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`RICHARD VAN NEE
`
`RAMJEE PRASAD
`
`iN Artech House Publishers sosron - tonoon
`
`DELL-1022
`
`DELL-1022
`10,079,707
`
`

`

`OFDM for Wireless Multimedia
`Communications
`
`

`

`Fora listing of recenttitles in the Artech House Universal Personal Communication
`Series, turn to the back of this book.
`
`

`

`OFDM for Wireless Multimedia
`Communications
`
`Richard van Nee
`Ramjee Prasad
`
`IM
`
`Artech House
`Boston e London
`
`

`

`Library of Congress Cataloging-in-Publication Data
`van Nee, Richard.
`OFDMfor wireless multimedia communications / Richard van Nee, Ramjee Prasad.
`p. cm. — (Artech House universal personal communicationslibrary)
`Includes bibliographical references and index.
`ISBN 0-89006-530-6 (alk. paper)
`1. Wireless communication systems. 2. Multimedia systems. 3. Multiplexing.
`I. Prasad, Ramjee. IJ. Title. II. Series.
`
`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 communicationslibrary)
`1.Wireless communication systems 2. Multimedia systems
`I. Title 11. Prasad, Ramjee
`621.3'82
`
`ISBN 0-89006-530-6
`
`Cover design by Igor Valdman
`
`© 2000 Richard van Nee and Ramjee Prasad
`
`All rights reserved. Printed and bound in the United States of America. No part ofthis boo
`maybe reproduced orutilized in any form or by any means, electronic or mechanical, incluc
`ing photocopying, recording, or by any informationstorage andretrieval system, withoutpe:
`mission in writing from the authors.
`All terms mentioned in this book that are known to be trademarks or service marks hav
`been appropriately capitalized. Artech House cannot attest to the accuracy of this inform:
`tion. Use of a term in this book should not be regardedas 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
`
`1098765
`
`

`

`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
`—Ramijee Prasad
`
`

`

`

`

`Contents
`
`2face
`
`‘-knowledgments
`
`tapter 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
`
`ferences
`
`apter 2
`
`OFDM Basics
`
`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
`
`OFDMSignal Processing
`
`Implementation Complexity of OFDM Versus
`Single Carrier Modulation
`
`Vii
`
`xiii
`
`XVii
`
`33
`
`33
`
`33
`
`39
`
`42
`
`46
`
`47
`
`48
`
`

`

`Vili
`
`References
`
`Chapter 3
`3.1
`
`3.2
`
`3.3
`
`3.4
`
`3.5
`
`References
`
`Coding and Modulation
`
`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
`
`Chapter 4
`4.1
`
`Synchronization
`
`Introduction
`
`4.2
`
`4.3
`
`4.4
`
`4.5
`
`4.6
`
`4.7
`
`References
`
`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
`
`1(
`
`1(
`
`If
`
`1¢
`
`1¢
`
`

`

`
`
`5.3.2 Differential Detection in the Frequency Domain
`
`
`
`
`
`ix
`
`112
`
`115
`
`117
`
`119
`
`119
`
`120
`
`123
`
`
`
`
`
`5.3.3 Differential Amplitude and Phase Shift Keying
`
`References
`
`Chapter 6
`
`
`The Peale Power Problem
`
`6.1
`
`Introduction
`
`6.2
`
`
`
`
`
`Distribution of the Peale-to-Average Power Ratio
`
`6.3
`
`
`
`Clipping and Peale Windowing
`
`127
`6.3.1 Required Backoffwith a Non-Ideal Power Amplifier
`
`
`
`
`
`6.3.2 Coding and Scrambling
`
`6.4
`
`Peale Cancellation
`
`6.5
`
`
`
`PAP Reduction Codes
`
`
`
`
`
`6.5.1 Generating Complementary Codes
`
`
`
`
`
`6.5.2 Minimum Distance of Complementary Codes
`
`130
`
`131
`
`138
`
`141
`
`144
`
`Codes 145
`6.5.3 Maximum Likelihood
`
`Decoding of Complementary
`
`
`
`
`
`
`
`6.5.4 Suboptimum Decoding of Complementary Codes 147
`
`6.5.5 Large Code Lengths
`
`6.6
`
`SYMBOL Scrambling
`
`References
`
`Chapter 7
`
`
`
`
`Basics of CDMA
`
`7.1
`
`Introduction
`
`7.2
`
`
`
`CDMA: Past, Present, and Future
`
`7.3
`
`CDMA Concepts
`
`7.3.1 Pure CDMA
`
`7.4
`
`Basic OS-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
`
`150
`
`150
`
`153
`
`155
`
`155
`
`156
`
`157
`
`161
`
`171
`
`171
`
`172
`
`173
`
`175
`
`175
`
`

`

`References
`
`Chapter 8
`
`Multi - Carrier CDMA
`
`8.1
`
`8.2
`
`8.3
`
`8.4
`
`8.5
`
`8.6
`
`8.7
`
`Introduction
`
`Channel Model
`
`DS-CDMA and MC-CDMASystems
`
`8.3.1 DS-CDMASystem
`
`8.3.2 MC-CDMASystem
`
`MC-CDMaASystem Design
`
`BEP LOWERBound
`
`8.5.1 DS-CDMASystem
`
`8.5.2. MC-CDMASystem
`
`8.5.3. BEP Lower Bound Equivalence
`Numerical Results
`
`8.6.1 MC-CDMASystem Design
`
`8.6.2 Down - Link BEP Performance
`
`8.6.3 Up - Link BER Performance
`Conclusions
`
`Appendix 8A
`References
`
`Chapter 9
`9.1
`
`Orthogonal Frequency Division Multiple Access
`Introduction
`
`9.2
`
`9.3
`
`9.4
`
`Frequency Hopping OFDMA
`
`Differences between OFDMA and MC-CDMA
`
`OFDMASystem Description
`
`9.4.1 Channel Coding
`
`9.4.2 Modulation
`
`9.4.3 Time and Frequency Synchronization
`
`9.4.4
`
`Initial Modulation Timing Synchronization
`
`9.4.5
`
`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
`
`

`

`xi
`
`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
`
`Chapter 10
`
`10.1
`
`10.2
`
`10.3
`
`10.4
`
`Applications of OFDM
`Introduction
`
`Digital Audio Broadcasting
`
`Terrestrial Digital Video Broadcasting
`
`Magic WAND
`
`10.4.1 Magic WANDPhysical 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
`
`10.5
`
`IEEE 802.11, HIPERLAN/2, and MMACWireless LAN Standards
`
`10.5.1 OFDM Parameters
`
`10.5.2 Channelization
`
`10.5.3 OFDMSignal Processing
`
`10.5.4 Training
`
`10.5.5 Differences between IEEE 802.11, HIPERLAN/2
`and MMAC
`
`10.5.6 Simulation Results
`
`Xeferences
`
`\bout the Authors
`
`ndex
`
`222
`
`223
`
`224
`
`225
`
`227
`
`227
`
`227
`
`228
`
`229
`
`229
`
`229
`
`231
`
`233
`
`234
`
`236
`
`236
`
`237
`
`238
`
`241
`
`243
`
`244
`
`245
`
`246
`
`249
`
`250
`
`252
`
`255
`
`257
`
`

`

`

`

`Preface
`
`adarey seskay ver vasa |
`at Fer cet fee fage avaticar
`sarva-dva@resu dehe ‘smin
`prak@Sa upajayate
`jfianam yada tada vidyad
`vivrddham sattvam ity uta
`
`The manifestations of the mode of goodness can be experienced whenall
`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 Arnout 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
`OFDMfor mobile multimedia communications. Until now, no such book wasavailable in
`the market. We have attempted tofill 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.
`
`xiii
`
`

`

`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
`1 presents a general
`Chapter
`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.
`
`Chapter6 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 CDMAare discussed in Chapter 7 to understand multi carrier
`CDMAandfrequency-hopping OFDMA,whichare 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 UMTSproposal, with main contributions of Ralf Bébnke from Sony,
`Germany, David Bhatoolaul and Magnus Sandell from Lucent Technologies, Matthias
`Wahlquist from Telia Research, Sweden, and Jan-Jaap 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 WANDproject, 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.
`
`

`

`Wehavetried 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.
`
`XV
`
`

`

`

`

`Acknowledgments
`
`Che material in this book originates from several projects at Lucent Technologies and
`esearch activities at Delft University of Technology, The Netherlands. A great deal of
`JFDM-knowledge was acquired during the Magic WAND project,
`in which several
`‘ompanies jointly managed to build a wireless ATM network demonstrator based on
`JFDM.Wewishto thank all Magic WAND members who were involved in the design of
`he OFDM modem,in particular Geert Awater, James Hopper, Rob Kopmeiners, Erik
`3usking, Han Schmitz, Theo Kleijne, Martin Janssen, Jan Kruys, Urs Bernhard, Urs Lott,
`\lex Grant, James Aldis, Thomas Mark, Rodolfo Mannpelz, and Ari Vaisanen. Another
`ruitful source of information was the OFDM-based proposal for UMTS, with main
`ontributions coming from Ralf Béhnke, David Bhatoolaul, MagnusSandell, and Jan-Jaap
`‘ran de Beek.
`
`Richard wishes to thank Masahiro Morikura and Hitoshi Takanashi for all their
`ontributions and the pleasant cooperation on the joint OFDM proposal for the IEEE
`02.11 wireless LAN standard. All members of IEEE 802.11 and Hiperl.AN/2 are thanked
`or numerous contributions, that greatly improved the quality of the final standards and
`elped to gain moreinsight in various OFDMtechniques.
`Geert Awater and Rob Kopmeiners made contributions and corrected numerous
`uistakes. Neeli Rashmi Prasad helped to prepare the complete manuscript, freeing us from
`ie enormous burden of editorial requirements. Shinsuke Hara from the University of
`Jsaka, Japan, Hiroshi Harada from the Communications Research Laboratory, Ministry of
`‘osts and Telecommunications, Yokosuka, Japan, Luis Correia from the Technical
`Iniversity of Lisbon, Portugal, Anand Raghawa Prasad from Lucent Technologies, and
`smout de Wild from Siemens, The Netherlands, are deeply acknowledged for their
`aluable contributions.
`
`After the Magic WANDproject, we studied several OFDM options for new high-
`ite wireless LAN products. A circle was completed by the selection of OFDM for the high
`ite extension of the IEEE 802.11 wireless LAN standard in July 1998. We hopethis book
`‘ill help to gain insight in the principles and design of OFDM-basedsystems, in particular
`1e new OFDM-based wireless LAN standards.
`
`Richard van Nee
`Ramjee Prasad
`October 1999
`
`xvii
`
`

`

`

`

`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 developmentare 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 Internet/multimedia
`communications
`is growing
`exponentially. Therefore, it is imperative that both wireless and Internet/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 WBMCSwill integrate various functions
`and applications. WBMCSis 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. The most 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 WBMCSis to provide its users a means of radio access to
`broadband services supported on customer premises networks or offered directly by
`public fixed networks. WBMCSwill provide a mobile/movable wireless extension to
`
`

`

`National and
`International zones...
`
`
`
`Global information
`village
`
`an ee
`“Microcells:
`™ City-centers
`™ Highways
`
`. Revional
`= National
`
` Macrocells:
`
`
`Wireless accessto
`Internet/multimedia
`fD
`i;
`‘ ol Server
`i & WirelessLAN
` , “Picocells:
`
`‘os
`
`cS
`me, ...Inhouse ee
`
`oo
`
`ae
`
`Figure 1.1 Global informationvillage.
`
`WBMCSis 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 WBMCShas drawn muchattention 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, WBMCSwill
`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:
`
`Frequencyallocation 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 efficient modulation, coding, and smart antenna
`techniques.
`
`

`

`°
`°
`
`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)
`[1-17]. Table 1.1 summarizes the
`European projects [11].
`
`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 (WATMnhnet), 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 Mbpsand an
`indoor high speed WLAN in SHFbandwith 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 MMChasthe following objectives to achieve at 60 GHz:
`
`e Wireless access of 155 Mbps using OFDM;
`
`e
`
`e
`
`Both indoor and outdoor use;
`
`Less complex, inexpensive mobile stations by moving mostfunctionality to
`the access points;
`
`e Modified OFDM;and
`
`e
`
`Constant bit rate (CBR), variable bit rate (VBR), and available bit rate
`(ABR)services.
`
`

`

`Table 1.1
`
`Summary of European ACTSProjects.
`
`AWACS
`SAMBA
`MEDIAN
`ACTSproject|WAND
`
`20 Mbps
`
`70 Mbps
`
`34 Mbps
`
`155 Mbps
`
`Modulation
`
`
`
`
` 10m
`
`
`
`
`ena|20-50m 50-100m 10-50m
`
`
`
`
`(omnidirectional
`(directional
`(directional
`(directional
`:
`antennas at access
`antennas)
`antennas,line-of-
`antennas)
`
`
`
`point)
`sight only)
`
`time division
`TDMA/TDD
`
`
`
`time division
`TDMA/TDD
`
`
`
`
`multiple access/
`multiple access
`
`time division
`/frequency division
`
`
`
`duplex
`duplex
`
`
`
`(TDMA/TDD)
`(TDMA/FDD)
`
`
`
`
`OFDM,
`OQPSK
`offset quadrature
`OFDM,16
`
`subcarriers with 8-|PSK (OQPSK) 512 carriers,
`PSK (phaseshift
`differential
`keying)
`QPSK
`(DQPSK)
`
`
`
`
`
`.
`Cell radius
`
`Radio access
`
`11
`
`STANDARDIZATION AND FREQUENCY BANDS
`
`standardization of wireless broadband
`the
`for
`There are three main forums
`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. Followingtheinitial 1- and 2-
`Mbpsstandard, 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 Mbpsasfallback 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
`
`

`

`\vailable since mid 1999. An industry alliance called the Wireless Ethernet Compatibility
`\lliance (WECA) has been established to promote the high rate IEEE 802.11
`echnology and to certify interoperability of products from different vendors [23]. The
`econd IEEE 802.11 standard extension targets a range of data rates from 6 up to 54
`Abps using OFDM in the 5-GHz band [24]. The OFDM standard was developedjointly
`vith ETSI BRAN and MMAC,making OFDMeffectively a worldwide standard for the
`i~GHz band.
`able 1.2 lists the main characteristics of the IEEE 802.11 and the ETSI High
`’erformance Local Area Network type 2 CHIPERLAN/2) standards. More details about
`hese standards can be found in Chapter 10.
`
`
`
`Figure 1.2 JEEE 802.11 modem for the 2.4-GHz band (WaveLAN™ from Lucent Technologies [25}).
`
`Figure 1.3 shows that 2-, 5- and 60-GHz are the commercially important
`requency bands because of geographically wide spectrum allocations in Europe, the
`Jnited States (U.S.), and Japan for the wireless broadband multimedia communications
`ietworks. The 2.4-GHz band is an ISM band, which can be used for many types of
`ransmission systems as long as they obey certain power, spectral density, and spreading
`rain requirements. The 5-GHz band is designated specifically for WBMCS. In Europe,
`mly HIPERLAN devices are currently allowed in this band. HIPERLAN actually
`consists of a family of standards, one of which is an OFDM-basedstandard that is very
`imilar to the IEEE 802.11 5-GHz standard. In Japan, MMACsupports both the JEEE
`{02.11 and the HIPERLAN standards. Notice that Japan only has 100 MHz available in
`he 5-GHz band, while the United States and Europe provide 300 and 455 MHz,
`epectively. In Europe, extra spectrum for HIPERLAN is available in the 17-GHz band,
`vhile 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
`nicrowaves, millimeterwaves, and infrared is presented in [26-31].
`
`

`

`
`
`Table 1.2
`
`Comparison of IEEE and HIPERLANstandards.
`
`IEEE 802.11 5 GHz
`
`HIPERLAN/2
`
`
`
`
`
`IEEE 802.11 2 GHz
`
`
`Configurations|Centralized system with|Centralized system with
`
`
`Centralized
`system w
`
`
`
`
`
`access points connected to|access points connected to access points connected
`
`wired network
`wired network, or peer-to-|wired network, or peer-to-
`
`
`peer networking
`peer networking
`
`
`
`
`
`
`Up to 60m at 11 Mbps and|Up to 30m at 24 Mbpsand
`Up to 30m at 24 Mbps a
`up to 100m at 2 Mbps with|up to 60m at 6 Mbps with
`up to 60m at 6 Mbps w
`
`
`
`omnidirectional antennas
`omnidirectional antennas
`omnidirectional antennas
`
`
`
`
`
`
`
`Channel access
`Reservation based acce
`
`
`CSMA/CA, variable size|CSMA/CA, variable size
`
`data packets (up to 8192|data packets (up to 8192
`scheduled by access poi
`
`Contention slots for maki
`bytes)
`bytes)
`
`
`
`slot reservations
`
`
`
`
`5.150-5.350 GHz;
`5.470-S.725 GHz;
`
`
`
`TDD
`
`
`
`1,2 Mbps (BPSK/QPSK)|6,9 Mbps (BPSK)
`6, 9 Mbps (BPSK)
`
`
`
`5.5, 11 Mbps (CCK)
`12, 18 Mbps (QPSK)
`12, 18 Mbps (QPSK)
`
`
`
`24, 36 Mbps (16-QAM)
`24, 36 Mbps (16-QAM)
`
`34 Mbps (64-QAM)
`54 Mbps (64-QAM)
`
`Frequency
`bands
`
`2.4-2.4835 GHz
`
`5.150-5.350 GHz;
`5.725-5.825 GHz
`
`P| HIPERLAN 2.40 2.4835
`
`5.15 5.25 5.35 5.47
`
`5.725 5.825
`
`10
`
`160
`
`17.1 17.3
`
`59
`
`—-» Frequency [GHz]
`
`Figure 1.3 Frequency band for wireless broadband communications.
`
`

`

`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 Mbpsare emerging
`rapidly, even if at this moment applications for very high transmission rates do, not
`exist.
`
`Several WBMCSsare 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 ofa 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 basestation; possible ATM technology
`use; and so on. Manyother cases can be listed as making the difference between various
`perspectives of a WBMCS, but two major approaches are emerging: WLANsdirected
`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 deploymentof 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 ofthat.
`
`This means that many decisions must be made on the several WBMCSsthat
`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
`systemsthere 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 camerasandthe central control room).
`
`Not only are market aspects at stake in the development and deployment of
`WBMCSs,but manytechnical challenges are posed as well. The transmission of such
`high data rates over radio in a mobile environment creates additional difficulties,
`
`

`

`compared with that of existing systems; these difficulties are augmented by the fact that
`frequencies higher than UHFare 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 WBMCSsdevelopment: 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 systemsthat offer a high data rate but do not support these capabilities to some
`extent.
`
`1.2.1 Need for High Data Rates
`
`the new TEEE and
`Data rate is really what broadband is about. For example,
`HIPERLANstandards specify bit rates of up to 54 Mbps, although 24 Mbpswill 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.
`Manypeople 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 developmentof new personal and mobile communications systems.
`
`Wecan 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. Thestory of fiber optics is an example.
`
`

`

`[.2.2 Services and Applications
`
`[he system concept of a WLAN such as IEEE 802.11 and of a mobile broadband
`cellular system such as MBSis totally different: each is directed to services and
`ipplications that differ in many aspects. A comparison ofseveral systems, based on two
`of the key features (mobility and data rate), is shown in Figure 1.4 [33], whereit is clear
`hat no competition exists between the different approaches.
`
`The applications and services of the various systems are also different. IEEE
`302.11 is mainly intended for communications between computers (thus being an
`*xtension 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
`
`Fixed
`
`
`
`HIPERLAN
`
`
`
`
`
`
`
`
`
`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
`nicroelectronics and signal processing, antennas and batteries tend to impose the size
`ind weight of mobile terminals. Of course, the higher one goes in frequency, the less
`Jeveloped the technology, and many problemsarestill found in size and weight at the
`nillimeter-wave band. Power consumption is one example. Though these are likely to
`ye solved in the near future. The numberof hours battery-powered equipment can work
`or operate on stand by, and the percentage of its weight corresponding to the battery, is
`
`

`

`10
`
`
`not a specific problem of WBMCS. Laptop computers and cellular telephones are the
`most common terminals relying on batteries these days. This technology continues to
`demand huge R&D,
`to extend working time and reduce weight. Although a 100g
`mobile telephone battery corresponding to several hours of continuous work and a few
`days on standby is already on the market, users still want more. Mobile multimedia
`te