¼ 3 km DL UL DL UL 12.27 64-QAM – 780 – 1,165 11.29 64-QAM 2/3 – 860 – 1,280 8.47 16-QAM – 1,240 – 1,850 5.64 16-QAM ½ – 1,540 – 2,295 4.23 QPSK – 1,985 – 2,955 2.82 QPSK ½ – 2,000 – 3,000

Table 8.8 Achievable distance, d, versus supported physical throughput and MCS, for R = 2 and 3 km in the presence of sub-channelisation and sectorization Rb (Mbps) MCS d (m) R ¼ 2 km R ¼ 3 km DL UL DL UL 12.27 64-QAM – 1,460 – 2,095 11.29 64-QAM 2/3 – 1,605 – 2,300 8.47 16-QAM – 2,000 – 3,000 5.64 16-QAM ½ – – – – 4.23 QPSK – – – – 2.82 QPSK ½ – – – –

Table 8.9 Percentage of use of each MCS for R = 2 km MCS DL UL Rb (Mbps) d (m) Area (%) d (m) Area (%) 11.29–12.27 64-QAM 995 24.75 820 16.51 5.64–8.47 16-QAM 1,740 50.94 1,475 37.58 2.82–4.23 QPSK 2,000 24.31 2,000 45.61

Table 8.10 Percentage of use of each MCS for R = 3 km d (m) DL Rb (Mbps) 11.29–12.27 5.64–8.47 2.82–4.23

MCS 64-QAM 16-QAM QPSK

d (m) 1,295 2,295 3,000

Area (%) 18.63 39.89 41.48

d (m) 1,130 2,025 3,000

UL&DL with sub-channelization d (m) Area (%) 860 18.48 1,540 40.80 2,000 40.71

UL Area (%) 14.19 31.37 54.44

UL&DL with sub-channelization d (m) Area (%) 1,280 18.20 2,295 40.32 3,000 41.48

Table 8.13 presents the results for the average of maximum throughput, Rb . They are obtained by combining the results for the supported throughput in each coverage ring with the values of the covered area of that crown (which is used as a weight), for both link directions in the presence and absence of sub-channelisation.

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Table 8.11 Percentage of use of each MCS in the absence of sub-channelisation but with sectorization Rb (Mbps) MCS R ¼ 2 km R ¼ 3 km d (m) Area (%) d (m) Area (%) 11.29–12.27 64-QAM 1,295 41.93 1,500 25.00 5.64–8.47 16-QAM 2,000 58.07 2,695 55.70 2.82–4.23 QPSK – – 3,000 19.30

Table 8.12 Percentage of use of each MCS in the presence of sub-channelisation and sectorization MCS R ¼ 2 km R ¼ 3 km Rb (Mbps) d (m) Area (%) d (m) Area (%) 11.29–12.27 64-QAM 1,605 64.40 2,300 58.78 5.64–8.47 16-QAM 2,000 35.60 3,000 41.22 2.82–4.23 QPSK – – – –

Table 8.13 Average of the maximum physical throughput for R = 2 and 3 km R ¼ 2 km R ¼ 3 km Rb (Mbps) No subWith subNo subWith sub channelisation channelisation channelisation channelisation DL UL UL DL UL UL Omnidirectional 7.624 6.473 6.803 6.753 5.886 6.751 Sectorial 9.664 9.664 10.808 7.756 7.756 10.605

In the absence of sectorization, while for R ¼ 2 km the consideration of subchannelisation only leads to an increase in UL throughput of 4.8%, from 6.473 to 6.803 Mbps, for R ¼ 3 km, the increase achieves 15.1%, from 5.886 to 6.751 Mbps. While for R ¼ 3 km the use of sub-channelisation leads to an almost perfect balance between the DL and UL, for R ¼ 2 km this improvement does not occur. This can also be verified by comparing the right hand columns of Tables 8.9 and 8.10. With sectorization, while for R ¼ 2 km the consideration of sub-channelisation leads to an increase in throughput in the UL of 11.84%, from 9.664 to 10.808 Mbps, for R ¼ 3 km, the respective increase is 36.73%, from 7.756 to 10.605 Mbps. In this case, with the use of sub-channelisation, UL throughput surpasses DL throughput. In the omnidirectional case, with the use of sub-channelisation, although the noise power decreases the improvement only allows for a perfect balance of the PHY throughputs between the UL and DL for R ¼ 3 km (but not for R ¼ 2 km). The use of sectorization reduces the interference, and an improvement on the supported physical throughput of 59% is obtained for R ¼ 2 km (from 6.803 to 10.808 Mbps). However, for R ¼ 3 km, as the impact of noise is higher, without the use of sub-channelisation, the improvement only reaches 32% (from 5.886 to 7.756 Mbps). For R ¼ 3 km, only with the use of sub-channelisation and sectorization an improvement of 57% is achieved (from 6.751 to 10.605 Mbps).

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Summary and Conclusions

From the analysis it is clear that both noise and interference present a strong limitation to the performance of fixed WiMAX, mainly for higher level MCSs. As a consequence, with a reuse pattern K ¼ 7, cell throughputs near the maximum are only achieved in the UL if sub-channelisation is used together with sectorization. For lower coverage distances, the use of sectorization alone in the UL allows for a substantial gain in the physical throughput. However, for larger coverage distances, in the absence of sub-channelisation the achieved gain is not comparable with the case where sub-channelisation is used. These results motivate that future research directions need to be explored to analyse the inclusion of sub-channelisation into the DL, as the IEEE 802.16e standard already supports. Although this will give extra flexibility on resource assignment the extra complexity in the dimensioning process will justify the need for new methodologies, for example, considering scheduling. Another conclusion that can be extracted from the work is the need to improve the results for the maximum physical throughput in the outer crowns of the cells as this is the zone that suffers the highest interference. The use of relays within fractional reuse schemes, as shown in Fig. 8.27, is being pointed out as a solution for this challenge, and it needs to be investigated. The presence of relay stations (either fixed or mobile), with limited coverage, will introduce new challenges into the design process, as interference can be mitigated in different ways whilst increasing coverage.

Fig. 8.27 Fractional frequency reuse in a relaybased system where the number of fractional relay stations is 3 (extracted from [14, 15])

Base station Relay station

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Fixed WiMAX Planning Platforms

8.4.1

Framework and Scenario

Models for the achievable physical throughput, cellular coverage, and frequency reuse are very useful for the automation of cellular planning procedures. Cellular planning is highly dependent on the propagation environment and a careful choice of the placement, height and tilt of the BS transmitter antennas is needed in order to ensure a high percentage of LoS within the cells. As a consequence, the use of Geographic Information System (GIS) is needed to account for the terrain profile. In the context of the MobileMAN project [16], a cellular fixed WiMAX PtM network [1] was deployed, covering the whole district of Covilha˜, and in particular the city area. While the overall cellular structure is mainly dedicated to emergency and security public services, urban micro-cells will support e-learning and e-health services, among others. Although the district of Covilha˜ area is 550 km2, the territorial framework of the frequency band license assigned by ANACOM, the Portuguese regulator, is broader, and includes the whole area under study within the MobileMAN project in Beira Interior, Portugal, where a cellular planning exercise was also performed. A GIS based WiMAX planning tool was conceived that includes aspects of coverage, frequency reuse, and the impact of classes of services and applications. The tool enables radio and network planning of WiMAX outdoor networks. It relates the geographical data of a given location to the number of BSs needed to cover that location. This WiMAX platform uses ArcGIS as a working environment [17]. ArcGIS allowed the development of the toolbar that works as a base for network planning. The radio characteristics of the system are studied, including the link budget, the radio capacity, and the definition of the radio propagation models. Although our tool does consider adaptive MCSs it did not include the functionality of distinguishing among different MCSs in the graphical presentation of the results, that is, it does not display different maps for each MCS. It is therefore worthwhile to explore the functionalities of commercially available tools. The choice was WinpropTM from AWE, which considers the information coming from the digital terrain profile (as our tool does) but displays the several different MCSs on different maps.

8.4.2

Wireless Planning Tool

8.4.2.1

Functionalities and Potentialities

The planning tool is made available as a toolbar in ArcGIS that allows for the user to choose several parameters, from the number of base stations to the number of

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users, allowing for network operation in different environments, providing important similarities with real-life situations. The inputs of the tool are the file with the map, including the elevation of the terrain, in digital format, the total coverage area, the most probable position of SSs, as well as the type of applications. The options included into the ArcGIS toolbar are accessed via buttons, Fig. 8.28, and include the following WiMAX planning functionalities: l

l

Definition of urban zones – With this button urban zones are defined for BSs not operating at the maximum transmitter power since, for these sites, as the user density is much higher than in rural areas, the limitation is the system capacity instead of the radio coverage. Figure 8.29 presents an example of the urban zone of Covilha˜ over the Digital Map Terrain (DMT). Equipment – There are two buttons that deal with the WiMAX equipment to be used. The first enables to choose the type of equipment while the second enables the visualization of the equipment data. The equipment list may include items either from a manufacturer available on the market, or customized by the user definitions. In the former case, it is possible to define the bandwidth, frequency, and type of antenna. In the latter, the planner may define all the parameters, for example, bandwidth, transmission power, sensitivity, frequency, and type of antenna, Fig. 8.30.

Fig. 8.28 Toolbar on the graphic environment of ArcGIS

Fig. 8.29 Urban zones in the digital map terrain

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Fig. 8.30 Equipment characteristics: example of a possible choice for the parameters, different from the manufacturer ones

Fig. 8.31 BS positioning and LoS and NLoS areas

l

l

Sites with LoS and NLoS – This option allows for verifying the existence of LoS, and helps to choose the propagation model to be used on each zone of the map, compute the received power and analyze the type of application. This verification is performed by one of the GIS tools, and allows for an optimum verification of the LoS regions originated from each BS, as depicted in Fig. 8.31, example for the district of Covilha˜. The actual ArcGIS function used in the tool is Viewshed, a 3D Analyst extension of ArcView. Received power and coverage – This functionality creates three different layers. One has the coloured map for each value computed for received power (at each point of the map), depicted in Fig. 8.32. The other shows the values for CNIR. By considering received power and CNIR values, it is possible to check the areas with appropriate coverage and select the spatial option for the capacity. The last layer is a scheme where the different areas covered by each BS can be visualized, as well as the interference areas and the areas with no coverage.

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Fig. 8.32 Map with different kind of users (district of Covilha˜)

Fig. 8.33 Definition of the distribution of users by classes, their real-time requirements and the density

l

Users – This button shows a menu to define the percentage of users in each class (e.g., percentages of users with real time services) and the density of users per km2, as shown in Fig. 8.33. Figure 8.32 shows that these users are then randomly distributed on the map, whilst distinguishing the different classes by different symbols.

The service classes (labelled as one, two and three), distinguish real-time applications at 64, 384, and 2,000 kbps, respectively. A given percentage of users has access to time-based applications (the ones where the time is an intrinsic component of the application), for example, voice or video [18], while others are using non time-based ones. Figure 8.34 depicts some of the results, namely the distribution of users by classes, percentage of area covered and subject to interference, MCSs for each BS, number of users at each cell, throughput and percentage of served users.

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Fig. 8.34 Results arising from the ArcGIS planning tool

Fig. 8.35 LoS coverage for the district of Covilha˜

8.4.2.2

Covilha˜ Rural and Urban Areas

LoS discovery should be applied for a better cellular planning. GIS functionalities were incorporated into the tool for the choice of the best placement of BSs, including their height. By considering the use of the modified Friis model, an initial application was made for the district of Covilha˜, an area of 550 km2. Because this zone is very hilly, cells with coverage distances around 3 km are used, differently from the whole region of Beira Interior, where larger cells were considered. By considering 18 BSs and by using digital terrain models and ArcGIS 9.0, 3D Analyst extension, one obtains LoS coverage in 70% of the area, Fig. 8.35. In this first case, omnidirectional antennas are mounted on 15 sites (although two of them only cover a 180 sector), while the remaining three sites have two 180 sectorial antennas. It was verified that there is an average of 83% LoS coverage in villages,

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Fig. 8.36 Use of omnidirectional antennas in the district of Covilha˜

Fig. 8.37 Use of sectorial antennas in the district of Covilha˜

towns and cities. This choice guarantees propagation exponents of g ¼ 2 in rural areas and g ¼ 3 in dense urban areas. Furthermore, main roads on the access to the mountain are covered with LoS. Another exercise using the ArcGIS platform, in a broader geographical scope, leads to the results from Figs. 8.36 and 8.37, where micro-cells are overlaid with the macro-cellular structure. The height of BS antennas is 30 m, and slightly higher antenna gains are considered compared to the experimental setup. Besides, the transmitter power in urban areas is 18 dB lower than in rural areas. The SUI-C model was considered in this second case. A comparison between the use of omnidirectional and tri-sectorial cells is performed. In terms of interference mitigation, the advantage of using sectorial antennas is clear. From Table 8.14 one can observe that, with sectorial antennas, the area of interference is reduced from 42%, in the omnidirectional case, down to 9.3%, while the covered area (without interference) increases from 52.3% to 85.0%.

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Table 8.14 Coverage and interference areas for the district of Covilha˜ Type of Antenna Coverage area (%) Without interference With interference (%) Omnidirectional 52.3 42.0 Sectorial 85.0 9.3

Non-covered Area (%) 5.7 5.7

Fig. 8.38 Cellular coverage using sectorial antennas in the whole region of Beira interior

8.4.2.3

Region of Beira Interior

For the WiMAX cellular coverage of the whole region of Beira Interior, a zone with an area of approximately 5,760 km2 was considered while exploring many combinations for the placement of BSs and types of antennas. One specific exercise compares the use of omnidirectional antennas with the use of sectorial ones over the whole region (Fig. 8.38). The advantages of using the latter in terms of interference mitigation are clear because the area of interference is reduced by 36.1%, from 36.4% to 0.3% while the covered area increases from 50.8% to 86.9%. Finally, it is worthwhile to note that, as the SUI model is pessimistic in terms of propagation, the results for coverage are appropriate from an engineering perspective, as they represent a worst-case situation. However, results for interference would be worse if a more optimistic model was used for propagation at 3.5 GHz. A strong need of using sectorial antennas is verified. Sectorial cells guarantee an adequate coverage and interference mitigation for several terrain types and environments, including hilly terrains. In the particular case of our experiments, optimal planning for the integration of WiMAX and Wi-Fi technologies enables real technical conditions to make the interoperability of these HSF networks available to the students of the Health Science Faculty of University of Beira Interior, where the demonstrator is placed. It provides excellent theoretical, laboratorial, simulation and practical lessons

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through multimedia and IP communications, for example, videoconference, voice over IP, and communication of high resolution video/image with the support of terminal mobility, a must for the practice and teaching of medicine. As a final note it is important to mention that these technologies are very attractive in economic terms, when compared to legacy network technologies.

8.4.3

Results with Adaptive Modulation and Coding Schemes

8.4.3.1

Scenario

In the cellular planning exercises with the WinpropTM tool, the geographical scope and the location of BSs were the same as previously considered in Fig. 8.35. However, in this case, 18 tri-sectorial BSs are considered in the district of Covilha˜, which corresponds to a total 54 sectors, Fig. 8.39. WinpropTM enables to present different maps distinguishing each MCS. It also facilitates to explore other propagation models [8], for example, the dominant path loss one, and actual antenna pattern characteristics (from a file with the manufacturer characteristics). In this part of the work, one considers the parameters from the WiMAX BreezeMAX Alvarion equipment [9], and the frequency bands assigned by ANACOM. The BreezeMAX 3,000 equipment is the Alvarion WiMAX platform for the 3–4 GHz licensed bands. Table 8.15 shows the parameters used in the planning.

Fig. 8.39 Topography of the district of Covilha˜ covered with 18 base stations

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Table 8.15 Parameters for the planning

Air interface Number of cell Number of sector per cell Operation frequency Duplexing mode Multiple access technique Bandwidth DL/UL separation Antenna pattern BSs height SS height Maximum BS output power BS antenna gain SS antenna gain BS Noise Figure SS Noise Figure Propagation model

IEEE 802.16-2004 18 3 3.5 GHz FDD TDMA 3.5 MHz 100 MHz WiMAX 3500 MHz 120 Several, according to the topography 1.5 m 43 dBm (19.95 W) 15.3 dBi 1 dBi 4 dB 7 dB Dominant path loss

Fig. 8.40 Zones with LoS to BS15

8.4.3.2

Propagation in the District of Covilha˜

As an example, Fig. 8.40 presents the LoS regions seen from BS 15 in red while the NLoS regions are presented in green. BS15 is located at the following coordinates: X ¼ 247,000 m, Y ¼ 369,700 m (whose reference is a point on the sea near Sagres Point in the south of Portugal), the one assumed by the Portuguese Army Surveying Institute. The altitude for BS 15 is 1758 m, near the highest point in Portugal continental, the Torre (1993 m), and the antenna tower height is 20 m. One verifies that there is

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Fig. 8.41 Prediction for the received power for BS15

–45

Power [dBm]

–50 –55 –60 –65 –70 –75 –80

0

1000

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3000

4000

5000

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7000

Distance [m]

Fig. 8.42 Curve for the received power versus the distance (extracted from the WinpropTM tool)

LoS to the highest regions of the district of Covilha˜, and there only is NLoS to the down region, near the city of Covilha˜. Figure 8.41 shows a prediction of the received power at each of the three sectors of BS15. Figure 8.42 is also extracted from the WinpropTM tool in an actual case and helps to analyse the variation of the received power with the distance. The arrow represents the orientation of the sector.

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Table 8.16 Correspondence between the MCSs, CNIR and transmission modes

8.4.3.3

ID

MCS

CNIRmin (dB)

1 2 3 4 5 6 7 8

BPSK 1/2 BPSK 3/4 QPSK 1/2 QPSK 3/4 16-QAM ½ 16-QAM 3/4 64-QAM 2/3 64-QAM 3/4

3.3 5.5 6.5 8.9 12.2 15.0 19.8 21.0

Physical throughput (Mbps) 1.41 2.12 2.82 4.23 5.64 8.47 11.29 12.27

Influence of the Adaptive Modulation and Coding Scheme

In the dimensioning process, it is important to analyse the spatial dependence of the available MCS on the signal strength. The WiMAX equipment uses eight different MCS with different CNIR thresholds (Table 8.16) corresponding to the values for the sensitivity presented in Table 8.2. Planning and network performance results are based on the predictions for the received power (or attenuation) that occurs for each BS sector. According to AWE WinpropTM terminology, WiMAX network design is essentially based on the detailed analysis of the spatial predictions for each MCS, for example, CNIR, received power at the SS and BS, number of channels. Based on these results, the tool determines the physical throughput in the different geographical zones.

8.4.3.4

Prediction of the Maximum Received Power

The tool defines a so-called maximum received power. Figure 8.43 presents its prediction for the DL for the whole district of Covilha˜. In the results shown in Fig. 8.43 all the BSs are simultaneously considered in the prediction of the maximum received power, leading to the results for the variation of the maximum received power with the distance from Fig. 8.44. One verifies that the decrease of the maximum received power is much smoother than the variation of the received power itself (represented in Fig. 8.42). Another approach may be to analyse the coverage through the consideration of a threshold for the received power. Figure 8.45 presents this analysis for a received power threshold of 80 dBm. A pixel is red if the power is above the threshold and is green if the power is below the threshold. One verifies that with the 18 sectorial BSs a high percentage of coverage is obtained.

8.4.3.5

Prediction of the Maximum Physical Throughput in the DL

Figure 8.46 presents the Prediction of the PHY Throughput in the DL in the whole area covered by the WiMAX network. These results can be analyzed to decide

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Fig. 8.43 Prediction for the maximum received power in the DL

Max. Received [dBm]

–40 –45 –50 –55 –60 –65 –70 0

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Distance [m]

Fig. 8.44 Curve for the prediction for the maximum received power as a function of the distance (extracted from the WinpropTM tool)

where to expect the maximum and the minimum bit rate. For the SSs closer to the BS, an higher order modulation, that is, 64-QAM, is used, whose corresponding bit rate is 12.27 Mbps. For the users located further away, at a medium distance (still not far away from the BS), the 16-QAM modulation is used, and the bit rate is 8.47 Mbps. For the most distant users, near the cell boundary, QPSK or BPSK modulations are used (supporting data rates of 4.23 and 2.12 Mbps, respectively). This means that, as expected, the farthest the SS is from the BS the lowest is the physical

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Fig. 8.45 Coverage by considering a threshold for the maximum received power

Fig. 8.46 Prediction of the maximum reachable PHY throughput in the DL

throughput. To better interpret these results, it is important to analyze the charts from Figs. 8.47, 8.48, and 8.49, which represent the maximum physical throughput versus the distance, the histogram of the maximum physical throughput, and the cumulative probability for the physical throughput, respectively.

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Max Bit Rate [KBit/s]

12000 10000 8000 6000 4000 2000 0

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Fig. 8.47 Maximum physical throughput versus the distance (extracted from WinpropTM)

0.35 0.30 Probability

0.25 0.20 0.15 0.10 0.05 0.00

0

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Fig. 8.48 Histogram for the maximum bit physical throughput, Rb (extracted from WinpropTM)

By assuming ideal propagation conditions, for distances up to 1.5 km, WiMAX links support the highest order modulation, which corresponds to bit rates that vary between 11.29 and 12.27 Mbps. Then, for distances up to 2.7 km, the order of modulation are the medium ones (bit rates from 5.64 to 8.47 Mbps) while for distances of approximately 6 km one only achieves the lowest order modulations, with bit rates varying from 1.41 to 4.23 Mbps. From Fig. 8.48 one concludes that the MCS mostly used is QPSK (4.23 Mbps), in approximately 35% of the cases, followed by the medium order modulation, 16-QAM (8.47 Mbps), in more than 20% of the cases. The highest order modulation is used with a frequency of 15%. Figure 8.49 represents the cumulative effect of the results from Fig. 8.48.

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Cummulated Probability

1.0 0.8 0.6 0.4 0.2 0.0

0

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Fig. 8.49 Cumulative histogram for the different supported maximum physical throughput (extracted from WinpropTM)

8.4.3.6

Prediction of “Best Server” Cells

In the representation of the “best server” each pixel (representing the SSs) is assigned to a BS sector, more precisely to the carrier assigned to the respective sector, by choosing different colours. As sectorial antennas are used, an aperture angle is defined to each sector antenna. If the pixel is within the range of two different apertures, the assignment is performed to the sector/BS with the lowest associated distance. Figures 8.50 and 8.51 present the maps with the predictions for the “best server” for each MCS. When the MCS level increases, the area of the “best server” cell/sector decreases as it is only possible to use the highest order MCSs in the regions closest to the BSs. The tool is also able to represent the number of received carriers and of received channels (number of carrier multiplied by the number of time slots). A carrier is received if the received power in a SS is above a pre-defined threshold. The number of received carriers is important to address handover issues, as it is easy to identify the number of different solutions to perform handover. However, as the fixed WiMAX does not support handover the results are not presented. 8.4.3.7

Carrier-to-Noise-plus-Interference Ratio in the DL

Maps with the prediction of CNIR (or SNIR, signal-to-noise-plus-interference ratio) in the DL are also individually produced for each MCS, Fig. 8.52. If the received CNIR is below the threshold established to each MCS the pixel is transparently filled; otherwise, it is filled with the colour represented on the scale. The WinpropTM tool does not consider the UL. Although the results for the UL are generally less favourable, the use of sub-channelisation may allow for overcoming these coverage limitations, as previously discussed.

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Fig. 8.50 Maps with the “best server” sectors for (a) BPSK ½ and (b) BPSK

8.4.4

Summary and Conclusions

Two different approaches were considered for cellular planning in the district of Covilha˜. On the one hand, one considered a GIS based WiMAX planning tool conceived by considering coverage issues, frequency reuse, the impact of the

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Fig. 8.51 Maps with the “best server” sectors for the remaining MCS

different classes of service. On the other, as adaptive MCS are considered WinpropTM was used. The GIS functionalities allow for appropriately adjusting azimuth and tilt of antennas. This cellular planning exercises confirm the results theoretical analysis, where different crowns are achieved for the coverage with each MCS (corresponding to a given range of values for SNIR), and also for the maximum PHY throughput and for the “best server” cells. The benefit of using sectorization was also demonstrated. Cost/revenue optimisation will allow for finding the optima for the planning. There are fixed costs (e.g., spectrum licenses), plus costs proportional to the number of cells, and the cost proportional to the number of “transceivers”. Typically, total costs depend on the size of the cells and on the reuse pattern. Revenues depend on the supported throughput (which also depends on the size of the cells and on the

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Fig. 8.52 Maps with the SNIR prediction in the DL

reuse pattern). They depend on prices and will be very sensitive to the number of supported users. Regarding the profit, the absolute profit is usually proportional to the supported “traffic” (e.g., per km2). The profit in percentage is, however, proportional to the

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“spectral efficiency”, and companies usually want to maximize the profit in percentage [19]. Further work is needed to seek for optimum coverage distances in different reuse configurations accounting for cost-benefit optimisation.

8.5

Conclusions

In this Chapter, one started by considering a PtM demonstrator for fixed WiMAX that allowed for extracting measurements for cellular coverage in the suburban area of Covilha˜, Portugal. For this zone, and for some ranges for the distances, by using a curve fitting approach one concluded that the modified Friis model can be used with a propagation exponent g ¼ 3. From the analysis of the results, one can also conclude that the Stanford University Interim model can be considered (mainly SUI-C but also SUI-B), as the mean square error is kept under reasonable values. Then, an analytical approach was used to determine the trade-offs between the coverage distance and interference minimisation whilst increasing system capacity. From the analysis, it is clear that both noise and interference present strong limitations to the performance of fixed WiMAX, mainly for higher MCS levels. With a reuse pattern K ¼ 7, cell throughputs near the maximum are only achieved, in the UL, if sub-channelisation is used together with sectorization. With the use of sub-channelisation alone, although the noise power decreases, the improvement is not so clear. For the shortest coverage distances, the use of sectorization alone in the UL allows for obtaining a substantial gain in the physical throughput. However, for larger coverage distances, in the absence of sub-channelisation, the achievable gain is not comparable with the case where sub-channelisation is used. In general terms, the use of sectorization in fixed WiMAX enables to reduce the reuse pattern while considering sub-channelisation allows for improvement on the coverage. The reduction of the reuse pattern directly corresponds to an increase in the system capacity but the improvement in the coverage range (through subchannelisation) can also allow for an improvement in UL system capacity, as adaptive MCS are used. The need to improve the results for the maximum achievable throughput in the outer coverage rings of the cells, as this is the zone that suffers the highest interference, motivates future research directions, for example, by using relays within fractional reuse schemes. The presence of relay stations (either fixed or mobile), with limited coverage, will introduce new challenges into the design process, as interference can be mitigated in different ways whilst increasing coverage (e.g., by decreasing the transmitter power or by using advanced scheduling techniques). One interesting aspect which is left for further study is on the dependence of the results on the propagation exponent, g. For example, if the propagation exponent decreases, for example, to g ¼ 2.3, the value of the asymptote for the coverage area

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will increase and the asymptotic value for the reuse factor, rcc, will increase, corresponding to a reduction on system capacity for each MCS. Two different approaches were considered for graphical cellular planning, and the district of Covilha˜ was considered as a case study. On the one hand, one considered a GIS based WiMAX planning tool conceived by considering coverage issues, frequency reuse, and the impact of the different classes of service. On the other, WinpropTM was used as it distinguishes among different MCS in the graphical presentation of the results. Both tools consider the information coming from the digital terrain profile. The GIS functionalities allow for appropriately adjusting azimuth and tilt of antennas. This cellular planning exercises confirm the results of theoretical analysis, where different crowns are achieved for the coverage with each MCS (corresponding to a given range of values for SNIR), for the maximum physical throughput, and for the “best server” cells. The frequency radio resources should be considered as the most valuable resource during the planning of wireless broadband access networks. As a rule, spectral efficiency needs to be optimized by using several advanced techniques, corresponding to an optimization from the cost-benefit point of view. Acknowledgement This work was partially funded by MobileMAN (Mobile IP for Broadband Wireless Metropolitan Area Network), an internal project from Instituto de Telecomunicac¸o˜es/ Laborato´rio Associado, by CROSSNET (Portuguese Foundation for Science and Technology POSC project with FEDER funding), by “Projecto de Re-equipamento Cientı´fico” REEQ/1201/ EEI/ 2005 (a Portuguese Foundation for Science and Technology project), and by the Marie Curie Intra-European Fellowship OPTIMOBILE (Cross-layer Optimization for the Coexistence of Mobile and Wireless Networks Beyond 3G, FP7-PEOPLE-2007-2-1-IEF). The authors acknowledge the fruitful contributions on ArcGIS tools from Engº Jose´ Roma˜o, Engº Jose´ Riscado and Prof. Victor Cavaleiro from STIG-UBI, and to the final year project students Hugo Carneiro, Jorge Oliveira, Dany Santos and Rui Marcos.

References 1. IEEE, Draft IEEE Standard for Local and Metropolitan Area Networks – Part 16: Air Interface for Fixed Broadband Wireless Access Systems, IEEE 802.16-REVd/D5, The Institute of Electrical and Electronics Engineers, New York, USA, May 2004 2. IEEE, Draft IEEE Standard for Local and Metropolitan Area Networks – Part 16: Air Interface for Fixed Broadband Wireless Access Systems – Amendment for Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands, IEEE 802.16e/D9, The Institute of Electrical and Electronics Engineers, New York, USA, June 2005 3. http://www.awe-communications.com 4. V. Erceg et al., An empirically based path loss model for wireless channels in suburban environments. IEEE J. Select. Areas Commun. 17(7), 1205–1211 (July 1999) 5. IEEE 802.16 Working Group, Channels models for fixed wireless applications, Document 802.16.3c-01/29r4 (July 2001) 6. K. Hari, Interim Channel Models for G2 MMDS Fixed Wireless Applications, in IEEE 802 plenary meeting, Tampa, USA, Sept 2000. www.ieee802.org/16/tg3/contrib/802163c00_49r2.pdf (March 2010)

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7. H.R. Anderson, Fixed Broadband Wireless Systems Design (Wiley, Chichester, West Sussex, UK, 2003) 8. R. Wahl, O. St€abler, G. Wo¨lfle, Propagation model and network simulator for stationary and nomadic WiMAX networks, in Proceedings of IEEE VTC 2007 Fall – IEEE 66th Vehicular Technology Conference, Baltimore, MD, USA, Sept 2007 9. http://www.alvarion.com 10. T.S. Rappaport, Wireless Communications: Principles and Practice (Prentice Hall, Upper Saddle River, NJ, 2002) 11. F.J. Velez, L.M. Correia, J.M. Bra´zio, Frequency reuse and system capacity in mobile broadband systems: comparison between the 40 and 60 GHz bands. Wireless Pers. Commun. 19(1), 1–24 (Aug 2001) 12. F.J. Velez, V. Carvalho, D. Santos, R.P. Marcos, R. Costa, P. Sebastia˜o, A. Rodrigues, Planning of an IEEE 802.16e network for emergency and safety services, in Proceedings of 3G 2005 – 6th IEE International Conference on 3G Mobile Communication Technologies, London, UK, Oct 2005 13. F.J. Velez, Aspects of cellular planning in Mobile Broadband Systems, PhD thesis, Instituto Superior Te´cnico, Universidade Te´cnica de Lisboa, Lisbon, Portugal (Dec 2000) 14. K.A. Rizvi, Young sun, D. Basgeet, Z. Fan, P. Strauch, Fractional frequency reuse for IEEE 802.16j relaying mode. IEEE C80216j-06_223, IEEE (Nov 2006) 15. http://www.wimaxforum.org/documents/downloads 16. http://www.e-projects.ubi.pt/mobileman 17. H. Carneiro, J. Oliveira, A. Rodrigues, P. Sebastia˜o, Software planning tool for WiMAX networks, in Proceedings of Conftele’ 2007 – 7th Conference on Telecommunications, Peniche, Portugal (May 2007) 18. F.J. Velez, L.M. Correia, Mobile broadband services: classification, characterisation and deployment scenarios. IEEE Commun. Mag. 40(4), 142–150 (Apr 2002) 19. F.J. Velez, L.M. Correia, Optimisation of mobile broadband multi-service systems based in economic aspects. Wireless Netw. 9(5), 525–533 (Sept 2003)

Chapter 9

System Capacity Fernando J. Velez, M. Kashif Nazir, A. Hamid Aghvami, Oliver Holland, and Daniel Robalo

Abstract In Fixed WiMAX, the contribution from each transmission mode can be incorporated into an implicit formulation to obtain the supported throughput as a function of the carrier-to-interference ratio. This is done by weighting the physical throughput in each concentric coverage ring by the size of the ring. In this paper, multi-hop cells are formed by a central coverage zone and three outer coverage zones served by cheaper low-complexity relays. It is assumed that line of sight propagation to the bases station is achieved in a high percentage of the cell, reducing the impact of selective fading, through allowing dimensioning to be done by GIS cellular planning tools. By using tri-sectorised equipment there is a need for three times more bandwidth, while hardware costs are higher. In our proposal for relays, the FDD mode is considered and the frames need to guarantee resources for BS-to-MS communications but also for BS-to-RS and RS-to-MS communications. These requirements leads to a 1/5 asymmetry factor between the UL and DL in the omnidirectional BS case and to a 3/7 asymmetry factor in the case of tri-sectored BSs. Although the reuse distance is augmented by a factor pffi 3, we show that with the use of relays in FDD mode only the consideration of tri-sectored BSs with reuse pattern K = 3 (at the cost of extra channels, corresponding to 9 channels) enables to obtain values for the throughput comparable to cases without the use of relays. The presence of sub-channelisation only improves the results for the highest values of R. The consideration of tri-sectored BS antennas with K = 1 (whilst keeping the number of required channels – equal to 3) did not enable to obtain values of the throughput comparable to the ones without using relays, although frame format is more favourable. Relays can be cheaper than BS with full functionalities. As the use of relays may lead to lower costs it is worthwhile to analyse the impact of using them on costs and revenues.

F.J. Velez (*) Instituto de Telecomunicac¸o˜es-DEM, Universidade da Beira Interior, Calc¸ada Fonte do Lameiro, 6201-001, Covilha˜, Portugal e-mail: [email protected]

R. Prasad and F.J. Velez, WiMAX Networks, DOI 10.1007/978-90-481-8752-2_9, # Springer ScienceþBusiness Media B.V. 2010

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Introduction

In the context of Worldwide Interoperability for Microwave Access (WiMAX) planning, research on the variation of the carrier-to-noise-plus-interference ratio (CNIR), against different system parameters, is of fundamental importance. As there are challenges in both the uplink (UL) and downlink (DL) in WiMAX, techniques such as sub-channelisation may be applied to reduce the impact of noise on link performance. However, only Mobile WiMAX allows for sub-channelisation in both the UL and DL; fixed WiMAX only allows for it in the UL this absence of sub-channelisation in the DL for fixed WiMAX may be a cause of performance degradation (mainly owing to the extra noise caused by the larger spectrum bandwidth). For cellular planning purposes, the UL and DL CNIRs from/at the wireless Subscriber Station (SS) are very significant parameters. From a detailed analysis of CNIR variation for different coverage and reuse distances, an evaluation of the achievable reuse patterns can be performed for different modulation and coding schemes (MCSs). In order to more effectively use radio frequency spectrum, it is important to choose a frequency reuse scheme that leads to coverage guarantee and improved system capacity whilst minimising interference. Broadband wireless access enabling the operation of multi-hop relay stations (RSs) aims not only to enhance the coverage but also the system capacity, as interference is mitigated owing to the lowest transmitter power associated to the small range of the RSs. Compared with base stations (BSs), RSs does not need a wire-line backhaul and has much lower hardware complexity; hence, using RSs can significantly reduce the deployment cost of the system. The main objective is to achieve the highest values for the carrier-to-interference ratio, C/I, and, in return, the maximum supported throughput, by using relays for a given frequency reuse pattern, for example, K ¼ 3. In this work, a comparison of the different values the throughput is performed between the RSs, BSs and SSs in topologies with relays. By weighting the physical throughput in each concentric cell coverage ring by the size of the ring, the contribution from each transmission mode (or MCS) is included in an implicit function formulation to obtain the average supported throughput. For consecutive MCSs, the step distances are determined by the correspondence between minimum values at the CNIR curves (for a given MCS) and the supported physical throughput by an inversion procedure (via the consideration of each MCS stepwise threshold). The remaining of this Chapter is organized as follows. Sections 9.2 and 9.3 presents the formulations and assumptions for the CNIR analysis in the DL and UL, for configurations without and with relays for fixed WiMAX configurations. The supported physical throughput is analyzed in Section 9.4, envisaging the cases without relays and with relays (DL and UL) Section 9.5 addresses the special case of unitary reuse pattern, where the use relays may present a slight advantage. Finally, Section 9.6 presents the conclusions.

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CNIR Versus Physical Throughput Without Relays

In Fixed WiMAX, the supported physical user throughput is a function of the supported MCS, which in turn depends on the achievable CNIR compared with the minimum CNIR, CNIRmin, for each MCS (see Tables 8.2 and 8.16). It is therefore important to analyse the evolution of the CNIR against choices of several system parameters as well as the chosen co-channel reuse factor. If Frequency Division Duplexing (FDD) is used, analytical modelling of coverage and frequency reuse problems can only be carried out in Fixed WiMAX. Our chosen approach simultaneously accounts for carrier-to-noise and carrierto-interference constraints [1, 2]. Figure 9.1 presents the distance associated with coverage and interference for a 2D geometry with six interferers, when the mobile user is at a distance d from its serving base station (BS). The worst-case scenario in the DL occurs when the BS of the serving cell transmits to the most distant possible location of subscriber station (SS) it is serving, using a channel (or sub-channel) on which the SS is also receiving interference from the BSs of the six co-channel hexagonal neighbouring co-cells. If d is replaced by R the cell coverage distance or radius (0  d  R), this worst case is as depicted in Fig. 9.1. Note that if D is the reuse distance, there are tiers of interference at distances D, 2D, etc. However, if a high value for the propagation decay exponent is set, it is a valid approximation to only consider the first tier of interference, as shown in Fig. 9.1. In the UL, the worst-case scenario occurs when the SS is transmitting to the BS from the cell edge, while interfering mobiles are on the boundary between interfering cells’ edges and the serving cell of the SS [3]. When sectorization is considered, the number of interfering cells is decreased and system capacity increases. Such coverage and reuse geometries are commonly found in rural and suburban environments. In urban areas, owing to the obstruction of buildings and other urban obstacles, perfect circular/hexagonal cell coverage cannot be assumed anymore. Here we assume the use of the modified Friis propagation model [3], and that values of the transmitter power, propagation exponent, and transmitter and receiver antenna gains are set at Pt = 2 dBW, g = 3, Gt = 17 dBi, and Gr = 9 dBi, respectively. The radio frequency bandwidth, noise figure, and frequency are brf = 3.5 MHz, Nf = 3 dB, and f = 3.5 GHz. The values of these parameters are extracted from the experimental fixed WiMAX demonstrator from [4]. In contrast with Mobile WiMAX, a limitation of IEEE 802.16-2004 is that it does not support sub-channelisation on the DL [5]. On the UL, the use of subchannelisation allows SS transmissions to only use 1/16 of the bandwidth assigned to transmissions from the BS, leading to a 12 dB link budget improvement [6]. The IEEE 802.16-2004 standard defines 16 sub-channels, where either 1, 2, 4, 8 or all sub-channels can be assigned to a SS. Each user in each different sub-channel may use a different MCS in successive bursts as long as he/she is using a different subchannel. Nevertheless, it is a worth noting that in the DL, because the MCS can be

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D+d

D

D+d R d

D D-d D-d

Fig. 9.1 Co-channel interference for the DL where the SS is at a distance d (0  d  R) from the centre of the cell (D is the reuse distance). The worst-case occurs when d = R

chosen at burst level, there is also the flexibility to in effect use different MCS by different users (even without sub-channelisation), as they may use consecutive bursts within a frame. In snap-shot simulations, averaging the generated interference by just placing all SSs in the center of the cell is not the correct procedure due to the non-linear influence of pathloss at different distances [7]. The contributions to interference from SSs equally distributed all over the cell surface area needs to be taken into account [7]. However, in this paper, in our chosen analytical approach for Fixed WiMAX, we do not follow this approach. Instead we consider the worst-case interference scenario, where the UL interferer is located at the edge of the neighbouring cell whilst considering that the user at the central cell can move between the centre and the edge of the cell.

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With omnidirectional antennas, the worst-case for interference geometry corresponds to the case where the SS in Fig. 9.1 is at the cell edge, hence d = R. The carrier-to-interference ratio in the DL is given by Eq. (8.11). With tri-sectored cells (120 sectors), Eq. (8.11) becomes [8]: 1 C= ¼ I ðr þ 0:7Þg þ ðr  0:22Þg ; cc cc

(9.1)

which is valid for both links; rcc is given by (8.12). Note that in the omnidirectional case, the equation for the carrier-to-interference ratio in the UL results from the respective reuse geometry, where interferers are all at a distance D-0.866R from the central cell BS. This is given by: g

C= ¼ ðrcc  0:866Þ : I 6

(9.2)

These above equations only consider the first tier of co-channel interference: this assumption is generally only valid if a high value of the propagation exponent is used. If lower values for the propagation exponent are considered, interference to at least the second tier needs to also be considered [2]. To satisfy this, for example, for Eq. (8.11), terms proportional to 2(2rcc+1)g, 2rccg and 2(2rcc1)g need to be added to the denominator. The differences caused by the presence of sub-channelisation and sectorization can be interpreted by analysing the curves for CNIR as a function of the co-channel reuse factor, rcc, with R as a parameter. To produce these curves, the power of the carrier is obtained by computing the power received by an SS at a distance R from the BS, while the computation of the interference depends on the UL and DL configuration, and also on the use of sectorization. This can be computed for a fixed R by making the same considerations for frequency reuse as in Eqs. (8.11), (9.1) and (9.2). For the sake of simplicity, the modified Friis equation is used with different values of the propagation exponent, g, depending on the environment (g = 3 is considered in many numerical examples, as it may be suggested from the experimental work in a suburban area from [4]). The noise power is computed by using the following equation:   N½dBW  ¼ 204 þ 10  log brf ½Hz ;

(9.3)

where brf is the channel radio frequency bandwidth. In the sub-channelisation case, brf should be divided by 16. From these curves for the achievable CNIR as a function of rcc, by considering the values of CNIRmin, it is straightforward to obtain the maximum supported physical throughput at the cell edge (distance R) in a simplified way, that is, by considering that users are uniformly distributed on the cell but not considering the mixture of services and applications and the exact details for the corresponding

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“multiplexing” characteristics. For hexagonal-shaped cells, K = 1, 3, 4, and 7 correspond to reuse factors rcc = 1.732, 3.000, 3.464, and 4.583. We have utilised these values. The variation of CNIR with rcc without considering relays are presented in Chapter 8.

CNIR Versus Physical Throughput with Relays

9.3 9.3.1

Formulation

In this section the analysis of throughput is performed by considering the use of relays. In these topologies, a cell is composed by the central coverage area, served by the BS, and three 240 sector coverage areas, served by individual RSs (RS1, RS2 and RS3), Fig. 9.2. While the BS backhaul is assured in the usual terms for mobile communications (e.g., cable or micro-wave radio link), RS backhauling is supported by using special specific sub-frames within the radio channel created for this purpose [9]. The central coverage area BS may have omnidirectional or tri-sectored antenna. In the latter case, if Frequency Division Duplexing (FDD) is considered, more channels are needed which, in turn, allows for making extra resources available to the RSs (as separate frequency channels are made available at itch sector). While the BS backhaul is assured in the usual terms for mobile communications (e.g., cable or micro-wave radio link), RS backhauling is supported by using special specific sub-frames within the radio channel created for this purpose. Figure 9.3 shows the fixed WiMAX FDD mode frame structure assumed in this work. The WiMAX frame is divided into DL and UL sub-frames which, in turn, include sub-sections with the following purpose, Fig. 9.3: l l

BS to MS communications MS to BS communications

RS2

RS1 BS RS3

UL DL

Fig. 9.2 BS, RS and respective “hexagonal” coverage areas

MS

MS

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2/9

2/9

2/9

DL (to RS2)

DL (to RS3)

DL Sub-frame DL (to MS)

DL (to RS1)

UL Sub-frame UL (from MS)

3/45

2/45

UL UL (from MS to BS) (from MS to RS1)

2/45

DL (from RS1 to MS)

2/45

UL UL (from MS (from MS to RS2) to RS3)

2/45

2/45

DL (from RS2 to MS)

DL (from RS3 to MS)

2/45

UL UL UL (from RS1 (from RS2 (from RS3 to BS) to BS) to BS)

Fig. 9.3 Frame structure for UL and DL sub-frames with relays (omnidirectional BS)

l l l l

BS to RS communications RS to BS communications RS to MS communications MS to RS communications

It is worthwhile to note that the UL sub-frame supports DL communications from RS to MS. As we assume asymmetrical communications between the UL and DL with an asymmetry factor of 1/5 as shown in Fig. 9.3, the UL sub-frame may make these extra resources available for DL RS communications. The advantage of using relays becomes from the fact that the co-channel interference now comes from cells at a longer distances because the real distance is given by: pffiffiffi D ¼ 3 kR

(9.4)

The corresponding cell geometry is presented in Fig. 9.4. The cell is formed by a central coverage zone with hexagonal shape and three hexagonal outer coverage areas with 240 sectored antennas, as shown in Fig. 9.4, each occupying two thirds of the area relatively to the central coverage zone. This different approach corresponds to consider three times the coverage area becomes [6, 7]: Amultihop ¼ 3:Asinglehop

(9.5)

Different cases are discussed for the DL and UL, for the communications from and to RS and BS.

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A multihop

= 3

3 2

3 R 2 = 3 * A singlehop

R

D

Fig. 9.4 Cell with RS at the edge of the central coverage area

9.3.2

Assumptions

A set of assumptions is considered in this research on frequency reuse for fixed WiMAX with relays with a frequency reuse pattern (or cluster size) K ¼ 3. For downlink (DL), the objective is to maximize the supported throughput. The optimization process is twofold [9]: l

l

l

l

The offered throughput from BS to RS needs to be maximized, that is, for a hexagonal coverage area with radius R the throughput Rb(R) needs to be the highest possible. The offered throughput to SSs needs to be maximized. It is further be divided into two points: Maximization of Rb-sup at the SSs on the central coverage area – By considering our assumptions for DL and UL frames (to cope with the Relay Station communications, Fig. 9.3) the DL throughput at the central coverage area is approximately 1/3 of the total one Maximization (Rb-sup)RS in SSs at the three relay coverage areas – The maximum throughput at the RS coverage area is Rbmax=min{Rb(R), (Rbsup)RS} multiplied by 2/9, that is, 2/9·Rbmax, where Rb(R) is the maximum throughput at

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the edge of the central cell, at a distance R from the BS, and (Rb-sup)RS is the total throughput that may be supported at the RS coverage area if the Rs backhaul could support it (and considering the total frame duration) Relay station antennas for the communication with the BS are considered to be directional (e.g., 120 sectored ones); so that they only receive/cause interference from/at two BSs at distance D+R, as it will be shown in the formulation. From the communications at the relay, in our hypothesis for frames, it is only possible to achieve 2/9·Rbmax for the supported throughput at the whole RS coverage area. However, only if the BS to RS link supported throughput is enough the total throughput is guaranteed. In practice, the throughput at a distance d from the RS, Rb(d) depends on the supported modulation and coding scheme (MCS), and is given by [9]: 2 Rb ðdÞ ¼ Rb ðRÞ  AuxFactorðdÞ 9

(9.6)

where d is the distance to the RS and Rb(R) is the maximum throughput at the edge of the central cell, at a distance R from the BS and AuxFactor(d) is given in Table 9.1. Let’s assume as an example that the 16-QAM ½ MCS is supported in the central coverage area. Table 9.1 shows the values for AuxFactor(d) if the MCS ID that may be guaranteed for the CNIR(d) from the RS coverage area is 1, 2, 3, 4, 5, 6, 7 or 8. The 16-QAM ½ MCS is shown in bold in Table 9.1. In practice, the rule for RS is the following: If the MCS supported at a distance d from the RS is higher or equal the one supported in the BS-to-RS link (16-QAM ½ in this example) the throughput for RS will be 2/9 Rb(R); otherwise the throughput will be 2/9 (Rb-sup)RS. For UL, the maximization of supported throughput, Rb-sup is also twofold [9]: l

l

The supported throughput from RS to BS needs to be maximized. At the BS from RS it is only possible to achieve 2/45 Rb-sup The supported UL throughput needs to be maximized. It is further divided into two parts

Table 9.1 AuxFactor (d) for different values of the MCS ID for the communications to the SSs at RS coverage area ID MCS CNIRmin (dB) Physical thr. (Mbps) AuxFactor(d) 1 BPSK ½ 3.3 1.41 1.41/5.64 2 BPSK 3/4 5.5 2.12 2.12/5.64 3 QPSK ½ 6.5 2.82 2.82/5.64 4 QPSK 3/4 8.9 4.23 4.23/5.64 5 16-QAM ½ 12.2 5.64 1 6 16-QAM 3/4 15.0 8.47 1 7 64-QAM 2/3 19.8 11.29 1 8 64-QAM 3/4 21.0 12.27 1

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Maximization of the supported UL throughput at the RS (from MS) in the central coverage area (the maximum achievable throughput is 3/45 Rb-sup) Maximization of the offered throughput from SSs to RSs at the three RS coverage areas (the maximum is 2/45 (Rb-sup)SS)

Since relay station antennas are directional thus base station only receive interference from two BS at distance D+R. At the relays station it is only possible to achieve 2/45 (Rbsup)SS, where (Rbsup)SS refers to the supported throughput from SS to RS. This traffic will only reach BS if the RS to BS radio link supports such value of the throughput.

9.3.3

DL Scenarios

For the DL there are three different cases that need to be individually analyzed: 1. BS to SS: BS to SS communication is the simple case Fig. 9.5 is discussed before the same formula for C/I is used as discussed in (8.23). 2. BS to RS: In the case of BS to RS communication one assumes that RSs are using directional antennas of 120 Fig. 9.6 and only receive interference from

Fig. 9.5 DL scenario

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Fig. 9.6 DL scenario with 120 RS sectorial antennas and 240 sector RS coverage area

two BSs, Fig. 9.8. This ultimately effects and enhances the C/I by a significant amount as shown in the later discussion. Therefore (D+aR)g/Rg=(rcc+a)g has a coefficient 2 while a = 1 and C/I is given by:   C 1 (9.7) ¼ I 2ðrcc þ 1Þg

3. RS to SS: In the case of RS to SS, the SS receives interference from four neighbouring RSs, Fig. 9.7. The distances between cell centres, RS and SS shown in Fig. 9.5 measured by using Autocad 2008 in a worst case situation where RS is at the edge of the coverage area. On the basis of measured distances the coefficients of R, in(D+aR)g, are calculated as given below [9]: pffiffiffi D ¼ 3R 3 ¼ 519:615 m

(9.8)

R ¼ 100 m

(9.9)

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Fig. 9.7 Distances from the RS interferers to the SS

There are two RS at 435.8899 m from the envisaged SS: 435:89  519:62 ¼ 0:837 100

(9.10)

There is one RS at 529.1503 m from the SS: 529:15  519:62 ¼ 0:0953 100

(9.11)

and one at a distance 608.27 m: 608:28  519:62 ¼ 0:8866 100

(9.12)

Hence, C/I is given by [9]: C Rg ¼ g 2ðD  0:8372RÞ þ ðD þ 0:09535RÞg þ ðD þ 0:8866RÞg I

(9.13)

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9.3.4

377

UL Scenarios

For the UL there also are three different cases that need to be analyzed individually: 1. From SS to BS: In case of SS to BS there is interference from six surrounding SS. Thus carrier-to-interference ratio is given by

C ðrcc  0:866Þg ¼ 6 I

(9.14)

2. From RS to BS: In this case we have assumed that RS antennas are 120 sectored one. Thus, the BS at the central cell only receives interference from two RS, at distance D+R, Figs. 9.8 and 9.9. The carrier-to-interference ratio is given by C ðrcc þ 1Þg ¼ 2 I

(9.15)

3. From SS to RS: In this case RS receives interference from four SSs in neighbouring cells. By using the same procedure to measure the distances

Fig. 9.8 The decrease of the co-channel interference by using directional antennas at RS

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Fig. 9.9 Distances from RS to BS in the UL

between cell centres, RS and SS, the following values were obtained for the coefficients a of R: 0.8761, 0.82776, 0.80762. As a consequence, C/I is given by: C Rg ¼ 2ðD  0:8761RÞg þ ðD  0:082776RÞg þ ðD  0:80762RÞg I

9.4 9.4.1

(9.16)

Supported Physical Throughput Implicit Function Formulation

To guarantee Fixed WiMAX coverage with no coverage gaps near cell edges, the CNIR must be higher than 3.3 dB throughout the cell. This value corresponds to the minimum CNIR in order to use the BPSK ½ MCS (see Table 9.1). The assessment of the supported cell/sector physical throughput (per transceiver), Rb, as a function of the distance, d, produces a staircase-shaped curve

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R

d

Fig. 9.10 Areas of the coverage rings where a given value of physical throughput is supported

indicating that higher maximum achievable throughputs are supported near the centre of the cell (see Fig. 9.10). As throughput is not constant over the whole coverage area for cellular planning proposes (where R is the cell radius), the supported throughput is obtained by computing the average supported throughput in the cell. As stated previously, in contrast to [6, 7], worst-case scenarios for interference geometry are considered here. There are J different coverage rings in each coverage zone, each supporting a different MCS (for instance, J = 4 in Fig. 9.10). The distances that correspond to the steps between consecutive MCS are represented by dj, j = 1, 2, . . ., J. Here we denote the order of the MCS as MCSj. The number of different coverage rings is given by: J ¼ MCS1st  MCSlast þ 1;

(9.17)

where MCS1st and MCSlast represent the MCS for the first and last coverage rings, respectively. If only one frequency channel is considered per cell, the supported throughput is obtained as [8, 10]:

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ÐÐ Rbsup ¼

O

  J  pffiffi  P 3 3 2 2  d  d ð Þ  R Rb ðd; R; K Þdxdy b MCS1st þ1j j j1 2 j¼1 pffiffi pffiffi ¼ ; 3 3 3 3 2 2 2 R 2 R

(9.18)

where the 2D integral is performed over the hexagonal shape of the cell. It is computed by weighting the supported physical throughput in each concentric coverage ring by the size of the ring where that value is supported. The contribution of each of the transmission modes is thus considered. MCS1st, MCS2nd, . . ., MCSJth can be obtained in the following way

  MCSj CNIR½dB ¼

8 > > > > > > > > > > > < > > > > > > > > > > > :

0; CNIR<3:3 1; 3:3bCNIR<5:5 2; 5:521:0

(9.19)

where j represents the coverage ring, CNIR½dB ¼ 10  logðcnir Þ, and MCSk = 0 means that there is not enough coverage in that part of the cell (or coverage ring); in this case, the system will not be viable. Besides, if l = MCSj, one can represent the physical throughput corresponding to each MCS, l = 0,1, . . ., 8, as 8 0; l ¼ 0 > > > > 1:41; l¼1 > > > > 2:12; l ¼ 2 > > > < 2:82; l ¼ 3 ð Rb Þ l ¼ 4:23; l ¼ 4 : > > > 5:64; l ¼ 5 > > > 8:47; l ¼ 6 > > > > 11:23; l¼7 > : 12:27; l ¼ 8

(9.20)

CNIR(Rb) is not a bijective function. Therefore, the value of CNIR that corresponds to a given Rb is the minimum value of CNIR, that is, CNIRmin, that supports a given throughput Rb. Hence d0 = 0, and     dj ¼ cnir 1 min CNIR ðRb ÞMCS1st þ1j ; j ¼ 1; . . . ; J:

(9.21)

Figure 9.11 presents the correspondence between the CNIR vs. propagation distance curve and the stepwise function that represents the CNIRmin threshold for each MCS versus Rb. This Figure illustrates how the mapping between CNIR and

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9

min CNIR MCS

J -2

min CNIR MCS

J -1

min CNIR MCS

dJ

d

Rb-MCS J -2

dJ-1

Rb-MCS J

dJ-2

Rb-MCS J -1

J

Rb

Fig. 9.11 Correspondence between the physical throughput for rings J, J1, J2, . . ., and the minimum CNIRs of consecutive MCS that map to step distances dJ, dJ1, dJ2, . . .

supported physical throughput relates to step distances between consecutive MCS dJ, dJ1, dJ2, . . . . This Figure illustrates how the mapping between CNIR and supported physical throughput relates to step distances between consecutive MCS dJ, dJ1, dJ2, . . . . In the context of the experimental work performed within our research group, results have fitted the modified Friis equation to some ranges of coverage distances in Fixed WiMAX [4]. According to the modified Friis equation, the received power is given by pr ðdÞ ¼

pt  gt  gr  l2 ð4pÞ2 d g

:

(9.22)

where 0  d  R, l is the wavelength, Pt, Gt and Gr (the latter ones are in dB), and g is the propagation exponent.

9.4.2

Without Relays

In the DL, for a given R, the reuse distance is given by D = rccR, and the interference at a distance d from the BS is computed by the following approximate equations iðd; D; RÞ ¼

p t gt gr l2 ð4pÞ2



 2 2 2 ; þ þ ðD  dÞg Dg ðD þ dÞg

(9.23)

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iðd; D; RÞ ¼

pt g t gr l2 ð4pÞ2



 1 1 : þ ðD  0:7  dÞg ðD  0:22dÞg

(9.24)

Equation (9.23) is applied in the omnidirectional BS antenna case while Eq. (9.24) is applied in the tri-sectored case. Under sectorization, only two interference sources need to be considered. Although these formulas are both valid for the DL (9.24) is also valid for the UL. For the omnidirectional case on the UL, Eq. (9.2) for interference can still be applied as it does not depend on d, as the distances from the SS interferes to the cell BS are D-R. Note that, as for Eqs. (8.11), (9.1) and (9.2), the second tier of interference would also need to be considered if lower values of the propagation exponent were used. We are aware that in this paper we do not consider per sub-channel equivalent SINR (or CNIR) computations when sub-channelisation is used. These computations could be performed accounting either for exponential effective SINR mapping (EESM [11–14]), effective code rate map (ECRM), or mean instantaneous capacity (MIC [6]). The consideration of these compression techniques may be needed in the presence of selective fading to adapt the curves to actual CNIRs in the UL. In the following, five different cases are addressed: l

l

l

l

l

The DL in the absence of sub-channelisation and sectorization (which we denote as the “DL – omnid”. case) The UL in the absence of sub-channelisation and sectorization (the “UL– omnid”. case) The UL in the presence of sub-channelisation and absence of sectorization (the “UL – sub-channel”. case) The UL and DL in the absence of sub-channelisation and the presence of sectorization (the “UL & DL – sector”. case) and The UL in the presence of sub-channelisation and sectorization (the “UL – subch. & sector”. case).

Figure 9.12 presents the curves for Rb(d) for K = 4 with a coverage distance R = 2,500 m. Without using sub-channelisation or sectorization, the DL performance is clearly better than the UL one. However, when sectorization is considered, higher physical throughputs are achievable. Besides, the better results are obtained when both sub-channelisation and sectorization are used. In this case, the highest physical throughput reaches 12.27 Mb/s, which is achieved for distances up to d  1,500 m. As an example, Fig. 9.13 presents a comparison of the results for the cell physical throughput for different reuse patterns K = 1, 3, 4 and 7, for “UL – subch. & sector”. and R = 2,500 m. If one carefully analyses the difference in the areas below the curves in these Figures, the following conclusions can be extracted: l

Although the physical throughput clearly increases with the use of sectorization only with the simultaneous use of sectorization and sub-channelisation in the UL the highest order MCSs are possible near the cell edge.

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System Capacity

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14 12

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10 8 6

DL - omnid. UL - omnid.

4

UL - subchannel.

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Fig. 9.12 Example of the variation of the physical throughput as a function of d for R = 2,500 m and K = 4

14 12

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K=7

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K=4 K=1

0 0

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1500

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Fig. 9.13 Variation of the physical throughput in the “UL – subch. & sector.” case versus d, for R = 2,500 m

l l

With no improvement technique the DL performs better than the UL. A value for the reuse pattern K = 7 only presents a slight advantage relatively to the consideration of K = 4 or 3, whose behaviour is very similar; this is mainly true in the “DL” and “UL & DL – sector”. Cases, whose curves are not presented here. It should be noted here that K = 1 is not supported without the use of sectorization.

By applying Eq. (9.18) to the results for the cell physical throughput (as the ones from Figs. 9.12–9.13), one obtains the curves for the supported throughput as a

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Rb-sup [Mb/s]

4

3 2 UL&DL - sector. 1 0

UL - subch. & sector.

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Fig. 9.14 Supported sector physical throughput versus R for K = 1

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7 6 5 4 3 DL - omnid.

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Fig. 9.15 Supported cell/sector physical throughput versus R for K = 3

function of R for K = 1, 3, 4 and 7 presented in Figs. 9.14 through 9.17, respectively. Some of the curves with no sub-channelisation are either impossible to obtain at all or after a given R, for example, for K = 1, 3 or 4. This is because the physical throughput on the outer coverage ring of the cell reaches 0 Mb/s and full cell coverage may not be guaranteed. The supported throughput results for K = 4 are slightly worse than the ones for K = 7 but they are still acceptable (where there is the advantage under K = 4 of using only 4/7 = 57% of the spectrum bandwidth). For K = 3, although the degradation compared to K = 7 seems high compared with K = 4, only 3/4 = 75% of the bandwidth is used. This reduction in spectrum bandwidth is, however, not as much as between K = 7 and K = 4. Using K = 1 is

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Rb-sup [Mb/s]

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6

4 DL - om nid. UL - om nid. UL - subchannel. UL&DL - sector. UL - subch. & sector.

2

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Fig. 9.16 Supported cell/sector physical throughput versus R for K = 4

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Fig. 9.17 Supported cell/sector physical throughput versus R for K = 7

advantageous because only a small portion of spectrum is needed. If tri-sectorization is used, as sub-channelisation is not supported in the DL, a fractional use of the WiMAX channels is not possible and three different channels are needed, one for each sector. In this case, the total supported throughput is three times the sector average throughput. With 3.5 MHz channels, only 10.5 MHz are needed for each link direction.

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Table 9.2 Average supported throughput for low coverage distances with different Ks with simple assumptions DL – omnid. UL – omnid. UL &DL – sector. UL – sector. & subch. Rbsup K¼1 K¼3 K¼4 K¼7

– 5.051 6.100 8.024

– – 4.623 6.985

4.515 8.160 9.149 10.689

4.591 8.241 9.255 10.813

100.0 80.0 Area [%]

1.41 2.12

60.0

2.82 4.23

40.0

5.64 8.47

20.0

11.29 12.27

250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500 3750 4000 4250 4500 4750 5000

0.0

R [m]

Fig. 9.18 Area covered by each MCS versus R for K = 4, in the “UL – subch. & sector” case

It is however worthwhile to compare results for the supported throughput among different values of K by assuming, for the sake of simplicity, that only one single channel could be used (even with tri-sectorization). For short coverage distances, that is, up to 1,500–2,500 m, depending on the cases (the highest Rs occur with sub-channelisation), the average values of achievable supported throughput are presented in Table 9.2. When K decreases, if sectorization is not used the reduction in physical throughput is higher; that is, high values of throughput are only achievable through the use of sectorization. Moreover, for this range of coverage distances, the values of supported throughput are only 1–2% lower without sub-channelisation compared with the case where both sub-channelisation and sectorization are used. The comparison between the “UL – sector. & subch”. and “DL” cases shows a reduction in the supported throughput for the DL case of 38.7, 34.1, and 25.8%, for K ¼ 3, 4, and 7, respectively (note that for K ¼ 1, it is not possible to support users in the DL without sectorization). While with omnidirectional antennas there is a clear asymmetry between UL and DL traffic (see Figs. 9.16 and 9.17) it is evident that the UL and DL can be balanced through the use of sectorization. These curves can be better interpreted by analysing the variation with R of the cell area, in percentage, corresponding to each supported data rate, that is, for each MCS (according to Table 9.1). Figure 9.18 presents the corresponding curves for

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Fig. 9.19 Area covered by each MCS versus R for K = 7, in the “UL & DL – sector” case

K = 4 in the “UL – subch. & sector” case. From this, it can be observed that the highest values of the throughput are supported in the presence of sub-channelisation plus sectorisation, and correspond to the exclusive operation with the four highest order MCS for coverage distances of up to 4,750 m. Figure 9.19 presents the variation of the coverage area, in percentage, against R, for each MCS, but this time for the case K = 7 and “UL – subch. & sector”, which is presented as an example. By comparing these results with the ones for K = 4 one concludes that, for K = 7, the three highest order MCS are only supported up to R = 1,750 m, whereas, for K = 4, four different MCS are needed. However, for K = 7 and coverage distances higher than 2,500 m, the trend of enabling larger coverage distances while solely using the highest order MCS is not maintained anymore.

9.4.3

DL with Relays

The Fig. 9.20 shows the throughputs of the different scenarios of DL. 1. From BS to MS: Throughput from BS to MS is sufficiently high and it gradually decreases with the increase of the cell coverage distance R. In our assumptions, the frame structure is assigned 1/3 for DL. So, the DL throughput is obtained by the multiplying this factor 1/3 by the total obtained one. If we want to compare this value with the throughput in the RS coverage area, as they only have the coverage area, a normalized should be needed that is obtained by multiplying the throughput by this factor 2/3. 2. From BS to RS: The throughput from RS to BS remains high at constant level until 4 km and then suddenly decreases after 4 km. This throughput is obtained

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3.5 3 2.5 2 1.5 from RS to MS from BS to RS from BS to MS from BS to MS normalized

1 0.5 0

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Fig. 9.20 Results for the supported throughput as function of R in the DL with relays (K = 3, omnidirectional BS)

by using directional antennas at RS which greatly decreases the co-channel interference, Fig. 9.5. Only two RS receive interference from the central cell BS.

iðdÞ ¼

Pt Gt Gr l 2 ð4pÞ2

ðD þ dÞg

(9.25)

The receiver antenna gain Gr value was set to 28 dBi to obtain this throughput. 3. From RS to SS: The throughput for RS to SS is almost of same value as BS to SS. In our assumptions the frame structure is assigned 2/9 in case of RS to SS for DL. So, this is obtained by the multiplying this factor to the total obtained throughput.

9.4.4

UL with Relays and K = 3

Figure 9.21 show the results for throughput for different UL scenarios. 1. From SS to BS: Throughput for SS to BS resembles the previous scenarios of DL. Throughput decreases with the increasing cell coverage area R. In our assumptions, for SS to BS, the frame structure is assigned 3/45 for UL. So, the UL throughput is obtained by multiplying this factor 3/45 the total obtained one. If we want to compare this value with the throughput in the RS coverage area, as they only have the coverage area, a normalized should be needed that is obtained by multiplying the throughput by this factor 2/3.

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0.6 0.5 0.4 0.3 from MS to BS from RS to BS from MS to RS from MS to BS normalized

0.2 0.1 0 0

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Fig. 9.21 Results for the supported throughput as function of R in the UL in the absence of subchannelisation (K = 3)

2. From RS to BS: The throughput from RS to BS remains high at constant level until 4 km and then suddenly decreases after 4 km. This throughput is obtained by the use of directional antennas at RS which greatly decreases the co-channel interference, Fig. 9.8. The receiver antenna gain Gr value is set to 28 dBi to obtain this throughput. 3. From SS to RS: Throughput for SS to RS is almost of same value as SS to BS. In our assumptions, for SS to RS, the frame structure is assigned 2/45 for UL. So, this is obtained by the multiplying this factor to the total obtained throughput.

9.4.5

Use of Sub-Channelisation

In the case of IEEE 802.16-2004 standard does not support the sub-channelisation for DL. However, it may be supported in the UL. Therefore, to obtain the sufficient level of throughput for UL the sub-channelisation is used. Throughput analysis for the UL scenario from the Fig. 9.22 is performed with sub-channelisation. The main change is the fact that the throughput from RS to BS now remains constant when the cell coverage area varies. However, there are no remarkable differences in the other curves. The throughput analysis from Fig. 9.11 for UL scenario is presented with subchannelisation. In the case of RS to BS throughput the main change is the fact that the throughput from RS to BS now remains constant when the cell coverage area increases. So, there is constant level of throughput at all distances of cell coverage area R. However, one can see from the results that there is no remarkable difference in the other curves.

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Supported Throughput [Mb/s]

0.6 0.5 0.4 0.3 from MS to BS from RS to BS from MS to RS from MS to BS normalized

0.2 0.1 0 0

1000

2000

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Fig. 9.22 Results for the supported throughput as function of R in the UL with sub-channelisation (K = 3)

9.5

Throughput with Sectorization, Relays and K = 1

The analysis with K = 1 was tried with omnidirectional cells but the communication from MS to BS was impossible. As the topologies with RSs are more favourable, it is worthwhile to consider tri-sectored antennas at the BS of the central coverage area. We used Eq. (8.23) to compute the carrier-to-interference ratio from/to pffiffiffi the BS at the central cell (for DL and UL, respectively) but now with D ¼ 3 kR. The formulation for the communications between RSs and MSs is the same, as well as the one for the communications between RSs and BSs. By considering trisectored antennas we need to have one different channel (i.e., frequency carrier) for each sector. This way, more resources are made available to the RSs, and we can consider the assumptions from Fig. 9.23 for the DL and UL sub-frames. The asymmetry factor between the UL and DL is 3/7 in this case. Figures 9.24 and 9.25 show the results for the supported throughput for the DL and UL, respectively. Although the supported throughput per channel may be lower (e.g., 8.25 Mb/s at 750 m against 9.79 Mb/s in the omnidirectional case), the supported throughput from BS to SS (with K = 1, tri-sectorization) is clearly higher than the one for “K = 3, omnidrectional BS” (e.g., a normalized throughput of 3.30 Mb/s in tri-sectored case at 750 m against 2.02 Mb/s in the omnidirectional case). This is owing to the more favourable frame format (the asymmetry factor is 3/7 against 1/5 in the omnidirectional case). Nevertheless, with tri-sectorization and K = 1 it is a worth noting that the BS to SS communication is not the most limitative one anymore. In fact, the RS to SS link shows now the lowest throughput (e.g., 2.17 Mb/s for R = 750 m). These values are still slightly larger than the achievable ones in the omnidirectional central coverage area case with K = 3. Besides, it is worthwhile to note that, as there is one channel

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System Capacity

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DL Sub-frame DL (to MS)

9/35

6/35

DL (to BS)

6/35

2/5

UL Sub-frame UL UL (MS to BS) (MS to RS)

UL (RS to BS)

DL (RS to MS)

Fig. 9.23 Frame structure for UL and DL sub-frames with relays (tri-sectored BS)

Supported Throughput [Mb/s]

5

4

3

2 BS-to-MS BS-to-RS RS-to-MS BS-to-MS-normalized

1

0

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Fig. 9.24 Results for the supported throughput as function of R in the DL with relays (K = 1, tri-sectored BS)

assigned to each sector the total cell throughput (to be fed into the cost/revenue optimization procedure) is achieved by multiplying this sector throughput by three. In the future, we also may analyse the presence of sub-channelization in the UL with K = 1, and its impact for the longest coverage distances. The case with trisectorized BS antenna and K = 3 is analyzed in [9].

9.6

Conclusions

In this work, a model to compute the supported physical throughput as a function of the achievable CNIR has been proposed for Fixed WiMAX. Frequency reuse topologies have been explored for 2D geometries that are commonly used in rural

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1 BS-to-MS BS-to-RS RS-to-MS BS-to-MS-normalized

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Fig. 9.25 Results for the supported throughput as function of R in the UL with relays (K = 1, tri-sectored BS)

and suburban environments, and the basic limits for system capacity and cost/ revenue optimisation have been obtained by considering simple assumptions. It is assumed that line of sight propagation to the bases station is achieved in a high percentage of the cell, reducing the impact of selective fading, through allowing dimensioning to be done by GIS cellular planning tools. For a given coverage area, throughput is a stepwise function that decreases as the distance to the base station increases. Its value depends on the supported MCS for each coverage ring. In this chapter, the supported throughput has been computed by weighting the available throughput at each coverage ring with the area (or size) of the ring. Throughput typically decreases as the cell radius increases, although through the use of sub-channelisation it is possible to keep its value steady at least up to a cell radius of 5,000 m. With the use of sectorization, the supported throughput is higher, corresponding to the use of the highest order MCSs. However, as sectorised equipment is more expensive and there is a need for three times more bandwidth, costs are also higher. In this Chapter formulations were also proposed to account for the interference in cellular coverage and reuse geometries without and with the use of relay. In our proposal for relays, the FDD mode is considered and the frames need to guarantee resources for BS-to-MS communications but also for BS-to-RS and RS-to-MS communications. These requirements leads to a 1/5 asymmetry factor between the UL and DL in the omnidirectional BS case and to a 3/7 asymmetry factor in the case of tri-sectored BSs. pffiffiffi Although the reuse distance is augmented by a factor of 3, it was first shown that the use of relays corresponds to lower values of the supported throughput for K = 3. The presence of sub-channelisation only improves the results for the highest values of R.

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The consideration of tri-sectored BS antennas with K = 1 (whilst keeping the number of required channels – equal to 3) did not enable to obtain values of the throughput comparable to the ones without using relays, although frame format is more favourable. Relays can be cheaper than BS with full functionalities. As the use of relays may lead to lower costs it is worthwhile to analyse the impact of using them on costs and revenues.

References 1. G. Bauer, R. Bose, R. Jakoby, Three-dimensional interference investigations for LMDS networks using an urban database. IEEE Trans. Antennas Propag. 53(8), 2464–2470 (Aug 2005) 2. F.J. Velez, L.M. Correia, J.M. Bra´zio, Frequency reuse and system capacity in Mobile Broadband Systems: comparison between the 40 and 60 GHz bands. Wireless Pers. Commun. 19(1), 1–24 (Aug 2001) 3. T.S. Rappaport, Wireless Communications: Principles and Practice (Prentice Hall, Upper Saddle River, NJ, 2002) 4. P. Sebastia˜o, F. Velez, R. Costa, D. Robalo, A. Rodrigues, Planning and deployment of WiMAX networks. WIRE – Wireless Pers. Commun. (Aug 2009). doi: 10.1007/s11277009-9803-3 5. Hui Liu, Guoqing Li, OFDM-based Broadband Wireless Networks – Design and Optimization (Wiley, Hoboken, NJ, 2005) 6. J.G. Andrews, A. Ghosh, R. Muhamed, Fundamentals of WiMAX – Understanding Broadband Wireless Networking (Prentice Hall, Upper Saddle River, NJ, 2007) 7. C. Hoymann, S. Goebbels, Dimensioning cellular WiMAX part I: singlehop networks, in Proceedings of EW’2007 – European Wireless 2007 (Paris, France, Apr 2007) 8. F.J. Velez, V. Carvalho, D. Santos, R.P. Marcos, R. Costa, P. Sebastia˜o, A. Rodrigues, Aspects of cellular planning for emergency and safety services in mobile WiMax networks, in Proceedings of ISWPC’ 2006 – 1st International Symposium on Wireless Pervasive Computing 2006, Phuket, Thailand, Jan 2006 9. F.J. Velez, M.K. Nazir, A.H. Aghvami, O. Holland, D. Robalo, Cost/revenue Trade-off in the optimization of Fixed WiMAX Deployment with Relays, submitted to IEEE Transactions on Vehicular Technology (Dec 2009) 10. F.J. Velez, A.H. Aghvami, O. Holland, Basic Limits for Fixed WiMAX Optimization Based in Economic Aspects, accepted for publication in IET Communications – Special Issue on WiMAX Integrated Communications (Mar 2009) 11. R. Jain, Chakchai So-In, A.-K. Al Tamimi, System-level modeling of IEEE 802.16e mobile WiMAX networks: key issues. IEEE Wireless Commun. 15(5) (Oct 2008) 12. Sergey N. Moiseev, Stanislav A. Filin, and Mikhail S. Kondakov, Analysis of the Statistical Properties of the Interference in the IEEE 802.16 OFDMA Network, IEEE Wireless Communications and Networking Conference (WCNC 2006), vol. 4, pp. 1830–1835, Apr 2006 13. M.S. Kondakov, A.V. Garmonov, Do Hyon Yim, Jaeho Lee, Sunny Chang, Yun Sang Park, Analysis of the statistical properties of the interference in the IEEE 802.16 OFDMA Network, in Proceedings of WCNC 2006 – IEEE Wireless Communications and Networking Conference, Las Vegas, Nevada, USA, Apr 2006 14. 3GPP, 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Feasibility Study for OFDM for UTRAN Enhancement (Release 6), 3GPP TR 25.892 V2.0.0, 2004-06

Chapter 10

Business Models and Cost/Revenue Optimization Fernando J. Velez, M. Kashif Nazir, A. Hamid Aghvami, Oliver Holland, and Daniel Robalo

Abstract This Chapter starts by covering general aspects about the business models for WiMAX and then addresses the cost/revenue optimization for these networks, for cellular configurations without and with relays. In Fixed WiMAX, radio and network planning can be optimised by tuning a cost/revenue function which incorporates de the cost of building and maintaining the infrastructure and the effect of the available resources on revenues. From the cost-benefit analysis, one conclusion of this work is that given today’s hypothesis of price per MByte of information transfer of somewhere between 0.0025 € and 0.010 €, it is clear that, without considering the use of relays, the choice of reuse patterns 3 or 4 with sectorial cells is preferable to the use of omnidirectional cells with reuse pattern, K, of 7, as three times more resources are available in each cell. Besides, in nowadays networks, if there is a need for sparse BS deployments whilst reducing costs, K ¼ 1 may be a solution, as it presents higher profit for the longest coverage distances. In future networks, when costs will be lower, the advantage of sectorization is kept and will drive the deployment of tri-sectorization forward. Nevertheless, in this case K ¼ 1 will not be advantageous with tri-sectorization for the longest coverage distances anymore. This study also concludes that cell radii in the range 1000–1500 m is preferable, corresponding to profit in percentage terms of near the achievable maximum, while keeping costs acceptable. The WiMAX cost-benefit optimization is also explored for the case where relays are used to help on improving coverage while mitigating the interference. Results show that the use of relays with no sectorization in the BS leads to a lower profit (K ¼ 3). Also the use of sectorization (an example is presented for K ¼ 1) does not seem to enable larger profit. The optimum (maximum) values occur for coverage distances up to 1,000 m. In the DL, when the price per MB, R144, increases from 0.0025 €/min to 0.005 €/min the profit increases more than 100%. F.J. Velez (*) Instituto de Telecomunicac¸o˜es-DEM, Universidade da Beira Interior, Calc¸ada Fonte do Lameiro, 6201-001 Covilha˜, Portugal e-mail: [email protected]

R. Prasad and F.J. Velez, WiMAX Networks, DOI 10.1007/978-90-481-8752-2_10, # Springer ScienceþBusiness Media B.V. 2010

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Introduction

Although the oldest wireless Internet providers have been providing narrowband since perhaps 1992, the broadband wireless access (BWA) business is a relatively new phenomenon. Some early wireless broadband technologies like LMDS and MMDS tried to establish their roots and to become popular. These were fragmented and competing proprietary standards and did not prove to be 100% successful. They also lacked the broad industrial support like WiMAX is having through the WiMAX Forum. Along with WiMAX, the other nowadays technologies providing wireless broadband are HSDPA, HSUPA, and EV-DO etc. WiMAX deployment optimisation can be achieved by appropriately parameterising a merit function, taking costs and revenues into account. The optimisation of the cost/revenue trade-off provides a means of combining several contributing factors in cellular planning: determination of the reuse pattern, coverage distance, and the resulting supported physical throughput. Given the current state of national frequency spectrum assignments throughout Europe, the Fixed WiMAX achievable frequency reuse pattern, K, determines the reduction in the initial fixed cost if the required spectrum bandwidth is reduced to values comparable to the ones for Wideband Code Division Multiple Access (WCDMA) systems. In turn, the supported throughput will determine the achievable revenue, which has interdependencies with the use (or not) of sub-channelisation and/or sectorization. The optimization of the cost/revenue trade-off for different topologies is thus of fundamental importance, and can be achieved by varying system parameters and implied coverage and reuse distances. A cost/revenue function has to be developed by taking into account the cost of building and maintaining the infrastructure, and the way the number of channels available in each cell affects operators’ and service providers’ revenues. Fixed costs for licensing and spectrum bandwidth auctions (often known as “beauty contests”) should also be taken into account. The economic analysis is referred as a cost/ revenue performance analysis, because the optimisation (i.e., minimization) of cost does not necessarily mean the optimization of net revenues. Although one considers a project duration of 5 years as a working hypothesis in radio and network planning, it is decided in this paper to analyse costs and revenues on an annual basis. Furthermore, our analysis is under the assumption of a null discount rate. By no means is it intended to perform a complete economic study in this paper, the aim is simply to present initial contributions that facilitate cellular planning optimisation. Appropriate refinements would be needed to perform a complete economic analysis based on discounted cash flows (e.g., to compute the net present value). Besides addressing business models and plans in Sections 10.2 through 10.4 the main contributions from this chapter are the following. Section 10.5 describes the range of services offered. Section 10.6 addresses cost/revenue optimization, presenting the models without and with considering relays, as well cost/revenue optimization results and profit.

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10.2

397

Business Model Definition

The term “business model” describes the interrelationship between different entities of the value network. A technology can be made successful only if it is supported by a successful business case. A complete business model comprises inputs from two domains, technical and economic. As shown in Fig. 10.1, a business model forms the link between creative technological ideas and the economic implementation of an innovation. A business model draws on a multitude of business subjects, including economics, entrepreneurship, finance, marketing, operations, and strategy. The business model itself is an important determinant of the profits to be made from an innovation. Sometimes it is seen that a mediocre innovation with a great business case may be more profitable than a great innovation with a mediocre business case. The basic business model is used to analyse the various service, organisational, technology and financial aspects. A right business model describes the interrelationships between different entities of the whole value network and the processes that take place between each of them.

10.3

Broadband Communications Business

There are many market drivers which has made broadband communications so popular. Some of them are new technologies, new applications, increased computing power and storage, mass production, price reductions, the Internet revolution and the competition. Also new technologies, the mass production of network components and low transmission costs are continuously creating new applications. At the same time, an extraordinary expansion of the Internet has occurred. It seems that it is not a killer application for the broadband market, but that Internet is a ‘killer network’, with a “killer” cocktail of applications and services. WiMAX is a highly versatile BWA technology platform and has relevance to a wide variety of application scenarios. The promise of WiMAX lays in its open

Technical Inputs

Fig. 10.1 Generic business model

Business Model Model

Economic Outputs

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standard design and capacity for interoperability. As a standard-based technology, with a huge ecosystem of developers and industry players, WiMAX is a technology of choice for the wireless broadband future. WiMAX wireless broadband is expected to evolve at a rapid pace, connecting the unconnected and bringing new possibilities to consumers and enterprises. With an OFDMA air interface, all IP architecture, adaptive modulation and coding techniques, and multiple advanced antenna options (including MIMO and beamforming), WiMAX promises high performance connections to deliver fixed broadband with deep penetration as well as high throughput. IEEE 802.16e, IEEE 802.16d and then IEEE 802.16m are expected to address a new breed of devices, applications and services that rely on broadband connections for enhanced user experience. Currently, there are very few commercial WiMAX compliant networks deployed. At the end of 2007 there were a total 181 operators globally. This number is expected to rise to 538 by 2012 [1]. New players are coming up in the WiMAX business. These are from diverse industries such as broadcasting, content studios, utilities and consumer electronics focused on providing fixed and mobile broadband mix services as an alternative to wireline technologies. The business model for the WiMAX deployment must consider all the aspects of design, deployment, and integration from the core network through the systems architecture, service edge, access network and devices.

10.4 10.4.1

Developing a WiMAX Business Plan Market Research: Gathering the Input Parameters for a WiMAX Business Case

In order to make a successful business case extensive market research has to be done. The inputs gathered from the research vary from country to country, but will help to deploy a feasible network deployment depending on the financial, technical and business parameters.

10.4.1.1

Target Market Characteristics

The first step in the market research is to decide the geographic area to be covered under the WiMAX services. This is measured in square kilometres of coverage for urban, suburban and rural geographies. The accurate network planning is possible when the terrain type of the geographical area is known. The terrain type can be classified under flat, moderate hilly or hilly. Geographic Information System (GIS) tools are used to explore aspects in network planning.

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10.4.1.2

399

Spectrum

Licensed radio spectrum is the prime asset of a WiMAX network, and its value is determined by many factors, including its frequency, capacity and whether it is fixed or mobile. Recognizing the virtues of WiMAX for broadband wireless access the global regulators have allocated new spectrum channels. Globally the spectrum allocated for WiMAX is around 2.5 and 3.5 GHz bands. Around 500 companies worldwide have BWA licenses in the 3,400–3,600 GHz frequency bands while a few have licenses in the 2,500–2,690 GHz band .The typical deployment characteristics of the BWA bands are listed in Table 10.1.

10.4.1.3

Technological Parameters

Once the target market characteristics are found out and the bandwidth is known the technological parameters need to be decided. Nowadays, the first technological selection is between 802.16d or 802.16e. To achieve ubiquitous coverage throughout the entire geographical area, technical parameters such as link budget, spectral efficiency and antenna configuration need to be decided. These parameters along with the frequency to be used will help to calculate the coverage area (with no considerable interference) per cell site, hence, the total number of base stations to cover the desired geography. The radio characteristics of the WiMAX equipment selected for the analysis in this Section are listed in Table 10.2.

Table 10.1 Characteristics of 3.5 and 2.5 GHz frequency bands Features 3.5GHz 2.5GHz Total available spectrum About 200 MHz between 195 MHz, including guard –bands and 3.4 GHz and 3.8 GHz the MDS channels ,between 2.495 (varies from country to and 2.690 GHz country) Serviced offered Fixed, may allow mobile Fixed and Mobile FDD or TDD Mixed, some countries TDD/FDD specify FDD only while others allow either FDD or TDD Spectrum per license Varies from 2*5 MHz to 22.5 MHz per license, a 16.6 MHz 2*56 MHz block paired with a 6 MHz block. Total eight licenses License aggregation No Yes Allocation Worldwide except in US U.S., Canada, Latin America, Australia, expected in Asia

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Table 10.2 Radio characteristics Attribute Duplexing Channel bandwidth Adaptive modulation System gain Path loss for indoor CPEs Propagation conditions

10.4.1.4

3.5 GHz 2.5 GHz FDD TDD 2  3.5 MHz 5 MHz BPSK, QPSK, 16QAM, 64QAM 158 dB 157 dB 15 dB Urban, suburban and rural under NLoS conditions

Determining Financial and Capital Expenditure (CapEx)

There are certain financial parameters which need to assumed or taken into account before the operator starts the actual network planning. Critical evaluation regarding interest rates on borrowing and the expected returns need to be forecasted. The tax rate on profits, depreciation and the amortization period should also be taken into account. As in any major network deployment, huge initial capital is required to procure the WiMAX equipment as well as to acquire or lease sites. The setup of the access network also adds to the capital expenses (CapEx). This includes not only the base station costs but also the other components in the access network.

10.4.2

Market Planning

10.4.2.1

Competitive Analysis

There are a host of broadband service providers in the market today. The operator must take into account the penetration, type of services and their pricing levels by the existing broadband players. These include DSL and cable providers, on the wire-line side, and the 3G service providers, on the wireless side. A complete and understanding of the competitive environment for the broadband services in the operators market is necessary to develop a viable business plan.

10.4.2.2

Coverage Requirements

The main goal of the WiMAX operator is always to achieve the ubiquitous coverage throughout the entire metropolitan target area. An operator can develop a plan for rolling out the network based on different scenarios, for example, to consider the number of customers.

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10.4.2.3

401

Capacity Requirements

Traditionally cellular networks were deployed to achieve ubiquitous coverage, with very little consideration for capacity requirements. This was the most reasonable approach as the only service offered was voice. More base stations were installed when the customer base and the number of services offered grew. However, with broadband, a range of services with varying Quality of Service (QoS) and Quality of Experience (QoE) are offered. To meet the customer expectations for these type of services it is of prime importance to predetermine the capacity requirements and accordingly deploy at the outset. This will ensure a quality user experience (even in the busiest ours in the highest density urban areas). Data density, expressed in Mbps per km2, is used to describe capacity requirements. Determining the data density requirements for a specific demographic region is multi-step process shown in Fig. 10.2. The service provider generally offer plans with varied service level agreements (SLAs) to appeal wide range of anticipated customer types in the target market segment. An SLA is a negotiated agreement between a service provider and a consumer for a subscription choice which typically defines the service level offered for a given monthly fee. There will be different sets of SLAs for residential and business segments. Depending upon the capacity to be offered the operator also need to decide on the oversubscription rate. Oversubscription means assigning a total committed information rate to a given base station that is greater than the base station capacity. This number is used to determine the peak busy hour traffic. As the number of users increases, a calculation using the oversubscription rate will tell the operator when to add new cells for the increased usage.

Market demand and forecast

Determine the target market segment

Area demographics

Services to be offered

Expected number of customers

Expected market take rate

Geographical Information System (GIS)

Fig. 10.2 Determining market driven capacity requirements

Required data rate (Mbps)

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10.4.2.4

Penetration

When building a broadband wireless access network, it is difficult (as well as challenging) to forecast number of subscribers that an operator can expect to sign over the life of the network. It generally takes a period of time for consumers to buy a new technology, a new service or opt for a new provider of that service. For some consumers the technology, service and provider have to be well-tested before they will sign up for the service. But the success of Wi-Fi will help WiMAX for a general acceptance of broadband wireless access. The rates charged for services by the operator will also have a marked effect on how quickly the technology and services will be adopted. Operators will also have a quicker adoption rate in past non-covered area than in areas that are currently well served. In Fig. 10.3, curves for the number of subscribers over a 10 year time frame are plotted. It shows that for first couple of years there are very few subscribers [2]. As the operator is deploying the network and expanding coverage the number of subscribers increases. Once the network is fully deployed, there will be an increase in subscribers until some level of saturation is reached.

10.4.2.5

CapEx

In analysing the business case, capital expenditure (CapEx) is calculated by taking into account the end to end network, as described in Fig. 10.4. The major CapEx components are the following: l l l

Spectrum licenses Customer Premise Equipment (CPE) Base station infrastructure 16 Percentage Penetration

14 12 10 8 6 4 2

10 ar

9 Ye

ar Ye

7

ar 8 Ye

ar

6 Ye

ar

5 Ye

ar

r4

Fig. 10.3 WiMAX penetration curve

Ye

3

Ye a

ar

2 Ye

ar

1 Ye

ar Ye

Ye

ar

0

0

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PSTN Fiber Network Businessl

Global Internet

Residential Market

Access Coverage Radio planning Capacity

BTS

Backhaul

WiMAX BS equipment WiMAX service edge network Wireless backhaul equipment Edge and core IP Wireline backhaul Installation & leasing

Edge

Core

Edge and core IP Networking elements Content management and delivery Media gateways

Fig. 10.4 WiMAX end-to-end network l l l

Edge, core and central office Wireless backhaul equipment Site development and acquisition cost

The CapEx is different for the incumbent compared to a new operator. For an incumbent wire-line operator, at least some part of the edge, core and central office equipment is ready. The only need is to add capacity to support the additional anticipated customers that would be covered by the WiMAX portion of the access network. Nevertheless, for the new operator large investment is required for edge, core and central office. As shown Fig. 10.4 the wireless portion the network begins at the fiber node or microwave link with a WiMAX BS or a wireless point-to-point link to a remotely located WiMAX BS. This backhaul link can be a WiMAX compliant point-to-point solution or some other point-to-point radio technology evolution. In addition to the WIMAX equipment, the base station may also include additional hardware such as the uninterruptible power supplies, electronic cabinets and some other additional equipment for the interface with the backhaul link. The costs for the civil works including antenna masts, conduits, cables, and the overall base station preparation also need to be considered. The base station infrastructure CapEx items are fixed in costs and are labour intensive. The cost is different for developing countries compared to developed ones. The civil works for urban area deployments are also higher compared to suburban and rural areas. 10.4.2.6

OpEx

As in any major network deployment, the total cost of ownership of a WiMAX network will comprise of operating expenses along with the capital expenditures.

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Table 10.3 Operating expenses

Operating expenses (OpEx) Site rental Site utilities Backhaul installation Backhaul cost Network maintenance Support and warranty Billing/CRM Marketing and advertisement Equipment maintenance Bad debt and churn General and administrative expenses

The operating cost comprises of the ongoing operational expense of managing and maintaining the WiMAX service. The major operational expenses are given in the Table 10.3. While considering the WiMAX business case its important for the operator to consider the various type of subscriber’s stations or terminals used with various SLAs. CPEs can be fixed (indoor and outdoor), WiMAX cards integrated in laptops, portable CPEs or embedded in consumer electronics (CE) devices. The business case should include the price of the CPE, it can be either subsidised by the operator or paid by the consumer.

10.5

Range of Services Offered

Today the broadband service no longer means just high speed Internet access. Broadband has successfully evolved to become the enabler of a bouquet of IP services. It’s no longer enough to provide the high speed internet facilitates such as surfing, e-mailing, file sharing, instant messaging, operators need to launch additional applications, too Therefore, an extensive review of service provider strategies must be made. WiMAX has to be more about services than it is about technology. The more services an operator is able to successfully leverage on its network, the more valuable the network becomes. The first step in defining the market is the range of services that would be offered to the potential customer. The right mix of services will allow the operator and the investors to realize swift return on their investment, generate strong revenue and grow market share. The portfolio of these services must address the various needs across the operators’ end user segments including basic residential, high speed residential, small to medium business, enterprise and government.

10.5.1

Classification of Services

The classification of services and applications can be segmented into three main groups (Table 10.4):

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Table 10.4 Broadband services Classification of services Content services

Information retrieval (browsing, surfing) Peer to peer and person to person

l l l

405

Applications Purchase of movies and music Leasing of movies and music Cultural services and entertainment: Video on demand(VoD) Events on demand TV channels and subscriptions On demand: news, sports, health, life style programs, etc. Substitutions: Performances like theatre, concerts, opera, cinema, etc. Lotteries and gambling: Online gambling Online betting Video transmission of the gambling event Gambling on automates Books, newspapers ,newsletters, journals: Books Online newspapers Newsletters Journals E-learning: Online education Online games Down loading and updating of gaming software Online games Traditional free surfing Information storage (film, photos, other information) Video conference Exchange of personal content Exchange of downloaded content Surveillance at home for elderly/sick Different home services

Content services Information retrieval and storage Person to person and peer to peer

10.5.2

Varying Terrain Conditions

The calculation of the coverage area and of the performance for WiMAX networks have to be based on the terrain conditions of the intended service area. 1. Dense Urban: This is the city centre where many of the businesses are located as well as high density multiple dwelling residential units. These areas represent a challenging propagation environment due to the multipath caused by the multistorey buildings.

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2. Urban: Immediately surrounding the city centre would be more businesses and moderate to high density multiple dwelling units. Average building heights may be lower but the propagation environment will be equally challenging. 3. Suburban: This describes areas with lower density housing, primarily single family dwellings, and fewer businesses. Average building heights are lower and, on average, structures are more spread out, thus creating a more favorable propagation environment. 4. Rural: Moving further from the city centre, homes are further apart resulting insignificantly lower population density with scattered small businesses.

10.6 10.6.1

Cost/Revenue Optimization Models

The economics of cellular systems can be viewed from the points of view of the different entities: subscribers, network operators, service providers, the regulator, and equipment vendors [4–6]. In this paper, although it is possible that for mobile multimedia networks the network operator and service providers can be different entities, we do not distinguish them. Thus we are considering the operator/service provider’s point of view, whose primary bottom line is to improve his business. In the cellular planning process, the objective of the operator is to determine an optimal operating point that maximizes expected revenues. Examples of major decisions affecting this include the type of technology to be used, the size of the cell, and the number of radio resources in use in each cell. It is important to identify the main components of the system’s cost and revenues, in particular those that bear a direct relationship to either the maximum cell coverage distance or the reuse pattern. Here we consider the cost per unit area of a 2D system incurred during the system lifetime. The system is considered to have a transmission structure formed by a set of frequency carriers or channels (or the corresponding WiMAX sub-channels), each supporting a TDM frame structure. Each base station comprises a number of transceivers equal to the number of carriers assigned to the BS (or to the BS sector), which is assumed to be one in this study. That is, it is assumed as a simplification that one carrier will be sufficient per cell/sector. System cost has two major parts: (a) capital costs (normal backhaul, cell site planning and installation), and (b) operating expenses (operation, administration and maintenance) [7, 8]. The capital cost is taken to consist of: l l

A fixed part (e.g., licensing and spectrum auctions or fees) A part proportional to the number of BSs per kilometre or square kilometre (e.g., the installation costs of BSs including the cost of obtaining cell sites, the normal backhaul, and the cost of hardware and core equipment common to all), and

10 l

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407

A part proportional to the total number of transceivers per kilometre or square kilometre (e.g., the cost of the transceivers)

It is assumed that the cost of the connection between BSs and the Switching Centre, that is, the fixed part of the network (e.g., the cost of laying fibre), is not a fixed cost. Instead, we consider this to be proportional to the number of BSs, which can be true if, for example, the mobile operator’s service is contracted from a fixed network operator. The operating cost during a system’s lifetime is taken to contain l l

A part proportional to the number of BSs per kilometre or square kilometre, A part proportional to the number of transceivers per kilometre or square kilometre.

These costs will be incurred on an annual basis. A similar approach was followed in [3] for hierarchical WiMAX–Wi-Fi networks. However, here we follow the approach from [9]. The cost per unit area is given by: C½=km2  ¼ Cfi½
=km2  þ Cb  Ncell=km2 :

(10.1)

where Cfi is the fixed term of the costs, and Cb is the cost per BS assuming that only one transceiver is used per cell/sector. The number of cells per unit area is given by: Ncell=km2 ¼

2 pffiffiffi ; 3  3  R2

(10.2)

and the cost per BS is given by [9]: Cb ¼

CBS þ Cbh þ CInst þ CM&O ; Nyear

(10.3)

where Nyear is the project’s lifetime (assumed here to be Nyear = 5), CBS is the cost of the BS, Cbh is the cost for the normal backhaul, CInst is the cost of the installation of the BS, and CM&O is the cost of operation and maintenance. The revenue per cell per year, (Rv)cell, can be obtained as a function of the supported throughput per BS or sector (in the omnidirectional and sectorial cases, respectively), Rb-sup[kb/s], and the revenue of a channel with a data rate Rb[kbps], RRb[€/min], by: ðRv Þcell ¼

Nsec  Rbsup½kb=s  Tbh  RRb ½
=min ; Rbch½kb=s

(10.4)

where Nsec is the number of sectors (one or three) Tbh is the equivalent duration of busy hours per day, and Rb-ch is the bit rate of the basic “channel”. In the

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tri-sectorial case, as one assumes that each sector has one different transceiver, there is a separate frequency channel available for it. The revenue per unit area per year, Rv[€/km]2, is obtained by multiplying the revenue per cell by the number of cells per unit area: Rv½
=km2  ¼ Ncell=km2  ðRv Þcell ¼ Ncell=km2 

Nsec  Rbsup½kbps  Tbh  RRb ½
=min : Rbch½kbps

(10.5)

The (absolute) profit is given by P½
=km2  ¼ Rv  C;

(10.6)

from which, the profit in percentage terms is given by: P½% ¼

10.6.2

Rv  C  100: C

(10.7)

Hypothesis Without Relays

Following the approach form [9], it is hypothesised that project duration is of 5 years and there is a null discount rate; costs and revenues are taken on an annual basis. We consider 6 busy hours per day, 240 busy days per year [10], and a revenue/price of a 144 kb/s “channel” per minute (approximately corresponding to the price of 1 MByte, as 144  60 = 8.640 kb  1 MByte), R144[€/min]. The revenue per cell can be obtained as: ðRv Þcell½
 ¼

Nsec  Rbsup½kbps  60  6  240  R144½
=min : 144½kbps

(10.8)

Diverse assumptions for the price of the 144 kb/s channel (or a MByte of information) are considered for each scenario. Two hypotheses are made for cost, denoted as A and B, as shown in Table 10.5. Hypothesis A is today’s situation. In the future, equipment prices will get lower with mass production, and spectrum bandwith prices will also reduce, thereby making Fixed WiMAX systems more accessible. This future case is hypothesis B. Assuming that the annual cost of a license is 50,000,000 € for 2  24.5 MHz bandwidth (UL & DL, K = 7), considering a total area of 91,391.5 km2 as the area of Portugal, for example, the fixed cost per unit area is Cfi ½
=km2  ¼

50;000;000 ¼ 108:24  110
/km2 : 91; 391:5  5

(10.9)

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Table 10.5 Fixed WiMAX cost assumptions Costs Omnidirectional A B Cfi (€/km2) K=1 15.71 15.71 K=3 47.14 47.14 K=4 62.86 62.86 K=7 110.00 110.00 CBS (€) 18,000 9,000 CInst (€) 10,000 1,000 5,000 2,500 Cbh (€) CM&O (€/year) 4,000 1,000 Table 10.6 Required spectrum bandwidth for different cell configurations and reuse patterns

K 1 3 4 7

409

A

Tri-sectored B

47.14 141.43 188.57 330.00 30,000 18,000 5,000 6,000 BW (MHz) Omnidirectional 3.5 10.5 14.0 24.5

47.14 141.43 188.57 330.00 15,000 1,500 2,500 1,500

Tri-sectored 10.5 31.5 42.0 73.5

If one considers that only one carrier will be allocated to each cell (or sector), if K = 4 or K = 3 then the available BW (and the respective cost) will be 4/7 or 3/7 of the value for K = 7, respectively. Given that the total bandwidth, BW, is given by: BWomni½MHz ¼ Nsec  K  3:5;

(10.10)

The necessary spectrum bandwidths can be obtained as in Table 10.6. Note that Nsec = 1 for omnidirectional cells and Nsec = 3 for sectorial cells.

10.6.3

Hypothesis and Assumptions with Relays

If the topology with relays from Chapter 9 is considered, the assumptions for costs with relays are the following: (i) Cost for BS and RSs l l l

CBS-omni = 9,000 € CRS =9,000/5 = 1,800 € CBS-trisect = 15,000 €

In these cells there are three coverage areas with an area and the BS plus three RS need to guarantee the coverage for the whole area of cell. The equivalent cost for the “BS” meaning an average between the BS and the RS is given by: CBSequivalent ¼

ðCBS þ 3CRS Þ 3

(10.11)

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ii) Cost for backhaul The cost for backhaul is the same as in case of without relays for RSs and BS that is: Cbhequivalent ¼ 1=3Cbh

(10.12)

for each hexagonal coverage area (as backhaul is only needed for the central coverage area of the BS). iii) Installation Cost The cost for installation is the same for every BS and RS. It is four times the installation cost of a BS, Cinst. Hence, we need to multiply Cinst by 1/3 to obtain the installation cost for each coverage area. It is given by: Cinstequivalent ¼ 4=3Cinst

(10.13)

iv) Maintenance and operation cost We assume that the maintenance and operation cost for the BS are the same as in the case without relays and the ones for the RS are ½. It is given by

CM&Oequivalent ¼

  CM&O þ 3=2CM&O 3

:

(10.14)

These equations may be applied to the topology with relays and omnidirectional BSs. In this case the following parameters were used, Table 10.7: l l l l

CBS-omni = 9,000 € and CRS = 1,800 € (i.e., CBS-equivalent = 4,800 €) Cinst = 1,000 € (i.e., Cinst-equivalent = 1,333.33 €) Cbh = 2,500 (i.e., Cbh-equivalent = 833.33 €) CM&O = 1,000 € (i.e., CM&O-equivalent833.33 €)

For the tri-sectored BS antennas the parameters are the following, Table 10.7 (note that the costs for the backhaul, and maintenance and operation are the same): l l l l

CBS-tri-sect = 15,000 € and CRS = 1,800 € (i.e., CBS-equivalent = 6,800 €) Cinst = 1,500 € (i.e., Cinst-equivalent = 2,000 €) Cbh = 2,500 (i.e., Cbh-equivalent = 833.33 €) CM&O = 1,000 € (i.e., CM&O-equivalent833.33 €) Table 10.7 Costs with relays for omnidirectional (K = 3) and tri-sectored (K = 1) BS antennas Costs Omnidirectional Tri-sectored K=3 K=1 47.14 47.14 Cfi(€/km2) CBS(€) 4,800 6,800 CInst(€) 1,333.33 2,000 833.33 833.33 Cbh(€) CM&O(€/year) 833.33 833.33

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It should be noted that l

l

With sectorization the cost for the licence with K = 1 are equal to the cost for the licence with omnidirectional BS antenna and K = 3. With tri-sectorization some costs are higher (e.g., BS and its installation). However, higher costs are compensated with the higher revenues. Because throughput is higher (mainly due to the difference on the sub-frame format), a 9 gain of 3=5 1=3 ¼ 5 ¼ 1:8occurs, which compensated the lowest value of the frame throughput. Besides, it is worthwhile to note that

l

l

For K = 3 with relays UL traffic is  15 times the DL traffic, hence revenues are lower; For K = 1 with relays and sectorization, UL traffic is 37  DL traffic, hence revenues may be relevant.

10.6.4

Optimization and Profit Without Relays

In seeking profit optimisation, revenues should be maximised with respect to costs. Under hypothesis B, which corresponds to the lowest cost case, and for K = 7, the variation of the cost and revenue in €/km2 with R is depicted in Figs. 10.5 and 10.6, for omnidirectional and tri-sectored cells respectively. The revenue curves were obtained for R144[€/min] = 0.0025 (which approximately corresponds to the price per MByte [5]). Note that the UL curves for the cases with omnidirectional BS antennas and suchannelisation and tri-sectorization are superimposed for distances up to

Hypothesis B

10000

Cost, Revenue [ /km2]

8000 C - omni. 6000

Rv - DL - omni. Rv - UL - omni. Rv - UL - Subchannel.

4000

2000

0

0

1000

3000

2000

4000

5000

R [m]

Fig. 10.5 Cost and revenues versus R for K = 7 under hypothesis B, for the omnidirectional case

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Cost, Revenue [ /km2]

250000

Hypothesis B

200000 C - Sector. Rv - UL&DL - Sector.

150000

Rv - UL - Subch. & Sector.

100000

50000

0

0

1000

2000

3000

4000

5000

R [m]

Fig. 10.6 Cost and revenues versus R for K = 7 under hypothesis B, for the tri-sectored case

3,000 m. With tri-sectorial BS antennas, as there is three time more available resources the revenues increase significatively. In order to optimize the broadband wireless access network, it is important to analyse the profit per unit area. However, it is not sufficient to compute the absolute profit because, as is shown in Figs. 10.5 and 10.6, a certain level of profit may correspond to different values of cost. For example, cost is higher for tri-sectorial cells; hence, revenue needs to be higher to obtain the same profit. It is worthwhile to note that, with tri-sectorial BS antennas, higher revenues are expectable not only due to the interference mitigation caused by the use of directional antennas but also because three channels are now available in the cell, one for each sector, leading to an higher supported throughput per km2. We have obtained results for the profit in percentage for two values of the price per MByte R144[€/min] = 0.005 and 0.010) in hypothesis A, corresponding to higher costs, in Figs. 10.7 and 10.8 respectively. It is particularly evident that profit increases as the price per MByte increases; nevertheless, the curves keep the same shape and behaviour. For tri-sectorial cells, as there is three carriers available in the cell, the profit in percentage is almost three times higher than the one for the case of omnidirectional cells for a considerable range of coverage distances, typically lower than 1,800 m, which only reaches 375%. For coverage distances larger than this value, this relative difference is only kept if sub-channelisation is considered. In hypothesis B (lower network cost), the advantage of using a tri-sectored configuration becomes even more evident for the shortest propagation distances of up to 1,250–1,500 m (see Fig. 10.9). Although the required bandwidth in each FDD link is three times higher, the profit in percentage terms is now more than three times higher than the one with omnidirectional cells. Figure 10.9 presents an example for R144[€/min] = 0.005 in hypothesis B, where it is clear that profit values

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Hypothesis A

600

DL - omnid. UL - omnid.

500

UL - subchannel. UL&DL - sector.

400 Profit [%]

UL - subch. & sector.

300 200 100 0 –100

0

1000

2000

3000

4000

5000

R [m]

Fig. 10.7 Profit in percentage terms versus R for K = 7 under hypothesis A, R144[€/min] = 0.005

Hypothesis A

1200

DL - omnid. UL - omnid.

1000

UL - subchannel. UL&DL - sector.

Profit [%]

800

UL - subch. & sector.

600

400

200

0

0

1000

3000

2000

4000

5000

R [m]

Fig. 10.8 Profit in percentage terms versus R for K = 7 under hypothesis A, R144[€/min] = 0.010

are more than four times the values in Fig. 10.7. As costs are lower, even with a price per MByte of only R144[€/min] = 0.005 the profit in percentage terms may exceed 1,500%. Although the curves are not presented here, even for R144[€/min] = 0.0025, the values of the profit are more than twice the ones from Fig. 10.7.

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2000

DL - omnid. UL - omnid.

1600

UL - subchannel.

Profit [%]

UL&DL - sector. 1200

UL - subch. & sector.

800

400

0

0

1000

3000

2000

4000

5000

R [m]

Fig. 10.9 Profit in percentage terms versus R for K = 7 under hypothesis B, R144[€/min] = 0.005

Hypothesis B

2000

K=7, tri-sect. K=4, tri-sect. K=3, tri-sect. K=1, tri-sect. K=7, omnid.

Profit [%]

1600

1200

800

400

0

0

1000

2000

3000

4000

5000

R [m]

Fig. 10.10 Profit in percentage terms versus R for different K’s under hypothesis B, with tri-sectored cells for the UL where R144[€/min] = 0.005

A comparison between K = 7, K = 4, K = 3 and K = 1 is presented in Fig. 10.10 (for tri-sectored cells in the UL and R144[€/min] = 0.005). Sub-channelisation is considered, as it is specified on the UL. Note that in the tri-sectorial case the required bandwidth in each FDD link is three times higher. For example, for K = 3,

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it increases from 10.5 to 31.5 MHz. The consideration of a reuse pattern K = 7 is ideal in terms of interference mitigation, although K = 1, K = 3 and K = 4 may also be interesting possibilities for coverage distances between 1,500 and 1,800 m. Note, however, that, from the spectrum regulation point of view, to use K = 7 and tri-sectored cells seems to be infeasible, as a spectral bandwidth of 73.5 MHz is needed. With K = 1 and K = 3, the use of omnidirectional configurations cannot be supported as the throughput on the outer coverage ring of the cell reaches 0 Mb/s and full cell coverage is not guaranteed. Although the curve is not presented here, in the omnidirectional case, with K = 4, profits of 260–290% are achieved in the UL (and of 370–420% in the DL) for coverage distances up to 1,500 m (R144[€/min] = 0.005). Only with K = 7 higher profits are achieved with omnidirectional cells, of the order of 400–490% in the UL, as shown in Fig. 10.10 (where sub-cahnnelisation is considered), and 470–580% in the DL. However, this compares poorly with the values varying from 1,400% to 1,900% for K = 3, 4 and 7 with tri-sectored cells. The cases K = 1, K = 3, K = 4 (all with tri-sectored cells), and K = 7 (with omnidirectional cells) correspond to a spectrum bandwidth of 10.5, 31.5, 42.0 and 24.5 MHz, respectively. K = 4 and K = 3 with tri-sectorial BS antennas seem to be the optimum choices, with an advantage for the choice of K = 3, as only 75% of the bandwidth is needed. With K = 1 and tri-sectored cells the profit in percentage terms is higher than with K = 7 and omnidirectional cells, with an additional advantage: only 43% of the bandwidth is needed. Besides, it is worthwhile to note that, for K = 1 and coverage distances longer than 4,000 m, the values for the profit in percentage terms become comparable to ones with K = 4 and K = 3 (tri-sectored cells), that is, for sparse BS deployments in low density user environments K = 1 may be a solution. If network costs are higher (hypothesis A), the relative behaviour is basically the same as in hypothesis B. Under the price per MByte of R144[€/min] = 0.010, the profit may reach values of somewhere between 780% and 1,060%. It seems that the relative disadvantage with K = 7 and omnidirectional cells becomes less evident, as shown in Fig. 10.11 under hypothesis A (in comparison to Fig. 10.10). With K = 1 and tri-sectored cells, the profit in percentage terms is again higher than with K = 7 and omnidirectional cells. However, for the longest coverage distances, no advantage of using K = 1 can be found in comparison to K = 3 or 4 anymore. In terms of the choice of optimum coverage distance, from analysis of the results in Figs. 10.5 and 10.6 it is evident that network cost strongly increases if the coverage distance decreases, particularly for the lowest coverage distances. Investigating the profit in percentage terms, it can be observed that significant falls occur for coverage distances of higher than 1,500 m. Hence coverage distances of around 1,000 m might be chosen as optimum, as they maximize profit in percentage terms while keeping costs acceptable. A daily equivalent operation in saturated conditions over 6 h has been assumed, which is only valid if the offered traffic is high enough in this time span. Otherwise, revenue will be lower, and low costs will definitively reduce the possibility of losses.

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Fig. 10.11 Profit in percentage terms versus R for different K’s under hypothesis A, for the UL where R144[€/min] = 0.010

10.6.5

Optimization and Profit with Relays

10.6.5.1

DL Analysis with K = 3 and K = 1

In seeking profit optimisation, revenues should be maximised with respect to costs. By using Table 10.7 (but also Table 10.6), and the results for the supported throughput from Chapter 9, we obtained the curves for costs, revenues and profit in percentage. The costs and revenues with relays (K = 3, omnidirectional BS antenna), in €/km2, are depicted in Figs. 10.12 and 10.13, for R144 = 0.0025 and 0.005 €/min, respectively. In order to optimize the broadband wireless access network, it is important to analyse the profit per unit area. However, it is not sufficient to compute the absolute profit because, as is shown in Figs. 10.12 and 10.13, a certain level of profit may correspond to different values of cost. For example, cost is higher for tri-sectorial cells; hence, revenue needs to be higher to obtain the same profit. This justifies the need to represent the profit in percentage, as defined by (10.7).The operator’s/ services provider’s goal is to optimise this profit in percentage. Results are obtained with relays and K = 1 (tri-sectorial BS antennas) and K = 3 (omnidirectional BS antennas) in the DL case. Figure 10.14 presents the results for R144 = 0.0025 €/min while Fig. 10.15 presents the case for R144 = 0.005 €/min. the case without relays (K = 3) is also presented, for comparison purposes. It is clear that the use of relays without sectorization in the BS leads to a lower profit (K = 3). Even the use of sectorization (an example is presented for K = 1) does not enable to achieve larger profit (note that for K = 1 interference poses an extra

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Fig. 10.12 Cost and revenues with relays (K = 3, omnidirectional BS antenna) for a price per MB R144 = 0.0025 €/min, in the DL

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Fig. 10.13 Cost and revenues with relays (K = 3, omnidirectional BS antenna) for a price per MB R144 = 0.005 €/min, in the DL

limitations; hence, results with K = 3 may be checked with sectorization). The optimum (maximum) values occur for coverage distances up to 1,000 m.

10.6.5.2

UL Analysis with K = 3 and K = 1

We also have performed analysis for UL with K = 3 and K = 1. By using the Table 10.7 (but also Table 10.6), and the results for the supported throughput from Chapter 5, we obtained the curves for the costs, revenues and profit in percentage.

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Fig. 10.15 Profit in percentage for a price per MB R144 = 0.005 €/min, in the DL

The costs and revenues with relays (K = 3, omnidirectional BS antenna), in €/km2, are depicted in Figs. 10.16 and 10.17, for R144 = 0.0025 and 0.005 €/min, respectively. It is shown that, in the UL, for K = 3 and omnidirectional BS antennas there is no profit, that is, revenues are always lower than costs. Results for the profit in percentage, as defined by Eq. (10.7), are obtained with relays and K = 1 (tri-sectorial BS antennas) and K = 3 (omnidirectional BS antennas) in the UL case. Figure 10.18 presents the results for R144 = 0.0025 €/min while Fig. 10.19 presents the case for R144 = 0.005 €/min. The case without relays (K = 3) is not presented, as it is impossible to obtain results with such low reuse pattern with no relays (and no sectorization, too). In the UL, with relays, only the use of sectorization (an example is presented for K = 1) enables to achieve positive profit in percentage only for R144 = 0.005 €/min

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Fig. 10.16 Cost and revenues with relays (K = 3, omnidirectional BS antenna) for a price per MB R144 = 0.0025 €/min, in the UL

5000 Cost, Revenue [ /km2]

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3000

C-Om ni 2000 1000 0

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2000

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Fig. 10.17 Cost and revenues with relays (K = 3, omnidirectional BS antenna) for a price per MB R144 = 0.005 €/min, in the UL

(nor for R144 = 0.0025 €/min). With omnidirectional BS antennas (an example is presented for K = 3) a positive profit is not achievable in any of the prices. As for the DL, the maximum values occur for coverage distances up to 1,000 m.

10.7

Conclusions

Appropriate business models are essential to establish the business case for WiMAX networks. This Chapter started by covering general aspects about the business models for WiMAX and then addressed the cost/revenue optimization

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Fig. 10.19 Profit in percentage for a price per MB R144 = 0.005 €/min, in the UL

for these networks, for cellular configurations without and with relays. From an undertaken cost-benefit analysis, one conclusion of this work is that given today’s hypothesis of price per MByte of information transfer of somewhere between 0.0025 € and 0.010 €, it is clear that, without considering the use of relays, the choice of reuse patterns 3 or 4 with sectorial cells is preferable to the use of omnidirectional cells with reuse pattern of 7, as three times more resources are available in each cell. Besides, in nowadays networks, if there is a need for sparse BS deployments whilst reducing costs, K = 1 may be a solution, as it presents higher profit for the longest coverage distances. In future networks, when costs will be lower, the advantage of sectorization is kept and will drive the deployment of

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tri-sectorization forward. Nevertheless, in this case K = 1 will not be advantageous with tri-sectorization for the longest coverage distances anymore. It has also been concluded in this paper, driven by our analysis as well as other observations, that cell radii in the range 1,000–1,500 m might be chosen. This range corresponds to a profit, in percentage terms, of near to the maximum achievable, while keeping costs acceptable. The WiMAX cost-benefit optimization is also explored for the case where relays are used to help on improving coverage while mitigating the interference. Results show that the use of relays with no sectorization in the BS leads to a lower profit (K = 3). Also the use of sectorization (an example is presented for K = 1) does not enable to achieve larger profit. The optimum (maximum) values occur for coverage distances up to 1,000 m. In the DL, when the price per MB, R144, increases from 0.0025 €/min to 0.005 €/min the profit increases more than 100%. Suggestion for future work on the optimization of cellular configurations with relays is to explore sectorization for K = 3 (as interference is mitigated for larger reuse patterns), consider different assumptions for the prices of the relays, and mainly to jointly achieve the profit curves joining together the UL and DL contributions for the supported traffic.

References 1. H. Chesbrough, R.S. Rosenbloom, The role of the business model in capturing value from innovation: evidence from Xerox Corporation’s technology spin-off companies. Ind. Corporate Change 11(3) (June 2002) 2. WiMAX Forum whitepaper, WiMAX Technology Forecast (2007–2012) (June 2008) 3. M. Ibrahim, K. Khawam, A.E. Samhat, S. Tohme, Analytical framework for dimensioning hierarchical WiMax-WiFi networks. Comput. Netw. 53(3), 299–309 (2009) 4. B. Gavish, S. Sridhar, Economic aspects of configuring cellular networks. Wireless Netw. 1(1), 115–128 (Feb 1995) 5. F.J. Velez, L.M. Correia, Optimisation of mobile broadband multi-service systems based in economics aspects. Wireless Netw. 9(5), 525–533 (Sept 2003) 6. K. Johansson, A. Furusk€ar, P. Karlsson, J. Zander, Relation between cost structure and base station characteristics in cellular systems, in Proceedings of PIMRC’ 2004 – 15th IEEE International Symposium on Personal, indoor and Mobile Radio Communications, Barcelona, Spain, Sept 2004 7. D. Reed, The cost structure of personal communications, IEEE Commun. Mag. 31(4), 102–108 (Apr 1993) 8. J. Sarnecki et al., Microcell design principles, IEEE Commun. Mag. 31(4), 76–82 (Apr 1993) 9. F.J. Velez, A.H. Aghvami, O. Holland, Basic limits for fixed WiMAX optimization based in economic aspects, accepted for publication in IET Communications – Special Issue on WiMAX Integrated Communications (Mar 2009) 10. F.J. Velez, L.M. Correia, Cost/revenue optimisation in multi-service mobile broadband systems, in Proceedings of PIMRC’ 2002-13th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, Lisbon, Portugal, Sept 2002

Chapter 11

Multiple Antenna Technology Ramjee Prasad and Fernando J. Velez

Abstract As the radio resources are scarce and data rate requirements keep increasing, spectral efficiency is a stringent requirement in present and future wireless communications systems, MIMO-OFDM has become a new “star” in the “constellation” of wireless and mobile communications. Its potential to increase spectral efficiency has not been reached by any other technology before. In addition to increasing spectral efficiency, MIMO can also be used to reduce transmitting power while keeping coverage areas constant. The use of MIMO technology in future transmission systems for broadcasting, multicasting and unicasting represents real business logic also for broadcasting corporations because of the possible reduction in transmission stations. This Chapter covers Closed Loop MIMO, multiantenna in OFDM, space diversity, space-time coding, Allamouti code, spatial multiplexing, collaborative spatial multiplexing, diversity and array gains, system model for MIMO OFDM, support of MIMO in IEEE 802.16, beamforming and trade-off between spatial multiplexing and spatial diversity, among other issues.

11.1

Introduction to MIMO

The major performance degradation factors for the mobile wireless channel are channel fading and co-channel interference. These degradation factors are better handled by using advanced antenna technologies. Advanced antenna technologies employ multiple antennas at the transmitter as well as at the receiver side to achieve more reliable and higher data rates. To put it in simple terms, Multiple Input Multiple Output (MIMO) can be used to refer any multiple antenna technologies.

R. Prasad (*) Center for TeleInFrastruktur (CTIF), Aalborg University, Niels Jernes Vej 12, DK–9220 Aalborg Øst, Denmark e-mail: [email protected]

R. Prasad and F.J. Velez, WiMAX Networks, DOI 10.1007/978-90-481-8752-2_11, # Springer ScienceþBusiness Media B.V. 2010

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MIMO Multiple Input Multiple Output

Open Loop MIMO

Matrix A Space Time Block Coding

Matrix B Spatial Multiplexing

Closed loop MIMO

Beamforcing Transmitter Adaptive Antenna

Fig. 11.1 WiMAX multi-antenna implementation chart

In application, the MIMO technology can be divided based on Open Loop MIMO techniques and Closed Loop MIMO techniques. MIMO systems that do not rely on knowledge of the channel responses at the transmitter are open loop. Closed loop is the case when the channel state information (CSI) is available at the transmitter through some form of feedback mechanism. Regarding MIMO options, the WiMAX standard includes two versions of Open Loop MIMO techniques, for the use on the downlink referred to as MIMO Matrix A and MIMO Matrix B. IEEE 802.16e supports both the techniques and therefore form a part of wave 2 certification. Closed Loop MIMO techniques are also called Transmitter Adaptive Antenna techniques or “beamforming” (Fig. 11.1). l l l

Space Diversity Spatial Multiplexing Beamforming

IEEE 802.16 uses a radio modulations scheme called Orthogonal Frequency Division Multiplexing (OFDM). The important characteristic of OFDM with regards to SISO/MIMO is that OFDM divides data frames into numerous smaller symbols for transmission. In SISO, each of these symbols is transmitted serially, one after the other. WiMAX is based on smart antenna friendly OFDM/OFDMA technology. OFDM/OFDMA is a powerful means to convert a frequency selective wideband channel into multiple flat narrow and subcarriers. This allows smart antenna operations to be performed on vector flat sub-carriers. The structure of the remaining of this Chapter is as follows. After presenting the MIMO wireless transmission system and the closed loop MIMO in this Section, Section 11.2 addresses the capacity of MIMO channels. Section 11.3 presents multi-antenna in OFDM. Sections 11.4 and 11.5 present spaced diversity and space-time coding. Section 11.6 addresses spatial multiplexing while Section 11.7

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Mt SpaceSpaceTime Mapper transmitter

...

Enc

Mr

...

binary I/P

Constel. mapping Constel. mapping

channel

SpaceSpaceTime detection detection & decoding decoding &

binary O/P

receiver

Fig. 11.2 MIMO wireless transmission system

describes collaborative spatial multiplexing. Section 11.8 presents the diversity gain and array gain while Section 11.9 addresses the comparison of MIMO options. Section 11.10 presents the MIMO model for MIMO OFDM. The support of MIMO technology in the IEEE 802.16 standard is introduced in Section 11.11 while Section 11.12 addresses beamforming. Section 11.13 covers the trade-off between spatial multiplexing and spatial diversity. Finally, conclusions are drawn in Section 11.14.

11.1.1

MIMO Wireless Transmission System

Figure 11.2 shows basic MIMO systems can be defined simply. Both the transmitting and the receiving ends are equipped with multiple antenna elements. In MIMO the signals on the transmitter (TX) antennas, at one end, and the receiver (RX) antennas, at the other end, are “combined” in such a way that the quality of the communications in terms of bit-error rate (BER) or data rate (bit/s) for each MIMO user will be improved. Such an advantage can be used to increase significantly both network’s QoS and operator’s revenues. As shown in the Fig. 11.2 input, in the form of a binary data stream, is fed to a simplified transmitting block encompassing the functions of error control coding and mapping to complex modulation symbols, for example, quaternary phase-shift keying (QPSK) or quadrature amplitude modulation with M symbols (M-QAM). Several separate symbol streams are produced. They range from independent to partially or fully redundant. Each stream is then mapped onto one of the multiple TX antennas. The signals are launched in the wireless channel after upward frequency conversion, filtering and amplification. At the receiver side the string of Mr multiple antennas capture the signals and demodulation and demapping operations are performed to recover the original message. MIMO takes advantage of random fading [1–3] and, when available, multipath delay spread [4, 5], for multiplying transfer rates. A key feature of MIMO systems is the ability to turn multipath propagation, traditionally a pitfall of wireless transmission, into a benefit for the user. The goal of MIMO is to improve the spectral efficiency (bit/s/Hz), the coverage area (cell radius) and the signal quality (bit-error rate or packet-error rate). MIMO systems are becoming popular and find and are applied for emerging wireless technologies, such as WLAN,

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Broadband Wireless Access (BWA) and cellular. These advances do however come at additional cost. Multiple antennas increase RF costs and complexities and mathematically complex DSP algorithms challenge the designers and manufacturers. Using MIMO communication system at the transmitter and the receiver end gives the following advantages: l l l l

Increase the coverage area Increase the achievable data rate Decrease in BER, hence increase the system reliability Decreases the required transmit power

11.1.2

Closed Loop MIMO

When the transmitter can acquire some sort of knowledge of the channel between it and the receiver, it can adjust the transmitted signal accordingly in order to optimize the system performance or the data rate. As the channel changes quickly in a highly mobile scenario closed loop transmission scheme are primarily feasible in fixed or low mobility scenarios. Channel state information (CSI) plays a critical role in achieving reliable and high rate communications. In closed-loop spatial multiplexing, every stream is transmitted from all of the antennas using weights computed from the channel estimation, as shown in Fig. 11.3. The CSI can be used to weight the signals transmitted from the BS antennas. The weighting should be such that the signals arrive co-phased in the receiver. Constructive signal combining increases the received signal power, therefore SNR gain and link capacity will also increase. Figure 11.4 presents a comparison between closed and open-loop MIMO. H s1 s2 . . .

Precoding

Rx

W

sm Nr

Nt

Feedback channel

Fig. 11.3 Closed loop transmit diversity

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Fig. 11.4 Comparison between closed-loop and open-loop MIMO: (a) 2  2 closed-loop equals 2  3 open-loop, and (b) 4  4 closed-loop 5 dB better than 4  4 open-loop

11.2

Capacity of MIMO Channel

In simple terms channel capacity refers to the maximum data rate. The sent signal is represented by s and the received signal is r [6]. A time-invariant and narrowband channel is assumed. The channel model includes the matrix H with the direct and the indirect channel components (Fig. 11.5). The received signal can be computed as follows r ¼ Hs þ n;

11.3

(11.1)

Multi-antenna in OFDM

The main motivation for using OFDM in a MIMO channel is because OFDM modulation turns a frequency-selective MIMO channel into a set of parallel frequency-at MIMO channels. This makes multi-channel equalization particularly simple, since for each OFDM-tone only a constant matrix has to be inverted [6, 7]. In frequency selective environments, however, the amalgamation of Spatial Multiplexing (SM) and OFDM techniques can be a potential source of high at reasonable complexity. Figure 11.6 shows a schematic of a MIMO-OFDM system [7]. OFDM Modulation (OMOD) and OFDM Demodulation (ODEMOD) denote an OFDM-modulator and demodulator, respectively. The basic principle that underlies OFDM is the insertion of a guard interval, called cyclic prefix (CP), which is a copy of the last part of the OFDM symbol, and has to be long enough to accommodate the delay spread of the channel. The use of the CP turns the action of the channel on the

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Space-Time encoder

h12

S2

h21 hMr 1

r1

h22

r2

hMr 2

h1Mt SMt s

Space-Time decoder

h2Mt

r1

r Mr

hMr Mt H

r

Fig. 11.5 Physical MIMO channel

OMOD

ODEMOD and separation

OMOD

OMOD

Fig. 11.6 Schematic of a MIMO-OFDM system (adapted from [7])

transmitted signal from a linear convolution into a cyclic convolution, so that the resulting overall transfer function can be diagonalized through the use of an IFFT at the transmitter and an FFT at the receiver. Hence, the overall frequency-selective channel is converted into a set of parallel flat fading channels, which drastically simplifies the equalization task. Let us assume an OFDM-MIMO system with Nt transmit antennas, Nr receive antennas and N subcarriers. The input-output relation for the MIMO system for the kth tone, k = 1,. . ., N may be expressed as rffiffiffiffiffiffi PT H k sk þ N k ; Yk ¼ NT

(11.2)

where Yk and Nk are NR  1, Hk is a NR  NT matrix, sk is a NT  1 vector, and PT is the total transmit power. The matrix Hk is the frequency response of the matrix channel corresponding to the kth tone.

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From the above equation we can see that, just as in SISO channels, OFDMMIMO decomposes the otherwise frequency selective channel of bandwidth 5 into N orthogonal flat fading MIMO channels, each with bandwidth B = N. MIMO signalling treats each OFDM tone as an independent narrowband frequency flat channel [8]. We must take care to ensure that the modulation and demodulation parameters (carrier, phasing, FFT/IFFT, prefixes, etc.) are completely synchronized across all transmit and receive antennas. With this precaution, every OFDM tone can be treated as a MIMO channel, and the tone index can be treated as a time index in the already existing Space-Time (ST) techniques.

11.4

Space Diversity

High degree of attenuation in a multipath wireless environment makes it extremely difficult for the receiver to determine the transmitted signal. This problem is addressed by transmitting less-attenuated replica of the original signal to the receiver, that is providing with some form of diversity. Diversity is proven to be an effective tool for coping with the challenges of NLoS propagation. Multi-path and reflections signals that occur in NLoS conditions may be effectively reduced by using diversity schemes. IEEE 802.16e uses transmit diversity in the downlink direction to provide spatial diversity that enhance the signal quality to a specific subscriber located anywhere within the range of the antenna beam. Receive diversity is obtained by various combining techniques to improve the availability of the system. For instance, maximum ratio combining (MRC) takes advantage of two separate receive chains to help in overcoming fading and reducing path loss [9]. On the one hand, transmit diversity provides less signal gain compared to beamforming. On the other, transmit diversity is more robust for mobile users since it does not require prior knowledge of the path characteristics for a subscriber’s particular frequency channel.

11.5

Space-Time Coding

Space-time coding (STC) is a family of techniques for implementing transmission diversity. The diversity gain is obtained by applying coding techniques across space and time. Among the various space time diversity codes, it is worthwhile to briefly describe the space-time-trellis code (STTC) and space-time block code (STBC). In its original form, STTC is a two dimensional trellis code and its complexity increases exponentially with the number of transmit antennas and the constellation

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order. Another popular form of STC technique is STTC Alamouti Code [9], which is defined for two transmit antennas. An STC is represented by a matrix. Each row of the matrix denotes a time slot while each column represents the different antennas transmissions over time. S11 S21  ST1

S12 S22  ST2

   

S1nT S2nT  STnT

(11.3)

The code rate of an STBC measures how many symbols per time slot (T represents number of time slot) it transmits on an average over the course of a block of size k. Thus, the code rate, r, can be obtained as follows r ¼ k=T ;

11.5.1

(11.4)

Alamouti Code

Among all the STCs defined for different number of transmit antennas, Alamouti Code is the simplest. The following matrix illustrates the STC Matrix A scheme 

S A¼ 1 S2

S2 S1

 (11.5)

Two information symbols S1 and S2 are transmitted over a period of 2 symbols and sent using a specific coding between the two antennas. Figure 11.7 shows the

h1 s1,s2

r1

s1 s2*

h2 s2 – s1* r1 = h1s1+ h2s2+ n1 r2 = h 1 s 2*– h2 s1*+ n2

Fig. 11.7 Matrix A Alamouti’s STC

r2

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space-time code of the 2  1 Alamouti Code solution, also called STC matrix A scheme. The first row corresponds to the symbols transmitted from the first antenna while the second one corresponds to the symbols transmitted from the second antenna. The first column represents the first transmission period while the second column the second transmission period. Elaborating further, during the first symbol period, the first antenna transmits S1 and the second antenna transmits S2. During the second symbol period, the first antenna transmits S1 and the second antenna transmits S2 , the complex conjugate of S1 and S2, respectively. This implies that we are transmitting both in space (across two antennas) and time (two transmission intervals). This is space-time coding. The signals received for two symbol periods are represented by, Suppose that (s1, s2) represent a group of two consecutive symbols in the input data stream to be transmitted. During a first symbol period t1, transmit (Tx) antenna 1 transmits symbol s1 and Tx antenna 2 transmits symbol s2. Next, during the second symbol period t2, Tx antenna 1 transmits symbol s2 and Tx antenna 2 transmits symbol  s1 . Denoting the channel response (at the subcarrier frequency at hand) from Tx1 to the receiver (Rx) by h1 and the channel response from Tx2 to the receiver by h2, the received signal samples corresponding to the symbol periods t1 and t2 can be written as 

r1 ¼ h1 s1 þ h2 s2 þ n1 ; r2 ¼ h1 s2 þ h2 s1 þ n2

(11.6)

where, n1 and n2 are samples of white Gaussian noise. Here, one denotes the channel response from Tx antenna 1 to the receiver by h1 and its response from Tx antenna 2 to the receiver by h2. Assuming a flat-fading channel, h1 is the complex channel gain from antenna 1 to the receive antenna, and h2 is from antenna 2, the received signal samples at the two transmission instants are given by (11.6). In matrix A, S1 and S2 are the symbols to be transmitted over the air. At the symbol k, symbol S1 is transmitted from antenna 1 while symbol S2 is transmitted from antenna 2. At the symbol k + 1, symbol –S1* is transmitted from the antenna 2. The receiver computes the following signals to estimate the symbols s1 and s2   x1 ¼ h1  r1  h2 r2  ¼ jh1 2 þ jh2 j2 s1 þ h1 n1  h2 n2   x2 ¼ h2  r1 þ h1 r2  ¼ jh1 2 þ jh2 j2 s1 þ h1 n1  h1 n2

(11.7)

These expressions clearly show that x1, x2 can be sent to a threshold detector to estimate symbol s1 and symbol s2 respectively without interference from the other symbol. Moreover, since the useful signal coefficient is the sum of the squared modules of two independent fading channels, these estimations benefit from perfect second-order diversity, equivalent to that of Rx diversity under Maximum-Ratio Combining (MRC).

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Alamouti’s transmit diversity can also be combined with MRC when two antennas are used at the receiver. In this scheme, the received signal samples that correspond to the symbol periods t1 and t2 can be written as 

11.5.2

r11 ¼ h11 s1 þ h12 s2 þ n11 ; r12 ¼ h11 s2  h12 s1 þ n12

(11.8)

Second-Order STC

Second-order STC in DL supports coding rates 1 and 2 by using the following two transmission format matrices. Here Sk’s are OFDM symbols in the frequency domain right before IFFT operation. The optional STC transmit diversity is also supported in UL using the transmission format matrix A of Eq. (11.4). Matrix B of Eq. (11.5) can be used by two SSs in a collaborative special multiplexing mode. MIMO Matrix A using STC improves the reliability of data transmission for mobile WiMAX using multiple transmit antennas. By adding redundant, parallel paths, the modem has twice as much chance of receiving a good copy of the data. Under stationary conditions, the gain provided by STC is only +3dB, but in a fading environment, such as when passing rapidly between buildings, the gain may be as much as +5dB for 16 QAM and +10dB for 64 QAM compared to a non-STC signal under the same conditions [11]. As a consequence, the system can hold a relatively high throughput under difficult conditions.

11.6

Spatial Multiplexing

Spatial Multiplexing increases spectral efficiency by transmitting multiple data streams simultaneously by using the same frequency channel at the same time by employing multiple transmit and multiple receive antennas [12]. With this
S1 S2

 (11.9)

The second MIMO profile included in mobile WiMAX systems is the 2  2 MIMO technique based on the so-called matrix B, Fig. 11.8. STC Matrix B provides the following benefits: l l

Double the rate of transmission Deliver order-2 diversity

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h11 s1, s2

r1

h21 h12

r2 h22

Fig. 11.8 22 MIMO, matrix B

This 2  2 special multiplexing is described by omitting the time and frequency dimensions, and by taking into consideration only the space dimension. The symbols transmitted by Tx1 and Tx2 are denoted by s1 and s2, respectively. The channel response from Txi to Rxj (i, j = 1, 2) is shown by hji. Hence, the signals received by two Rx antennas are given by  r1 ¼ h11 s1 þ h12 s2 þ n1 ; (11.10) r2 ¼ h21 s1  h22 s12 þ n2 In the matrix form, these equations are represented by        r1 h n h12 s1 ¼ 11 þ 1 ; r2 h21 h22 s2 n2

(11.11)

Different layered space-time codes such as Bell Labs Layered Space-Time (BLAST) are used for space multiplexing to increase the channel capacity. The BLAST structure does not introduce orthogonality by signal changes like coding and modulation, but by fully utilizing the multi-path feature of channels to eliminate the correlations between signals. The BLAST structure is divided into two main categories: Vertical Bell Labs Layered Space-Time (V-BLAST) and Diagonal Bell Labs Layered Space-Time (D-BLAST) (Fig. 11.9). V-BLAST sends M bit flows out by mutually independent antennas after they are encoded, mapped and interleaved, so that the diversity gain is fully tapped, and each message flow can be tested separately. D-BLAST goes through the same procedure as V-BLAST, but coding blocks are assigned to different antennas for sending, thus reducing the possibility of performance degrading of the entire system due to the unsatisfactory transmission effect of an independent channel.

11.6.1

Vertical Encoding SM & Horizontal Encoding SM

The two different types of predominant encoding schemes associated with spatial multiplexing break are horizontal encoding and vertical encoding [13], [14]. As

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Fig. 11.9 V-BLAST and D-BLAST

Antenna

Time s1

s1

s1

s1

s1

s1

s2

s2

s2

s2

s2

s2

s3

s3

s3

s3

s3

s3

s0

Data

C R C

FEC

Modulation

s1

s2

s0

s1

s2

s0

s1

s2

s0

s1

s0

s1

s2

s0

V-BLAST

D-BLAST

Subcarrier mapping

IFFT

Subcarrier mapping

IFFT

DMUX

Fig. 11.10 Vertical Encoding Spatial Multiplexing (VESM)

Data

C R C

FEC

Modulation

Subcarrier mapping

IFFT

Data

C R C

FEC

Modulation

Subcarrier mapping

IFFT

Fig. 11.11 Horizontal Encoding Spatial Multiplexing (HESM)

shown in Fig. 11.10, horizontal encoding for STC specifies that separate FEC blocks are encoded for each of the parallel spatial and channels separately the bit stream to be transmitted is de-multiplexed into T separate data streams. Each of these data streams is then temporally encoded, interleaved and converted to transmission symbols, with different modulation schemes allowed on each transmit channel. In contrast, vertical encoding (Fig. 11.11) specifies that one FEC block is encoded and multiplexed onto all the spatial channels for spatial diversity. The

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bit stream to be transmitted is encoded using a space-time block code and then converted into transmission symbols. The transmission symbols are then de-multiplexed into T bit streams and transmitted. Vertical encoding offers improved diversity gain over horizontal encoding because each data bit can be spread across all of the transmit antennas. But the advantage of using horizontal encoding is that it allows the users to control the modulation and coding rate based on the individual SNR of the spatial transmit mode. Another benefit of horizontal encoding is offered at the receiver side. As the individual data streams are decoded separately, typically using a relatively simple linear receiver design complexity reduces considerably. Vertical encoding, on the other hand requires joint decoding at the receiver, which significantly increases receiver complexity [15]. The system employing STC Matrix B performs pure spatial multiplexing and does not offer any diversity gain from the transmitter side. On the receiver side such a system offers a diversity gain of two when detected using maximum-likelihood (ML) detection [16].

11.7

Collaborative Spatial Multiplexing

Collaborative Uplink MIMO is a method designed specially to increase the spectral efficiency and capacity of uplink communication paths. In UL, when each user has only one transmit antenna, two users can transmit collaboratively at the same frequency allocation to communicate the dual antenna WiMAX base stations. Uplink Collaborative MIMO enables the use of the same channel sub-carriers by multiple devices and subscribers – effectively allowing them to share the same subcarrier without interference [17]. Without Collaborative MIMO, the traffic being carried on a single sub-carrier would not be maximized across multiple subscribers. The result would be that the traffic would be severely limited, preventing users from having a true broadband experience and limiting VoIP capacity such that conversations would be unintelligible. A practical realization of this technique would allow for two separate end user WiMAX devices, each having a single transmit line-up, to utilize the same frequency allocation to communicate with the dual antenna WiMAX base station. This technique can effectively double the uplink capacity of the WiMAX system.

11.7.1

Collaborative SM for UL PUSC

Partial Usage of Subchannels (PUSC) scheme is used in for the uplink Mobile WiMAX case. In case of UL PUSC, each tile contains 12 subcarriers, including four pilot tones, as shown in Fig. 11.12. The four pilot tones are divided into two pairs,

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Fig. 11.12 Pilot patterns in UL PUSC tile for MS#1 and MS#2

MS1

+

MS2

Pilots (with 3dB boosting) Data No Pilots

Table 11.1 Mapping of CSM data in UL PUSC

MSs Subcarrier#0 Subcarrier#1 .. . Subcarrier#46 Subcarrier#47

MS#1 x01 x11

MS#2 x02 x12

x461 x471

x462 x462

and each pair is allocated to one transmit antenna. The pilot tones are boosted by 3.0dB to compensate the decreased number of pilot tones. The transmission scheme for the Collaborative Spatial Multiplexing (CSM) is same as that of Simple Input Simple Output (SISO) except the pilot tones are used in half. Two sets of the 48 data symbols are mapped to the 48 data subcarriers in the subchannels of MS#1 and MS#2, as shown in Table 11.1 (Fig. 11.13). Figure 11.14 shows a graphical comparison of packet error rate (PER) between Collaborative MIMO and Spatial Multiplexing. Further gain of collaborative MIMO over SU-MIMO spatial multiplexing may be achieved by proper MS scheduling and pairing.

11.8

Diversity Gain and Array Gain

The signal level at the receiver fluctuates or fades in a wireless system. When the signal power drops significantly, the channel is said to be in fade. Diversity is used to combat fading. Diversity gain results from the creation of multiple independent

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Fig. 11.13 Collaborative MIMO

MS 1

s1 , – s2

Base Station

s2 , s1

MS 2

s3 ,− s4

s4 , s3

0

1x2 Collaborative MIMO, MLD, 2 MS, UL PUSC, ITU Ped -B (3 kmph)

10

10

2x2 SM, MLD, UL PUSC, ITU Ped -B (3 kmph)

0

CTC QPSK R=1/2 CTC QPSK R=3/4 CTC 16QAM R=1/2 CTC 16QAM R=3/4

CTC QPSK R=1/2 CTC QPSK R=3/4 CTC 16QAM R=1/2 CTC 16QAM R=3/4

–1

–1

PER

10

PER

10

–2

–2

10

10

10

–3

–3

10 2

4

6

8

10

12

14

16

SNR, dB

Collaborative MIMO

18

20

22

2

4

6

8

10

12

14

16

18

20

22

SNR, dB

Spatial Multiplexing

Fig. 11.14 Comparison between collaborative MIMO and spatial multiplexing

channels between the transmitter and the receiver and is a product of the statistical richness of those channels. When multiple antennas are present at the receiver, two forms of gain are available: diversity gain and array gain. Array gain is employed at the both side receiver and transmitter for increased average signal to noise ratio (SNR) at the receiver those signal comes from coherent combining effect in the multiple antennas. Channel knowledge is required for transmitter/receiver to obtain array gain and depends on number of transmitter/ receiver antenna. If the transmitters know the channel then transmitter will weight the transmission with weights, depending on the channel coefficients, so that there is coherent combining at the single antenna receiver.

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Array gain does not rely on statistical diversity between the channels and instead achieves its performance enhancement by coherently combining the energy received by each of the antennas. Even if the channels are completely correlated, as might happen in a line-of-sight system, the received SNR increases linearly with the number of receive antennas, Nr, owing to the array gain. Array gain improves resistance to noise, thereby improving the coverage and the range of wireless networks.

11.9

Comparison of MIMO Options

Since the Alamouti/MRC scheme has fourth-order diversity and the 2  2 spatial multiplexing scheme has second-order diversity, the former obviously has better BER performance (at high SNR) when the same modulation and coding schemes are used in both systems. Consequently, the Alamouti/MRC scheme can use a higherlevel modulation if the two schemes are required to give the same BER performance. Of utmost interest is the performance comparison between the two MIMO schemes when they are used at the same spectral efficiency. Figure 11.15 shows the results for BER on an uncorrelated Rayleigh fading channel when the Alamouti/ MRC scheme uses 16-QAM and the spatial multiplexing scheme uses QPSK (4 bits per symbol period in both cases).

100

Alamouti - 16QAM - 2 Rx antennas Spatial multiplexing - QPSK - ZF receiver Spatial multiplexing - QPSK - ML receiver

10–1

Uncoded BER

10–2

10–3

10–4

10–5

10–6

0

5

10

15

20

25

SNR (dB)

Fig. 11.15 Comparison of Alamouti/MRC with 2  2 spatial multiplexing (from [18])

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Spectral efficiency (bit per complex symbol)

It can be observed that the ZF receiver does not exploit the diversity of the spatial multiplexing scheme and that the slope of its BER curve is only half that of the ML receiver. The other interesting observation is that the slope of the Alamouti/ MRC scheme is twice as large as that of the spatial multiplexing ML receiver, which is due to the diversity factor of 4 for the former and of 2 for the latter. Results shown in Fig. 11.15 also confirm that, at high SNR values, the simple Alamouti/ MRC scheme with 16-QAM achieves better performance than the 2  2 spatial multiplexing MIMO system with QPSK and ML detection. This suggests that the best MIMO scheme to use in practice depends on the channel SNR and on the required throughput as well as on other issues such as the interference cancellation capability. However, since the WiMAX specifications have a limited number of modulation options, the Alamouti/MRC option cannot always compete with 2  2 spatial multiplexing in terms of spectral efficiency. To maximize network capacity, the MIMO option needs to be selected as a function of the channel SNR in the same way as modulation and coding (Fig. 11.16; Table 11.2).

5 QPSK 1/2 QPSK 3/4 16QAM 1/2 16QAM 3/4 64QAM 1/2 64QAM 3/4

4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 0

2

4

6

8

10 12 SNR (dB)

14

16

18

20

Fig. 11.16 SNR thresholds for adaptive modulation and coding (from [18])

Table 11.2 Constellations and convolutional coding schemes in WiMAX systems Constellation QPSK QPSK 16QAM 16QAM 64QAM Code rate 1/2 3/4 1/2 3/4 1/2 Spectral efficiency (bits/symbol) 1 1.5 2 3 3

64QAM 3/4 4.5

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11.10

System Model for MIMO OFDM

Figure 11.17 shows the functional block diagram of MIMO-OFDM system model. This model is applicable for open loop as well as closed loop MIMO systems. Packets of size Nep, each including the cyclic redundancy check (CRC) bits are used as an input to the transmitter. After the input packets are encoded at the FEC encoder block, the encoded bits are modulated at the modulation block. The encoded and modulated signal together forms a layer. In order to process multiple layer signals, MIMO system employ multiple sets of FEC encoders and symbol mappers. Thus the multiple encoded and the modulated signals forms ‘layers’ denoted by L in the figure. As shown in the Fig. 11.17 the STC encoder matrix is an MtL matrix. This matrix characterizes the employed multiantenna technique among transmit diversity, special multiplexing and the collaborative spatial multiplexing. Mt denotes the number of STC output streams, Nt is the number of BS transmit antennas. W denotes the precoding matrix which is included in the closed loop systems, as the channel state information (CSI) need to be made available to the transmitter through feedback. W is an NtMt, making the Mt dimensional streams transformed into Nt dimensional transmit signals. The value for Nt and Mt varies when multiple layer transmission is enabled with multiple modulation and coding blocks for each spatial layer in spatial multiplexing (SM) scheme. This scheme is called horizontal encoding (HE) and this mode enables adaptive rate control for each spatial layer. The other class of spatial multiplexing schemes is called vertical encoding (VE) and it features a common modulation and coding block. Transmit diversity (TD) can be

C Data R C C Data R C

FEC

Modulation L

FEC

STC Encoder Matrix (B , C)

Precoding Mt matrix W

Modulation

Subcarrier mapping

IFFT

Subcarrier mapping

IFFT

Nt

BS

Nep

FFT

FFT

Subcarrier mapping

Nr

ST Decoder

L

Subcarrier mapping

Log Likelihood Ratios

Decoder

CRC check

Log Likelihood Ratios

Decoder

CRC check

SS

Fig. 11.17 MIMO-OFDM system Model [19]

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also regarded as single layer technique. For open loop systems Mt is always equal to Nt and therefore the precoding matrix is an identity matrix. The output of the precoder is then separately mapped to the subcarriers for different transmit antennas and then converted to OFDM symbols through IFFT processing. At the receiver side, FFT block converts the received streams to frequency domain and the signals are then demapped at the subcarrier demapping blocks in group of Nr streams. Then the STC decoder block decodes the streams into L layers of FEC coded data streams, which forms the input for the FEC decoding and the CRC checking process blocks. Log-likelihood ratio (LLR) information is extracted at the LLR block in case turbo coding is used at the FEC encoding. This information is delivered to the FEC decoder together with the FEC coded data stream.

11.11

Support of MIMO Technology in the IEEE 802.16 Standards

In order to increase the range and reliability of WiMAX systems, the IEEE 802.162004 as well as IEEE 802.16e standard supports different multiple-antenna techniques. The older version of the standard that is IEEE 802.16-2004 provides a few supports for MIMO. Only the Alamouti Space-Time Coding (STC) scheme is defined and is not mandatory for fixed/nomadic WiMAX systems. IEEE 802.16e specifications which support mobile services also include optional space/time codes (STC) for implementing MIMO techniques with 2, 3, and 4 transmit and receive antennas respectively. Thus for Mobile WiMAX systems STC encoder matrices for the downlink are specified as follows 2

s1 6 s2 A¼6 40 0

s2 s1 0 0

0 0 s3 s4

3 2 s1 0 6 s2 0 7 7; B ¼ 6 4 s3 s4 5 s4 s3

s2 s1 s4 s3

s5 s6 s7 s8

3 2 3 s7 s1 6 s1 7 s8 7 7; C ¼ 6 7 4 s3 5 s5 5  s6 s4

(11.12)

The multiple layer transmission is enabled when spatial multiplexing (SM) schemes are employed with multiple modulation and coding blocks implemented for each spatial layer. This mode is called horizontal encoding (HE) and enables adaptive rate control for each spatial layer. The other class of spatial multiplexing schemes is called vertical encoding (VE) and it features a common modulation and coding block. Transmit diversity (TD) can be also regarded as single layer technique. Figure 11.10 shows an example of 2  2 VE MIMO system, whereas Fig. 11.11 illustrates 2  2 HE MIMO system. In both figures, L equals the number of layers, Mt. Their relations according to the current standard are tabularized in Table 11.3.

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Table 11.3 Summary on number of layers, Mt streams and type of matrix Layer = 1 (TD or VE only) L = 2 (HE only) L = 3 (HE only) 3 4 Mt = 2 3 4 Mt = 3 4 Mt = 1 2 AAS A (TD) A(TD)* A(TD)* B(VE)* B(VE)* B(HE)* B(HE)* C (VE) C(VE) C(VE) C(HE) C (HE)

L = 4 (HE only) Mt = 4

C (HE)

symbols 4k +3 symbols 4k +2 symbols 4k +1 symbols 4k data sub-carriers pilot sub-carriers for antenna 0 pilot sub-carriers for antenna 1

Fig. 11.18 Cluster structure for two transmit antenna MIMO systems

11.11.1

Two-Antenna Downlink STC Transmission

There are several types of subchannelization schemes used for the downlink of Mobile WiMAX such as PUSC, FUSC, and adaptive modulation and coding (AMC). Here, we consider PUSC as it can be easily extended to other cases. Figure shows the distribution of pilots and data subcarriers for two transmit antenna MIMO systems (Fig. 11.18). The pilot subcarriers for each transmit antenna are distinctly allocated in a period of four symbols and separately for each transmit antenna. The allocation of pilot subcarriers for each transmitting antenna separately helps the receiver to get the channel state information (CSI). While mapping input data to data subcarriers for each transmit antenna, the method differs depending upon the STC scheme employed. For STBC case data are mapped in group of 48 symbols per subchannel and for VESM, data are mapped in groups of 96 symbols. Figure 11.19 depicts the mappings done for STBC and VESM schemes. In the case of STBC data mapping is done as follows: Assuming the 48 input data are given by (x0, x1, x2, x3,..., x47), STBC is applied with coding rate 1. Two consecutive symbols form a pair (i.e., (s1, s2) = (x2n, x2n+1) where n = 0, 1, 2, . . ., 23) and the pair is encoded by the STBC encoder. The encoded bits are transmitted on the same subcarrier in two consecutive OFDM symbols using two transmit antennas, as described in Table 11.4 (Fig. 11.20). For the VESM case, data mapping is done as follows: Assuming the 96 input data are given by (x0, x1, x2, x3,.... . . x95), and applying coding rate = 2, a set of two

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Symbols 4k

Symbols 4k+1

Symbols 4k+2

Symbols 4k+3

Symbol Symbol 2n 2n+1

Ant0 Ant1

Data subcarrier

S1 –S2* S2 S1* STBC

Pilot for 1st ant.

Pilot for 2nd ant. Ant0 S1 Ant1 S2 VESM Cluster

Fig. 11.19 Mapping of STBC & VESM data in a two-transmit antenna system

Table 11.4 Mapping of STBC data in DL PUSC Antennas Antenna #0 Symbols Even symbol Odd symbol x1* Subcarrier #0 x0 Subcarrier #1 x. 2 x3* ... .. ... x45* Subcarrier #22 x44 Subcarrier #23 x46 x47*

Antenna #1 Even symbol x1 x. 3 .. x45 x47

Odd symbol x0* * x .. 2 . x44* x46*

symbols 4k+3 symbols 4k+2 symbols 4k+1 symbols 4k data sub-carriers pilot sub-carriers for antenna 0 pilot sub-carriers for antenna 1 pilot sub-carriers for antenna 2 pilot sub-carriers for antenna 3

Fig. 11.20 Cluster structure for four transmit antenna MIMO systems

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Table 11.5 Mapping of VESM data in DL PUSC Antennas Antenna #0 Symbols Even symbol Odd symbol x48 Subcarrier #0 x0 Subcarrier #1 x 2 .. .. ..x50 . . . Subcarrier #22 x44 x92 Subcarrier #23 x46 x94

Antenna #1 Even symbol x1 x. 3 .. x45 x47

Odd symbol x48 x. 51 .. x93 x95

consecutive data symbols form a pair (s1, s2) = (x2n, x2n+1) where n ¼ 0, 1, 2,. . ., 47 and the pair is transmitted on one subcarrier using two transmit antennas (Table 11.5)

11.12

Beamforming

In general, the term “Smart Antenna” may be used to describe any antenna system that incorporates some degree of adaptation to the RF environment, enabling to improve performance. There are a number of alternative approaches to incorporating this adaptation. These include methods that are based on beam space, signal space, space-time processing and space-time detection. The Wave 2 testing incorporates additional modes of operation (for example: idle, pager, and sleep modes) and requires mobile subscriber units to incorporate smart antenna technologies, such as beamforming and MIMO, for improved network performance. Beamforming is the method used to create the radiation pattern of an antenna array. It can be applied in all antenna array systems as well as MIMO Systems. Beamforming provides substantial improvement in the link budget in both the downlink and uplink directions by increasing the effective antenna gain in addition to reducing fade margin requirements due to interference. The most common directive antennas are switched-beam or phased (directional) antenna arrays, as shown in Fig. 11.21. In these systems, there are multiple fixed antenna beams formed by the array, and the system switches between these different beams to obtain the best performance, i.e., the strongest Signal-to-Interference-plus-Noise-Ratio (SINR) of the desired signal, as shown in Fig. 11.22. The benefits of directionality that can be obtained with multiple antennas must be weighed against the potential diversity or multiplexing benefits of the antennas.

11.12.1

Switched-Beam Antenna Arrays

Switched-beam antenna arrays are designed to provide high gain across a range of signal arrival angles, and can also be used to sectorize the directions that signals

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Fig. 11.21 Switched and adaptive beamforming

Fig. 11.22 Improving C/I by emphasizing the gain in the direction of the user and suppressing the gain in the direction of the interference

arrive from. They form multiple fixed beams with heightened sensitivity in particular directions. These antenna systems detect signal strength, choose from one of several predetermined fixed beams, and switch from one beam to another as the mobile moves throughout the sector, Fig. 11.21. Switched beam systems combine the outputs of multiple antennas in such a way as to form finely directional beams with more spatial selectivity than can be achieved with conventional, singleelement approaches (Table 11.6). Through adaptive array, base stations can form narrower beams towards the desired user and nulls towards interfering users, considerably improving the signalto-interference-plus noise ratio. Adaptive antenna technology represents the most advanced smart antenna approach to date. Using a variety of new signal-processing algorithms, the adaptive system takes advantage of its ability to effectively locate and track various types of signals to dynamically minimize interference and maximize intended signal reception. When compared with switched beam antenna

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Table 11.6 Comparison of switched beam antenna and adaptive arrays Criteria Switched Beam Adaptive Array l Easy to implement l Transceiver complexity Integration l Low cost l High cost l Less hardware redundancy l More coverage compared to conventional l Broader coverage compared to Range/ systems switched beam system coverage l Less coverage compared to adaptive array l Difficulty in distinguishing between desired l Focusing is narrower Interference rejection signal and interferer l Does not react to the movement of interferers l Capable of nulling interfering signals

Table 11.7 Features and benefits of smart antenna systems Features Signal gain—Inputs from multiple antennas are combined to optimize available power required to establish given level of coverage.

Benefit Better coverage—Increase in base station range and coverage. Lower power requirements also enable a greater battery life and smaller/lighter handset size.

Interference rejection—Antenna pattern can be generated toward co-channel interference sources, improving the signal-to-interference ratio of the received signals.

Increased capacity—Precise control of signal nulls quality and mitigation of interference combine to frequency reuse reduce distance improving capacity.

Spatial diversity—Composite information from the array is used to minimize fading and other undesirable effects of multipath propagation .

Multipath rejection—can reduce the effective delay spread of the channel, allowing higher bit rates to be supported without the use of an equalizer

Power efficiency—combines the inputs to multiple elements to optimize available processing gain in the downlink.

Reduced expense—Lower amplifier costs, power consumption, and higher reliability will result.

arrays adaptive system provides optimal gain while simultaneously identifying, tracking and minimizing interfering signals.

11.12.2

Adaptive Antenna Systems (AAS) in IEEE 802.16e-2005

AAS was opted by IEEE 802.16 standard to accomplish the key designated features and expectation on WiMAX. The reason is AAS technology can be effectively used in improving range and system capacity, spectral efficiency, increasing SNR, and effectively suppressing the interference (Table 11.7). The multiple antenna technology is especially applied for OFDM Systems and is part of many standards. MIMO will become an increasing key technology over the next years for increasing the channel capacity.

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Trade-Off Between Spatial Multiplexing and Spatial Diversity

A MIMO system can provide diversity as well as multiplexing gains. There are schemes which switch between these two modes, depending on the instantaneous channel condition [20]. But maximizing one type of gain may not necessarily maximize the other. In fact, each of the two design goals addresses only one aspect of the problem. This makes it difficult to compare the performance between diversity-based and multiplexing-based schemes. The diversity-multiplexing tradeoff d(r) of a MIMO channel is the best possible diversity-multiplexing tradeoff achievable by any scheme. The concept of switching between diversity and multiplexing was first introduced in [21] and then developed into an elegant theory in [22]. In a MIMO channel with rich scattering maximum diversity ¼ NT:NR

(11.13)

degrees of freedom ¼ minfNT; NRg

(11.14)

In a given a MIMO channel, both gains can be simultaneously obtained, but there is fundamental tradeoff between how much of each type of gain any coding scheme can extract: higher spatial multiplexing gain comes at the price of sacrificing diversity. A scheme is said to have a spatial multiplexing gain r and a diversity advantage d if the rate of the scheme scales like r log p and the average error probability decays like 1/pd, where p is the SNR. The trade-off curve bridges between these two extremes, as can be seen in Figs. 11.23 and 11.24. Clearly, r cannot exceed the total number of degrees of freedom min{NT, NR] provided by the channel, and d(r) cannot exceed the maximal diversity gain (NT, NR) of the channel. Table 11.8 gives an overview of all current MIMO standards and their technologies. It is clear to see, that with the exception of 3GPP Release 7, all standards

Diversity gain, d(r)

4 2 x 2 MIMO

1

Fig. 11.23 Diversitymultiplexing trade-off for 2  2 MIMO

1 2 Spatial Multiplexing gain (r = R .log SNR )

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Diversity gain, d (r)

(0,NT,NR )

(1,(NT –1) (NR –1))

(2,(NT –2) (NR – 2)) (r,(NT –r) (NR –r )) (r, (NT –r) (NR –r )) (min (NT ,NR ), 0) Spatial multiplexing gain (r )

Fig. 11.24 Spatial multiplexing gain versus diversity gain trade Table 11.8 MIMO Standards and the corresponding technology

Standard WLAN 802.11n WiMAX 802.16-2004 WiMAX 802.16e 3GPP Release 7 3GPP Release 8 (LTE) 802.20 802.22

Technology OFDM OFDM/OFDMA OFDMA WCDMA OFDMA OFDM OFDM

Table 11.9 Various standards and the type of antenna constellation, STC & Spatial streams used Standard Antenna constellation Space-time code Spatial streams IEEE 802.11n 2  2 later 4  4 Alamouti 3 with Alamouti, max. 4 IEEE 802.16-2004 2  1 later 4  4 Alamouti 2 with Alamouti, max. 4 IEEE 802.16e 2  1 later 4  4 Alamouti 2 with Alamouti, max. 4 3GPP Release 7 2  1 later 4  2 Alamouti 2 with Alamouti, max. 4 3GPP Release 8 (LTE) 2  2 later 4  4 n/a n/a

work with OFDM. The advantages of OFDM can obviously be linked to MIMO (Table 11.9).

11.14

Conclusions

As the radio resources are scarce and data rate requirements keep increasing, spectral efficiency is a stringent requirement in present and future wireless communications systems MIMO-OFDM has become a new “star” in the “constellation”

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of wireless and mobile communications. Its potential to increase spectral efficiency has not been reached by any other technology before. In addition to increasing spectral efficiency, MIMO can also be used to reduce transmitting power while keeping coverage areas constant. The use of MIMO technology in future transmission systems for broadcasting, multicasting and unicasting represents real business logic also for broadcasting corporations because of the possible reduction in transmission stations.

References 1. G.J. Foschini, M.J. Gans, On limits of wireless communications in a fading environment when using multiple antennas. Wireless Pers. Commun. 6, 311–335 (Mar 1998) 2. G.J. Foschini, Layered space–time architecture for wireless communication in a fading environment when using multielement antennas. Bell Labs Tech. J. Autumn, 41–59 (1996) 3. E. Telatar, Capacity of multiantenna Gaussian channels. AT&T Bell Laboratories, Tech. Memo. (June 1995) 4. G. Raleigh, J.M. Cioffi, Spatial-temporal coding for wireless communications. IEEE Trans. Commun. 46, 357–366 (1998) 5. H. Bo¨lcskei, D. Gesbert, A.J. Paulraj, On the capacity of OFDMbased spatial multiplexing systems. IEEE Trans. Commun. 50, 225–234 (Feb 2002) 6. G.G. Raleigh, J.M. Cioffi, Spatio-temporal coding for wireless communication. IEEE Trans. Commun. 46(3), 357–366 (1998) 7. H. Bolcskei, D. Gesbert, A.J. Paulraj, On the capacity of OFDM-based spatial multiplexing systems. IEEE Trans. Commun. 50(2), 225–234 (Feb 2002) 8. A.J. Paulraj, R. Nabar, D. Gore, Introduction to Space-Time Wireless Communications, 1st ed. (Cambridge University Press, Cambridge, Sept 2003) 9. http://www.srtelecom.com/uploads/File/whitepapers/WiMAX-LOS-and-NLOS-Technology. pdf (March 2010) 10. S.M. Alamouti, A simple transmit diversity technique for wireless communications. IEEE JSAC 16, 1451–1458 (Oct 1998) 11. A. Salvekar, S. Sandhu, Qinghua Li, Minh-Anh Vuong, Xiaoshu Qian, all of Intel Communications Group, Multiple-Antenna Technology in WiMAX Systems. Intel Corporation, Santa Clara, CA, USA (August 2004) 12. G. Foschini, Layered space–time architecture for wireless communication in a fading environment when using multi-element antennas. Bell Labs Tech. J. 1(2), 41–59 (1996) 13. D. Gesbert, M. Shafi, D. Shiu, P. Smith, A. Naguib, From theory to practice: an overview of MIMO space-time coded wireless systems. IEEE J. Select. Areas Commun. 21(3) (Apr 2003) 14. http://ieee802.org/16/tge/contrib/C80216e-04_193.pdf 15. Grant, Joint Decoding and Channel Estimation for Linear MIMO Channels. http://www.itr. unisa.edu.au/steven/turbo/WCNC00.pdf (March 2010) 16. D. Tse, P. Viswanath, Fundamentals of Wireless Communications (Cambridge University Press, Cambridge, 2005) 17. P. Mitran, H. Ochiai, V. Tarokh, Space-time diversity enhancements using collaborative communications. IEEE Trans. Info. Theory 51, 2041–2057 (June 2005) 18. B. Muquet, E. Biglieri, H. Sari, MIMO Link Adaptation in Mobile WiMAX Systems, in Proceedings of WCNC 2007 – IEEE Wireless Communications and Networking Conference, Hong Kong, China, Mar 2007 19. W. Roh et al., Framework for enabling closed-loop MIMO for OFDMA. IEEE C802.16e04_552r4 (Jan 2005)

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20. R. Heath, A. Paulraj, Switching between diversity and multiplexing in MIMO systems. IEEE Trans. Comm. 53(6) (June 2005) 21. R. Heath Jr., A. Paulraj, Switching between multiplexing and diversity based on constellation distance, in Proceedings Allerton Conference Communication, Control and Computing, Oct 2000 22. L. Zheng, D.N.C. Tse, Diversity and multiplexing: A fundamental tradeoff in multiple antenna channels. IEEE Trans. Info. Theory 49(4), 1073–1096 (May 2003)

Chapter 12

WiMAX and Wireless Standards Ramjee Prasad and Fernando J. Velez

Abstract Service providers must make difficult decisions as to which technology to choose in order to enable them to offer advanced services and demand for high bandwidth throughput as subscribers want their broadband connection “anytime, anywhere and anyway”. As WiMAX offers a low cost per subscriber and a rapid return on investment, it will enable a new market entrant to reach profitability quickly, especially in underserved markets where incumbents cannot afford to roll out economical (as compared to a telephone company’s data T1 service) broadband solutions. The bottom line indicates that mobile WiMAX is a superior 4G technology designed to provide for 4G services, beyond the current 3G technologies’ horizon. It is also the only 4G technology available today. While Long Term Evolution (3GPP-LTE) may provide competition to mobile WiMAX it will only be available in 4–5 years time. A comparison between IEEE 802.16m and LTEAdvanced is performed and the potentialities of IEEE 802.21 and 802.22 are highlighted as well.

12.1

Introduction

WiMAX wireless MAN, based on IEEE 802.16 family of standards, is a solution that can offer wireless broadband Internet access at low cost and is among the best technologies for last mile wireless. WiMAX has both fixed wireless and mobile protocols to serve residences, public safety and business. WiMAX-certified equipment will be an affordable choice for businesses, consumers and operators who need reliable longer-range wireless connections. A host of other companies are developing wireless technologies and products that will compete directly with R. Prasad (*) Center for TeleInFrastruktur (CTIF), Aalborg University, Niels Jernes Vej 12, DK–9220 Aalborg Øst, Denmark e-mail: [email protected]

R. Prasad and F.J. Velez, WiMAX Networks, DOI 10.1007/978-90-481-8752-2_12, # Springer ScienceþBusiness Media B.V. 2010

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Table 12.1 Comparison between different wireless wide- and broadband technologies Technology Parameters Bandwidth Max. Speed to deliver Data Number of Total Max Speed to Channels in deliver video and steaming audio 10 MHz WCDMA 5 MHz 14.4 Mbps (fixed and 2 28.8 Mbps HSDPA mobile) CDMA2000 1.25 MHz 3.2 Mbps (fixed and mobile) 7 31.1 Mbps 1 x EV-DO RA WiMAX 20 MHz 75 Mbps (fixed/nomadic) 2 8–46 Mbps 5 MHz 4–18 Mbps (fixed/nomadic) Mobile WiMAX 5 MHz Up to 15 Mbps (mobile) 2 Up to 30 Mbps

WiMAX in the market. Some of these technologies will likely be favoured by mobile operators over WiMAX since they can be installed via upgrades rather than through the rollout of new networks. When compared with the upcoming wireless standards, we foresee that success of WiMAX will be intrinsically linked to the success of some of these competing technologies. It is commonly believed that WiMAX will compete with current 3G Wideband Code Division Multiple Access (WCDMA), CDMA-2000 and their evolution systems. The “Super 3G” standard based on an upgrade for WCDMA is reported to support data rates ten times faster than UMTS; hence, it is also expected to compete with WiMAX. Some telecommunication carriers are looking forward to future 3G enhancements such as High Speed Downlink Packet Access (HSDPA) and further revisions to CDMA2000 that may offer data rates closer to predicted ones for WiMAX. Table 12.1 provides a comparison between different technologies. It is clearly seen that mobile version of WiMAX reportedly supports high data rates and it promises to provide mobile support for terminal velocities up to 150 km/h. The remaining of this Chapter is organized as follows. Section 12.2 discusses the advantages of WiMAX over DSL. Section 12.3 presents Wi-Fi while Section 12.4 addresses WiBro. ETSI HiperACCESS and ETSI HiperMAN are presented in Sections 12.5 and 12.6. Sections 12.7 and 12.8 addresses iBurst and Flash- OFDM. Section 12.9 presents a comparison between IEEE 802.16 and 3G. Section 12.10 describes 3G standards while HSDPA and HSUPA are discussed in detail in Section 12.11. Section 12.12 analyses IEEE 802.16m versus IMT-ADVANCED. Section 12.13 presents IEEE 802.20/MobileFI while Section 12.14 briefly addresses interoperability aspects and IEEE 802.21. Section 12.15 presents IEEE 802.22. Finally, Section 12.16 presents the conclusions.

12.2

Advantages of WIMAX Over DSL

As DSL is a wired technology it is essential to lay wires up to the last mile in order to provide connectivity. It becomes an expensive and difficult job to lay lines underground as it requires lot of hard work and labor whereas in wireless no such

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RAN <100km 802.22(proposed)-18-24Mbps WAN WAN <15km <15km 802.20(proposed) 802.20(proposed) GSM,GPRS, GPRS,CDMA, CDMA,2.5G, 2.5G,3G 3G -10 GSM, kbps toto 2.4Mbps kbps 2.4Mbps MAN <5km 802.16d/e -70Mbps LMDS -38Mbps LAN <150m 11-54Mbps PAN <10m 802.15.1 (Bluetooth)-1Mbps 802.15.3 > 20Mbps 802.15.3a (UWB) < 480Mbps

Fig. 12.1 Types of access networks

labor is required. Also WiMAX eliminates the mess of Ethernet wires throughout the home. Users can seamlessly roam from one location to another, that is, portability is fully supported. Roaming is not possible at all in DSL whereas this is not a problem in case of WiMAX. The question of whether or not WiMAX could replace DSL will vary from region to region and depends on past availability of a cable infrastructure. Many developing countries do not still have the required infrastructure for wired based broadband technologies. WiMAX is well-suited for such environment. Even in countries where there is already a wired infrastructure, in rural area there is a huge base for potential customer groups that are currently served with no or limited broadband access service. The value proposition in such market is to provide an economical, flexible and fast deployed solution, to improve the Internet access data rate and reliability. WiMAX can be installed in urban area or remote villages where DSL has difficulty to reach by high expense and long term deployment. To provide coverage it only needs just a few wireless base stations and some small CPE mounted on the building or home to provide coverage in the surrounding area (Fig. 12.1). The cheapest solutions use to dominate the market, depending upon the business case and basic infrastructure. It can be foreseen that WiMAX wireless broadband technology will benefit traditional wireline carriers and customers by encouraging innovation and improved services.

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Table 12.2 Comparison between WiMAX and xDSL Characteristics WiMAX Media specific Shared media between subscribers Maximum coverage 12–15 km (LOS) 1–2 km (NLOS) Bit rate (maximum) QoS Symmetry Roaming Architecture

Native MAC QoS support Service differentiation levels Asymmetrical and symmetrical Yes Central end-DSLAM Subscriber-xDSL NT

Power requirements for SS Battery or mains

xDSL Dedicated media 5–7 km DL:2–20 Mbps UL:800 kbps–1 Mbps

Asymmetrical and symmetrical No Central end–base station Subscriber-subscriber station Topologies: PTP, PMP, Mesh Mains

Table 12.2 compares the basic features for WiMAX and xDSL.

12.3

Wi-Fi

Wi-Fi, which is a short word for Wireless Fidelity (Wi-Fi), is a wireless version of Ethernet operating in the 2.4 and 5 GHz frequency band range. This technology received wide popularity around 2005, as the devices became inexpensive and widely available everywhere (basically, in every computer, PDA, tablet PC or even many models of mobile phones). Wi-Fi is the first high speed wireless technology which is deployed on large scale. It is very popular as hotspots around the world including home, offices, coffee shops, gas stations, hotels and airports. The first IEEE 802.11 standard was released in 1997 but was never widely accepted due to its low value for the throughput (1Mbps). IEEE 802.11-based WLAN was the first and prominent among the several WLAN standards that have come in to being in recent years [1, 2]. Improved service quality is gradually being supported. In 1999, the Wireless Ethernet Compatibility Alliance (WECA) was formed to allow for interoperability amongst IEEE 802.11 products of various vendors. A Wireless-Fidelity (Wi-Fi) interoperability test was developed by the alliance and the logos were provided as product certification. Today, Wi-Fi has become the synonym of IEEE 802.11 and the alliance is now named as the Wi-Fi Alliance [3, 4]. Within the IEEE 802.11 Working Group, there are the following IEEE Standards Association Standard and Amendments: l

IEEE 802.11: the WLAN standard was originally at 1 and 2 Mbps, operating at 2.4 GHz RF and IR standard (1997). All the other data rates listed in Table 12.3 are Amendments to this standard.

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Table 12.3 IEEE 802.11 family (Source [5–10]) 802.11 Standard/ Purpose amendments 802.11 2 Mbps, 2.4 GHz standard (original standard) 802.11a 54 Mbps, 5 GHz PHY layer standard 802.11b 11 Mbps, 2.4 GHz PHY layer standard 802.11d International roaming extensions for 5 GHz band 802.11e QoS enhancements 802.11g 54 Mbps, 2.4 GHz PHY layer standard (current standard) 802.11h Spectrum managed 802.11a for satellite and radar compatibility 802.11i Security enhancements 802.11j Extensions for Japan 802.11k Radio resource measurement extensions (for areas with multiple APs) 802.11n Up to 540 Mbps, 2.4 GHz higher throughput 802.11p Wireless access for the vehicular environment (WAVE) 802.11r Fast roaming between WLANs 802.11s Mesh topology support 802.11u Internetworking between different WLANs 802.11v Wireless network management 802.11w Protected management frames 802.11y 3.65–3.7 GHz PHY layer standard

l

l

l l l

l

l l

l

l

455

Publishing date 1999 1999 1999 2001 2005 2003 2004 2004 2004 Enhancements 2008 Expected 2009 Expected 2008 Expected 2008 Expected 2008 Preliminary Preliminary Expected 2008 Preliminary

Subsequent standard IEEE 802.11b provided a theoretical bit rate up to 11 Mbps, with a range varying from 100 m to a maximum of a few 100 m. It operates in 2.4 GHz unlicensed band. IEEE 802.11a reaches a theoretical data rate of 54 Mbps but the data rate decreases more quickly with the distance than in IEEE 802.11b (due to its operating frequency of 5 GHz). It has a range of over 100 m. IEEE 802.11e includes MAC enhancements for QoS extension. IEEE 802.11f is an extension for managing handover. Ratified in 2003 IEEE 802.11g has a maximum theoretical data rate of 54 Mbps and operates in the 2.4 GHz unlicensed band. IEEE 802.11h addresses European Radio Communications Committee requirements at 5 GHz addition of Transmission Power Control (TPC) and Dynamic Channel Selection (DCS). IEEE 802.11i provides security extension. IEEE 802.11j provides enhancements and amendments; adds channel selection for 4.9 GHz and 5 GHz in Japan. IEEE 802.11k defines Radio Resource Measurement enhancements, to provide mechanisms to higher layers for radio and network measurements. IEEE 802.11n has a theoretical data rate of 320 Mbps utilizing Multiple Input Multiple Output (MIMO) and receiver techniques to boost peak data rate and

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throughput. It operates at the 2.4 and 5 GHz bands. The provisioning of QoS is included. IEEE 802.11r addresses fast roaming mainly for Voice over IP (VoIP). IEEE 802.11s addresses AP-based mesh networks. IEEE 802.11t focuses on wireless performance prediction.

IEEE 802.11 family of standards is chronologically listed in Table 12.3. Today in the market we see that about 90% of laptops are now delivered with built-in support for Wi-Fi and the technology has been widely adopted both in enterprises and the home. In addition, the number of public Wi-Fi hotspots continues to grow [11]. Wi-Fi hotspots became popular almost immediately and have been applauded by road warriors for their ability to improve productivity. Wi-Fi is limited, however, by its range: high-speed connectivity is possible only as long as a user remains within range of the wireless access point, which is optimum within 300 ft. Wi-Fi was one of the earliest high-speed wireless data technologies and now benefits from a broad availability of supporting products and technologies. Intel Centrino mobile technology optimizes performance in mobile data platforms, helping users get the most from the expanding Wi-Fi infrastructure. Some of the newest platforms even support multiple Wi-Fi standards (e.g. 802.11a, b and/or g) for compatibility among several wireless networks. Table 12.4 Comparison between WiMAX and Wi-Fi Parameter 802.16/WiMAX Distance 30 miles LoS 6 miles NLoS Up to 75 Mbps Spectrum Channel size

Maximum PHY data rate Maximum efficiency (bit/s)/Hz Modulation Protocol QoS Minimum MAC overhead Security Application Scalability Interoperability

2.5 GHz, 3.5 GHz, 5.8 GHz (licensed & unlicensed) 22 MHz (IEEE std 802.11b) 20 MHz (IEEE std 802.11a and IEEE std 802.11g) 10 MHz (IEEE std 802.11j) 54 Mbps 2.7 OFDM, OFDMA Grant/Request, TDM, and TDMA Five classes of QoS 28 bytes( header + CRC) X.509 certificate 56-bit DES 128-bit AES MAN, WAN High High

Wi-Fi/802.11 WLAN 100 m – omni directional antenna; 20 miles – directional antenna 11 Mbps for “b” 54 Mbps for “g/a” 2.5 GHz, 5 GHz (unlicensed) 1.25–28 MHz

72 Mbit/s (10 MHz channel) 5 DSSS – “b” OFDM – “g/a” CSMA/CA contention-based Best Effort, very limited 6 bytes Very limited LAN Low Very high

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WiMAX is a broadband wireless standard based on the IEEE 802.16–2004 standard published in 2004, whose mobility version was published in February 2006. The difference in the chronology of the two standards is around 6 years. However, Wi-Fi is not a threat to WiMAX. In general, IEEE 802.16 and IEEE 802.11 technologies are complementary, as one is targeted for wireless MANs and the other for LANs. The differences between IEEE 802.16 and IEEE 802.11 are highlighted in Table 12.4 QoS feature was added later in the IEEE 802.11 standard. IEEE 802.11e supports a form of QoS with eight priorities or classes. However, WiMAX MAC is QoS centric that has been designed for QoS as an integral part of the MAC functions. Also IEEE 802.16 MAC is more efficient than the IEEE 802.11standard for outdoor applications, with packing, ARQ, dynamic fragmentation and smaller header overhead.

12.4

WiBRo

Wireless Broadband (WiBro) is the Korean equivalent of WiMAX being developed by the Korean telecommunication community (i.e., manufacturers, operators, service providers and academia [1]). WiBro was formerly known as the High-speed Portable Internet (HPi) initiated by the Korean telecommunications industry to provide better data handling than 3G cellular systems [12], [13]. The standard was renamed wireless broadband (WiBro) once it adopted IEEE 802.16e as its standard for global harmonization. WiBro services use the 2.3 GHz band in Korea. The initial driving force behind WiBro was to provide an affordable Internet service everywhere in important cities of Korea, with particularly high data rate, to fix, nomadic and moving terminals. In practice WiBro delivers up to 1 MBps/user (50 MBps aggregated data rate) at a maximum speed of 60 km/h, with QoS support and within a range not exceeding 1 km. WiBro was developed around the IEEE 802.16 standard, and in fact it uses a complete subset of specifications from both 802.16d and 802.16e. The WiBro air interface specification is fully compatible with IEEE 802.16e [13]. It has several features like handoff, sleeping mode, periodic ranging, and bandwidth stealing [1]. WiBro services were launched commercially by two Korean operators, Korea Telecom and SK Telecom, at the end of 2006 [1]. Table 12.5 shows the comparison between the PHY layer of IEEE 802.16 and WiBro. There are few differences between IEEE 802.16 and WiBro regarding the MAC layer too. As WiBro targets mostly mobile users, CBR QoS service layer is not present in the standard, but the rest of the QoS service layers are available. Other MAC layer features like ARQ support, the PHS mechanism, packing, fragmentation and QoS service layers of IEEE 802.16 are also available for WiBro. Furthermore, a handover mechanism is included in the standard [14]. The system architecture of WiBro is similar to cellular technologies rather than IEEE 802.16. The BS is called Radio Access Station (RAS) in WiBro.

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Table 12.5 PHY comparison of IEEE 802.16 and WiBro Item WiBro IEEE 802.16e OFDMA Frequency service 2.3–2.4 GHz 11 GHz fixed/mobile WirelessMAN Vehicle Duplexing TDD TDD/FDD Multiple access OFDMA OFDMA Channel coding CTC subchannel Concatenated RSconcatenation convolutional code BTC (optional), subchannel concatenation QPSK/16-QAM/64-QAM Modulation QPSK-16QAM64QAM,AMC on CQI Sub-channelization Flexible Flexible Coverage 1–1.5 km 3–7 km

IEEE 802.16 OFDMA 11 GHz fixed WirelessMAN TDD/FDD OFDMA RS-convolutional code BTC (optional)

QPSK/16-QAM/64QAM Flexible 3.5–7 km

WiBro was harmonized with IEEE standard to become interoperable with the other 802.16e-2005 products.

12.5

ETSI HiperACCESS

High Performance Radio Access (HiperACCESS) was standardized by ETSI in 2002, to provide broadband wireless access for LoS SSs. HiperACCESS is a part of ETSIs BRAN project [15–18]. It uses frequencies between 11 and 43.5 GHz and targets Small-to-Medium Size Enterprise (SME) and residential customers in the urban areas. HiperACCESS also provides backbone support for other cellular networks such as GSM. HiperACCESS has the following properties: l

l l

l

HiperACCESS uses a PtM topology with the AP (at the center) and Access Terminals (ATs) as the end nodes; It is a connection-oriented protocol with detailed QoS mechanisms; It supports both FDD and TDD duplexing schemes (Half-FDD support is also available for cheaper ATs); A variety of PHY layer modulation schemes are available for different link conditions.

The differences between IEEE 802.16 and HiperACCESS are presented in Table 12.6.

12.6

ETSI HiperMAN

High Performance Radio Metropolitan Access Network (HiperMAN) is another ETSI standard, from the BRAN (Broadband Radio Access Networks) group, published in 2003.

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Table 12.6 Comparison between ETSI HiperACCESS and IEEE 802.16 Features IEEE 802.16 ETSI HiperACCESS Operating mode PtM, Mesh PtM Subscriber type LoS, NLoS LoS Packet length Fixed, Variable Fixed Operation frequency 2–66 GHz 11–43.5 GHz Mobility support Yes No PHY layer SC, OFDM, OFDMA OFDM Channel bandwidth Variable 28 MHz

The HiperMAN standard is designed for Fixed Wireless Access provisioning to SMEs and residences using the basic MAC (DLC and CLs) of the IEEE 802.16–2001 standard [19]. It has been developed in very close cooperation with IEEE 802.16,http://en.wikipedia.org/wiki/HIPERMAN – cite_note-2 such that the HiperMAN standard and a subset of the IEEE 802.16a-2003 standard will interoperate seamlessly [20]. HiperMAN is designed to operate in 2–10 GHz band and is focused on IP-based services. This standard has a defined QoS framework, fast connection control management, strong security and supports AMC and dynamic power allocation for NLoS communications. HiperMAN enables both PtM and mesh network configurations in its standard. It also supports both TDD and FDD frequency allocations and hybrid FDD (H-FDD) terminals. As the targeted user profile is home and SOHO users, there is no CBR service class [21].

12.7

iBURST

iBurst is a niche wireless broadband technology based on smart antennas developed specifically from Australia’s ArrayComm (www.arraycomm.com). Working with a Taiwan Semiconductor Manufacturing Company (www.tsmc.com) chipset partner and with a base station provider, Kyocera (www.kyocera.com), ArrayComm deployed a trial iBurst network around Sydney in the year 2004. iBurst was subsequently adopted as the High Capacity – Spatial Division Multiple Access (HC-SDMA) radio interface standard by the Alliance of Telecommunications Industry Solutions (ATIS) [22]. The standard was prepared by ATIS’ Wireless Technology and Systems Committee’s (WTSC) Wireless Wideband Internet Access subcommittee and has been accepted as an American National Standard. The iBurst technology is purely based on IP and its end-to-end system is built onto two primary components: base stations deployed by a network operator, much as in today’s cellular mobile services, and wireless modems (or PC cards) that a customer uses with an existing Internet appliance to access the service, such as a notebooks or desktop computers. In iBurst security is handled at all layers, using a combination of MPLS and IPsec. Because iBurst supports IPv6, it can take advantage of the additional security features not available in IPv4.

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By the year 2008 iBurst Systems were commercially deployed in 14 countries. iBurst has been adopted as its own standard of IEEE 802.20. The air interface combines smart antenna techniques with industry best practices for wireless data, including adaptive modulation, fast ARQ, and a QoS-cognizant scheduler, to create a high-performance, reliable, and high-capacity data delivery mechanism.

12.8

Flash- OFDM

Flash-OFDM stands for Fast Low-Latency Access with Seamless Handoff OFDM. This is a proprietary wireless broadband technology developed by Flarion Technologies which was later acquired by Qualcomm (www.qualcomm.com) [23]. It uses a technique called fast hopping, a new signal-processing scheme that supports high data rates with very low packet and delay losses, over a distributed all-IP wireless network. It can operate in several licensed frequency bands, such as the 450 MHz, 700 MHz, 800 MHz, 1.9 GHz and 2.1 GHz ones. Flash OFDM reaches user data rates of 1–1.5 Mbps in downlink and 300–500 Kbps in uplink [24]. Flash-OFDM is a vertically integrated design spanning the physical, MAC, and link layers, while the network layer and the remaining layers are horizontally layered, inter-networked and purely IP-based [25]. The design specially enables reuse of existing off-the-shelf IP infrastructure equipment and protocols. Flash-OFDM has a spectrally efficient, high-capacity PHY layer and uses a packet-switched air interface. As Flash-OFDM uses fast hopping across all tones in a pseudorandom predetermined pattern it can be called as spread spectrum technology [26]. Flash OFDM also has a contention-free, QoS-aware MAC layer. It provides support for interactive data applications, including voice, and efficient operation using all existing Internet protocols such as TCP/IP too. It also offers full vehicular mobility, and it offers low costs for subscribers. Flash-OFDM is also a candidate for the IEEE 802.20 standardisation effort. Compared to Mobile WiMAX.

12.9

IEEE 802.16 and 3G

Third Generation (3G) are systems to provide enhanced range of multimedia services like high speed internet access. The goal of 3G includes high-quality audio and video and advanced global roaming. The services link networks that are not themselves interconnected. 3G is defined by the ITU under International Mobile Telecommunications (IMT 2000) global framework.

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Fig. 12.2 Convergence of services in IMT-2000 Telephony • Voice • Video • Fax • Mailbox

Internet • Web surfing • Email • Information • M-commerce IMT - 2000

Multimedia • Radio • Television • Location Services

IMT-2000 provides a framework for worldwide wireless access by linking the diverse systems of terrestrial and/or satellite based networks. Figure 12.2 shows the recommendations behind defining IMT 2000. These were made back in 1992, when the Internet was still not widely known outside of academic and technical circles. It is foreseen that IMT- 2000 will exploit the potential synergy between digital mobile telecommunications technologies and systems for fixed and mobile wireless access systems [27].

12.10

3G Standards

The 3G Partnership Project (3GPP) and 3G partnership project 2 (3GPP2) have been defining standards for enhancements to today’s 3G systems.

12.10.1

3GPP

The 3G Partnership Project (3GPP) was formed in 1998, under the European Telecommunications Standards Institute (ETSI), to make a globally applicable 3G mobile phone system specification within the scope of the ITU’s IMT-2000 project. 3GPP specifications are based on evolved GSM specifications, today popularly known as the UMTS system. 3GPP organizational members include ARIB (Japan), ATIS (United States), CCSA (China), ETSI (Europe), TTA (Korea), and TTC (Japan). 3GPP has five main UMTS standardization areas listed below:

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Table 12.7 3GPP releases Release Explanation Release 98 Specifies pre-3G GSM networks. Release 99 Specifies the first UMTS 3G networks, incorporating a CDMA air interface. Release 4 Originally called Release 2000, adds features that include an all-IP core network. Release 5 Introduces IMS and HSDPA. Release 6 Integrates operation with WLAN networks and adds HSUPA. Release 7 Focuses on better integration with wired networks and examines advanced receivers [28]. This specification also focus on HSPA, SIM high-speed protocol and contactless front-end interface enabling operators to deliver contactless services like Mobile Payments), EDGE Evolution. Release 8(in LTE, All-IP Network (SAE). Release 8 constitutes a refactoring of UMTS progress) as an entirely IP based fourth-generation network.

l l l l l

Radio access network Core network Terminals Services and system aspects GERAN

3GPP standards are structured as releases. Current 3GPP releases include the following releases listed in Table 12.7. The 3GPP envisions additional long term WCDMA enhancements leading to UMTS terrestrial radio access node long term evolution (known as 3GPP-LTE or UTRAN LTE) also referred to as 3.99G or evolved UMTS. The objective of this long-term evolution (LTE) is to enable to support a peak data rate of 100 Mbps in the downlink and of 50 Mbps in the uplink, with an average spectral efficiency that is three to four times that of Release 6 HSPA. The air interface will likely be based on OFDM/OFDMA and multiple input/multiple output (MIMO).

12.10.2

3GPP2

The 3G Partnership Project 2 (3GPP2) was formed when ETSI refused to expand the scope of 3GPP to address CDMA2000. Thus 3GPP2 is the standardization group for CDMA2000, the set of 3G standards based on earlier 2G CDMA technology. The 3GPP2 organizational members include ARIB (Japan), CCSA (China), TIA (United States), TTA (Korea), and TTC (Japan). The technical specification groups for 3GPP2 include: l

l

TSG-A: Access Network Interfaces; http://www.3gpp2.org/Public_html/C/ index.cfm TSG-C: Radio Access; http://www.3gpp2.org/Public_html/C/index.cfmhttp:// www.3gpp2.org/Public_html/S/index.cfm

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TSG-S: Service and System Aspects; http://www.3gpp2.org/Public_html/X/ index.cfm TSG-X: Core Networks

The CDMA family with its different technologies is shown in Table 12.8. 3GPP2 is on a similar path with LTE for CDMA2000. Since approved standards for LTE are not expected until 2008, it is unlikely that products will be available until 2009 or later. For current UMTS network operators the most likely evolution path will be to LTE. There will be seamless connectivity of the new LTE radio network to their existing core network infrastructure, billing systems and services. The objective is to support up to 70–200 Mbps in the downlink and up to 30–45 Mbps in the uplink in EV-DO Revision C, using a bandwidth of up to 20 MHz. Table 12.9 summarizes comparisons between Mobile WiMAX and 3GPP-LTE. Third Generation network deployment is done on a huge scale by the mobile operators to deliver broadband applications to their subscribers. GSM is upgraded to UMTS and HSDPA as part of their 3G evolution. CDMA operators around the

Table 12.8 CDMA family and its different technologies

Family CDMA

WCDMA

Technology 1 x 1.25 MHz 1 x EV-DO Rev 0 (1.25 MHz) 1 x EV-DO Rev A (1.25 MHz) 1 x EV-DO Rev B (1.25 MHz) GPRS (200 KHz) EDGE (200 KHz) HSDPA Release 5 (5 MHz) WCDMA Release 99 (5 MHz) HSUPA Release 6 (5 MHz)

Table 12.9 Comparison between Mobile WiMAX and 3GPP-LTE Feature 3GPP-LTE Mobile WiMAX Air interface OFDMA based OFDMA based QPSK – 64QAM QPSK – 64QAM Duplexing FDD/TDD TDD Mobility/vehicular 350 km/h 60–120 km/h speed Bandwidth 1.25, 1.6, 2.5, 5, 10, 15, 20 MHz 3.5, 5, 7, 8.75, 10 MHz Core network All-IP All-IP Spatial multiplexing MIMO models Spatial multiplexing Transmit diversity (Alamouti, CDD) Transmit diversity (Alamouti) CDD – R 1.5 UE specific beam-forming UE specific beam-forming Collaborative UL SM Multi technology GERAN, UTRAN, non-3GPP CDMA, GERAN, UTRAN, support Non 3GPP: CDMA, WLAN WLAN (WiMAX) CMIP, PMIP, IMS PMIP and IMS/VCC

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world are developing 1  Evolution-Data Optimized (1  Ev-Do) as their 3G solution for broadband data. The capabilities of these 3G technologies are as follows. Evolution-Data Optimized or Evolution-Data only Evolution-Data Optimized or Evolution-Data only, abbreviated as Ev-Do or EVDO, is a telecommunications standard for the wireless transmission of data through radio signals, typically for broadband Internet access. It uses multiplexing techniques including CDMA as well as TDMA to maximize both individual user’s throughput and the overall system throughput. It is standardized by 3GPP2 as part of the CDMA2000 family of standards and has been adopted by many mobile phone service providers around the world – particularly those previously employing CDMA networks. It has been adopted by a number of CDMA mobile telecommunications service providers across the world, particularly in the USA, South Korea, Japan, Eastern European countries, Australia, Canada and New Zealand. 1 Ev-Do supports a peak downlink data rates of 2.4 Mbps in a 2.5 MHz channel. 1 x EV-DO-Rev 0 was principally designed to support packet data services and not conversational services. In a later release, called 1 x EVDO-Rev A, additional enhancements were added to the 1 x EV-DO specification. In the forward link, these enhancements include smaller packet sizes, higher DL peak data rate (up to 3.1 Mbps), and multiplexing packets from multiple users in the MAC layer. In the UL Rev A included support of H-ARQ, AMC, higher peak rates of 1.8 Mbps, and smaller frame size (6.67 ms. The enhancements in DL and UL supported conversational services, for example, VoIP and gaming, in the newly enhanced 1 x EVDORev A systems A further enhancement to the CDMA2000 standard is 1 x EVDO-Rev B (also known as DO Multi-Carrier). The revision increased the DL spectral efficiency and data throughput by adding 64QAM to the DL modulation scheme. It also provides for dynamic allocation of up to fifteen 1.25 MHz carriers in a 20 MHz bandwidth. As a result, the 1 x EVDO-Rev B enhancement will increase the DL peak over the air data rate for a 1.25 MHz carrier to 4.9 Mbps and, by aggregating three carriers (known as 3 x EVDO) in a nominal 5 MHz channel bandwidth, will provide peak DL and UL rates of 14.7 Mbps of 5.4 Mbps

12.11

HSDPA and HSUPA

3GPP Release 5 extends the WCDMA specification with HSDPA. HSDPA includes advanced features such as adaptive modulation and coding (AMC), hybrid automatic repeat request (HARQ), and de-centralized scheduling architecture. The 3GPP has also defined WCDMA enhancements for the uplink path. This enhancement is known as high speed uplink packet access (HSUPA); the combination of HSDPA and HSUPA is simply known as high speed packet Access (HSPA), that is, HSDPA þ HSUPA ¼ HSPA.

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The features designed to enhance data throughput and are common to Ev-Do, HSDPA/HSPA and Mobile WiMAX are the following: l l l l l l l

Adaptive modulation and coding (AMC) Multi-code operation Fast scheduling Bandwidth efficient handoff Hybrid Automatic Repeat Request (HARQ) Higher DL peak rates De-centralized architecture where scheduling functions are moved from the Radio Network Controller (RNC) to Node-B thus reducing latency and enabling fast scheduling

Table 12.10 presents the comparison between these systems and the performance parameters for Mobile WiMAX. Depending on system configuration, mobile WiMAX has a clear performance edge in terms of data rates over HSDPA/HSUPA or Ev-Do. The use of advanced antenna technologies in current 1 x EVDO and HSPA solutions has been limited. As the processing complexity for smart antenna technologies scales with the channel bandwidth, supporting advanced antenna technologies in broadband wireless channels (as the signals occupy the entire Table 12.10 Summary of comparative features of WiMAX, EVDO and HSPA (Source [29, 30]) Feature 1 x EVDO Rev A HSDPA/HSUPA Mobile WiMAX (HSPA) Base standard CDMA2000/IS-95 WCDMA IEEE 802.16e Duplex method FDD FDD TDD (FDD optional) Downlink TDM CDM-TDM OFDM Uplink multiple CDMA CDMA OFDMA access Channel BW 1.25 MHz 5.0 MHz Scalable: 5, 7, 8.75, 10 MHz Frame size 6.67 ms (DL) 2 ms (DL) 5 ms TDD (DL) 1.67 ms (UL) 2.10 ms (UL) 5 ms TDD (UL) Modulation DL QPSK/8PSK/ QPSK/16QAM QPSK/16QAM/ 16QAM 64QAM Modulation UL BPSK,QPSK/8PSK BPSK/QPSK QPSK/16QAM DL peak over 3.1 Mbps 14 Mbps 46 Mbps (10 MHz the Air TDD) UL peak over 1.8 Mbps 5.8 Mbps 14 Mbps (10 MHz the Air TDD) Scheduling Fast Scheduling in Fast Scheduling in the DL Fast Scheduling in the DL the DL Handoff Virtual Soft Handoff Network initiated hard Network Optimized handoff Hard Handoff Tx diversity Simple open loop Simple open & closed STBC, SM and MIMO Diversity loop diversity Beamforming No Yes Yes (dedicated pilots)

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bandwidth in CDMA-based systems) is a significant challenge. However, as Mobile WiMAX supports scalable channel bandwidth in the context of OFDMA, smart antenna technologies like beamforming can be easily used. Mobile WiMAX supports a full range of smart antenna technologies to enhance performance including Beam-forming, Space Time Coding (STC) and Spatial Multiplexing (SM). These technologies can improve both system coverage and capacity. Both 1 x EVDO and HSPA support simple transmit diversity and the HSPA standard has an option to support beamforming. A standard-based long distance technology will avoid many of the problems of high upfront costs, lack of roaming and unreliability that those ahead of their time pioneers encountered. However, it will still need to gain market share rapidly before 3G takes an unassailable hold. 3G, third-generation wireless technology, has had limited success for several key reasons. First, its data rates, particularly for video streaming applications, are quite limited for most users. The rates range from 144 kbps for mobile, to 384 kbps for pedestrian, and up to 3 Mbps for fixed environment. Second, large-scale network deployment has been impeded due to competing technologies, Wideband Code Division Multiple Access (W-CDMA) versus CDMA2000, or Global System for Mobile (GSM) supporters versus Qualcomm’s CDMA supporters. Building a nationwide W-CDMA network and providing ubiquitous coverage costs much more than letting operators build their own networks. Verizon and Sprint have been offering CDMA2000 Evolution Data Only (EVDO) data services for a couple of years. Third, due to competing technologies and lack of a single industry standard, economy of scale to drive network equipment and end user equipment costs to a mass market level does not exist. And last, but not least, 3G is primarily a cellular-based technology, which has limited application for fixed infrastructure applications, such as last-mile, point-to-point connectivity, or backhaul application. IEEE 802.16/WiMAX is a complementary rather than a replacement technology for 3G wireless systems. 3G and WiMAX will compete, but will also co-exist. The technology roadmap of cellular and WiMAX is therefore converging fast towards OFDM, IP core and IMS. 3G and WiMAX differ in their approach towards wireless data in the way, 3G is a voice technology moving towards data, while WiMAX is a data technology moving towards mobility. But both 3G & WiMAX meet the requirements of Wireless Broadband. Figure 12.3 shows the roadmap of the various third Generation technologies and WiMAX. It is clearly visible that Mobile WiMAX is leading and will be available before 3G-LTE. WiMAX networks can serve as backhaul for 3G networks. Since such a network can provide high bandwidth with large coverage area, 3G BSs can be deployed easily and flexibly to extend the cellular coverage area. However, one challenge here is efficient topology management to minimize the network deployment cost while satisfying the QoS requirements for cellular services. While 3G systems are designed primarily for mobile voice and data users, IEEE 802.16/WiMAX systems are optimized to provide high-rate wireless connectivity for a large set of services and applications that require QoS guarantees. In addition, IEEE 802.16/WiMAX systems

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467 Potential 2-year time time to market the advantage of Mobile WiMAX

WiMAX 802.16 Evolution

3GPP UMTS Evolution

Fixed WiMAX (802.16d)

Mobile WiMAX (802.16 e)

HSDPA / HSUPA/ HSPA+

3G UMTS

2006

Next-generation WiMAX (802.16 m)

2007

2008

2009

3GLTE

2010

2011

2012

Fig. 12.3 Roadmap, Mobile WiMAX will be available before 3G – LTE

can be used along with 3G wireless systems to provide QoS to wireless Internet users in a cost-effective manner. Specifically, designed for mobile users, IEEE 802.16e can be an alternative to 3G cellular networks while IEEE 802.20 is being developed.

12.12

IEEE 802.16m and IMT-ADVANCED

The next-generation mobile WiMAX will expand fundamental concepts that were originally considered in mobile WiMAX. The IEEE 802.16m will be suitable for both new and mixed deployments with legacy mobile stations (MSs) and base stations (BSs). The backward compatibility feature will allow smooth upgrades and an evolution path for the existing deployments. It will enable roaming and seamless connectivity across IMT-advanced and IMT-2000 systems through the use of appropriate interworking functions. In addition, the IEEE 802.16m system may use multi-hop relay architectures for improved coverage and performance. IMT-advanced requirements are a subset of, and less stringent than, the IEEE 802.16m system requirements. Therefore, the IEEE 802.16m standard can qualify as an IMT-advanced technology [31]. Table 12.11 summarizes the IEEE 802.16m baseline system requirements and the corresponding requirements specified by Report ITU-R M.2134 [32]. The IEEE 802.16m systems are expected to meet all service requirements for IMT-advanced systems as specified by Report ITU-R M.1822 [33], where compliance is verified through inspection [34].

12.13

IEEE 802.20/Mobile FI

The idea to develop Mobile Broadband Wireless Access (MBWA) or mobileFI was born in the process of bringing mobility support to IEEE 802.16. IEEE approved Task Group 20 to develop a standard based on mobile user support. IEEE 802.20,

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Table 12.11 IEEE 802.16m and IMT-Advanced requirements (Source [31]) Requirements IMT-Advanced [32] IEEE 802.16m [35] Peak data rate (b/s/Hz) DL: 15(4  4) DL: 8.0/15.0 (2  2/4  4) UL: 6.75 (2  4) UL: 2.8/6.75 (1  2/2  4) Cell spectral efficiency (b/s/ DL (4  2) = 2.2 DL (2  2) = 2.6 Hz/sector) UL (2  4) = 1.4 UL (1  2) = 1.3 (base coverage urban) (mixed mobility) Cell-edge user spectral DL (4  2) = 0.06 DL (2  2) = 0.09 efficiency (b/s/Hz) UL (2  4) = 0.03 UL (1  2) = 0.05 (base coverage urban) (mixed mobility) C-plane: 100 ms (idle to active) Latency C-plane: 100 ms (idle to U-plane: 10 ms active) U-plane: 10 ms Optimal performance up to 10 km/h Mobility (b/s/Hz at km/h) 0.55 at 120 km/h Graceful degradation up to 120 km/h 0.25 at 350 km/h Connectivity up to 350 km/h (link-level) Up to 500 km/h depending on operating frequency Handover interruption Intra-frequency: 27.5 Intra-frequency: 27.5 time (ms) Inter-frequency: 40 (in a Inter-frequency: 40 (in a frequency frequency band) band) 60 (between frequency 60 (between frequency bands) bands) VoIP capacity 40 (4  2 and 2  4) 60 (DL 2  2 and UL 1  2) (Active users/sector/MHz) (Base coverage urban) Antenna configuration Not specified DL: 2  2 (baseline), 2  4, 4  2, 4  4, 8  8 UL: 1  2 (baseline), 1  4, 2  4, 44 Cell range and coverage Not specified Up to 100 km Optimal performance up to 5 km Multicast and broadcast Not specified 4 b/s/Hz for ISD 0.5 km service (MBS) 2 b/s/Hz for ISD 1.5 km MBS channel reselection Not specified 1.0 s (intrafrequency) interruption time 1.5 s (interfrequency) Location-based services Not specified Location determination latency < 30 s (LBS) MS-based position determination accuracy < 50 m Network-based position determination accuracy < 100 m Operating bandwidth Up to 40 MHz 5–20 MHz (up to 100 MHz through (with band aggregation) band aggregation) Duplex scheme Not specified TDD, FDD (support for H-FDD terminals) IMT bands Operating frequencies IMT bands 450–470 (MHz) 450–470 698–960 698–960 1710–2025 1710–2025 2110–2200 2110–2200 2300–2400 2300–2400 2500–2690 2500–2690 3400–3600 3400–3600

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Mobile Broadband Wireless Access (MBWA) or mobileFI was born this way in December 2002. Since the main concern of IEEE 802.20 is to provide mobility to vehicles with speeds up to 250 km/h, the considered bandwidth is much lower than the ones form IEEE 802.16 and IEEE 802.11. The foreseen cell radius for IEEE 802.20 will be around 15 km [36]. The basic features of IEEE 802.20 include compatibility, coexistence, distinct identity, technology feasibility, and economic feasibility [36]. The standard specifies physical and medium access control layers of an air interface for interoperable mobile broadband wireless access systems, [37]. In order to utilize NLoS signalling the standard amends working in licensed frequencies below 3.5 GHz and supporting both FDD and TDD, optimized for IP-data transport, with peak data rates per user in excess of 1 Mbps. It supports various vehicular mobility classes up to 250 km/h in a Metropolitan Area Network (MAN) environment and targets spectral efficiencies, sustained user data rates and numbers of active users that are all significantly higher than achieved by existing mobile systems [38]. To avoid the latency problems, IEEE 802.20 does not include any connection establishment mechanism, unlike IEEE 802.16. The standard was first planned to be available by the end of 2004, but a delay occurred and in June 2006, the IEEE-SA Standards Board directed that all activities of the 802.20 Working Group be temporarily suspended [39]. The standardisation work was resumed in n in September 2006. The IEEE-SA Standards Board approved a plan to enable the IEEE 802.20 Working Group to move forward with its work to develop a mobile broadband wireless access standard and provide the best opportunity for its completion and approval [40]. In July 2007, the IEEE 802 Executive Committee along with its 802.20 Oversight Committee approved a change to voting in the 802.20 working group. Going forward voting was changed from an individual voting member to an entity based system. Since the original allegation of dominance and lack of transparency of the process had been raised this was a solution. With some of those issues possibly again being an issue the IEEE 802 management groups took this proactive step in another attempt to secure the IEEE process for this particular standard [41]. On 12 June 2008, IEEE finally approved the new standard [38].

12.14

IEEE 802.21 and Media Independent Handover

Media Independent Handover (MIH) is the heart of the 802.21 standard’s framework that is defined to enhance user experience of mobile devices by supporting handovers between heterogeneous networks and to support the use of both mobile terminals and network infrastructure. MIH is a Layer 2.5 in the standard which resides above different MACs. It can use inputs from layer 2 such as trigger events, hints, access to information about different networks, etc. and can help in the handover decision making process. Layer 2.5 would also include inputs based on user policy and configuration that might affect the handover process [42].

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The Media Independent Handover Function (MIHF) facilitates a MIH user during the mobility management and handover process. The MIHF provides convergence of link-layer state information from multiple heterogeneous access technologies into a unified presentation to the upper layers of the mobility-management protocol stack [42]. Figure 12.4 illustrates the interaction of the MIH functions with the upper and lower layers of the protocols stack [43] and the placement of these functions within the mobility-management protocol stack for handovers in heterogeneous environments. The key element of the MIH Functions includes a Media Independent Event Service (MIES), a Media independent Command Service (MICS, and a Media Independent Information Service [MIIS]). l

l

l

MIES collect a set of events and triggers from local as well as remote interfaces and provide them to the upper layers or the mobility management layers for any change in link characteristics, link stat and link. MICS provides set of commands that enables higher layer to control lower layers. These commands carry decisions of the upper layers to the lower layers to control link behaviour relevant to handovers. MIIS provides an information model to make more effective handover decisions. This information may be present in some information server from where the MIH Function can access it. This information can help a MIHF entity to discover and obtain static and dynamic network information existing within a geographical area to facilitate the handovers.

Application (video, VoIP) SIPIHO HO Monitoring SIP Client

HO Decision

MIIS

MIES

IP Layer

MICS

HO Execution

Transport (UDP/IP)

MIH_SAP (Media Independent) 802.21 MIH Functions MIHF MIES

MICS

MIIS

MIH_LINK_SAP (Media Dependent)

Fig. 12.4 Media independent Handover and its functions

WiFi

WiMax

3GPP

3GPP2

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The MIH Function provides services to the upper layers through a well defined service access point (SAP) and obtains services from the lower layers through a variety of technology-dependent interfaces (SAP).

Session Initiation Protocol (SIP) is becoming the leading protocol for multimedia call control in IP networks and is expected to be widely deployed in the near future. The existing SIP infrastructures and signalling could be optimized to provide a good solution for mobility support. Reference [44] proposes the architectures and vertical handover procedures for actual SIP-based media independent handover between different networks with the triggers being provided by MIH for efficient terminal mobility management in a SIP environment.

12.15

IEEE 802.22

IEEE 802.22 is a working group of IEEE 802 LAN/MAN standards committee which aims at constructing Wireless Regional Area Network (WRAN) utilizing white spaces in the allocated TV frequency spectrum. The aim of the project is to develop a fixed broadband access standard for use in licensed but unused spectrum in an opportunistic way, to avoid interference with any transmitting TV channel. The IEEE 802.22 project was formally called as “Standard for Wireless Regional Area Networks (WRAN) – Specific requirements – Part 22: Cognitive Wireless RAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications: Policies and procedures for operation in the TV Bands”. IEEE 802.22 WG has been chartered with the specific task of developing an air interface (i.e., PHY and MAC layers) based on cognitive radios (CRs) for unlicensed operation in the VHF/UHF TV broadcast bands between 54 and 862 MHz. All these channels are 6 MHz wide, and span from 54–72 MHz, 76–88 MHz, 174–216 MHz, and 470–806 MHz. In addition to the TV service, also called primary service, other services such as wireless microphones are also allowed by FCC to operate on vacant TV channels on a non-interfering basis and so are Private Land and Commercial Mobile Radio Services (PLMRS/CMRS) including Public Safety [45–47]. The 802.22 system is expected to have spectral efficiencies in the range of 0.5 bit/s/Hz up to 5 bit/s/Hz. If an average of 3 bit/s/Hz is considered, the total PHY data rate achieved is 18 Mbps in a 6 MHz TV channel. In DL the minimum peak throughput at cell edge is required to be 1.5 Mbps per CPE. In the upstream direction, a peak throughput of 384 kbps is specified, which is comparable to DSL services. The service coverage of a WRAN system is nominally 30 km. However, if regulation permits higher transmit power limits, its range must reach up to 100 km. FCC selected the TV bands for providing such service because these frequencies feature very favourable propagation characteristics, which would allow far out users to be serviced and hence provide a suitable business case for Wireless Internet

Table 12.12 Comparison between various wireless broadband technologies Technology Standard Usage Throughput UWB 802.15.3a WPAN 110–480 Mbps Wi-Fi 802.11a WLAN Up to 54 Mbps Wi-Fi 802.11b WLAN Up to 11 Mbps Wi-Fi 802.11g WLAN Up to 54 Mbps WiMAX 802.16d WMAN Up to 75 Mbps (20 MHz BW) WiMAX 802.16e Mobile WMAN Up to 30 Mbps (10 MHz BW) WiMAX 802.16m Mobile Up to 15 Mbps WMANWWAN WCDMA/UMTS 3G WWAN Up to 2 Mbps (up to 10 Mbps with HSDPA technology) CDMA2000 1 x EV-DO 3G WWAN Up to 2.4 Mbps (typical 300–600 kbps) IMT-advanced Beyond WWAN Up to 15 Mbps 3G 4G EDGE 2.5G WWAN Up to 348 kbps 2–6 GHz IMT-bands

Typical 1–3 mile Up to 100 km Optimal up to 5 km Typical 1–5 mile

400, 800, 900, 1700, 1800, 1900, 2100 MHz IMT-bands 1900 MHz

Typical 1–5 mile

Not specified Typical 1–5 mile

1800, 1900, 2100 MHz

Frequency 7.5 GHz 5 GHz 2.4 GHz 2.4 GHz Sub 11 GHz

Range Up to 30 feet Up to 300 feet Up to 300 feet Up to 300 feet Typical 4–6 mile

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Service Providers (WISPs). Another added advantage is that IEEE 802.22 devices in the TV bands will be unlicensed, which further lowers cost and is conducive to providing a more affordable service. The most prominent target application of 802.22 WRANs is wireless broadband access in residential, small/home office (SOHO), small business, multitenant dwellings, and campuses. IEEE 802.22 is intended to provide these customers with performance comparable to those of existing fixed broadband access technologies (e.g., DSL and cable modems) serving urban and suburban areas. The technology aims to provide services such as data, voice, as well as audio and video traffic with appropriate QoS support. IEEE 802.22 is mostly targeted at rural and remote areas and its coverage range is considerably larger than 802.16. This is the core difference between IEEE 802.22 and IEEE 802.16 (WiMAX).

12.16

Conclusion

Demand for bandwidth intensive services is on the rise. Service providers must make difficult decisions as to which technology to choose in order to enable them to offer advanced services and demand for high bandwidth throughput as subscribers want their broadband connection “anytime, anywhere and anyway”, one of the characteristics of WiMAX. As WiMAX offers a low cost per subscriber and a rapid return on investment, it will enable a new market entrant to reach profitability quickly, especially in underserved markets where incumbents cannot afford to roll out economical (as compared to a telephone company’s data T1 service) broadband solutions. The bottom line indicates that mobile WiMAX is a superior 4G technology designed to provide for 4G services, beyond the current 3G technologies’ horizon. It is also the only 4G technology available today. While 3GPP-LTE may provide competition to mobile WiMAX it will only be available in 4–5 years time, Table 12.12.

References 1. IEEE 802.11, Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications (Nov 1997) 2. N.R. Prasad, A.R. Prasad (eds.), WLAN Systems and Wireless IP for Next Generation Communications (Artech House, Norwood, MA, 2002) 3. A.R. Prasad, N.R. Prasad, 802.11 WLANs and IP Networking: Security, QoS and Mobility (Artech House, Boston, MA, 2005) 4. Technical White Paper, Broadband Wireless: The New Era in Communications, Intel (2004) 5. IEEE 802.11-1999, IEEE Standard for Local and Metropolitan Area Networks Specific Requirements – Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications (12 June 1999)

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6. IEEE 802.11b-1999, IEEE Standard for Local and Metropolitan Area Networks Specific Requirements – Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications High Speed Physical Layer Extension in the 2.4 GHz Band (16 Sept 1999) 7. IEEE 802.11a-1999, IEEE Standard for Local and Metropolitan Area Networks Specific Requirements – Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications High Speed Physical Layer in the 5 GHz Band (1999) 8. IEEE 802.11g-2003, IEEE Standard for Local and Metropolitan Area Networks Specific Requirements – Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications Amendment 4: Further Higher Data Rate Extension in the 2.4 GHz Band (27 June 2003) 9. IEEE 802.11e-2005, IEEE Standard for Local and Metropolitan Area Networks Specific Requirements – Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications MAC Enhancements for QoS (2005) 10. IEEE 802.11i-2004, IEEE Standard for Local and Metropolitan Area Networks Specific Requirements – Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications Amendment 6: Medium Access Control (MAC) Security Enhancements (23 July 2004) 11. P. Bell, M. Roberts, Asian Public Wi-Fi Market Expands 6% in 2Q05: Wireless Broadband Analyst (2005) 12. T. Kwon, H. Lee, S. Choi, J. Kim, D. Cho, S. Cho, S. Yun, W. Park, K. Kim, Design and implementation of a simulator based on a cross-layer protocol between MAC and PHY layers in a WiBro Compatible IEEE 802.16e OFDMA system. IEEE Commun. Mag. 43(12), 136–146 (Dec 2005) 13. S.Q. Lee, N. Park, C. Cho, H. Lee, S. Ryu, The wireless broadband (wibro) system for broadband wireless internet services. IEEE Trans. Commun. Mag. 44(7), 106–112 (July 2006) 14. S.Y. Yoon, WiBro Technology, Samsung Electronics Co, Ltd. Technical Report Sep (2004). www.itu.int/ITU-D/imt-2000/documents/Busan/Session3_Yoon.pdf 15. ETSI HiperACCESS, Broadband Radio Access Networks (BRAN); Requirements and Architecture for Broadband Fixed Radio Access Networks (HIPERACCESS) (May 1998) 16. ETSI HiperACCESS, Broadband Radio Access Networks (BRAN); HIPERACCESS System Overview (March 2002) 17. ETSI HiperACCESS, Broadband Radio Access Networks (BRAN); HIPERACCESS PHY Protocol Specification (Apr 2002) 18. ETSI HiperACCESS, Broadband Radio Access Networks (BRAN); HIPERACCESS DLC Protocol Specification (June 2002) 19. ETSI HiperACCESS, Broadband Radio Access Networks (BRAN); HIPERACCESS DLC Protocol Specification (June 2002) 20. ETSI BRAN HiperMAN Liaison Report. http://www.ieee802.org/16/liaison/docs/80216l-01_ 21.pdf (March 2010) 21. ETSI HiperMAN, Broadband Radio Access Networks (BRAN); Functional Requirements for Fixed Wireless Access Systems Below 11 GHz: HIPERMAN Data Link Layer (DLC) Layer (Nov 2003) 22. http://www.iburst.co.za/default.aspx?link=iburst_technology 23. http://www.qualcomm.com/products_services/networks/flash-ofdm/ 24. Flarion Technologies, OFDM for Mobile Data Communications. White paper (Mar 2003) 25. P. Newman, Netillion Inc. In search of the All-IP Mobile Network. IEEE Radio Communications (Dec 2004) 26. G. Song, Y. Li, Cross-layer optimization for OFDM wireless networks-part I: theoretical framework. IEEE Trans. Wireless Commun. 4(2), 614–624 (Mar 2005) 27. http://www.itu.int/home/imt.html 28. Review of the Work Plan at Plenaries #31, 3GPP, SP-060232 3GPP TSG SA#31 Sanya (13–16 Mar 2006)

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WiMAX and Wireless Standards

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29. WiMAX Forum, Mobile WiMAX-Part I: A Technical Overview and Performance Evaluation (June 2006) 30. WiMAX Forum, Mobile WiMAX-Part II: A Comparative Analysis (May 2006) 31. S. Ahamdi, An overview of next-generation mobile WiMAX technology. Commun. Mag. 47(6), 84–98 (June 2009) 32. ITU-R M.2134, Requirements Related to Technical System Performance for IMT-Advanced Radio Interface(s) [IMT.TECH]. Draft new report (Nov 2008) 33. ITU-R M.1822 Rec., Framework for Services Supported by IMT (Oct 2007) 34. ITU-R M.2135, Guidelines for Evaluation of Radio Interface Technologies for IMTAdvanced [IMT.EVAL]. Draft new report (Nov 2008) 35. IEEE 802.16m-07/002r8, IEEE 802.16m System Requirements (Jan 2009). http://ieee802.org/ 16/tgm/index.html 36. F. Zou, X. Jiang, Z. Lin, IEEE 802.20 based broadband digital network – the infrastructure for m-commerce on the train, in: The 4th International Conference on Electronic Commerce (ICEB’04) (2004), pp. 771–776 37. IEEE 802.20 Working Group, System Requirements for IEEE 802.20 Mobile Broadband Wireless Access Systems – Version 14 (2004). http://grouper.ieee.org/groups/802/20/ Contribs/C802.20-05-65r1.pdf 38. http://standards.ieee.org/announcements/802.20approval.html 39. EETimes.com – Updated: IEEE 802.20 working group declares ‘cooling off’ period (15 June 2006) 40. IEEE-SA ADOPTS PLAN TO MOVE 802.20(TM) BROADBAND WIRELESS STANDARD FORWARD. http://standards.ieee.org/ announcements/ pr_80220plan.html 41. Media Statement from IEEE Standards Association Regarding the Status of the IEEE 802.20 Standard and Working Group. http://standards.ieee.org/announcements/802.20std_ status.html 42. IEEE P802.21/D00.03; Draft IEEE Standard for Local and, Metropolitan Area Networks: Media Independent Handover 43. IEEE P802.21/D01.00; Draft IEEE Standard for Local and Metropolitan Area Networks: Media Independent Handover Services (Mar 2006) 44. T. Al Mosawi, D. Wisely, H. Aghvami, A novel micro mobility solution based on media independent handover and SIP, in Proceedings of IEEE VTC2009-Fall – IEEE Semi Annual Vehicular Technology Conference, Anchorage, Alaska, USA, Sept 2009 45. C. Cordeiro, K. Challapali, D. Birru, S. Shankar, IEEE 802.22: the first worldwide wireless standard based on cognitive radios. New Frontiers in Dynamic Spectrum, DySPAN 2005 (2005) 46. IEEE 802.22 Working Group on Wireless Regional Area Networks. http://www.ieee802. org/22/ 47. IEEE 802.22 draft standard, IEEE P802.22 Wireless Regional Area Networks – Requirements (Jan 2006). http://www.ieee802.org/22/, doc. no. 22-05-0007-00-0000

Index

A Adaptive antenna systems (AAS), 446 Adaptive modulation and coding best server cells, 358–360 carrier-to-noise-plus-interference ratio, 358, 361 influence of, 354 maximum physical throughput in downlink, 354–356 histogram and cumulative histogram, 356–358 maximum received power, 354–355 propagation, Covilha district, 352–353 scenario, 350–352 Advanced encryption standard (AES), 218 Aghvami, A.H., 315, 365, 395 Alamouti code, 430–432 ArcGIS planning tool equipment characteristics, 345–346 LoS and NLoS, 346 received power and coverage, 346 service classes, 347–348 toolbar, 345 Architecture forum network reference model, 255–256 handover confirm (HO-CNF), 261 hard handover (HHO), 259 IEEE 802.21 media independent handover, 261–263 IEEE 802.16 reference model, 256–259 intra-ASN handover, 259, 260 mobility handover indication (MOB-HO-IND), 260, 261 mobility neighbor advertisement (MOB-NBR-ADV), 260 soft handover (SHO), 259

ARQ. See Automatic repeat request Authorization module, 205–206 Automatic repeat request (ARQ) blocks, 166–167 error control, 165–166 HARQ, 171–174 methodology block usage and rearrangement, 167–168 BSN comparison, 170 feedback information element (IE), 168–170 parameters, 170, 171 transmitter state machine, 170–171 B Backhaul networks, 32 Bandwidth, 193 Bandwidth allocation and request mechanisms grants, 177 polling, 178–183 requests, 176–177 SSs role, 175–176 Base station (BS), 198 Beamforming IEEE 802.16e-2005, AAS, 446 switched-beam antenna arrays, 444–446 Bell Labs Layered Space-Time (BLAST), 433 Best effort (BE), 195–196 Block turbo codes (BTCs), 102 Broadband access DSL technologies, 15–16 types, 13–15 wireless communication systems, 11–13 Broadband communications business, 397–398 Broadband wireless access

477

478 Broadband wireless access (cont.) licensed frequency bands, 23–24 license-exempt frequency bands, 24–25 Burst, 86 Burst frame, 86 Burst profiles, 86 Burst set, 86 Business models broadband communications business, 397–398 business plan development market planning, 400–404 market research, 398–400 services ranges classification, 404–405 Business plan development market planning capacity requirements, 401 capital expenditure (CapEx), 402–403 competitive analysis, 400 coverage requirements, 400 operating expenses (OpEx), 403–404 penetration, 402 market research financial and capital expenditure (CapEx), 400 spectrum, 399 target market characteristics, 398 technological parameters, 399

C Capital expenditure (CapEx) end-to-end network, 403 penetration curve, 402 Carrier-to-noise-plus-interference ratio (CNIR) co-channel reuse factor rcc without sub-channelisation, 335 with sub-channelisation, 336 with sub-channelisation and sectorization, 336–337 in downlink (DL), 358, 361 fractional frequency reuse, relay-based system, 343 vs. physical throughput without relays co-channel interference, 367–368 sectorization, 369 snap-shot simulations, 368 vs. physical throughput with relays assumptions, 373–374 DL scenarios, 374–377 formulation, 370–372 UL scenarios, 377–378

Index and supported physical throughput vs. achievable distance, 340–341 in downlink, 336 function of rcc, in UL with sub-channelisation, 336–337 with sub-channelisation and sectorization, 336–338, 340 in uplink, 335 without sub-channelisation and sectorization, 338–339 CCI. See Co-channel interference Cellular backhaul, 52–53 Cellular era, 5 Cellular planning interference-to-noise ratio and reuse pattern, 329–331 with sectorisation, 333 with sectorisation and subchannelisation, 333–334 with sub-channelisation, 331–332 without sub-channelisation, 328–329 signal-to-noise-plus-interference ratio, 326–328 simplified analysis, limitations, 325 Cipher-based message authentication code (CMAC), 219 CNIR. See Carrier-to-noise-plus-interference ratio Co-channel interference (CCI), 81, 317–318 Code division multiple access (CDMA), 6 Comissa´rio, C., 315 Common part sub-layer (CPS) addressing and connections, 150–151 mission, 150 PDU format, 151–152 Competitive analysis, 400 Concatenated Reed–Solomon convolutional code (RS-CC) AAS Systems, control mechanism, 110 bandwidth requesting, 110 block turbo codes (BTCs), 102 channel quality measurements, 110–111 frame structure and interleaving, 103 mandatory channel coding, 101, 102 mesh, 105–106 modulation, 103, 104 network control sub-frame, 106–108 pilot modulation, 103 point-to-multipoint (PtM), 104–105 power control, 110 ranging and initial ranging, control mechanism, 109–110

Index RS-CC encoding process, 102 synchronization, control mechanism, 108–109 Convergence/personalization era, 7–8 Costa, R., 315 Cost/revenue optimization hypothesis and assumptions with relays, 409–411 hypothesis without relays, 408–409 models cellular planning process, 406 system cost, 406–408 optimization and profit without relays, 411–416 optimization and profit with relays DL analysis with K ¼ 3 and K ¼ 1, 416–417 UL analysis with K ¼ 3 and K ¼ 1, 417–419 Coverage requirements, 400 Curado, M., 251 Curve fitting, 323 D Data carriers, 111 Data encryption methods AES in CCM mode, 220–221 DES in CBC mode, 219–220 IEEE 802.16e, 221 Data encryption standard (DES), 218 Digital subscriber line (DSL) vs. WIMAX, 452–454 Downlink channel descriptor (DCD), 86 Downlink interval usage codes (DIUCs), 86 Downlink MAP (DL MAP), 86–87 Downlink sub-carrier allocation semi-analytical evaluation distance calculation, 309 reuse one, reuse three and soft reuse, 306 propagation loss factors, 307–308 resource units (RU), 306, 307 signal-to-interference-and-noise ratio (SINR), 307 simulation evaluation effective exponential SIR mapping, 301 MATLAB simulations, 302 parameters, 304 partitioning reuse, 302, 303 soft reuse, 302 transmission time interval, 300–301 Downlink (DL) with relays BS to MS throughput, 387

479 BS to RS throughput, 387–388 RS to SS throughput, 388 DSL technologies, 15–16 Dynamic host configuration protocol (DHCP), 322 E Encryption algorithms, 218–219 ETSI. See European Telecommunications Standards Institute European Telecommunications Standards Institute (ETSI) HiperACCESS, 458 HiperMAN, 458–459 Evolution broadband access, 11–16 broadband wireless access, 23–25 fixed, portable, and mobile terminals, 59–60 fixed wireless access, 20–23 forum, 34–44 frequency band allocations, 45–47 personal broadband, 32–33 voice over IP (VoIP), 51–54 wireless broadband evolution, 17–19 wireless transmission history, 3–11 Evolution-Data only (EVDO), 464, 465 Extended rtps (Ertps), 196 Extensible authentication protocol (EAP), 248–249 F FDD. See Frequency division duplexing FDM. See Frequency division multiplexing Fifth generation (5G) communication technology, 2 Financial and capital expenditure (CapEx), 400 Fixed broadband wireless applications, 49–50 Fixed, portable, and mobile terminals base station (BS), 59 ecosystem, 59–60 Fixed wireless access mesh networks, 22–23 NLoS point-to-multipoint networks, 22 point-to-multipoint networks, 21 point-to-point networks, 20 Flash-OFDM, 460 Fractional frequency reuse, 343 Frame control header (FCH), 293 Frequency band allocations electromagnetic spectrum, 45 regions, 47 RF spectrum, 45

480 Frequency band allocations (cont.) unlicensed national information infrastructure (U-NII) band, 46 Frequency division duplexing (FDD), 317–318 Frequency division multiple access (FDMA), 5, 6 Frequency division multiplexing (FDM), 67–69 Frequency reuse pattern in downlink (DL) without subchannelisation, 329, 330 reuse co-channel factor, 329, 330 uplink (UL) with sectorisation, 333 with sectorisation and subchannelisation, 333–334 with sub-channelisation, 331–332 without sub-channelisation, 329–331 Fully used sub-carrier (FUSC), 294 G 3G, 213 General packet switched service (GPRS), 6 Geographic information systems (GIS), 318–319, 344 GIMCV. See Global information multimedia communication village GIS. See Geographic information systems Global information multimedia communication village (GIMCV), 10 H HARQ, 171–174 Hashed message authentication code (HMAC), 219 High performance radio access (HiperACCESS), 458–459 High performance radio metropolitan access network (HiperMAN), 458–459 High speed downlink packet access (HSDPA). See High speed packet access High speed packet access (HSPA) features, 464–465 smart antenna technology, 465–466 vs. WiMAX, EVDO, 465 WiMAX networks, 466–467 High-speed portable internet (HPi), 457 High-speed transmission technologies, 14–16 High speed uplink packet access (HSUPA). See High speed packet access Holland, O., 365, 395 HO preparation and conclusion

Index MIHF processing time, 284 mobile-initiated handover, 282 MS Ethernet connection, 282, 283 processing time, 282–283 Hypothesis and assumptions with relays, 409–411 Hypothesis without relays, 408–409 I iBURST wireless broadband technology, 459–460 IEEE 802.11, 454–456 IEEE 802.16 basic management connection, 158 management message format, 159–161 primary management connection, 158 secondary management connection, 159 IEEE 802.16-2004, 27, 317–318, 321–322 IEEE 802.20, 467, 469 IEEE 802.21, 469–471 IEEE 802.22, 471, 473 IEEE 802.16a, 26–27 IEEE 802.16e, 27–29 IEEE 802.16 evolution, 26 IEEE 802.16m, 467 IEEE 802.16 MAC Protocol base station (BS), 198 subscriber stations (SSs), 196, 197 time-division multiple access (TDMA), 196 IEEE 802.16 physical interface variants, 84–87 IEEE 802.16 physical layer, 84–87 IEEE 802.16 security architecture and functions, 216–218 data encryption methods AES in CCM mode, 220–221 DES in CBC mode, 219–220 IEEE 802.16e, 221 encryption algorithms, 218–219 key management protocol, 222–223 secure encapsulation of MPDUs, 218 Implicit function formulation, 379–381 Improved mobile telecommunications system (IMTS), 5 Interference-to-noise ratio and reuse pattern in DL without sub-channelisation, 329–330 in UL without sub-channelisation, 329–331 in UL with sectorisation, 333

Index in UL with sectorisation and sub-hannelisation, 333–334 in UL with sub-channelisation, 331–332 with sub-channelisation, 331 without sub-channelisation, 328–329 International Mobile Telecommunications (IMT) 2000, 460–461 International telecommunication union (ITU) classification, 48 IP connectivity stages, 189 IP multimedia subsystem (IMS), 266, 267 J Jitter, 193–194 K Key management authorisation key (AK) management BS usages, 241–243 node re-authorization, mesh mode, 244 TEK lifetime, 243 PKM version 2, 246–247 SS key usage AK, 244–245 reauthorization, 244 TEK, 245–246 L Landi, G., 251 Latency, 193 Link layer controller, 273–274 M MAC frame, 86 MAC management messages PKM request and response, 225 PtM topology, 238–240 security associations, 227–228 SS authorization AK encryption, 229–230 process, 228 request, 229 TEK exchange, 230–237 authorization state machine, 232–234 FSM description, 234–237 key exchange, 232 mesh mode, 232 PtM topology, 230–232 TEK state machine, 237–238 Market planning capacity requirements, 401 capital expenditure (CapEx)

481 end-to-end network, 403 penetration curve, 402 competitive analysis, 400 coverage requirements, 400 operating expenses (OpEx), 403–404 penetration, 402 Market research financial and capital expenditure (CapEx), 400 spectrum, 399 target market characteristics, 398 technological parameters 3.5 and 2.5 GHz frequency bands characteristics, 399 radio characteristics, 400 Matos, R., 251 Media independent command service (MICS), 470 Media independent event service (MIES), 470 Media independent handover (MIH) key elements, 470–471 session initiation protocol (SIP), 471 Media independent information service (MIIS), 470 Medium access control (MAC) layer automatic repeat request (ARQ) ARQ Blocks, 166–167 ARQ methodology, 167–171 error control, 165–166 HARQ, 171–174 bandwidth allocation and request mechanisms grants, 177 polling, 178–183 requests, 176–177 SSs role, 175–176 common part sub-layer (CPS) addressing and connections, 150–151 mission, 150 PDU format, 151–152 concatenation, 163–164 contention resolution, 183–185 convergence sub-layer (CS) connection ID (CID), 142–150 mission and functions, 140–142 CRC calculation, 164–165 encryption of, 165 fragmentation, 161–162 header formats generic MAC header, 152 header without payload, 152–155 IEEE 802.16 basic management connection, 158

482 management message format, 159–161 primary management connection, 158 secondary management connection, 159 network entry process authentication, 188 capabilities negotiation, 187–188 downlink channel synchronization, 186 initial ranging, 186–187 IP connectivity stages, 189 MAC management connections, 185, 186 registration, 188 transport connection creation, 189 packing, 162–163 protocol data unit (PDU), 139, 140 scheduling control, 174–175 service access point (SAP), 139 service data unit (SDU), 139, 151 sub-headers classificatiom, 156 special payload ordering, 156, 157 type field significance, 157 sub layers, 138–139 Mesh networks, 22–23 MIHF framework, 272–273 MIH transport mechanism, 285 MIHUs and link layer controllers, 267, 268 MM and CSC, 275–276 Mobile broadband wireless access (MBWA), 467, 469 Mobile FI, 467, 469 Mobility management architecture forum network reference model, 255–256 handover confirm (HO-CNF), 261 hard handover (HHO), 259 IEEE 802.21 Media Independent Handover, 261–263 IEEE 802.16 reference model, 256–259 intra-ASN handover, 259, 260 mobility handover indication (MOBHO-IND), 260, 261 mobility neighbor advertisement (MOB-NBR-ADV), 260 soft handover (SHO), 259 CSC_ASN, 266 generic transport internet signaling (GIST), 268 implementation link layer controller, 273–274 MIHF framework, 272–273 MM and CSC, 275–276

Index mobility, 277–279 QoS and MIH transport, 274–275 QoS signalling and resource reservation, 276–277 IP multimedia subsystem (IMS), 266, 267 MIHUs and link layer controllers, 267, 268 mobility manager (MM), 268 QoS aware mobility management inter-technology handovers, 269–271 mobility management, 265–269 SIP/SDP signaling, 266, 267 testbed evaluation handover process overview, 281 HO preparation and conclusion, 282–285 MIH transport mechanism, 285 mobility manager initialization, 282 MPDUs secure encapsulation, 218 MS Ethernet connection, 282, 283 Multiple antenna technology beamforming IEEE 802.16e-2005, AAS, 446 switched-beam antenna arrays, 444–446 closed loop MIMO, 426–427 collaborative spatial multiplexing, 435–436 diversity and array gain, 436–438 IEEE 802.16 standards, MIMO technology, 442–444 MIMO channel capacity, 427 MIMO OFDM, system model, 440–441 MIMO options comparison, 438–439 MIMO wireless transmission system, 425–426 multi-antenna implementation chart, 424 OFDM, 427–429 space diversity, 429 space-time coding (STC) Alamouti code, 430–432 second-order STC, 432 spatial multiplexing Bell Labs Layered Space-Time (BLAST), 433 vertical and horizontal encoding SM, 433–435 spatial multiplexing and diversity, trade-off, 447–448 Multiple input multiple output (MIMO) channel capacity, 427 IEEE 802.16 standards, 442–444 OFDM, system model, 440–441 options comparison, 438–439 wireless transmission system, 425–426

Index N Nazir, M.K., 365, 395 Network coverage area calculation, terrain conditions, 405–406 Network entry process authentication, 188 capabilities negotiation, 187–188 downlink channel synchronization, 186 initial ranging, 186–187 IP connectivity stages, 189 MAC management connections, 185, 186 registration, 188 transport connection creation, 189 Neves, P., 251 NLoS point-to-multipoint networks, 22 Non-real-time polling service (nrtPS), 195 Null carriers, 112 O Object model attributes, 199–201 conventions, 201 global service flow class name parameters, 201–203 global service flows, 201 service flow creation, 203–204 OFDMA. See Orthogonal frequency division multiplexing (OFDM) OFDMA system, 294 OFDM-based PHY layer, 55 Operating expenses (OpEx), 403–404 Optimization and profit with relays DL analysis with K ¼ 3 and K ¼ 1, 416–417 UL analysis with K ¼ 3 and K ¼ 1, 417–419 without relays, 411–416 Organisation for Economic Co-operation and Development (OECD) broadband subscriptions, 14–15 Orthogonal frequency division multiple access (OFDMA), 56 Orthogonal frequency division multiplexing (OFDM) advantages, 78–80 disadvantages co-channel interference (CCI), 81 peak to average power ratio (PAPR), 80–81 strict synchronization requirement, 80 frequency description, 74, 75 fundamentals

483 vs. frequency division multiplexing (FDM), 67–69 signal characteristics, 69–71 history and development applications, 67 evolution, 64–67 IEEE 802.16 physical layer interface variants, 84–87 supported frequency bands, 84 ISI and ICI mitigation cyclic prefix (CP), uses, 75, 76 symbol duration, 76 orthogonal frequency division modulation access (OFDMA) improvements, 77 subchannelization, 77–78 scalable parameters and principles, 81–83 reference model, 83 spectral efficiency, 77 symbol description, 74 symbol time structure, 74, 75 transmission concept, 71–72 demodulator, 73–74 serial to parallel conversion, 73 WirelessMAN-OFDMA PHY overview, 111–112 subcarrier allocation modes, 113–133 WirelessMAN-OFDM PHY channel coding, 99–101 concatenated Reed–Solomon convolutional code (RS-CC), 101–111 WirelessMAN-SC PHY downlink PHY, 91–97 FDD frame structure, 88 frame structure, 90 full duplex and H-FDD framing, 88, 89 overview, 87–88 TDD frame structure, 88, 89 uplink PHY, 97–99 P Packet convergence sub-layer (PCS), 145 Packet header suppression (PHS) mechanism, 142, 457 operation, 146–149 packet convergence sub-layer (PCS), 145 and rules, 145–146, 199–201 signalling, 149–150 Packet loss, 194

484

Index

PAPR. See Peak to average power ratio Partially used sub-carrier (PUSC), 294, 435–436 Payload, 86 Peak to average power ratio (PAPR), 80–81 Pentikousis, K., 251 Permutation formula, 123, 127 Personal broadband, 32–33 Pilot carriers, 111 Pilot modulation, 103 Pioneer era, 4 PKM version 2, 246–247 Planning platforms, fixed WiMAX framework and scenario, 344 wireless planning tool Beira Interior region, 350–351 Covilha˜ rural and urban areas, 348–350 functionalities and potentialities, 344–348 Plugfest, 38–40 Point-to-multipoint (PtM) networks, 21 Alvarion WiMAX equipment, 321–322 Point-to-point networks, 20 Polling multicast and broadcast, 179–182 PM bit, 182–183 unicast, 179, 180 Prasad, R., 1, 63, 137, 191, 215, 423, 451 Propagation models experimental results BreezeMAX duplexing frequency, 322–323 PtM Alvarion WiMAX equipment, 321–322 vs. SUI model, 324–325 SUI vs. modified Friis model AT&T wireless PL model, 319–320 basic terrain types, 320–321 Provisioning service flow, 198–199 service flow attributes, 199 PtM Alvarion WiMAX equipment, 321–322 PtM topology, 238–240

IP multimedia subsystem (IMS), 266, 267 MIHUs and link layer controllers, 267, 268 mobility manager (MM), 268 SIP/SDP signaling, 266, 267 QoS signalling and resource reservation, 276–277 Quality of service (QoS) authorization module, 205–206 classes best effort (BE), 195–196 extended rtps (Ertps), 196 non-real-time polling service (nrtPS), 195 real-time polling service (rtPS), 195 unsolicited grant service (UGS), 194–195 definition, 191 IEEE 802.16 MAC Protocol base station (BS), 198 subscriber stations (SSs), 196, 197 time-division multiple access (TDMA), 196 object model, 199–204 parameters bandwidth and latency, 193 jitter, 193–194 packet loss, 194 provisioning service flow, 198–199 service flow attributes, 199 service classes, 204–205 service flow creation dynamic service flow creation, 209–210 dynamic service flow modification and deletion, 210–214 three-way handshaking protocol, 208–209 service flow types active service flow, 207–208 admitted service flow, 207 provisioned service flow, 206–207

Q QoS and MIH transport, 274–275 QoS aware mobility management CSC_ASN, 266 generic transport internet signaling (GIST), 268 inter-technology handovers hand-over preparation phase, 271 service flows, 270 SS and BS, 269–271

R Radio and network planning cellular coverage, 316 cellular planning CNIR and supported throughput, 334–342 frequency reuse, relay-based system, 343 interference-to-noise ratio and reuse pattern, 328–334

Index limitations of simplified analysis, 325 signal-to-noise-plus-interference ratio, 326–328 co-channel interference, 317–318 frequency division duplexing (FDD), 317 geographic information systems (GIS), 318–319 planning platforms adaptive modulation and coding schemes, 351–361 cost/revenue optimisation, 360–362 framework and scenario, 344 wireless planning tool, 344–351 point-to-multipoint (PtM) network, 317–318 propagation models experimental results, 321–325 SUI vs. modified Friis model, 319–321 Radio resource management (RRM) algorithms maximum C/I, 299–300 proportional fair (PF), 300 reuse-one, 296 reuse-three, 296–297 soft re-use, 297–299 definition, 293–294 downlink sub-carrier allocation semi-analytical evaluation, 305–310 simulation evaluation, 300–305 problem base stations (BS), 290 objective functions, 292 power and rate assignments, 293 radio link gains, 290–291 semi-analytical and simulation results, 310–312 Real-time polling service (rtPS), 195 Receive transition gaps (RTG), 293 Resource unit (RU), 293–313 Reuse-one, 296 Reuse-three, 296–297 RF spectrum, 45 Rivest Shamir Adleman (RSA), 218 Robalo, D., 315, 365, 395 Rodrigues, A., 315 RS-CC encoding process, 102 S Sargento, S., 251 Sebastia˜o, P., 315

485 Sectorization, 317, 325, 332–334, 336, 338–340, 342, 362, 367, 369, 382, 386, 390–391 Security sublayer authentication protocol PKM EAP authentication, 224 RSA authentication, 223–224 IEEE 802.16 architecture and functions, 216–218 data encryption methods, 219–221 encryption algorithms, 218–219 key management protocol, 222–223 secure encapsulation of MPDUs, 218 key management authorisation key (AK) management, 240–244 PKM version 2, 246–247 SS key usage, 244–246 MAC management messages PKM request and response, 225 PtM topology, 238–240 security associations, 227–228 SS authorization, 228–230 TEK exchange, 230–237 TEK state machine, 237–238 network aspects of security extensible authentication protocol (EAP), 248–249 radius, 248 PKM protocol, 224 Service classes, 204–205 Service classifications, 404–405 Service flow creation dynamic service deletion comparison, 212–213 3G, 213 SS and BS initiated, 212 Wi-Fi, 213–214 dynamic service flow creation BS Initiated, 210 SS initiated, 209–210 dynamic service flow modification, 210–211 three-way handshaking protocol, 208–209 Services ranges classification, 404–405 terrain conditions, 405–406 Session initiation protocol (SIP), 471 Signal-to-interference and noise ratio (SINR), 73, 291, 295, 300, 301, 326–328, 335, 382, 444 Simulation evaluation effective exponential SIR mapping, 301

486 Simulation evaluation (cont.) MATLAB simulations, 302 parameters, 304 partitioning reuse, 302, 303 soft reuse, 302 transmission time interval, 300–301 SIP/SDP signaling, 266, 267 Soft re-use, 297–299 Sousa, B., 251 Space diversity, 429 Space-time coding (STC) Alamouti code, 430–432 second-order STC, 432 Spatial multiplexing Bell Labs Layered Space-Time (BLAST), 433 and diversity, 447–448 vertical and horizontal encoding SM, 433–435 SS key usage AK, 244–245 reauthorization, 244 TEK, 245–246 Stanford University Interim (SUI) models basic terrain types, 320 empirical models, 319–320 parameters, 320–321 Subcarrier allocation modes adjacent subcarrier permutation, 127–128 bit interleaving, 132 channel coding, 131 data randomization, 131 distributed and adjacent comparison, 113, 114 permutation, 113 downlink and uplink, algorithms, 119 encoding, 132 FUSC, symbol structure, 123–124 multiple subcarrier allocation zones, 115 OFDMA frame, 114–115 OFDMA ranging, 129–131 PUSC downlink subchannels, 122–123, 124–127 symbol structure, 119–122 UL, 127 ranging codes, 131 repetition process, 132–133 time frequency mapping, 116–118 Sub-channelisation, 77–78, 294, 316, 325, 328–330, 333–335, 340–342, 362, 369, 382, 389–390, 392 Subscriber stations (SSs), 196, 197

Index SUI. See Stanford University Interim models Supported physical throughput vs. achievable distance, 340–341 DL with relays, 387–388 in downlink, 336 function of rcc, in UL with subchannelisation, 336–337 implicit function formulation, 378–381 with sub-channelisation and sectorization, 336–338, 340 sub-channelisation, usage, 389–390 UL with relays and K ¼ 3, 388–389 in uplink, 335 without relays, 381–387 without sub-channelisation and sectorization, 338–339 Switched-beam antenna arrays, 444–446 System capacity CNIR vs. physical throughput without relays co-channel interference, 367–368 sectorization, 369 snap-shot simulations, 368 CNIR vs. physical throughput with relays assumptions, 372–374 DL scenarios, 374–376 formulation, 370–372 UL scenarios, 377–378 GIS cellular planning tools, 392 supported physical throughput DL with relays, 387–388 implicit function formulation, 378–381 sub-channelisation, usage, 389–390 UL with relays and K ¼ 3, 388–389 without relays, 381–387 throughput with sectorization, relays and K ¼ 1, 390–391 tri-sectored BS antennas, 370, 393 T Terrain conditions, network coverage area calculation, 405–406 Testbed evaluation handover process overview, 281 HO preparation and conclusion MIHF processing time, 284 mobile-initiated handover, 282 MS Ethernet connection, 282, 283 processing time, 282–283 MIH transport mechanism, 285 mobility manager initialization, 282 Third generation (3G) standards 3GPP, 461–462

Index 3GPP2 capabilities, 464 CDMA family, 463 evolution-data only (EVDO), 464 mobile WiMAX vs. 3GPP-LTE, 463 technical specification, 462–463 IMT 2000, 460–461 Time division duplex (TDD), 293 Time-division multiple access (TDMA), 196 Traffic encryption keys (TEK) BS usage, 243 exchange authorization state machine, 232–234 FSM description, 234–237 key exchange, 232 mesh mode, 232 PtM topology, 230–232 lifetime, 243 PtM topology, 238–240 SS usage, 245–246 state machine, 237–238 Trans-Atlantic wireless service, 4 Transmission time intervals (TTI), 294 Transmit transition gaps (TTG), 293 U Unlicensed national information infrastructure (U-NII) band, 46 Unsolicited grant service (UGS), 194–195 Uplink channel descriptor (UCD), 86 Uplink interval usage codes (UIUCs), 86 Uplink MAP (UL MAP), 87 Uplink partial usage of subchannels (UL PUSC), 435–436 Uplink (UL) with relays and K ¼ 3 RS to BS throughput, 389 SS to BS throughput, 388–389 SS to RS throughput, 389 V Velez, F.J., 1, 63, 137, 191, 215, 315, 365, 395, 423, 451 Voice over IP (VoIP) applications and missions, 51–52 business users, 53–54 cellular backhaul, 52–53 municipal and law enforcement, 54 real-time applications, 50 rural connectivity, 53 Wi-Fi backhaul, 52

487 W Wi-Fi. See Wireless-fidelity networks WiMAX Forum certification roadmap, 41–42 certified products, 44 certified program milestones, 41 vs. IEEE 802.16, 34 industry standard and certified products, benefits, 42–44 members, 34–35 products certification, 35–40 working groups, 35 Winprop™, 319 Wireless broadband (WiBro) high-speed portable internet (HPi), 457 vs. PHY IEEE 802.16, 457–458 Wireless broadband evolution first generation, 17–18 global standard based, 19 narrowband, 17 second generation, 18–19 Wireless communication systems, 11–13 Wireless-fidelity (Wi-Fi) networks backhaul, 52 dynamic service flow modification and deletion, 213–214 IEEE 802.11 WLAN standard, 454–456 QoS, 457 vs. WiMAX, 456–457 WirelessHUMAN, 85 Wireless Innovative System for Dynamic Operating Megacommunications (WISDOM), 7, 8 Wireless MAN-OFDMA PHY, 85 WirelessMAN-OFDM PHY, 85 WirelessMAN-SCa PHY, 85 WirelessMAN-SC PHY, 85 downlink PHY channel encodings, 93–94 FDD downlink sub-frame structure, 92, 93 multilevel modulation, 96–97 receive transition gap (RTG), 92 TDD downlink sub-frame, 91, 92 transmission convergence sub-layer, 94–96 FDD frame structure, 88 frame structure, 90 full duplex and H-FDD framing, 88, 89 overview, 87–88 TDD frame structure, 88, 89 uplink PHY channel quality measurements, 99

488 sub-frame, 97–98 sub-layer, 98 Wireless metropolitan area network (WMAN), 32 Wireless planning tool Beira Interior region, 350–351 Covilha˜ rural and urban areas coverage and interference areas, 349–350 LoS coverage, 348 omnidirectional and sectorial antennas, 349 functionalities and potentialities ArcGIS toolbar, 345–347 service classes, 347–348 Wireless regional area network (WRAN), 471–473 Wireless standards advantages over DSL access network types, 453 WiMAX vs. xDSL, 454 ETSI HiperACCESS, 458–459 ETSI HiperMAN, 458–459 flash-OFDM, 460 3G standards 3G partnership project 2 (3GPP2), 462–464 3G partnership project (3GPP), 461–462 IMT-2000, 460–461 HSDPA and HSUPA design features, 465 roadmap, mobile WiMAX and 3G–LTE, 466–467 smart antenna technology, 465–466 W-CDMA network, 466 vs. WiMAX, EVDO, 465 iBURST, 459–460

Index IEEE 802.22, 471, 473 IEEE 802.21 and media independent handover, 469–471 IEEE 802.16m and IMT-advanced, 467–468 IEEE 802.20/mobile FI, 467, 469 vs. wide-and broadband technologies, 452 wireless broadband (WiBro) high-speed portable internet (HPi), 457 vs. PHY IEEE 802.16, 457–458 wireless broadband technologies, comparison, 472–473 wireless fidelity (Wi-Fi) IEEE 802.11 WLAN standard, 454–456 QoS, 457 vs. WiMAX, 456–457 Wireless transmission history cellular era, 5 code division multiple access (CDMA), 6 convergence/personalization era and elements, 7–9 frequency division multiple access (FDMA), 5, 6 general packet switched service (GPRS), 6 GIMCV networks applications, 11 global information multimedia communication village (GIMCV), 10 improved mobile telecommunications system (IMTS), 5 narrowband, 6 periods, 3–4 pioneer era, 4 pipeline, 6 1 Tb/s wireless aggregation examples, 9–10 trans-Atlantic wireless service, 4 WISDOM, 7–9