WMN_textbook.pdf

Schiller_ppr 9/19/07 3:38 PM Page 1 Second Edition JOCHEN SCHILLER The mobile communications market remains the fastest growing segment of the global computing and communications business.The rapid progress and convergence of the field has created a need for new techniques and solutions, knowledgeable professionals to create and implement them, and courses to teach the background theory and technologies while pointing the way towards future trends. In this book Jochen Schiller draws on his extensive experience to provide a thorough grounding in mobile communications, describing the state of the art in industry and research while giving a detailed technical background to the area.The book covers all the important aspects of mobile and wireless communications from the Internet to signals, access protocols and cellular systems, emphasizing the key area of digital data Second Edition transfer. It uses a wide range of examples and other teaching aids, making it suitable for self-study and university classes. The book begins with an overview of mobile and wireless applications, covering the history and market, and providing the foundations of wireless transmission and Medium Access Control. Four different groups of wireless network technologies are then covered: telecommunications systems, satellite systems, broadcast JOCHEN SCHILLER systems and wireless LAN.The following chapters about the network and transport layers address the impairments and solutions using well-known Internet protocols such as TCP/IP in a mobile and wireless environment.The book concludes with a chapter on technologies supporting applications in mobile networks, focusing on the Web and the Wireless Application Protocol (WAP). Each chapter concludes with a set of exercises for self-study (with solutions available to instructors) and references to standards, organizations and research work related to the topic. New to this edition Second ➤ Integration of higher data rates for GSM (HSCSD, GPRS) Edition ➤ New material on 3rd generation (3G) systems with in-depth discussion of UMTS/W-CDMA ➤ Addition of the new WLAN standards for higher data rates: 802.11a, b, g and HiperLAN2 ➤ Extension of Bluetooth coverage to include IEEE 802.15, profiles and applications SCHILLER ➤ Increased coverage of ad-hoc networking and wireless profiled TCP ➤ Migration of WAP 1.x and i-mode towards WAP 2.0 Jochen Schiller is head of the Computer Systems and Telematics Working Group in the Institute of Computer Science, Freie Universität Berlin, and a consultant to several companies in the networking and communications business. His research includes mobile and wireless communications, communication architectures and operating systems for embedded devices, and QoS aspects of communication systems. Cover image © Photonica ADDISON-WESLEY ADDISON A Pearson Education book www.pearson-books.com WESLEY 01Prelims 8804 (i-xx) 30/5/03 11:03 am Page i Mobile Communications 01Prelims 8804 (i-xx) 30/5/03 11:03 am Page ii 01Prelims 8804 (i-xx) 30/5/03 11:03 am Page iii Jochen H. Schiller Mobile Communications Second Edition 01Prelims 8804 (i-xx) 30/5/03 11:03 am Page iv PEARSON EDUCATION LIMITED Edinburgh Gate Harlow CM20 2JE Tel:+44 (0)1279 623623 Fax:+44 (0)1279 431059 Website: www.pearsoned.co.uk First Published in Great Britain 2000 Second edition 2003 © Pearson Education Limited 2003 ISBN 0 321 12381 6 The right of Jochen Schiller to be identiﬁed as author of this work has been asserted by him in accordance with the Copyright, Designs, and Patents Act 1988. All rights reserved; no part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise without either the prior written permission of the Publishers or a licence permitting restricted copying in the United Kingdom issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London W1T 4LP. The programs in this book have been included for their instructional value. The publisher does not offer any warranties or representations in respect of their ﬁtness for a particular purpose, nor does the publisher accept any liability for any loss or damage (other than for personal injury or death) arising from their use. All trademarks used herein are the property of their respective owners. The use of any trademark in this text does not vest in the author or publisher any trademark ownership rights in such trademarks, nor does the use of such trademarks imply any afﬁliation with or endorsement of this book by such owners. British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. Library of Congress Cataloging in Publication Data A catalog record for this book is available from the Library of Congress. 10 9 8 7 6 5 4 3 2 1 08 07 06 05 04 Text design by barker/hilsdon @ compuserve.com Typeset by Pantek Arts Ltd., Maidstone, Kent Printed and bound in Great Britain by Biddles Ltd, www.biddles.co.uk The publishers’ policy is to use paper manufactured from sustainable forests. 01Prelims 8804 (i-xx) 30/5/03 11:03 am Page v To my students and Cora 01Prelims 8804 (i-xx) 30/5/03 11:03 am Page vi 1 01Prelims 8804 (i-xx) 30/5/03 11:03 am Page vii Contents About the author xiv Preface xv Acknowledgements xix 1 Introduction 1 1.1 Applications 3 1.1.1 Vehicles 3 1.1.2 Emergencies 4 1.1.3 Business 4 1.1.4 Replacement of wired networks 5 1.1.5 Infotainment and more 5 1.1.6 Location dependent services 6 1.1.7 Mobile and wireless devices 7 1.2 A short history of wireless communication 9 1.3 A market for mobile communications 15 1.4 Some open research topics 16 1.5 A simpliﬁed reference model 18 1.6 Overview 20 1.7 Review exercises 23 1.8 References 23 2 Wireless transmission 25 2.1 Frequencies for radio transmission 26 2.1.1 Regulations 27 2.2 Signals 31 2.3 Antennas 32 2.4 Signal propagation 35 2.4.1 Path loss of radio signals 36 2.4.2 Additional signal propagation effects 37 2.4.3 Multi-path propagation 39 01Prelims 8804 (i-xx) 30/5/03 11:03 am Page viii viii Mobile communications 2.5 Multiplexing 41 2.5.1 Space division multiplexing 41 2.5.2 Frequency division multiplexing 43 2.5.3 Time division multiplexing 44 2.5.4 Code division multiplexing 45 2.6 Modulation 46 2.6.1 Amplitude shift keying 48 2.6.2 Frequency shift keying 49 2.6.3 Phase shift keying 49 2.6.4 Advanced frequency shift keying 50 2.6.5 Advanced phase shift keying 51 2.6.6 Multi-carrier modulation 53 2.7 Spread spectrum 54 2.7.1 Direct sequence spread spectrum 56 2.7.2 Frequency hopping spread spectrum 59 2.8 Cellular systems 61 2.9 Summary 64 2.10 Review exercises 65 2.11 References 66 3 Medium access control 69 3.1 Motivation for a specialized MAC 70 3.1.1 Hidden and exposed terminals 70 3.1.2 Near and far terminals 71 3.2 SDMA 72 3.3 FDMA 72 3.4 TDMA 73 3.4.1 Fixed TDM 74 3.4.2 Classical Aloha 75 3.4.3 Slotted Aloha 76 3.4.4 Carrier sense multiple access 76 3.4.5 Demand assigned multiple access 77 3.4.6 PRMA packet reservation multiple access 78 3.4.7 Reservation TDMA 79 3.4.8 Multiple access with collision avoidance 79 3.4.9 Polling 82 3.4.10 Inhibit sense multiple access 82 3.5 CDMA 82 3.5.1 Spread Aloha multiple access 87 01Prelims 8804 (i-xx) 30/5/03 11:03 am Page ix Contents ix 3.6 Comparison of S/T/F/CDMA 89 3.7 Review exercises 91 3.8 References 92 4 Telecommunications systems 93 4.1 GSM 96 4.1.1 Mobile services 98 4.1.2 System architecture 100 4.1.3 Radio interface 105 4.1.4 Protocols 110 4.1.5 Localization and calling 113 4.1.6 Handover 117 4.1.7 Security 120 4.1.8 New data services 122 4.2 DECT 130 4.2.1 System architecture 131 4.2.2 Protocol architecture 132 4.3 TETRA 134 4.4 UMTS and IMT-2000 136 4.4.1 UMTS releases and standardization 141 4.4.2 UMTS system architecture 142 4.4.3 UMTS radio interface 143 4.4.4 UTRAN 149 4.4.5 Core network 151 4.4.6 Handover 154 4.5 Summary 156 4.6 Review exercises 158 4.7 References 160 5 Satellite systems 165 5.1 History 165 5.2 Applications 166 5.3 Basics 169 5.3.1 GEO 173 5.3.2 LEO 174 5.3.3 MEO 175 01Prelims 8804 (i-xx) 30/5/03 11:03 am Page x x Mobile communications 5.4 Routing 175 5.5 Localization 176 5.6 Handover 176 5.7 Examples 177 5.8 Summary 179 5.9 Review exercises 180 5.10 References 181 6 Broadcast systems 183 6.1 Overview 183 6.2 Cyclical repetition of data 185 6.3 Digital audio broadcasting 186 6.3.1 Multi-media object transfer protocol 190 6.4 Digital video broadcasting 191 6.4.1 DVB data broadcasting 193 6.4.2 DVB for high-speed internet access 194 6.5 Convergence of broadcasting and mobile communications 195 6.6 Summary 196 6.7 Review exercises 198 6.8 References 198 7 Wireless LAN 201 7.1 Infra red vs radio transmission 204 7.2 Infrastructure and ad-hoc network 205 7.3 IEEE 802.11 207 7.3.1 System architecture 208 7.3.2 Protocol architecture 210 7.3.3 Physical layer 211 7.3.4 Medium access control layer 214 7.3.5 MAC management 225 7.3.6 802.11b 231 7.3.7 802.11a 234 7.3.8 Newer developments 238 7.4 HIPERLAN 239 7.4.1 Historical: HIPERLAN 1 240 7.4.2 WATM 244 7.4.3 BRAN 255 7.4.4 HiperLAN2 257 7.5 Bluetooth 269 7.5.1 User scenarios 270 7.5.2 Architecture 271 01Prelims 8804 (i-xx) 30/5/03 11:03 am Page xi Contents xi 7.5.3 Radio layer 276 7.5.4 Baseband layer 276 7.5.5 Link manager protocol 282 7.5.6 L2CAP 285 7.5.7 Security 287 7.5.8 SDP 289 7.5.9 Proﬁles 290 7.5.10 IEEE 802.15 291 7.6 Summary 293 7.7 Review exercises 297 7.8 References 298 8 Mobile network layer 303 8.1 Mobile IP 304 8.1.1 Goals, assumptions and requirements 304 8.1.2 Entities and terminology 307 8.1.3 IP packet delivery 309 8.1.4 Agent discovery 310 8.1.5 Registration 312 8.1.6 Tunneling and encapsulation 315 8.1.7 Optimizations 319 8.1.8 Reverse tunneling 321 8.1.9 IPv6 323 8.1.10 IP micro-mobility support 324 8.2 Dynamic host conﬁguration protocol 328 8.3 Mobile ad-hoc networks 330 8.3.1 Routing 332 8.3.2 Destination sequence distance vector 335 8.3.3 Dynamic source routing 336 8.3.4 Alternative metrics 339 8.3.5 Overview ad-hoc routing protocols 340 8.4 Summary 343 8.5 Review exercises 345 8.6 References 346 9 Mobile transport layer 351 9.1 Traditional TCP 352 9.1.1 Congestion control 352 9.1.2 Slow start 352 01Prelims 8804 (i-xx) 30/5/03 11:03 am Page xii xii Mobile communications 9.1.3 Fast retransmit/fast recovery 353 9.1.4 Implications of mobility 354 9.2 Classical TCP improvements 355 9.2.1 Indirect TCP 355 9.2.2 Snooping TCP 358 9.2.3 Mobile TCP 360 9.2.4 Fast retransmit/fast recovery 362 9.2.5 Transmission/time-out freezing 363 9.2.6 Selective retransmission 363 9.2.7 Transaction-oriented TCP 364 9.3 TCP over 2.5/3G wireless networks 366 9.4 Performance enhancing proxies 368 9.5 Summary 369 9.6 Review exercises 371 9.7 References 372 10 Support for mobility 375 10.1 File systems 376 10.1.1 Consistency 377 10.1.2 Coda 378 10.1.3 Little work 380 10.1.4 Ficus 380 10.1.5 Mlo-NFS 381 10.1.6 Rover 381 10.2 World wide web 381 10.2.1 Hypertext transfer protocol 382 10.2.2 Hypertext markup language 385 10.2.3 Some approaches that might help wireless access 386 10.2.4 System architecture 389 10.3 Wireless application protocol (version 1.x) 392 10.3.1 Architecture 393 10.3.2 Wireless datagram protocol 396 10.3.3 Wireless transport layer security 397 10.3.4 Wireless transaction protocol 400 10.3.5 Wireless session protocol 404 10.3.6 Wireless application environment 412 10.3.7 Wireless markup language 414 10.3.8 WMLScript 416 01Prelims 8804 (i-xx) 30/5/03 11:03 am Page xiii Contents xiii 10.3.9 Wireless telephony application 419 10.3.10 Push architecture 426 10.3.11 Push/pull services 428 10.3.12 Example stacks with WAP 1.x 429 10.4 i-mode 430 10.5 SyncML 433 10.6 WAP 2.0 434 10.7 Summary 437 10.8 Review exercises 440 10.9 References 441 11 Outlook 449 11.1 The architecture of future networks 449 11.2 References 453 Appendix 1– Acronyms 455 Appendix 2 – Glossary 471 Index 477 01Prelims 8804 (i-xx) 30/5/03 11:03 am Page xiv About the author Jochen Schiller is head of the working group Computer Systems & Telematics at the Institute of Computer Science, FU Berlin, Germany. He received his MS and PhD degrees in Computer Science from the University of Karlsruhe, Germany, in 1993 and 1996, respectively. As a postdoc he joined Uppsala University, Sweden, and worked in several industry co-operations and European projects. Since April 2001 he has been a full professor at FU Berlin. The focus of his research is on mobile and wireless communications, communication architectures and operat- ing systems for embedded devices, and quality of service aspects in communication systems. He is a member of IEEE and GI and acts as consultant for several companies in the networking and communication business. 01Prelims 8804 (i-xx) 30/5/03 11:03 am Page xv Preface elcome to the second edition of Mobile Communications – and wel- W come to the confusing, complex, but very interesting world of wireless and mobile technologies! In the last few years, we have all experienced the hype and frustration related to mobile technology. Once praised as the Internet on the mobile phone, the frustration with third genera- tion mobile phone systems came at the same time the dotcoms crashed. The reader should remember that all technologies need their time to develop. Nevertheless, we are experiencing huge growth rates in mobile communica- tion systems (mainly in Asia), increasing mobility awareness in society, and the worldwide deregulation of former monopolized markets. While traditional com- munication paradigms deal with fixed networks, mobility raises a new set of questions, techniques, and solutions. For many countries, mobile communica- tion is the only solution due to the lack of an appropriate fixed communication infrastructure. Today, more people use mobile phones (over one billion!) than traditional fixed phones. The trends mentioned above create an ever-increasing demand for well-educated communication engineers who understand the devel- opments and possibilities of mobile communication. What we see today is only the beginning. There are many new and exciting systems currently being devel- oped in research labs. The future will see more and more mobile devices, the merging of classical voice and data transmission technologies, and the extension of today’s Internet applications (e.g., the world wide web) onto mobile and wire- less devices. New applications and new mobile networks will bring ubiquitous multimedia computing to the mass market; radios, personal digital assistants (PDAs), laptops and mobile phones will converge and many different functions will be available on one device – operating on top of Internet technologies. This book is an introduction to the field of mobile communications and focuses on digital data transfer. The book is intended for use by students of EE or CS in computer networking or communication classes, engineers working with fixed networks who want to see the future trends in networking, as well as managers who need a comprehensible overview in mobile communication. The reader requires a basic understanding of communication and a rough knowl- edge of the Internet or networking in general. While resources are available which focus on a particular technology, this book tries to cover many aspects of mobile communications from a computer science point of view. Furthermore, 01Prelims 8804 (i-xx) 30/5/03 11:03 am Page xvi xvi Mobile communications the book points out common properties of different technical solutions and shows the integration of services and applications well-known from fixed net- works into networks supporting mobility of end systems and wireless access. If the reader is interested in more detailed information regarding a certain topic, he or she will find many pointers to research publications or related websites. Teachers will find this book useful for a course that follows a general data communication or computer networking class. The book can also replace parts of more general courses if it is used together with other books covering fixed networks or aspects of high-speed networks. It should be straightforward to teach a mobile networking class using this book together with the course mater- ial provided online via the following link: http://www.jochenschiller.de/ The material comprises all of the figures, over 500 slides in English and German as PDF and PowerPoint™ files, a list of all acronyms, and many links to related sites. Additionally, the questions included in the book can provide a good self-test for students. Solutions to all the questions in the book can be found at the publisher’s password-protected site: http://www.booksites.net/schiller This book addresses people who want to know how mobile phone systems work, what technology will be next in wireless local area networks, and how mobility will influence applications, security, or IP networks. Engineers working in fixed networks can see paths of migration towards mixed fixed/mobile networks. The book follows a ‘tall and thin’ approach. It covers a whole course in mobile communication, from signals, access protocols, up to application require- ments and security, and does not stress single topics to the neglect of others. It focuses on digital mobile communication systems, as the future belongs to digi- tal systems such as CDMA, GSM, DECT, W-CDMA, cdma2000, UMTS, DAB. New and important topics in the higher layers of communication, like the wireless application protocol (WAP), i-mode, and wireless TCP are included. Chapter 1 introduces the field of mobile and wireless communication, pre- sents a short history and challenges for research, and concludes with a market vision, which shows the potential of mobile technology. Chapter 2 follows the classical layers of communication systems and explains the basics of wireless technology from a computer science point of view. Topics in this chapter are signal propagation, multiplexing, and modulation. Profound electrical engineer- ing knowledge is not required; however, it is necessary to comprehend the basic principles of wireless transmission to understand the design decisions of higher layer communication protocols and applications. Chapter 3 presents several media access schemes and motivates why the standard schemes from fixed net- works fail if used in a wireless environment. Chapters 4–7 present different wireless communication systems and may be read in any order. All the systems involve wireless access to a network and they can transfer arbitrary data between communication partners. Chapter 4 comprises the global system for mobile communications (GSM) as today’s most 01Prelims 8804 (i-xx) 30/5/03 11:03 am Page xvii Preface xvii successful public mobile phone system, cordless phone technology, trunked radios, and the future development with the universal mobile telecommunica- tions system (UMTS). Satellite systems are covered in chapter 5, while chapter 6 discusses digital broadcast systems such as digital audio broadcasting (DAB) which can be one component of a larger communication system providing end- users with mass data. Wireless LANs as replacement for cabling inside buildings are presented in chapter 7. Examples are IEEE 802.11, HiperLAN2, and Bluetooth. A special feature of HiperLAN2 is the provisioning of quality of ser- vice (QOS), i.e., the system can give guarantees for certain parameters, such as bandwidth or error rates. Chapter 8 mainly presents mobile IP, the extension of the Internet protocol (IP) into the mobile domain. Ad-hoc networks with their requirements for spe- cific routing protocols are also covered. The subsequent layer, the transport layer, is covered in chapter 9. This chapter discusses several approaches of adapt- ing the current transmission control protocol (TCP), which is well known from the Internet, to the special requirements of mobile communication systems. Chapter 10 presents the wireless application protocol (WAP) standard that enables wireless and mobile devices to use parts of the world wide web (www) from today’s fixed Internet. Additionally, this chapter shows the migration to WAP 2.0, which includes components from i-mode and the Internet. The book closes with an outlook to fourth generation systems in chapter 11. The book is based on a course I have taught several times at the University of Karlsruhe and the Free University of Berlin. The course typically consists of 14 lectures of 90 minutes each (typically, not every topic of the book is covered during the lecture in the same detail). Over 100 universities, colleges, and other institutions around the world have already used the material compiled for this book. Teachers may include the online material in their courses or even base whole courses on the material. What is new in the second edition? Over three years have passed since the publication of the first edition. During this time, many new ideas showed up, several ideas were dropped, and many systems have been improved. The main changes, besides updates of all refer- ences and links, are the following: Integration of higher data rates for GSM (HSCSD, GPRS). Complete new section about third generation systems with in-depth discus- sion of UMTS/W-CDMA. Addition of the new WLAN standards for higher data rates: 802.11a,.11b,.11g and HiperLAN2. Extension of the Bluetooth section: IEEE 802.15, profiles, applications. 01Prelims 8804 (i-xx) 30/5/03 11:03 am Page xviii xviii Mobile communications More on ad-hoc networking and wireless profiled TCP. Migration of WAP 1.x and i-mode towards WAP 2.0. You are encouraged to send any comments regarding the book or course material to [email protected]. Finally, I hope you enjoy reading this com- pletely revised book and forgive me for simplifications I have used to avoid blurring the big picture of mobile communications. Many such details may change as research and standards evolve over time. As this book covers many aspects of mobile communications it cannot dig into each and every detail with the same scientific depth. Finally, the famous quote from Goethe is valid for this book, too: Properly speaking, such work is never finished; one must declare it so when, according to time and circumstances, one has done one's best. 01Prelims 8804 (i-xx) 30/5/03 11:03 am Page xix Acknowledgements First of all, I want to thank the numerous students from my Mobile Communi- cations courses who pushed me towards writing this book by requesting more information regarding wireless and mobile communication. The students’ ques- tions and answers were a great help to shaping the contents. I also want to thank the numerous readers around the world for their comments and reviews. You all helped me a lot fixing unclear explanations. For the first edition, many of my former colleagues at the University of Karlsruhe gave generously of their intellect and time, reading, commenting, and discussing the chapters of the book. I am especially grateful to Marc Bechler, Stefan Dresler, Jochen Seitz, and Günter Schäfer. I want to thank Hartmut Ritter for his support by taking over some of my daily routine work. I also had help from Verena Rose and Elmar Dorner during the early stages of the course mater- ial. I also want to thank the former head of the Institute of Telematics, Prof. Gerhard Krüger, for giving me the freedom and support to set up the Mobile Communications course in an inspiring environment. For many insightful comments to the book, I thank Per Gunningberg from Uppsala University, Sweden. I am profoundly grateful to Angelika Rieder and Kerstin Risse for their help in polishing the first edition. Without their help, it would not be as easy to read. For the second edition, which I wrote at the Free University of Berlin, I am particularly grateful to Thiemo Voigt from SICS, Sweden, who helped me a lot integrating the new ideas of mobile and wireless technology. Furthermore, I want to thank all the anonymous reviewers, colleagues, and students from many dif- ferent places around the world for their valuable contributions to this edition. As for the first edition, I have to thank the Addison-Wesley team in the UK for all their support during the making of the book, special thanks to Bridget Allen, Tessa Fincham and Michael Strang who firmly pushed me towards the final manuscript for this edition. 01Prelims 8804 (i-xx) 30/5/03 11:03 am Page xx 02Chap01 8804 (1-24) 30/5/03 11:03 am Page 1 Introduction 1 hat will computers look like in ten years? No one can make a wholly W accurate prediction, but as a general feature, most computers will cer- tainly be portable. How will users access networks with the help of computers or other communication devices? An ever-increasing number with- out any wires, i.e., wireless. How will people spend much of their time at work, during vacation? Many people will be mobile – already one of the key charac- teristics of today’s society. Think, for example, of an aircraft with 800 seats. Modern aircraft already offer limited network access to passengers, and aircraft of the next generation will offer easy Internet access. In this scenario, a mobile network moving at high speed above ground with a wireless link will be the only means of transporting data to and from passengers. Think of cars with Internet access and billions of embedded processors that have to communicate with, for instance, cameras, mobile phones, CD-players, headsets, keyboards, intelligent traffic signs and sensors. This plethora of devices and applications show the great importance of mobile communications today. Before presenting more applications, the terms ‘mobile’ and ‘wireless’ as used throughout this book should be defined. There are two different kinds of mobil- ity: user mobility and device portability. User mobility refers to a user who has access to the same or similar telecommunication services at different places, i.e., the user can be mobile, and the services will follow him or her. Examples for mechanisms supporting user mobility are simple call-forwarding solutions known from the telephone or computer desktops supporting roaming (i.e., the desktop looks the same no matter which computer a user uses to log into the network). With device portability,1 the communication device moves (with or without a user). Many mechanisms in the network and inside the device have to make sure that communication is still possible while the device is moving. A typical example for systems supporting device portability is the mobile phone system, where the system itself hands the device from one radio transmitter (also called a base sta- tion) to the next if the signal becomes too weak. Most of the scenarios described in this book contain both user mobility and device portability at the same time. 1 Apart from the term ‘portable’, several other terms are used when speaking about devices (e.g., ‘mobile’ in the case of ‘mobile phone’). This book mainly distinguishes between wireless access to a network and mobility of a user with a device as key characteristics. 1 02Chap01 8804 (1-24) 30/5/03 11:03 am Page 2 2 Mobile communications With regard to devices, the term wireless is used. This only describes the way of accessing a network or other communication partners, i.e., without a wire. The wire is replaced by the transmission of electromagnetic waves through ‘the air’ (although wireless transmission does not need any medium). A communication device can thus exhibit one of the following characteristics: Fixed and wired: This configuration describes the typical desktop computer in an office. Neither weight nor power consumption of the devices allow for mobile usage. The devices use fixed networks for performance reasons. Mobile and wired: Many of today’s laptops fall into this category; users carry the laptop from one hotel to the next, reconnecting to the company’s network via the telephone network and a modem. Fixed and wireless: This mode is used for installing networks, e.g., in his- torical buildings to avoid damage by installing wires, or at trade shows to ensure fast network setup. Another example is bridging the last mile to a customer by a new operator that has no wired infrastructure and does not want to lease lines from a competitor. Mobile and wireless: This is the most interesting case. No cable restricts the user, who can roam between different wireless networks. Most technol- ogies discussed in this book deal with this type of device and the networks supporting them. Today’s most successful example for this category is GSM with more than 800 million users. The following section highlights some application scenarios predestined for the use of mobile and wireless devices. An overview of some typical devices is also given. The reader should keep in mind, however, that the scenarios and devices discussed only represent a selected spectrum, which will change in the future. As the market for mobile and wireless devices is growing rapidly, more devices will show up, and new application scenarios will be created. A short history of wireless communication will provide the background, briefly summing up the development over the last 200 years. Section 1.3 shows wireless and mobile communication from a marketing perspective. While there are already over a billion users of wireless devices today and the wireless business has experienced some problems in the last few years, the market potential is still tremendous. Section 1.4 shows some open research topics resulting from the fundamen- tal differences between wired and wireless communication. Section 1.5 presents the basic reference model for communication systems used throughout this book. This chapter concludes with an overview of the book, explaining the ‘tall and thin’ approach chosen. Tall and thin means that this book covers a variety of different aspects of mobile and wireless communication to provide a com- plete picture. Due to this broad perspective, however, it does not go into all the details of each technology and systems presented. 02Chap01 8804 (1-24) 30/5/03 11:03 am Page 3 Introduction 3 1.1 Applications Although many applications can benefit from wireless networks and mobile communications, particular application environments seem to be predestined for their use. The following sections will enumerate some of them – it is left to you to imagine more. 1.1.1 Vehicles Today’s cars already comprise some, but tomorrow’s cars will comprise many wireless communication systems and mobility aware applications. Music, news, road conditions, weather reports, and other broadcast information are received via digital audio broadcasting (DAB) with 1.5 Mbit/s. For personal communica- tion, a universal mobile telecommunications system (UMTS) phone might be available offering voice and data connectivity with 384 kbit/s. For remote areas, satellite communication can be used, while the current position of the car is determined via the global positioning system (GPS). Cars driving in the same area build a local ad-hoc network for the fast exchange of information in emer- gency situations or to help each other keep a safe distance. In case of an accident, not only will the airbag be triggered, but the police and ambulance service will be informed via an emergency call to a service provider. Cars with this technol- ogy are already available. In the future, cars will also inform other cars about accidents via the ad-hoc network to help them slow down in time, even before a driver can recognize an accident. Buses, trucks, and trains are already transmit- ting maintenance and logistic information to their home base, which helps to improve organization (fleet management), and saves time and money. Figure 1.1 shows a typical scenario for mobile communications with many wireless devices. Networks with a fixed infrastructure like cellular phones (GSM, UMTS) will be interconnected with trunked radio systems (TETRA) and wireless LANs (WLAN). Satellite communication links can also be used. The networks between cars and inside each car will more likely work in an ad-hoc fashion. Wireless pico networks inside a car can comprise personal digital assistants (PDA), laptops, or mobile phones, e.g., connected with each other using the Bluetooth technology. This first scenario shows, in addition to the technical content, something typical in the communication business – many acronyms. This book contains and defines many of these. If you get lost with an acronym, please check the appendix, which contains the complete list, or check the terms and definitions database interactive (TEDDI) of ETSI (2002). Think of similar scenarios for air traffic or railroad traffic. Different prob- lems can occur here due to speed. While aircraft typically travel at up to 900 km/h and current trains up to 350 km/h, many technologies cannot oper- ate if the relative speed of a mobile device exceeds, e.g., 250 km/h for GSM or 100 km/h for AMPS. Only some technologies, like DAB work up to 900 km/h (unidirectional only). 02Chap01 8804 (1-24) 30/5/03 11:03 am Page 4 4 Mobile communications Figure 1.1 A typical application of mobile communications: road trafﬁc oc UMTS, WLAN, DAB, d-h GSM, cdma2000, a TETRA,... Personal Travel Assistant, DAB, PDA, laptop, GSM, UMTS, WLAN, Bluetooth,... 1.1.2 Emergencies Just imagine the possibilities of an ambulance with a high-quality wireless con- nection to a hospital. Vital information about injured persons can be sent to the hospital from the scene of the accident. All the necessary steps for this particu- lar type of accident can be prepared and specialists can be consulted for an early diagnosis. Wireless networks are the only means of communication in the case of natural disasters such as hurricanes or earthquakes. In the worst cases, only decentralized, wireless ad-hoc networks survive. The breakdown of all cabling not only implies the failure of the standard wired telephone system, but also the crash of all mobile phone systems requiring base stations! 1.1.3 Business A travelling salesman today needs instant access to the company’s database: to ensure that files on his or her laptop reflect the current situation, to enable the company to keep track of all activities of their travelling employees, to keep data- bases consistent etc. With wireless access, the laptop can be turned into a true mobile office, but efficient and powerful synchronization mechanisms are needed to ensure data consistency. Figure 1.2 illustrates what may happen when employ- ees try to communicate off base. At home, the laptop connects via a WLAN or LAN and DSL to the Internet. Leaving home requires a handover to another tech- nology, e.g., to an enhanced version of GSM, as soon as the WLAN coverage ends. Due to interference and other factors discussed in chapter 2, data rates drop while cruising at higher speed. Gas stations may offer WLAN hot spots as well as gas. Trains already offer support for wireless connectivity. Several more handovers to different technologies might be necessary before reaching the office. No matter 02Chap01 8804 (1-24) 30/5/03 11:03 am Page 5 Introduction 5 LAN, WLAN GSM 53 kbit/s UMTS, GSM LAN Figure 1.2 780 kbit/s Bluetooth 500 kbit/s 115 kbit/s 100 Mbit/s, Mobile and wireless WLAN services – always best 54 Mbit/s connected UMTS, DECT 2 Mbit/s GSM/EDGE 384 kbit/s, GSM 115 kbit/s, UMTS, GSM WLAN 780 kbit/s WLAN 11 Mbit/s 384 kbit/s when and where, mobile communications should always offer as good connectiv- ity as possible to the internet, the company’s intranet, or the telephone network. 1.1.4 Replacement of wired networks In some cases, wireless networks can also be used to replace wired networks, e.g., remote sensors, for tradeshows, or in historic buildings. Due to economic reasons, it is often impossible to wire remote sensors for weather forecasts, earthquake detection, or to provide environmental information. Wireless con- nections, e.g., via satellite, can help in this situation. Tradeshows need a highly dynamic infrastructure, but cabling takes a long time and frequently proves to be too inflexible. Many computer fairs use WLANs as a replacement for cabling. Other cases for wireless networks are computers, sensors, or information dis- plays in historical buildings, where excess cabling may destroy valuable walls or floors. Wireless access points in a corner of the room can represent a solution. 1.1.5 Infotainment and more Internet everywhere? Not without wireless networks! Imagine a travel guide for a city. Static information might be loaded via CD-ROM, DVD, or even at home via the Internet. But wireless networks can provide up-to-date information at any appropriate location. The travel guide might tell you something about the history of a building (knowing via GPS, contact to a local base station, or trian- gulation where you are) downloading information about a concert in the building at the same evening via a local wireless network. You may choose a seat, pay via electronic cash, and send this information to a service provider (Cheverst, 2000). Another growing field of wireless network applications lies in entertainment and games to enable, e.g., ad-hoc gaming networks as soon as people meet to play together. 1.1.6 Location dependent services 02Chap01 8804 (1-24) 30/5/03 11:03 am Page 6 6 Mobile communications Many research efforts in mobile computing and wireless networks try to hide the fact that the network access has been changed (e.g., from mobile phone to WLAN or between different access points) or that a wireless link is more error prone than a wired one. Many chapters in this book give examples: Mobile IP tries to hide the fact of changing access points by redirecting packets but keep- ing the same IP address (see section 8.1), and many protocols try to improve link quality using encoding mechanisms or retransmission so that applications made for fixed networks still work. In many cases, however, it is important for an application to ‘know’ some- thing about the location or the user might need location information for further activities. Several services that might depend on the actual location can be distinguished: Follow-on services: The function of forwarding calls to the current user location is well known from the good old telephone system. Wherever you are, just transmit your temporary phone number to your phone and it redi- rects incoming calls.2 Using mobile computers, a follow-on service could offer, for instance, the same desktop environment wherever you are in the world. All e-mail would automatically be forwarded and all changes to your desktop and documents would be stored at a central location at your com- pany. If someone wanted to reach you using a multimedia conferencing system, this call would be forwarded to your current location. Location aware services: Imagine you wanted to print a document sitting in the lobby of a hotel using your laptop. If you drop the document over the printer icon, where would you expect the document to be printed? Certainly not by the printer in your office! However, without additional information about the capabilities of your environment, this might be the only thing you can do. For instance, there could be a service in the hotel announcing that a standard laser printer is available in the lobby or a color printer in a hotel meeting room etc. Your computer might then trans- mit your personal profile to your hotel which then charges you with the printing costs. Privacy: The two service classes listed above immediately raise the question of privacy. You might not want video calls following you to dinner, but maybe you would want important e-mails to be forwarded. There might be locations and/or times when you want to exclude certain services from reaching you and you do not want to be disturbed. You want to utilize loca- tion dependent services, but you might not want the environment to know exactly who you are. Imagine a hotel monitoring all guests and selling these profiles to companies for advertisements. Information services: While walking around in a city you could always use 2 Actually, this is already done with the phone network – your phone just handles some signalling. 02Chap01 8804 (1-24) 30/5/03 11:03 am Page 7 Introduction 7 your wireless travel guide to ‘pull’ information from a service, e.g., ‘Where is the nearest Mexican restaurant?’ However, a service could also actively ‘push’ information on your travel guide, e.g., the Mexican restaurant just around the corner has a special taco offer. Support services: Many small additional mechanisms can be integrated to support a mobile device. Intermediate results of calculations, state informa- tion, or cache contents could ‘follow’ the mobile node through the fixed network. As soon as the mobile node reconnects, all information is avail- able again. This helps to reduce access delay and traffic within the fixed network. Caching of data on the mobile device (standard for all desktop systems) is often not possible due to limited memory capacity. The alterna- tive would be a central location for user information and a user accessing this information through the (possibly large and congested) network all the time as it is often done today. 1.1.7 Mobile and wireless devices Even though many mobile and wireless devices are available, there will be many more in the future. There is no precise classification of such devices, by size, shape, weight, or computing power. Currently, laptops are considered the upper end of the mobile device range.3 The following list gives some examples of mobile and wireless devices graded by increasing performance (CPU, memory, display, input devices etc.). However, there is no sharp line between the cate- gories and companies tend to invent more and more new categories. Sensor: A very simple wireless device is represented by a sensor transmitting state information. One example could be a switch sensing the office door. If the door is closed, the switch transmits this to the mobile phone inside the office which will not accept incoming calls. Without user interaction, the semantics of a closed door is applied to phone calls. Embedded controllers: Many appliances already contain a simple or some- times more complex controller. Keyboards, mice, headsets, washing machines, coffee machines, hair dryers and TV sets are just some examples. Why not have the hair dryer as a simple mobile and wireless device (from a communication point of view) that is able to communicate with the mobile phone? Then the dryer would switch off as soon as the phone starts ringing – that would be a nice application! Pager: As a very simple receiver, a pager can only display short text mes- sages, has a tiny display, and cannot send any messages. Pagers can even be integrated into watches. The tremendous success of mobile phones, has made the pager virtually redundant in many countries. Short messages have replaced paging. The situation is somewhat different for emergency services 3 Putting a mainframe on a truck does not really make it a mobile device. 02Chap01 8804 (1-24) 30/5/03 11:03 am Page 8 8 Mobile communications where it may be necessary to page a larger number of users reliably within short time. Mobile phones: The traditional mobile phone only had a simple black and white text display and could send/receive voice or short messages. Today, mobile phones migrate more and more toward PDAs. Mobile phones with full color graphic display, touch screen, and Internet browser are easily available. Personal digital assistant: PDAs typically accompany a user and offer simple versions of office software (calendar, note-pad, mail). The typical input device is a pen, with built-in character recognition translating hand- writing into characters. Web browsers and many other software packages are available for these devices. Pocket computer: The next steps toward full computers are pocket comput- ers offering tiny keyboards, color displays, and simple versions of programs found on desktop computers (text processing, spreadsheets etc.). Notebook/laptop: Finally, laptops offer more or less the same performance as standard desktop computers; they use the same software – the only tech- nical difference being size, weight, and the ability to run on a battery. If operated mainly via a sensitive display (touch sensitive or electromagnetic), the devices are also known as notepads or tablet PCs. The mobile and wireless devices of the future will be more powerful, less heavy, and comprise new interfaces to the user and to new networks. However, one big problem, which has not yet been solved, is the energy supply. The more features that are built into a device, the more power it needs. The higher the perfor- mance of the device, the faster it drains the batteries (assuming the same technology). Furthermore, wireless data transmission consumes a lot of energy. Although the area of mobile computing and mobile communication is developing rapidly, the devices typically used today still exhibit some major drawbacks compared to desktop systems in addition to the energy problem. Interfaces have to be small enough to make the device portable, so smaller key- boards are used. This makes typing difficult due to their limited key size. Small displays are often useless for graphical display. Higher resolution does not help, as the limiting factor is the resolution capacity of the human eye. These devices have to use new ways of interacting with a user, such as, e.g., touch sensitive displays and voice recognition. Mobile communication is greatly influenced by the merging of telecommu- nication and computer networks. We cannot say for certain what the telephone of the future will look like, but it will most probably be a computer. Even today, telephones and mobile phones are far from the simple ‘voice transmission devices’ they were in the past.4 Developments like ‘voice over IP’ and the gen- eral trend toward packet-oriented networks enforce the metamorphosis of telephones (although voice services still guarantee good revenue). While no one 4 Chapter 4 will present more features of modern mobile phone systems, including the growing demand for bandwidth to use typical Internet applications via the mobile ‘phone’. 02Chap01 8804 (1-24) 30/5/03 11:03 am Page 9 Introduction 9 can predict the future of communication devices precisely, it is quite clear that there will still be many fixed systems, complemented by a myriad of small wire- less computing devices all over the world. More people already use mobile phones than fixed phones! 1.2 A short history of wireless communication For a better understanding of today’s wireless systems and developments, a short history of wireless communication is presented in the following section. This cannot cover all inventions but highlights those that have contributed fun- damentally to today’s systems. The use of light for wireless communications reaches back to ancient times. In former times, the light was either ‘modulated’ using mirrors to create a cer- tain light on/light off pattern (’amplitude modulation’) or, for example, flags were used to signal code words (’amplitude and frequency modulation’, see chapter 2). The use of smoke signals for communication is mentioned by Polybius, Greece, as early as 150 BC. It is also reported from the early (or west- ern) Han dynasty in ancient China (206 BC–24 AD) that light was used for signaling messages along a line of signal towers towards the capitol Chang’an (Xi’an). Using light and flags for wireless communication remained important for the navy until radio transmission was introduced, and even today a sailor has to know some codes represented by flags if all other means of wireless com- munication fail. It was not until the end of the 18th century, when Claude Chappe invented the optical telegraph (1794), that long-distance wireless com- munication was possible with technical means. Optical telegraph lines were built almost until the end of the following century. Wired communication started with the first commercial telegraph line between Washington and Baltimore in 1843, and Alexander Graham Bell’s invention and marketing of the telephone in 1876 (others tried marketing before but did not succeed, e.g., Philip Reis, 1834–1874, discovered the tele- phone principle in 1861). In Berlin, a public telephone service was available in 1881, the first regular public voice and video service (multimedia!) was already available in 1936 between Berlin and Leipzig. All optical transmission systems suffer from the high frequency of the car- rier light. As every little obstacle shadows the signal, rain and fog make communication almost impossible. At that time it was not possible to focus light as efficiently as can be done today by means of a laser, wireless communi- cation did not really take off until the discovery of electromagnetic waves and the development of the equipment to modulate them. It all started with Michael Faraday (and about the same time Joseph Henry) demonstrating elec- tromagnetic induction in 1831 and James C. Maxwell (1831–79) laying the theoretical foundations for electromagnetic fields with his famous equations (1864). Finally, Heinrich Hertz (1857–94) was the first to demonstrate the wave 02Chap01 8804 (1-24) 30/5/03 11:03 am Page 10 10 Mobile communications character of electrical transmission through space (1886), thus proving Maxwell’s equations. Today the unit Hz reminds us of this discovery. Nikola Tesla (1856–1943) soon increased the distance of electromagnetic transmission. The name, which is most closely connected with the success of wireless communication, is certainly that of Guglielmo Marconi (1874–1937). He gave the first demonstration of wireless telegraphy in 1895 using long wave transmis- sion with very high transmission power (> 200 kW). The first transatlantic transmission followed in 1901. Only six years later, in 1907, the first commer- cial transatlantic connections were set up. Huge base stations using up to thirty 100 m high antennas were needed on both sides of the Atlantic Ocean. Around that time, the first World Administration Radio Conference (WARC) took place, coordinating the worldwide use of radio frequencies. The first radio broadcast took place in 1906 when Reginald A. Fessenden (1866–1932) trans- mitted voice and music for Christmas. In 1915, the first wireless voice transmission was set up between New York and San Francisco. The first com- mercial radio station started in 1920 (KDKA from Pittsburgh). Sender and receiver still needed huge antennas and high transmission power. This changed fundamentally with the discovery of short waves, again by Marconi, in 1920 (In connection with wireless communication, short waves have the advantage of being reflected at the ionosphere.) It was now possible to send short radio waves around the world bouncing at the ionosphere – this technique is still used today. The invention of the electronic vacuum tube in 1906 by Lee DeForest (1873–1961) and Robert von Lieben (1878–1913) helped to reduce the size of sender and receiver. Vacuum tubes are still used, e.g., for the amplification of the output signal of a sender in today’s radio stations. One of the first ‘mobile’ transmitters was on board a Zeppelin in 1911. As early as 1926, the first tele- phone in a train was available on the Berlin-Hamburg line. Wires parallel to the railroad track worked as antenna. The first car radio was commercially available in 1927 (‘Philco Transitone’); but George Frost an 18-year-old from Chicago had integrated a radio into a Ford Model T as early as 1922. Nineteen twenty-eight was the year of many field trials for television broadcasting. John L. Baird (1888–1946) transmitted TV across the Atlantic and demonstrated color TV, the station WGY (Schenectady, NY) started regular TV broadcasts and the first TV news. The first teleteaching started in 1932 from the CBS station W2XAB. Up until then, all wireless communication used amplitude modulation (see section 2.6), which offered relatively poor quality due to interference. One big step forward in this respect was the invention of frequency modulation in 1933 by Edwin H. Armstrong (1890–1954). Both fundamental modulation schemes are still used for today’s radio broadcasting with frequency modulation resulting in a much better quality. By the early 1930s, many radio stations were already broadcasting all over the world. After the Second World War, many national and international projects in the area of wireless communications were triggered off. The first network in Germany was the analog A-Netz from 1958, using a carrier frequency of 160 MHz. Connection setup was only possible from the mobile station, no 02Chap01 8804 (1-24) 30/5/03 11:03 am Page 11 Introduction 11 handover, i.e., changing of the base station, was possible. Back in 1971, this system had coverage of 80 per cent and 11,000 customers. It was not until 1972 that the B-Netz followed in Germany, using the same 160 MHz. This network could initiate the connection setup from a station in the fixed telephone net- work, but, the current location of the mobile receiver had to be known. This system was also available in Austria, The Netherlands, and Luxembourg. In 1979, the B-Netz had 13,000 customers in West Germany and needed a heavy sender and receiver, typically built into cars. At the same time, the northern European countries of Denmark, Finland, Norway, and Sweden (the cradle of modern mobile communications) agreed upon the nordic mobile telephone (NMT) system. The analogue NMT uses a 450 MHz carrier and is still the only available system for mobile communication in some very remote places (NMT at 900 MHz followed in 1986). Several other national standards evolved and by the early 1980s Europe had more than a handful of different, completely incompatible analog mobile phone standards. In accordance with the general idea of a European Union, the European coun- tries decided to develop a pan-European mobile phone standard in 1982. The new system aimed to: use a new spectrum at 900 MHz; allow roaming5 throughout Europe; be fully digital; and offer voice and data service. The ‘Groupe Spéciale Mobile’ (GSM) was founded for this new development. In 1983 the US system advanced mobile phone system (AMPS) started (EIA, 1989). AMPS is an analog mobile phone system working at 850 MHz. Telephones at home went wireless with the standard CT1 (cordless telephone) in 1984, (fol- lowing its predecessor the CT0 from 1980). As digital systems were not yet available, more analog standards followed, such as the German C-Netz at 450 MHz with analog voice transmission. Hand-over between ‘cells’ was now possible, the signalling system was digital in accordance with the trends in fixed networks (SS7), and automatic localization of a mobile user within the whole network was sup- ported. This analog network was switched off in 2000. Apart from voice transmission the services offered fax, data transmission via modem, X.25, and electronic mail. CT2, the successor of CT1, was embodied into British Standards published in 1987 (DTI, 1987) and later adopted by ETSI for Europe (ETS, 1994). CT2 uses the spectrum at 864 MHz and offers a data channel at a rate of 32 kbit/s. The early 1990s marked the beginning of fully digital systems. In 1991, ETSI adopted the standard digital European cordless telephone (DECT) for digital cordless telephony (ETSI, 1998). DECT works at a spectrum of 1880–1900 MHz with a range of 100–500 m. One hundred and twenty duplex channels can carry 5 Roaming here means a seamless handover of a telephone call from one network provider to another while crossing national boundaries. 02Chap01 8804 (1-24) 30/5/03 11:03 am Page 12 12 Mobile communications up to 1.2 Mbit/s for data transmission. Several new features, such as voice encryp- tion and authentication, are built-in. The system supports several 10,000 users/km2 and is used in more than 110 countries around the world (over 150 million shipped units). Today, DECT has been renamed digital enhanced cord- less telecommunications for marketing reasons and to reflect the capabilities of DECT to transport multimedia data streams. Finally, after many years of discus- sions and field trials, GSM was standardized in a document of more than 5,000 pages in 1991. This first version of GSM, now called global system for mobile communication, works at 900 MHz and uses 124 full-duplex channels. GSM offers full international roaming, automatic location services, authentication, encryption on the wireless link, efficient interoperation with ISDN systems, and a relatively high audio quality. Furthermore, a short message service with up to 160 alphanumeric characters, fax group 3, and data services at 9.6 kbit/s have been integrated. Depending on national regulations, one or several providers can use the channels, different accounting and charging schemes can be applied etc. However, all GSM systems remain compatible. Up to now, over 400 providers in more than 190 countries have adopted the GSM standard (over 70 per cent of the world’s wireless market). It was soon discovered that the analog AMPS in the US and the digital GSM at 900 MHz in Europe are not sufficient for the high user densities in cities. While in the US, no new spectrum was allocated for a new system, in Europe a new frequency band at 1800 MHz was chosen. The effect was as follows. In the US, different companies developed different new, more bandwidth-efficient tech- nologies to operate side-by-side with AMPS in the same frequency band. This resulted in three incompatible systems, the analog narrowband AMPS (IS-88, (TIA, 1993a)), and the two digital systems TDMA (IS-136, (TIA, 1996)) and CDMA (IS-95, (TIA, 1993b)). The Europeans agreed to use GSM in the 1800 MHz spectrum. These GSM–1800 networks (also known as DCS 1800, digital cellular system) started with a better voice quality due to newer speech codecs. These net- works consist of more and smaller cells (see chapters 2 and 4). GSM is also available in the US as GSM–1900 (also called PCS 1900) using spectrum at 1900 MHz like the newer versions of the TDMA and CDMA systems. Europe believes in standards, while the US believes in market forces – GSM is one of the few examples where the approach via standardization worked. So, while Europe has one common standard, and roaming is possible even to Australia or Singapore, the US still struggles with many incompatible systems. However, the picture is different when it comes to more data communication- oriented systems like local area networks. Many proprietary wireless local area network systems already existed when ETSI standardized the high performance radio local area network (HIPERLAN) in 1996. This was a family of standards and recommendations. HIPERLAN type 1 should operate at 5.2 GHz and should offer data rates of up to 23.5 Mbit/s. Further types had been specified with type 4 going up to 155 Mbit/s at 17 GHz. However, although coming later than HIPERLAN in 1997, the IEEE standard 802.11 was soon the winner for local area 02Chap01 8804 (1-24) 30/5/03 11:03 am Page 13 Introduction 13 networks. It works at the license-free Industrial, Science, Medical (ISM) band at 2.4 GHz and infra red offering 2 Mbit/s in the beginning (up to 10 Mbit/s with proprietary solutions already at that time). Although HIPERLAN has better per- formance figures, no products were available while many companies soon offered 802.11 compliant equipment. Nineteen ninety-eight marked the beginning of mobile communication using satellites with the Iridium system (Iridium, 2002). Up to this time, satel- lites basically worked as a broadcast distribution medium or could only be used with big and heavy equipment – Iridium marked the beginning of small and truly portable mobile satellite telephones including data service. Iridium consists of 66 satellites in low earth orbit and uses the 1.6 GHz band for communication with the mobile phone. In 1998 the Europeans agreed on the universal mobile telecommunications system (UMTS) as the European proposal for the International Telecommunication Union (ITU) IMT-2000 (international mobile telecommunications). In the first phase, UMTS combines GSM network technol- ogy with more bandwidth-efficient CDMA solutions. The IMT-2000 recommendations define a common, worldwide framework for future mobile communication at 2 GHz (ITU, 2002). This includes, e.g., a framework for services, the network architecture including satellite communica- tion, strategies for developing countries, requirements of the radio interface, spectrum considerations, security and management frameworks, and different transmission technologies. Nineteen ninety nine saw several more powerful WLAN standards. IEEE published 802.11b offering 11 Mbit/s at 2.4 GHz. The same spectrum is used by Bluetooth, a short-range technology to set-up wireless personal area networks with gross data rates less than 1 Mbit/s. The ITU dropped the plan of a single, worldwide standard for third generation mobile phone systems and decided on the IMT-2000 family concept that includes several technologies (UMTS, cdma2000, DECT etc. see chapter 4). The wireless application protocol (WAP) started at the same time as i-mode in Japan. While WAP did not succeed in the beginning, i-mode soon became a tremendous success (see chapter 10). The year 2000, came with higher data rates and packet-oriented transmis- sion for GSM (HSCSD, GPRS – see chapter 4). It should not be forgotten that the late nineties was the time when a lot of hype about the communications busi- ness started. Thus it was relatively easy for marketing people to portray third generation technology as high-performance Internet on mobile phones. In Europe, UMTS was announced as capable of handling live, interactive video streaming for all users at 2 Mbit/s. All technically-oriented people knew that this promise could not be fulfilled by the system, but the auctions and beauty con- tests for licensing 3G spectrum started. In Europe alone more than €100 billion had been paid before the disillusionment set in. Companies that had never run a network before paid billions for licenses. Many of these companies are now bankrupt and the remaining companies suffer from the debts. Most of the hype is over, but the third generation of mobile communication 02Chap01 8804 (1-24) 30/5/03 11:03 am Page 14 14 Mobile communications Figure 1.3 cellular phones satellites cordless wireless Overview of some phones LAN wireless communication systems 1980: CT0 1981: NMT 450 1982: Inmarsat-A 1983: AMPS 1984: CT1 1986: NMT 900 1987: CT1+ 1988: Inmarsat-C 1989: CT 2 1991: 1991: 1991: CDMA D-AMPS DECT 1992: 1992: 199x: GSM Inmarsat-B proprietary 1993: Inmarsat-M PDC 1997: 1994: IEEE 802.11 DCS 1800 1998: Iridium 1999 802.11b, Bluetooth 2000: 2000: GPRS IEEE 802.11a 2001: IMT d-2000 analog digital 200?: Fourth Generation (Internet based) started in 2001 in Japan with the FOMA service, in Europe with several field trials, and in, e.g., Korea with cdma2000 (see Figure 4.2 for the evolution of 3G systems). IEEE released a new WLAN standard, 802.11a, operating at 5 GHz and offering 02Chap01 8804 (1-24) 30/5/03 11:03 am Page 15 Introduction 15 gross data rates of 54 Mbit/s. This standard uses the same physical layer as HiperLAN2 does (standardized in 2000), the only remaining member of the HIPERLAN family. In 2002 new WLAN developments followed. Examples are 802.11g offering up to 54 Mbit/s at 2.4 GHz and many new Bluetooth applications (headsets, remote controls, wireless keyboards, hot syncing etc.). The network providers continued to deploy the infrastructure for 3G networks as many licens- ing conditions foresee a minimum coverage at a certain date. While digital TV via satellite has existed for several years, digital terrestrial TV (DVB-T, see chapter 6) started as regular service in Berlin in November 2002. This system allows for high- quality TV on the move and requires only an antenna of a few centimeters. Figure 1.3 gives an overview of some of the networks described above, and shows the development of cellular phone systems and cordless phones together with satellites and LANs. While many of the classical mobile phone systems con- verged to IMT-2000 systems (with cdma2000 and W-CDMA/UMTS being the predominant systems), the wireless LAN area developed more or less indepen- dently. No one knows exactly what the next generation of mobile and wireless system will look like, but, there are strong indicators that it will be widely Internet based – the system will use Internet protocols and Internet applications. While the current third generation systems still heavily rely on classical tele- phone technology in the network infrastructure, future systems will offer users the choice of many different networks based on the internet (see chapter 11). However, no one knows exactly when and how this common platform will be available. Companies have to make their money with 3G systems first.

Document Details

Related

Full Transcript

Upgrade to continue