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`.m2e9aDI
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`73.1
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`Paw S.
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`OFDM for Wireless Multimedia
`
`Communications
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`For a listing of recent titles in the Arteck House Universal Personal Communications
`Series, turn to the back of this book.
`
`Page 5 of 137
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`OFDM for Wireless Multimedia
`
`Communications
`
`Richard van Nee
`
`Ramjee Prasad
`
`H4
`
`Artech House
`
`Boston - London
`
`Page 6 of 137
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`

`
`Library of Congress Cataloging—in—Publication Data
`van Nee, Richard.
`OFDM for wireless multimedia communications / Richard van Nee, Ramjee Prasad.
`p. cm. — (Artech House universal personal communications library)
`Includes bibliographical references and index.
`ISBN 0-89006-530-6 (alk. paper)
`1. Wireless communication systems. 2. Multimedia systems. 3. Multiplexing.
`I. Prasad, Ramjee. II. Title. III. Series.
`
`I TK5103.2.N44 2000
`621 .3845—dc21
`
`99-052312
`CIP
`
`British Library Cataloguing in Publication Data
`van Nee, Richard
`OFDM for wireless multimedia communications. — (Artech House
`universal personal communications library)
`1.Wireless communication systems 2. Multimedia systems
`I. Title II. Prasad, Ramjee
`6213,82
`'
`
`ISBN 0-89006-530-6
`
`Cover design by Igor Valdman
`
`© 2000 Richard van Nee and Rarnjee Prasad
`
`All rights reserved. Printed and bound in the United States of America. No part of this book
`may be reproduced or utilized in any form or by any means, electronic or mechanical, includ-
`ing photocopying, recording, or by any information storage and retrieval system, without per-
`mission in writing from the authors.
`’
`All terms mentioned in this book that are known to be trademarks or service marks have
`been appropriately capitalized. Artech House cannot attest to the accuracy of this informa-
`tion. Use of a term in this book should not be regarded as affecting the validity of any trade—
`mark or service mark.
`‘
`
`International Standard Book Number: 0-89006-530-6
`Library of Congress Catalog Card Number: 99-052312
`
`109876543
`
`Page 7 of 137
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`Page 7 of 137
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`

`
`To my wife Iris, to our son Floris, to our daughters Roselinde and Mirrelijn, and to our
`newly born baby
`~—Richard van Nee
`
`To my wife Jyoti, to our daughter Neeli, and to our sons Anand and Rajeev
`—Ramjee Prasad
`
`Page 8 of 137
`
`Page 8 of 137
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`

`
`Contents
`
`Preface
`
`Acknowledgments
`
`Chapter 1
`
`Introduction
`
`1.1
`
`1.2
`
`Standardization and Frequency Bands
`
`Multimedia Communications
`
`1.2.1
`
`The Need for High Data Rates
`
`1.2.2
`
`Services and Applications
`
`1.2.3 Antennas and Batteries
`
`1.2.4
`
`Safety Considerations
`
`1.2.5 ATM-Based Wireless (Mobile) Broadband
`
`Multimedia Systems
`
`1.3
`
`Multipath Propagation
`
`1.3.1 Multipath Channel Models
`
`1.3.2 Delay Spread Values
`
`Time Variation of the Channel
`
`History of OFDM
`
`Preview of the Book
`
`1.4
`
`1.5
`
`1.6
`
`References
`
`Chapter 2
`
`OFDM Basics
`
`A
`
`2.1
`
`2.2
`
`2.3
`
`2.4
`
`2.5
`
`2.6
`
`2.7
`
`Introduction
`
`Generation of Subcarriers using the IFFT
`
`Guard Time and Cyclic Extension
`
`Windowing
`
`Choice of OFDM Parameters
`
`OFDM Signal Processing
`
`Implementation Complexity of OFDM Versus
`Single Carrier Modulation
`
`Xiii
`
`XVii
`
`1
`
`4
`
`7
`
`8
`
`9
`
`9
`
`10
`
`12
`
`15
`
`16
`
`17
`
`19
`
`20
`
`24
`
`25
`
`33
`
`33
`
`33
`
`39
`
`42
`
`46
`
`47
`
`48
`
`vii
`
`Page 9 of 137
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`Page 9 of 137
`
`

`
`viii
`
`References
`
`Chapter 3
`
`Coding and Modulation
`
`3.1
`
`3 .2
`
`3.3
`
`3.4
`
`3.5
`
`Introduction
`
`Forward Error Correction Coding
`
`3.2.1 Block Codes
`
`3.2.2 Convolutional Codes
`
`3.2.3 Concatenated Codes
`
`Interleaving
`
`Quadrature Amplitude Modulation
`
`Coded Modulation
`
`References
`
`Chapter 4
`
`Synchronization
`
`4.1
`
`4.2
`
`4.3
`
`4.4
`
`4.5
`
`4.6
`
`4.7
`
`References
`
`Introduction
`
`Sensitivity to Phase Noise
`
`Sensitivity to Frequency Offset
`
`Sensitivity to Timing Errors
`
`Synchronization using the Cyclic Extension
`
`Synchronization using Special Training Symbols
`
`Optimum Timing in the Presence of Multipath
`
`Chapter 5
`
`Coherent and Differential Detection
`
`5.1
`
`5.2
`
`Introduction
`
`Coherent Detection
`
`5.2.1 Two Dimensional Channel Estimators
`
`5.2.2 One Dimensional Channel Estimators
`
`5.2.3
`
`Special Training Symbols
`
`5.2.4 Decision Directed Channel Estimation
`
`5.3
`
`Differential Detection
`
`5.3.1 Differential Detection in the Time Domain
`
`51
`
`53
`
`53
`
`54
`
`54
`
`55
`
`58
`
`59
`
`60
`
`62
`
`70
`
`73
`
`73
`
`74
`
`77
`
`78
`
`80
`
`86
`
`88
`
`92
`
`95
`
`95
`
`95
`
`96
`
`103
`
`104
`
`106
`
`107
`
`107
`
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`

`
`ix
`
`5.3.2 Differential Detection in the Frequency Domain
`
`5.3.3 Differential Amplitude and Phase Shift Keying
`
`References
`
`Chapter 6
`
`The Peak Power Problem
`
`6. 1
`
`6.2
`
`6.3
`
`6.4
`
`6.5
`
`Introduction
`
`Distribution of the Peak—to—Average Power Ratio
`
`Clipping and Peak Windowing
`
`6.3.1 Required Backoff with a Non-Ideal Power Amplifier
`
`6.3.2 Coding and Scrambling
`
`Peak Cancellation
`
`PAP Reduction Codes
`
`6.5.1 Generating Complementary Codes
`
`6.5.2 Minimum Distance of Complementary Codes
`
`6.5.3 Maximum Likelihood Decoding of Complementary Codes
`
`6.5.4 Suboptimum Decoding of Complementary Codes
`
`6.5.5 Large Code Lengths
`
`6.6
`
`SYMBOL Scrambling
`
`References
`
`Chapter 7
`
`Basics of CDMA
`
`7. 1
`
`7.2
`
`7.3
`
`Introduction
`
`CDMA: Past, Present, and Future
`
`CDMA Concepts
`
`7.3.1
`
`Pure CDMA
`
`7.4
`
`Basic DS-CDMA Elements
`
`7.4.1 RAKE Receiver
`
`7.4.2 Power Control
`
`7.4.3
`
`Soft Handover
`
`7.4.4
`
`Interfrequency Handover
`
`7.4.5 Multiuser Detection
`
`6
`
`112
`
`115
`
`1 17
`
`119
`
`1 19
`
`120
`
`123
`
`127
`
`130
`
`131
`
`138
`
`141
`
`144
`
`145
`
`147
`
`150
`
`150
`
`153
`
`155
`
`15 5
`
`156
`
`157
`
`161
`
`171
`
`171
`
`172
`
`173
`
`175
`
`175
`
`Page 11 of 137
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`

`
`References
`
`Chapter 8
`
`Multi — Carrier CDMA
`
`8.1
`
`8.2
`
`8.3
`
`8.4
`
`8.5
`
`Introduction
`
`Channel Model
`
`DS—CDMA and MC—CDMA Systems
`
`8.3.1 DS—CDMA System
`
`8.3.2 MC—CDMA System
`
`MC—CDMA System Design
`
`BEP LOWER Bound
`
`8.5.1 DS—CDMA System
`
`8.5.2 MC—CDMA System
`
`8.5.3 BEP Lower Bound Equivalence
`
`8.6
`
`Numerical Results
`
`8.6.1 MC~CDMA System Design
`
`8.6.2 Down — Link BEP Performance
`
`8.6.3 Up - Link BER Performance
`
`8 .7
`
`Conclusions
`
`Appendix 8A
`
`References
`
`Chapter 9
`
`Orthogonal Frequency Division Multiple Access
`
`9.1
`
`9.2
`
`9.3
`
`9.4
`
`Introduction
`
`Frequency Hopping OFDMA
`
`Differences between OFDMA and MC—CDMA
`
`OFDMA System Description
`
`9.4.1
`
`Channel Coding
`
`9.4.2
`
`Modulation
`
`9.4.3
`
`9.4.4
`
`9.4.5
`
`Time and Frequency Synchronization
`
`Initial Modulation Timing Synchronization
`
`Initial Frequency Offset Synchronization
`
`176
`
`179
`
`179
`
`180
`
`182
`
`182
`
`185
`
`189
`
`194
`
`194
`
`195
`
`196
`
`197
`
`197
`
`199
`
`203
`
`206
`
`208
`
`209
`
`213
`
`213
`
`213
`
`215
`
`217
`
`220
`
`220
`
`221
`
`221
`
`222
`
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`

`
`9.4.6
`
`Synchronization Accuracy
`
`9.4.7
`
`Power Control
`
`9.4.8 Random Frequency Hopping Operation
`
`9.4.9 Dynamic Channel Allocation (Fast DCA)
`
`9.4.10 Dynamic Channel Allocation ( Simple DCA )
`
`9.4.11 Capacity of OFDMA
`
`9.5
`
`Conclusions
`
`References
`
`V
`
`Chapter 10
`
`Applications of OFDM
`
`10.1
`
`Introduction
`
`10.2
`
`10.3
`
`10.4
`
`Digital Audio Broadcasting
`
`Terrestrial Digital Video Broadcasting
`
`Magic WAND
`
`10.4.1 Magic WAND Physical Layer
`
`10.4.2 Coding
`
`10.4.3 Simulated Error Probabilities
`
`10.4.4 Effects of Clipping
`
`10.4.5 Magic WAND Medium Access Control Layer
`
`xi
`
`222
`
`223
`
`224
`
`225
`
`227
`
`227
`
`227
`
`228
`
`229
`
`229
`
`229
`
`231 p
`
`233
`
`234
`
`.
`
`236
`
`236
`
`237
`
`238
`
`10.5
`
`IEEE 802.11, HIPERLAN/2, and MMAC Wireless LAN Standards
`
`241
`
`10.5.1 OFDM Parameters
`
`10.5.2 Channelization
`
`10.5.3 OFDM Signal Processing
`
`10.5.4 Training
`
`10.5.5 Differences between IEEE 802.11, HIPERLAN/2
`and MMAC
`
`10.5.6 Simulation Results
`
`References
`
`About the Authors
`
`Index
`
`243
`
`244
`
`245
`
`246
`
`249
`
`250
`
`252
`
`255
`
`257
`
`Page 13 of 137
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`Page 13 of 137
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`

`
`Preface
`
`sarva-dvciresu dehe ’smz'n
`prakc'1's'a upajciyate
`jfifinam yadci radii vidycid
`vivrddham satzvam ity uta
`
`The manifestations of the mode of goodness can be experienced when all
`the gates of the body are illuminated by knowledge
`
`The Bhagavad Gita (14.11)
`
`During the joint supervision of a Master’s thesis “The Peak-to-Average Power Ratio of
`OFDM,” of Amout de Wild from Delft University of Technology, The Netherlands, we
`realized that there was a shortage of technical information on orthogonal frequency division
`multiplexing (OFDM)
`in a
`single reference. Therefore, we decided to write
`a
`comprehensive introduction to OFDM. This is the first book to give a broad treatment to
`OFDM for mobile multimedia communications. Until now, no such book was available in
`the market. We have attempted to fill this gap in the literature.
`
`Currently, OFDM is of great interest by the researchers in the Universities and
`research laboratories all over the world. OFDM has already been accepted for the new
`wireless local area network standards from IEEE 802.11, High Performance Local Area
`Network type 2 (HIPERLAN/2) and Mobile Multimedia Access Communication (MMAC)
`Systems. Also,
`it
`is expected to be used for
`the wireless broadband multimedia
`communications.
`
`xi“
`
`Page 14 of 137
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`Page 14 of 137
`
`

`
`xiv
`
`OFDM for Wireless Multimedia Communications is the first book to take a
`comprehensive look at OFDM, providing the design guidelines one needs to maximize
`benefits from this important new technology. The book gives engineers a solid base for
`assessing the performance of wireless OFDM systems. It describes the new OFDM-based
`wireless LAN standards; examines the basics of direct-sequence and frequency-hopping
`CDMA, helpful in understanding combinations of OFDM and CDMA. It also looks at
`applications of OFDM, including digital audio and video broadcasting, and wireless ATM.
`Loaded with essential
`figures
`and equations,
`it
`is
`a must-have
`for practicing
`communications engineers,
`researchers, academics, and students of communications
`technology.
`
`introduction to wireless broadband multimedia
`Chapter’ 1 presents a general
`communication systems (WBMCS), multipath propagation, and the history of OFDM. A
`part of this chapter is based on the contributions of Luis Correia from the Technical
`University of Lisbon, Portugal, Anand Raghawa Prasad from Lucent Technologies, and
`Hiroshi Harada from the Communications Research Laboratory, Ministry of Posts and
`Telecommunications, Yokosuka, Japan.
`
`Chapters 2 to 5 deal with the basic knowledge of OFDM including modulation and
`coding, synchronization, and channel estimation, that every post-graduate student as well as
`practicing engineers must learn. Chapter 2 contains contributions of Rob Kopmeiners from
`Lucent Technologies on the FFT design.
`
`Chapter 6 describes the peak-to—average power problem, as well as several solutions
`to it. It is partly based on the contribution of Arnout de Wild.
`
`Basic principles of CDMA are discussed in Chapter 7 to understand multi carrier
`CDMA and frequency-hopping OFDMA, which are described in Chapters 8 and 9. Chapter
`8 is based on the research contributions from Shinsuke Hara from the University of Osaka,
`Japan, a postdoctoral student at Delft University of Technology during 1995-96. Chapter 9
`is based on a UMTS proposal, with main contributions of Ralf Bohnke from Sony,
`Germany, David Bhatoolaul and Magnus Sandell from Lucent Technologies, Matthias
`Wahlquist from Telia Research, Sweden, and Jan-J aap van de Beek from Lulea University,
`Sweden.
`
`Chapter 10 was witten from the viewpoint of top technocrats from industries,
`government departments, and policy-making bodies. It describes several applications of
`OFDM, with the main focus on wireless ATM in the Magic WAND project, and the new
`wireless LAN standards for the 5 GHZ band from IEEE 802.11, HIPERLAN/2 and MMAC.
`
`It is partly based on contributions from Geert Awater from Lucent Technologies, and
`Masahiro Morikura and Hitoshi Takanashi from NTT in Japan and California, respectively.
`
`Page 15 of 137
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`Page 15 of 137
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`

`
`XV
`
`We have tried our best to make each chapter quite complete in itself. This book will
`help generate many new research problems and solutions for future mobile multimedia
`communications. We cannot claim that this book is errorless. Any remarks to improve the
`text and correct any errors would be highly appreciated.
`T
`
`Page 16 of 137
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`Page 16 of 137
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`

`
`Acknowledgments
`
`The material in this book originates from several projects at Lucent Technologies and
`research activities at Delft University of Technology, The Netherlands. A great deal of
`OFDM-knowledge was acquired during the Magic WAND project,
`in which several
`companies jointly managed to build a wireless ATM network demonstrator based on
`OFDM. We wish to thank all Magic WAND members who were involved in the design of
`the OFDM modem,
`in particular Geert Awater, James Hopper, Rob Kopmeiners, Erik
`Busking, Han Schmitz, Theo Kleijne, Martin J anssen, Jan Kruys, Urs Bernhard, Urs Lott,
`Alex Grant, James Aldis, Thomas Mark, Rodolfo Mannpelz, and Ari Vaisanen. Another
`fruitful source of information was the OFDM-based proposal for UMTS, with main
`contributions coming from Ralf Bohnke, David Bhatoolaul, Magnus Sandell, and J an-J aap
`van de Beek.
`
`Richard wishes to thank Masahiro Morikura and Hitoshi Takanashi for all their
`contributions and the pleasant cooperation on the joint OFDM proposal for the IEEE
`802.11 wireless LAN standard. All members of IEEE 802.11 and HiperLAN/2 are thanked
`for numerous contributions, that greatly improved the quality of the final standards and
`helped to gain more insight in various OFDM techniques.
`
`Geert Awater and Rob Kopmeiners made contributions and corrected numerous
`mistakes. Neeli Rashmi Prasad helped to prepare the complete manuscript, freeing us from
`the enormous burden of editorial requirements. Shinsuke Hara from the University of
`Osaka, Japan, Hiroshi Harada from the Communications Research Laboratory, Ministry of
`Posts and Telecommunications, Yokosuka, Japan, Luis Correia from the Technical
`University of Lisbon, Portugal, Anand Raghawa Prasad from Lucent Technologies, and
`Amout de Wild from Siemens, The Netherlands, are deeply acknowledged for their
`valuable contributions.
`
`After the Magic WAND project, we studied several OFDM options for new high-
`rate wireless LAN products. A circle was completed by the selection of OFDM for the high
`rate extension of the IEEE 802.11 wireless LAN standard in July 1998. We hope this book
`will help to gain insight in the principles and design of OFDM-based systems, in particular
`the new OFDM-based wireless LAN standards.
`
`Richard van Nee
`
`Ramjee Prasad
`October I 999
`
`XV“
`
`Page 17 of 137
`
`Page 17 of 137
`
`

`
`Chapter 1
`
`Introduction
`
`The spectacular growth of video, voice, and data communication over the Internet, and
`the equally rapid pervasion of mobile telephony, justify great expectations for mobile
`multimedia. Research and development are taking place all over the world to define the
`next generation of wireless broadband multimedia communications systems (WBMCS)
`that may create the “global information village.” Figure 1.1 illustrates the basic concept
`of the global information village, which consists of various components at different
`scales ranging from global to picocellular size. As we know, the demand for wireless
`(mobile)
`communications
`and Intemet/multimedia communications
`is growing
`exponentially. Therefore,
`it
`is imperative that both wireless and Intemet/multimedia
`should be brought together. Thus, in the near future, wireless Internet Protocol (IP) and
`wireless asynchronous transfer mode (ATM) will play an important role in the
`development of WBMCS.
`
`While present communications systems are primarily designed for one specific
`application, such as speech on a mobile telephone or high—rate data in a wireless local
`area network (LAN), the next generation of WBMCS will integrate various functions ’
`and applications. WBMCS is expected to provide its users with customer premises
`services that have information rates exceeding 2 Mbps. Supporting such large data rates
`with sufficient robustness to radio channel impairments, requires careful choosing of
`modulation technique. Themost suitable modulation choice seems to be orthogonal
`frequency division multiplexing (OFDM). Before going into the details of OFDM,
`however, first we give some background information on the systems that will be using
`it.
`
`The theme of WBMCS is to provide its users a means of radio access to
`broadband services supported on customer premises networks or offered directly by
`public fixed networks. WBMCS will provide a mobile/movable wireless extension to
`
`1
`
`Page 18 of 137
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`Page 18 of 137
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`

`
`
`1;‘ ug
`
`National and
`
`
`
`International Z0n¢S_
`
`Macrocells:
`
`I Subllrban
`I Reglonal
`I National
`
`Global information
`village
`
`Wireless access to
`Internet/multimedia
`
`E
`
`
`Server
`
`..,»
`
`Microcells.
`' City-centers
`' HighWaYS
`
`
`
`Wireless LAN
`
`Figure 1.1 Global information village.
`
`WBMCS is under investigation in North America, Europe, and Japan in the
`microwave and millimeter—wave bands to accommodate the necessary bandwidth. The
`research in the field of WBMCS has drawn much attention because of the increasing role
`of multimedia and computer applications in communications. There is a major thrust in
`three research areas: (1) microwave and millimeter-wave bands for fixed access in
`outdoor, public commercial networks, (2) evolution of WLAN for inbuilding systems,
`and (3) use of LAN technology outdoors rather than indoors. In short, WBMCS will
`provide novel multimedia and video mobile communications services, also related to
`wireless customer premises network (WCPN) and wireless local loop (WLL).
`
`To implement the wireless broadband communication systems, the following
`challenges must be considered:
`
`Frequency allocation and selection;
`
`Channel characterization;
`
`Application and environment recognition, including health hazard issues;
`Technology development;
`Air interface multiple access techniques;
`
`Protocols and networks; and
`
`Systems development with efiicient modulation, coding, and smart antenna
`techniques.
`
`Page 19 of 137
`
`Page 19 of 137
`
`

`
`0
`
`0
`
`Protocols and networks; and
`
`Systems development with efficient modulation, coding, and smart antenna
`techniques.
`
`A significant number of research and development (R&D) projects are set up in
`the area of WBMCS. Within the European Advanced Communication Technologies
`and Services (ACTS) program are four European Union—funded R&D projects, namely
`Magic Wand (Wireless ATM Network Demonstrator), ATM Wireless Access
`Communication System (AWACS), System for Advanced Mobile Broadband
`Applications (SAMBA), and wireless broadband CPN/LAN for professional and
`
`residential multimedia applications (MEDIAN)
`European projects [11].
`
`[1—17]. Table 1.1 summarizes the
`
`In the United States, seamless wireless network (SWAN) and broadband
`adaptive homing ATM architecture (BAHAMA), as well as two major projects in Bell
`Laboratories and a wireless ATM network (WATMnet), are being developed in the
`computer and communications
`(C&C)
`research laboratories of Nippon Electric
`
`Company (NEC) in the United States [2—6].
`
`In Japan, Communication Research Laboratory (CRL) is working on several
`R&D projects, such as a broadband mobile communication system in the super high
`frequency (SHF) band (from 3 to 10 GHz) with a channel bit rate up to 10 Mbps and an
`indoor high speed WLAN in SHF band with a target bit rate of up to 155 Mbps [12].
`
`In the Netherlands, Delft University of Technology has been busy with a multi-
`disciplinary research project, “Mobile Multimedia Communication (MMC),” since
`April 1996. The team consists of experts from the telecommunications and traffic
`control and information theory groups of the department of Electrical Engineering, the
`Product Ergonomics group of the department of Industrial Design Engineering, and the
`Organizational Psychology group of the department of Technology and Society.
`
`The MMC has the following objectives to achieve at 60 GHz:
`
`0 Wireless access of 155 Mbps using OFDM;
`
`0
`
`0
`
`Both indoor and outdoor use;
`
`Less complex, inexpensive mobile stations by moving most functionality to
`the access points;
`
`0 Modified OFDM; and
`
`0
`
`Constant bit rate (CBR), variable bit rate (VBR), and available bit rate
`(ABR) services.
`
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`

`
`
`
`Table 1.1
`
`Summary of European ACTS Projects.
`
`ACTS project WAND
`
`AWACS
`
`SAMBA
`
`MEDIAN
`
`“HZ
`70 Mbps
`offset quadrature
`PSK (OQPSK)
`
`20 Mbps
`OFDM, 16
`subcarriers with 8-
`PSK (phase shift
`keying)
`
`
`
`
`
`
`
`“HZ
`34 Mbps
`
`WGHZ
`155 Mbps
`OFDM,
`512 carriers,
`differential
`QPSK
`(DQPSK)
`
`
`Modulation
`
`Radio access
`
`
`
`
`
`
`
`10m
`
`(directional
`antennas)
`
`
`
`
`
`
`
`(directional
`antennas at access
`
`oint)
`time division
`
`(directional
`antennas, line—of—
`_
`siht onl )
`TDMA/TDD
`
`20—50m
`
`(omnidirectional
`antennas)
`
`
`
`time division
`
` TDMA/TDD
`
`multiple access
`multiple access/
`/frequency division
`time division
`
`duplex
`duplex
`
`(TDMA/TDD)
`(TDMA/FDD)
`
`1.1
`
`STANDARDIZATION AND FREQUENCY BANDS
`
`There are
`
`three main forums
`
`for
`
`the
`
`standardization of wireless broadband
`
`communication systems; namely, IEEE 802.11 [18], European»Telecommunication
`Standards Institute Broadband Radio Access Networks (ETSI BRAN)
`[19], and
`Multimedia Mobile Access Communications (MMAC) [20]. IEEE 802.11 made the
`first WLAN standard for the 2.4-GHz Industrial, Scientific, and Medical band (ISM). It
`specifies the medium access control and three different physical
`layers—direct-
`sequence spread spectrum, frequency hopping, and infrared—which give a data rate of
`2 Mbps. Products based on this standard became available in 1998. Figure 1.2 shows an
`example of an IEEE 802.11 modem in a PCMCIA card. Following the initial 1- and 2-
`Mbps standard, IEEE 802.11 developed two new physical layer standards. One delivers
`data rates of up to 11 Mbps in the 2.4-GHz band, using complementary code keying
`[21,22]. Products based on this standard—with the old 1 and 2 Mbps as fallback rates——
`are available since mid 1999. An industry alliance called the Wireless Ethernet
`Compatibility Alliance (WECA) has been established to promote the high rate IEEE
`
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`
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`
`

`
`
`
`available since mid 1999. An industry alliance called the Wireless Ethernet Compatibility
`Alliance (WECA) has been established to promote the high rate IEEE 802.11
`technology and to certify interoperability of products from different vendors [23]. The
`second IEEE 802.11 standard extension targets a range of data rates from 6 up to 54
`Mbps using OFDM in the 5-GHz band [24]. The OFDM standard was developed jointly
`with ETSI BRAN and MMAC, making OFDM effectively a worldwide standard for the
`5-GHz band.
`
`Table 1.2 lists the main characteristics of the IEEE 802.11 and the ETSI High
`Performance Local Area Network type 2 (HIPERLAN/2) standards. More details about
`these standards can be found in Chapter 10.
`
`
`
`Figure 1.2 IEEE 802.11 modem for the 2.4-GHz band (WaveLANTM from Lucent Technologies [25]).
`
`Figure 1.3 shows that 2-, 5- and 60-GHz are the commercially important
`frequency bands because of geographically wide spectrum allocations in Europe, the
`United States (U.S.), and Japan for the wireless broadband multimedia communications
`networks. The 2.4-GHz band is an ISM band, which can be used for many types of
`transmission systems as long as they obey certain power, spectral density, and spreading
`gain requirements. The 5-GHZ band is designated specifically for WBMCS. In Europe,
`only HIPERLAN devices are currently allowed in this band. HIPERLAN actually
`consists of a family of standards, one of which is an OFDM-based standard that is very
`similar to the IEEE 802.11 5-GHz standard. In Japan, MMAC supports both the IEEE
`802.11 and the HIPERLAN standards. Notice that Japan only has 100 MHZ available in
`the 5-GHZ band, while the United States and Europe provide 300 and 455 MHZ,
`repectively. In Europe, extra spectrum for HIPERLAN is available in the 17-GHz band,
`while Japan has allocated spectrum from 10- to 16-GHZ to mobile broadband systems
`(MBS). An analysis of the propagation aspects at the bands foreseen for WBMCS
`microwaves, millimeterwaves, and infrared is presented in [26—3 1].
`
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`
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`
`

`
`
`
`Table 1.2
`
`Comparison of IEEE and HIPERLAN standards.
`
`HIPERLAN/2
`IEEE 802.11 5 GHz
`IEEE 802.11 2 GHz
`Centralized
`system with Centralized
`system with Centralized
`system with
`access points connected to
`access points connected to
`access points connected to
`wired network, or peer-to- wired network, or peer-to- wired network
`peer networking
`peer networking
`
`
`
`
`
`
`
`Up to 30m at 24 Mbps and
`up to 60m at 6 Mbps with
`omnidirectional antennas
`
`
`
`Up to 60m at 11 Mbps and
`up to 100m at 2 Mbps with
`omnidirectional antennas
`
`Up to 30m at 24 Mbps and
`up to 60m at 6 Mbps with
`omnidirectional antennas
`
`
`
`
`
`
`
`Configurations
`
`
`
`
`
`CSMA/CA, variable
`size
`CSMA/CA, variable
`size
`Channel access
`Reservation based access,
`data packets (up to 8192
`scheduled by access point.
`data packets (up to 8192
`bytes)
`bytes)
`Contention slots for making
`
`slot reservations
`
`
`
`
`
`
`
`
`
`
`
`2.4-2.4835 GHz
`
`
`5.150—5.350 GHz;
`5.725—5.825 GHz
`
`5.150—5.350 GHz;
`5.470—5.725 GHz;
`
`
`
`6,9 Mbps(BPSK)
`
`12, 18 Mbps (QPSK)
`24, 36 Mbps (16—QAM)
`54 Mbs (64—QAM)
`
`
`
`6,9 Mbps(BPSK)
`
`12, 18 Mbps (QPSK)
`24, 36 Mbps (16-QAM)
`54 Mbs (64—QAM)
`
`5.5, 11 Mbps (CCK)
`
`1,2 Mbps(BPSK/QPSK)
`
`
`
`
`
`Frequency
`bands
`D”P‘°’““g
`
`
`
`
`WLAN / MBS
`
`_ HIPERLAN
`UNII
`
`WLAN / MBS
`WLAN / MBS
`
`2.40 2.4835
`
`5.15 5.25 5.35 5.47
`
`5.725 5.825
`
`10’
`
`16
`
`17.1 /17.3 _
`
`59
`
`64
`
`——>
`
`Frequency [GHz]
`
`Figure 1.3 Frequency band for wireless broadband communications.
`
`Page 23 of 137
`
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`

`
`1.2 MULTIMEDIA COMMUNICATIONS
`
`Multimedia and computer communications are playing an increasing role in today’s
`society,
`creating new challenges
`to
`those working in
`the development of
`telecommunications systems. Besides that, telecommunications is increasingly relying
`upon wireless links. Thus, the pressure for wireless systems to cope with increasing
`data rates is enormous, and WBMCSS with data rates higher than 2 Mbps are emerging
`rapidly, even if at this moment applications for very high transmission rates do_ not
`exist.
`
`Several WBMCSS are being considered for different users with different needs.
`They may accommodate data rates ranging between 2 and 155 Mbps; terminals can be
`mobile (moving while communicating) or portable (static while communicating);
`moving speeds can be as high as that of a fast train; users may or may not be allowed to
`use more than one channel if their application requires so; the system bandwidth may be
`fixed, or dynamically allocated according to the user’s needs; communication between
`terminals may be direct or must go through a base station; possible ATM technology
`use; and so on. Many other cases can be listed as making the difference between various
`perspectives of a WBMCS, but two major approaches are emerging: WLANS directed
`to communication among computers,
`from which IEEE 802.11
`[16,
`18]
`and
`HIPERLAN [19, 20] are examples, with MBS [17]
`intended as a cellular system
`providing full mobility to B-ISDN users.
`
`The different requirements imposed by the various approaches to WBMCSS
`have consequences on system design and development. The tradeoffs between
`maximum flexibility on one hand and complexity and cost on the other are always
`difficult to decide, as they have an impact not only on the deployment of a system, but
`also on its future evolution and market acceptance. GSM is a good example of a system
`foreseen to accommodate additional services and capacities to those initially offered,
`and the fact that operators are already implementing phase 2+ is proof of that.
`
`This means that many decisions must be made on the several WBMCSS that
`will appear on the market. For IEEE 802.11, for example, those decisions have already
`been made, as the system will be commercialized in the very near future, but for other
`systems there are still many undecided aspects. Of course this depends on what are the
`applications intended to be supported by the systems, and whether these applications
`are targeted to the mass market or only to some niches. The former (from which mobile
`telephones are a good example) will certainly include WLANS, because the expansion
`of personal computers will dictate this application as a great success in WBMCSS; the
`latter will possibly have television broadcasters among their users (to establish links
`between HDTV cameras and the central control room).
`
`Not only are market aspects at stake in the development and deployment of
`WBMCSS, but many technical challenges are posed as well. The transmission of such
`high data rates over radio in a mobile environment creates additional difficulties,
`
`Page 24 of 137
`
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`
`

`
`compared with that of existing systems; these difficulties are augmented by the fact that
`frequencies higher than UHF are needed to support the corresponding bandwidths, thus
`pushing mobile technology challenges (size and weight among other
`things)
`to
`frequencies where these aspects were not much considered until now. However,
`additional challenges are posed to those involved in WBMCSs development: in today’s
`world, where consumers are in the habit of using a communications system that is
`available in different places (e. g., GSM roaming capability, because users can make and
`receive telephone calls in an increasing number of countries worldwide), or being able
`to exchange information among different systems (e.g., the exchange of files between
`different computer applications and systems), for future use it does not make sense to
`consider systems that offer a high data rate but do not support these capabilities to some
`extent.
`
`1.2.1 Need for High Data Rates
`
`the new IEEE and
`Data rate is really what broadband is about. For example,
`HIPERLAN standards specify bit rates of up to 54 Mbps, although 24 Mbps will be the
`typical rate used in most applications. Such high data rates impose large bandwidths,
`thus pushing carrier frequencies for values higher than the UHF band: HIPERLAN has
`frequencies allocated in the 5- and 17-GHz bands; MBS will occupy the 40- and
`60—GHz bands; and even the infrared band is being considered for broadband WLANS.
`Many people argue whether there is a need for such high-capacity systems, however,
`bearing in mind all the compression algorithms developed and the type of applications
`that do require tens of megabits per second. We can examine this issue from another
`perspective.
`
`The need for high-capacity systems is recognized by the “Visionary Group”
`[32], put together by the European Commission, to give a perspective of what should be
`the hot topics in the telecommunications for research in the next European programs
`(following R&D in Advanced Communications Technologies for.Europe (RACE) and
`ACTS). In this visionary perspective, to meet the needs of society in the years to come
`as far as communications is concerned, capacity is one of the major issues to be
`developed because of the foreseen increase in demand for new services (especially
`those based on multimedia). Along with this, mobility will impose new challenges to
`the development of new personal and mobile communications systems.
`
`We can conclude the following: even if at a certain point it may look academic
`to develop a system for a capacity much higher than what seems reasonable (in the
`sense that there are no applications requiring such high capacity), it is worthwhile to do
`so, as almost certainly in the future (which may be not very far off) applications will
`need those capacities and even more. The story of fiber optics is an example.
`
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`
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`

`
`1.2.2 Services and Applications
`
`The system concept of a WLAN such as IEEE 802.11 and of a mobile broadband
`cellular system such as MBS is totally different: each is directed to services and
`applications that differ in many aspects. A comparison of several systems, based on two
`of the key features (mobility and data rate), is shown in Figure 1.4 [33], where it is clear
`that no competition exists between the different approaches.
`
`The applications and services of the various systems are also different. IEEE
`802.11 is mainly intended for communications between computers (thus being an
`extension of wired LANS); nevertheless,
`it can support real—time voice and image
`signals, and users are allowed some mobility and can have access to public networks.
`
`User mobility
`
`Fast mobile
`
`‘slow mobile
`
`Moveable
`
`
`
`IEEE 802.11
`HIPERLAN
`
`
`
`Fixed
`
` m?+
`
`9.6k
`
`64k
`
`128k
`
`2M
`
`20M
`
`155M
`
`Data rate (bps)
`
`Figure 1.4 Comparison of mobility and data rates for several systems.
`
`1.2.3 Antennas and Batteries
`
`Antennas and batteries play a key role in wireless systems. With the advent of
`microelectronics and signal processing, antennas and batteries tend to impose the size
`and weight of mobile terminals. Of course, the higher one goes in frequency, the less
`developed the technology, and many problems are still found in size and weight at the
`millimeter-wave band. Power consumption is