Principal Handbook of Antennas in Wireless Communications
Handbook of Antennas in Wireless CommunicationsLester Packer, Enrique Cadenas
The move toward worldwide wireless communications continues at a remarkable pace, and the antenna element of the technology is crucial to its success. With contributions from more than 30 international experts, the Handbook of Antennas in Wireless Communications brings together all of the latest research and results to provide engineering professionals and students with a one-stop reference on the theory, technologies, and applications for indoor, hand-held, mobile, and satellite systems.Beginning with an introduction to wireless communications systems, it offers an in-depth treatment of propagation prediction and fading channels. It then explores antenna technology with discussion of antenna design methods and the various antennas in current use or development for base stations, hand held devices, satellite communications, and shaping beams. The discussions then move to smart antennas and phased array technology, including details on array theory and beamforming techniques. Space diversity, direction-of-arrival estimation, source tracking, and blind source separation methods are addressed, as are the implementation of smart antennas and the results of field trials of systems using smart antennas implemented. Finally, the hot media topic of the safety of mobile phones receives due attention, including details of how the human body interacts with the electromagnetic fields of these devices.Its logical development and extensive range of diagrams, figures, and photographs make this handbook easy to follow and provide a clear understanding of design techniques and the performance of finished products. Its unique, comprehensive coverage written by top experts in their fields promises to make the Handbook of Antennas in Wireless Communications the standard reference for the field.
Most frequently terms
HANDBOOK OF ANTENNAS IN WIRELESS COMMUNICATIONS © 2002 by CRC Press LLC THE ELECTRICAL ENGINEERING AND APPLIED SIGNAL PROCESSING SERIES Edited by Alexander Poularikas The Advanced Signal Processing Handbook: Theory and Implementation for Radar, Sonar, and Medical Imaging Real-Time Systems Stergios Stergiopoulos The Transform and Data Compression Handbook K.R. Rao and P.C. Yip Handbook of Multisensor Data Fusion David Hall and James Llinas Handbook of Antennas in Wireless Communications Lal Chand Godara Forthcoming Titles Propagation Data Handbook for Wireless Communications Robert Crane The Digital Color Imaging Handbook Guarav Sharma Handbook of Neural Network Signal Processing Yu Hen Hu and Jeng-Neng Hwang Applications in Time Frequency Signal Processing Antonia Papandreou-Suppappola Noise Reduction in Speech Applications Gillian Davis Signal Processing in Noise Vyacheslav Tuzlukov Electromagnetic Radiation and the Human Body: Effects, Diagnosis and Therapeutic Technologies Nikolaos Uzunoglu and Konstantina S. Nikita Digital Signal Processing with Examples in MATLAB® Samuel Stearns © 2002 by CRC Press LLC HANDBOOK OF ANTENNAS IN WIRELESS COMMUNICATIONS Edited by LAL CHAND GODARA CRC Press Boca Raton London New York Washington, D.C. Library of Congress Cataloging-in-Publication Data Catalog record is available from the Library of Congress This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming, and recording, or by any information storage or retrieval system, without prior permission in writing; from the publisher. All rights reserved. Authorization to photocopy items for internal or personal use, or the personal or internal use of specific clients, may be granted by CRC Press LLC, provided that $1.50 per page photocopied is paid directly to Copyright clearance Center, 222 Rosewood Drive, Danvers, MA 01923 USA. The fee code for users of the Transactional Reporting Service is ISBN 0-8493-0124-6/02/$0.00+$1.50. The fee is subject to change without notice. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. The consent of CRC Press LLC does not extend to copying for general distribution, for promotion, for creating new works, or for resale. Specific permission must be obtained in writing from CRC Press LLC for such copying. Direct all inquiries to CRC Press LLC, 2000 N.W. Corporate Blvd., Boca Raton, Florida 33431. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation, without intent to infringe. Visit the CRC Press Web site at www.crcpress.com © 2002 by CRC Press LLC No claim to original U.S. Government works International Standard Book Number 0-8493-0124-6 Printed in the United States of America 1 2 3 4 5 6 7 8 9 0 Printed on acid-free paper Preface I authored a two-part article for the Proceeding of the Institute of Electrical and Electronics Engineers (IEEE) on the application of antenna arrays to mobile communications in 1997. It provided the current state of antenna array research and described how an array of antennas may be used to help meet the ever-growing demand of increased channel capacity for wireless mobile communications services. The amount and the kind of feedback I received on the subject, particularly from graduate students and practicing engineers, indicated to me that there is a need for a more comprehensive source of this material than a journal article. One day in late 1998, I received an e-mail from Dr. Alexander D. Poularikas, who coordinates the Electrical Engineering and Signal Processing series for CRC Press, inviting me to be the editor of a handbook covering the fundamental developments of this field so that the engineers in practice or the ones who want to start in this area have a good source to guide them. I accepted his invitation and prepared a list of topics to be covered by the handbook. Because the handbook was meant to be a major reference source on this subject, I invited the leading experts in the field to contribute material on topics of their special interest. I am very excited about the final outcome and trust that you share my enthusiasm as I briefly describe what the handbook has to offer. The handbook has successfully brought together every aspect of antennas in wireless communications with 26 chapters filled with the latest research and development results compiled by leading researchers in a manner that is easy to follow. The material has been developed logically, requiring no prerequisite and thus making it extremely useful not only for researchers and practicing engineers as a reference book but also for newcomers as a great source of learning. It is a unique book covering all facets of antennas for wireless communications providing detailed treatment of cellular systems, antenna design techniques, practical antennas, phased-array technology, theory and implementation of smart antennas, and interaction of EM radiation with the human body. It contains more than 1200 references for the readers to probe further. The handbook would be useful for • Practicing electrical engineers, in general, and communication engineers, in particular, as a reference book • Academics in the area of mobile communications, signal processing, antenna theory, and smart antennas • Graduate students and researchers in this area • Antenna designers in general • Those who are fascinated by the field of mobile communications and smart antennas The chapters in the book have been selected to provide coverage of different topics. However, some overlap between various chapters has been allowed to provide discussion from a different point of view. © 2002 by CRC Press LLC The handbook has been organized into six parts outlined as follows: A B C D E F Wireless communication systems and channel characteristics Antenna technology and numerical methods Antenna developments and practical antennas Smart antennas and array theory Implementation of smart antenna systems Electromagnetic radiation and the human body Chapters 1 through 4 are devoted to wireless communications systems and channel characterization. Chapter 1, “Cellular Systems,” presents cellular fundamentals by describing the working of mobile communications systems and discussing concepts of multiple access schemes, channel reuse, channel allocation and assignments, and handoff and power control. It then briefly describes various popular standards. Chapter 2, “Satellite-Based Mobile Communications,” discusses satellite orbital fundamentals and the satellite radiopath, and describes various mobile satellite communications systems. Chapter 3, “Propagation Prediction for Urban Systems,” treats the prediction of the average signal strength for a variety of physical parameters and conditions such as range, antenna height, presence of foliage, and terrain; and discusses site specific predictions using ray models. Chapter 4, “Fading Channels,” emphasizes fundamental fading manifestations, types of degradation, and methods for mitigating the degradation. It presents examples to mitigate the effects of frequency-selective fading in time division multiple access (TDMA) and code division multiple access (CDMA) systems. Chapters 5 through 10 provide coverage of antenna technology and numerical methods. Chapter 5 introduces basic antenna parameters and terminology; and discusses commonly used antenna types, impedance matching, feeding arrangements, and available software for antenna analysis and design. Chapter 6 introduces microstrip patch antennas by discussing their general characteristics. It describes various feed techniques and methods to enhance bandwidth of patch antenna and to reduce the size of conductors. Examples of active patch antennas are also included in this chapter. Chapter 7 introduces the finite difference time domain (FDTD) method with emphasis on its applications to printed antenna and antenna arrays. The chapter discusses fundamentals of FDTD, absorbing boundary conditions, and radiation patterns; and presents examples of various microstrip antenna analyses. Chapter 8, “Method of Moments Applied to Antennas,” concentrates on the application of integral equations to antenna problems and their solution using the method of moments (MOM). It presents the basic philosophy of MOM and its application to wire antennas, arbitrary metallic structures, and combined metallic and dielectric structures. Chapter 9 introduces genetic algorithms and shows how these may be applied to find good solutions to wireless antenna problems. Chapter 10, “High-Frequency Techniques,” presents high-frequency applications for antennas by discussing modern geometric optics, geometric theory of diffraction, physical optics, and physical theory of diffraction. Chapters 11 through 15 constitute Part C of the handbook and are devoted to antenna developments and practical antennas. Chapter 11 presents development in outdoor and indoor base station antennas in Japan by describing various base station antennas for cellular systems, diversity antennas for macrocellular systems, antennas for micro- and picocellular systems, and personal handy phone system (PHS) base station antennas. Chapter 12, “Handheld Antennas,” describes various antennas used for handheld phones and presents a detailed study of meander line antennas for personal wireless communications. Chapters 13 and 14 provide coverage on antenna development for satellite communications; Chapter 13 concentrates on aeronautical and maritime antennas whereas Chapter 14 focuses on fixed and mobile © 2002 by CRC Press LLC antennas. Chapter 13 presents antennas and tracking systems for International Maritime Satellite (INMARSAT)-A, -B, -C, -F, -M, and -AERO; and antennas for land mobile earth stations and handcarried terminals. Chapter 14 presents space segment antennas, earth-segment antennas, and gateway antennas for satellite communications; microstrip antennas for fixed and mobile satellite communications; and mobile antennas for receiving direct-broadcast satellite service television (DBS TV) and SATPHONE antenna systems. Chapter 15, “Shaped-Beam Antennas,” focuses on shaped dielectric lens antennas and presents design guidelines for these antennas along with the discussion of some practical aspects, focusing on mobile applications. Part D of this handbook on smart antennas and array theory contains Chapters 16 to 21. Chapter 16 presents basic array theory and pattern synthesis techniques by discussing basic theory of antenna arrays, array weight synthesis techniques, and array geometry consideration for pattern adjustment. Many examples are included in the chapter to emphasize the concepts. Chapter 17, “Electromagnetic Vector Sensors with Beamforming Applications,” describes advantages and developments of vector sensors, solves a beamforming problem using these sensors, and compares the results with that of scalar sensors. Chapter 18, “Optimum and Suboptimum Transmit Beamforming,” discusses channel characterization and presents beamforming strategies for transmit arrays including beamforming algorithms and robust beamforming methods. Chapter 19, “Spatial Diversity for Wireless Communications,” treats the basic principles of spatial diversity combining and discusses the performance improvement that can be accomplished by a diversity array using various combined techniques. The chapter also presents the results on the effect of branch correlation and mutual coupling. Chapter 20, “Direction-of-Arrival Estimation in Mobile Communication Environments,” presents various methods for estimating direction of arrival (DOA) of point sources and tracking of moving sources. A detailed treatment of estimation for the wireless channel is also included in the chapter. Chapter 21, “Blind Channel Identification and Source Separation in Space Division Multiple Access Systems,” addresses the problem of discriminating radio sources in the context of cellular mobile wireless digital communications systems. The chapter describes several deterministic as well as stochastic maximum likelihood methods to solve the blind sources separation and channel identification problem. Chapter 22 through Chapter 24 are devoted to implementation of smart antenna systems. Chapter 22, “Smart Antenna System Architecture and Hardware Implementation,” presents an overview of system architecture and implementation and discusses various important design issues. The chapter describes some real-time implemented systems using digital signal processor (DSP) modules. Chapter 23 presents phased-array technology for wireless systems by discussing phased-array antennas for land mobile communications systems, stratospheric communications systems, and satellite communications systems. Chapter 24, “Adaptive Antennas for Global System for Mobile Communications and Time Division Multiple Access (Interim Standard-136) Systems,” starts with an overview of these systems and then outlines some of the most important issues to consider when applying adaptive antenna techniques to existing cellular systems. A discussion of some possible system architectures suitable for implementation is presented and issues related to signal-processing algorithms are considered. The chapter presents a detailed simulation of the system and compares the results with those obtained from field trials. Chapters 25 and 26 are devoted to the final part on electromagnetic radiation and the human body. Chapter 25 mainly deals with the effect on the human body of the radiation characteristics of handheld antennas whereas Chapter 26 concentrates on health hazards of electromagnetic (EM) radiation. Chapter 25, “Electromagnetic Interactions of Handheld Wireless Communication Antennas with the © 2002 by CRC Press LLC Human Body,” reviews exposure standards for radio-frequency (RF) fields and different types of handheld wireless devices, and describes numerical techniques and experimental methods used to quantify and characterize the interactions of the radiated field with humans. Examples showing the effect of these interactions on the radiation and input impedance characteristics of antennas in handheld devices are presented. Chapter 26, “Safety Aspects of Radio-Frequency Effects in Humans from Communication Devices,” considers how guidelines for human exposures to RF are derived, known interactions with human tissues and their measurements, and the evidence for the existence of health effects. © 2002 by CRC Press LLC Contributors Sören Andersson Christos Christodoulou Lal C. Godara Ericsson Radio Systems Stockholm, Sweden University of New Mexico Albuquerque, New Mexico School of Electrical Engineering University College, University of New South Wales Australian Defence Force Academy Canberra, Australia Hiroyuki Arai Division of Electric and Computer Engineering Yokohama National University Yokohama, Japan Victor Barroso Instituto Superior Tecnico Instituto de Sistemas e Robotica Lisboa, Portugal Mats Bengtsson Henrik Dam Ericsson LMD Copenhagen, Denmark Paul W. Davis School of Computer Science and Electrical Engineering University of Queensland St. Lucia, Queensland, Australia Department of Signals, Sensors and Systems Royal Institute of Technology Stockholm, Sweden Antonije R. Djordjevic Magnus Berg Atef Z. Elsherbeni Ericsson Radio Systems Stockholm, Sweden Jennifer T. Bernhard Department of Electrical and Computer Engineering University of Illinois at UrbanaChampaign Urbana, Illinois School of Electrical Engineering University of Belgrade Belgrade, Yugoslavia Marek E. Bialkowski School of Computer Science & Electrical Engineering University of Queensland Brisbane, Queensland, Australia © 2002 by CRC Press LLC Electrical Engineering Department ITESM Guadalajara, Mexico Bo Hagerman Ericsson Radio Systems S-164 80 Stockholm, Sweden Kwok Chiang Ho Addest Technovation Pte. Ltd. Singapore, Republic of Singapore Chun-Wen Paul Huang Electrical Engineering Department University of Mississippi University, Mississippi Meng Hwa Er Nanyang Technological University School of Electrical and Electronic Engineering Singapore, Republic of Singapore Henry L. Bertoni Department of Electrical & Computer Engineering Polytechnic University Brooklyn, New York Javier Gómez-Tagle Carlos A. Cardoso Fernandes Instituto Superior Técnico Instituto de Telecomunicações Lisboa, Portugal Ulf Forssén Ericsson Radio Systems Stockholm, Sweden Electrical Engineering Department University of Mississippi University, Mississippi Magdy F. Iskander Electrical Engineering Department University of Utah Salt Lake City, Utah Ramakrishna Janaswamy Code EC/Js, Naval Postgraduate School Monterey, California Ami Kanazawa Yokosuka Radio Communications Research Center Communication Research Laboratory Ministry of Posts and Telecommunications Yokosuka, Japan Jonas Karlsson José M. F. Moura Roberto G. Rojas Ericsson Radio Systems Stockholm, Sweden Department of Electrical and Computer Engineering Carnegie Mellon University Pittsburgh, Pennsylvania Department of Electrical Engineering/ESL The Ohio State University Columbus, Ohio Nemai C. Karmakar School of Electrical and Electronic Engineering Nanyang Technological University Singapore, Republic of Singapore Branko M. Kolundzija School of Electrical Engineering University of Belgrade Belgrade, Yugoslavia Fredric Kronestedt Ericsson Radio Systems Stockholm, Sweden Te-Hong Lee Department of Electrical Engineering/ESL The Ohio State University Columbus, Ohio Sara Mazur Ericsson Radio Systems Stockholm, Sweden Eric Michielssen Center for Computational Electromagnetics Department of Electrical and Computer Engineering University of Illinois at UrbanaChampaign Urbana, Illinois Ryu Miura Yokosuka Radio Communications Research Center Communications Research Laboratory Ministry of Posts and Telecommunications Yokosuka, Kanagawa, Japan Karl J. Molnar Ericsson Inc. Research Triangle Park, North Carolina © 2002 by CRC Press LLC Arye Nehorai Department of EECs (M/C 154) University of Illinois at Chicago Chicago, Illinois Michael J. Ryan School of Electrical Engineering Australian Defence Force Academy Canberra, Australia Tapan K. Sarkar Boon Poh Ng School of Electrical and Electronic Engineering Nanyang Technological University Singapore, Republic of Singapore H. Ogawa Communications Research Laboratory Ministry of Posts and Telecommunications Yokosuka, Kanagawa, Japan Shingo Ohmori Communication Systems Division Communications Research Laboratory Tokyo, Japan Björn Ottersten Department of Signals, Sensors and Systems Royal Institute of Technology Stockholm, Sweden A. W. Preece Medical Physics University Research Centre Bristol Oncology Centre Bristol, United Kingdom Sembiam R. Rengarajan Department of Electrical and Computer Engineering California State UniversityNorthridge Northridge, California Department of Electrical and Computer Engineering Syracuse University Syracuse, New York Bernard Sklar Communications Engineering Services Tarzana, California Charles E. Smith Electrical Engineering Department University of Mississippi University, Mississippi Hyok J. Song HRL Laboratories, LLC Malibu, California Thomas Svantesson Department of Signals and Systems Chalmers University of Technology Göteborg, Sweden B. T. G. Tan Faculty of Science National University of Singapore Singapore, Republic of Singapore Masato Tanaka Kashima Space Research Center Communications Research Laboratory Ministry of Posts and Telecommunications Kashima, Ibaraki, Japan Saúl A. Torrico Comsearch Reston, Virginia Hiroyuki Tsuji T. Bao Vu Wesley O. Williamson Yokosuka Radio Communications Research Center Communication Research Laboratory Ministry of Posts and Telecommunications Yokosuka, Japan Department of Electronic Engineering City University of Hong Kong Kowloon, Hong Kong TRW, Inc. Redondo Beach, California Mats Viberg Department of Signals and Systems Chalmers University of Technology Göteborg, Sweden © 2002 by CRC Press LLC Rod Waterhouse Department of Communication and Electronic Engineering RMIT University Melbourne, Victoria, Australia J. Xavier Instituto Superior Tecnico, Instituto de Sistemas e Robotica Lisboa, Portugal Zhengqing Yun Electrical Engineering Department University of Utah Salt Lake City, Utah Contents PART A Wireless Communication Systems and Channel Characteristics 1 Cellular Systems 2 Satellite-Based Mobile Communications 3 Propagation Prediction for Urban Systems Saúl A. Torrico 4 Fading Channels PART B Lal C. Godara Michael J. Ryan Henry L. Bertoni and Bernard Sklar Antenna Technology and Numerical Methods 5 Antenna Parameters, Various Generic Antennas and Feed Systems, and Available Softwares Jennifer Bernhard and Eric Michielssen 6 Microstrip Patch Antennas 7 The Finite Difference Time Domain Technique for Microstrip Antenna Applications Atef Z. Elsherbeni, Christos G. Christodoulou, and Javier Gómez-Tagle 8 Method of Moments Applied to Antennas Tapan K. Sarkar, Antonije R. Djordjevic, and Branko M. Kolundzija 9 Genetic Algorithms Rengarajan 10 Wesley O. Williamson and Sembiam R. High-Frequency Techniques © 2002 by CRC Press LLC Rod Waterhouse Roberto G. Rojas and Teh-Hong Lee PART C Antenna Developments and Practical Antennas 11 Outdoor and Indoor Cellular/Personal Handy Phone System Base Station Antenna in Japan Hiroyuki Arai 12 Handheld Antennas Charles E. Smith 13 Aeronautical and Maritime Antennas for Satellite Communications Shingo Ohmori 14 Fixed and Mobile Antennas for Satellite Communications Marek Bialkowski, Nemai C. Karmakar, Paul W. Davis, and Hyok J. Song 15 Shaped-Beam Antennas Atef Z. Elsherbeni, Chun-Wen Paul Huang, and Carlos A. Fernandes PART D Smart Antennas and Array Theory 16 Basic Array Theory and Pattern Synthesis Techniques and Meng Hwa Er 17 Electromagnetic Vector Sensors with Beamforming Applications Arye Nehorai, Kwok-Chiang Ho, and B. T. G. Tan 18 Optimum and Suboptimum Transmit Beamforming and Björn Ottersten 19 Spatial Diversity for Wireless Communications Janaswamy 20 Direction-of-Arrival Estimation in Mobile Communication Environments Mats Viberg and Thomas Svantesson 21 Blind Channel Identification and Source Separation in Space Division Multiple Access Systems Victor Barroso, João Xavier, and José M. F. Moura © 2002 by CRC Press LLC Boon Poh Ng Mats Bengtsson Ramakrishna PART E Implementation of Smart Antenna Systems 22 Smart Antenna System Architecture and Hardware Implementation T. Bao Vu 23 Phased-Array Technology for Wireless Systems Hiroyo Ogawa, Hiroyuki Tsuji, Ami Kanazawa, Ryu Miura, and Masato Tanaka 24 Adaptive Antennas for Global System for Mobile Communications and Time Division Multiple Access (Interim Standard-136) Systems Sören Andersson, Bo Hagerman, M. Berg, H. Dam, Ulf Forssén, J. Karlsson, F. Kronestedt, S. Mazur, and K. J. Molnar PART F Electromagnetic Radiation and the Human Body 25 Electromagnetic Interactions of Handheld Wireless Communication Antennas with the Human Body Magdy F. Iskander and Zhengqing Yun 26 Safety Aspects of Radio Frequency Effects in Humans from Communication Devices Alan W. Preece © 2002 by CRC Press LLC PART A Wireless Communication Systems and Channel Characteristics 1 Cellular Systems Lal C. Godara Introduction • Cellular Fundamentals • First-Generation Systems • Second-Generation Systems • Third-Generation Systems 2 Satellite-Based Mobile Communications Michael John Ryan Introduction • Satellite Orbit Fundamentals • Satellite Radio Path • Multiple Access Schemes • Mobile Satellite Communications Systems • Summary 3 Propagation Prediction for Urban Systems Henry L. Bertoni and Saúl A. Torrico Introduction • Range Dependence for Macrocellular Applications • Range Dependence for Microcells in Low-Rise Environments • Effects of Vegetation • Accounting for Terrain • Site-Specific Predictions • Conclusions 4 Fading Channels Bernard Sklar The Challenge of Communicating over Fading Channels • Characterizing Mobile-Radio Propagation • Signal Time Spreading • Time Variance of the Channel Caused by Motion • Mitigating the Degradation Effects of Fading • Summary of the Key Parameters Characterizing Fading Channels • Applications: Mitigating the Effects of Frequency-Selective Fading • Conclusion © 2002 by CRC Press LLC 1 Cellular Systems 1.1 1.2 Introduction Cellular Fundamentals Communication Using Base Stations • Channel Characteristics • Multiple Access Schemes • Channel Reuse • Cellular Configuration • Channel Allocation and Assignment • Handoff • Cell Splitting and Cell Sectorization • Power Control 1.3 First-Generation Systems Characteristics of Advanced Mobile Phone Service • Call Processing • Narrowband Advanced Mobile Phone Service, European Total Access Communication System, and Other Systems 1.4 Second-Generation Systems United States Digital Cellular (Interim Standard-54) • Personal Digital Cellular System • Code Division Multiple Access Digital Cellular System (Interim Standard-95) • Pan European Global System for Mobile Communications • Cordless Mobiles 1.5 Lal C. Godara University of New South Wales Third-Generation Systems Key Features and Objectives of International Mobile Telecommunications-2000 • International Mobile Telecommunications-2000 Services • Planning Considerations • Satellite Operation 1.1 Introduction The cellular concept was invented by Bell Laboratories and the first commercial analog voice system was introduced in Chicago in October 1983 [1, 2]. The first generation analog cordless phone and cellular systems became popular using the design based on a standard known as Advanced Mobile Phone Services (AMPS). Similar standards were developed around the world including Total Access Communication System (TACS), Nordic Mobile Telephone (NMT) 450, and NMT 900 in Europe; European Total Access Communication System (ETACS) in the United Kingdom; C-450 in Germany; and Nippon Telephone and Telegraph (NTT), JTACS, and NTACS in Japan. In contrast to the first-generation analog systems, second-generation systems are designed to use digital transmission. These systems include the Pan-European Global System for Mobile Communications (GSM) and DCS 1800 systems, North American dual-mode cellular system Interim Standard (IS)-54, North American IS-95 system, and Japanese personal digital cellular (PDC) system [1, 3]. The third-generation mobile communication systems are being studied worldwide, under the names of Universal Mobile Telecommunications System (UMTS) and International Mobile Telecommunications (IMT)-2000 [4, 5]. The aim of these systems is to provide users advance communication services, having wideband capabilities, using a single standard. Details on various systems could be found in References [1, 6–9]. In third-generation communication systems, satellites are going to play a major © 2002 by CRC Press LLC role in providing global coverage [10–16]. Chapter 2 of this book provides more details on satellite communications. The aim of this chapter is to present fundamental concepts of cellular systems by explaining various terminology used to understand the working of these systems. The chapter also provides details on some popular standards. More details on cellular fundamentals may be found in References [17–20]. The chapter is organized as follows. In Section 1.2 fundamentals of cellular systems are presented for understanding how these systems work. Sections 1.3 and 1.4 are devoted to first-generation and second-generation systems, respectively, where a brief description of some popular standards is presented. A discussion on third-generation systems is included in Section 1.5. 1.2 Cellular Fundamentals The area served by mobile phone systems is divided into small areas known as cells. Each cell contains a base station that communicates with mobiles in the cell by transmitting and receiving signals on radio links. The transmission from the base station to a mobile is typically referred to as downstream, forwardlink, or downlink. The corresponding terms for the transmission from a mobile to the base are upstream, reverse-link, and uplink. Each base station is associated with a mobile switching center (MSC) that connects calls to and from the base to mobiles in other cells and the public switched telephone network. A typical setup depicting a group of base stations to a switching center is shown in Fig. 1.1. In this section terminology associated with cellular systems is introduced with a brief description to understand how these systems work . Base Station Base Station Link Mobile Switching Centre Link Link Base Station Base Station Link Public Switched Telephone Networks FIGURE 1.1 A typical cellular system setup. © 2002 by CRC Press LLC 1.2.1 Communication Using Base Stations A base station communicates with mobiles using two types of radio channels, control channels to carry control information and traffic channels to carry messages. Each base station continuously transmits control information on its control channels. When a mobile is switched on, it scans the control channels and tunes to a channel with the strongest signal. This normally would come from the base station located in the cell in which the mobile is also located. The mobile exchanges identification information with the base station and establishes the authorization to use the network. At this stage, the mobile is ready to initiate and receive a call. 22.214.171.124 A Call from a Mobile When a mobile wants to initiate a call, it sends the required number to the base. The base station sends this information to the switching center that assigns a traffic channel to this call because the control channels are only used for control information. Once the traffic channel is assigned, this information is relayed to the mobile via the base station. The mobile switches itself to this channel. The switching center then completes the rest of the call. 126.96.36.199 A Call to a Mobile When someone calls a mobile, the call arrives at the mobile switching center. It then sends a paging message through several base stations. A mobile tuned to a control channel detects its number in the paging message and responds by sending a response signal to the nearby base station. The base station informs the switching center about the location of the desired mobile. The switching center assigns a traffic channel to this call and relays this information to the mobile via the base. The mobile switches itself to the traffic channel and the call is complete. 188.8.131.52 Registration A mobile is normally located by transmitting a paging message from various base stations. When a large number of base stations are involved in the paging process, it becomes impractical and costly. It is avoided by a registration procedure where a roaming phone registers with an MSC closer to itself. This information may be stored with the switching center of the area as well as the home switching center of the phone. The home base of the phone is the one where it is permanently registered. Once a call is received for this phone, its home switching center contacts the switching center where the phone is currently roaming. Paging in the vicinity of the previous known location helps to locate the phone. Once it responds, the call may be connected as discussed previously. 1.2.2 Channel Characteristics An understanding of propagation conditions and channel characteristics is important for an efficient use of a transmission medium. Attention is being given to understanding the propagation conditions where a mobile is to operate and many experiments have been conducted to model the channel characteristics. Many of these results could be found in review articles [22–24] and references therein. Two chapters of this book are devoted to propagation prediction and channel characterization. 184.108.40.206 Fading Channels The signal arriving at a receiver is a combination of many components arriving from various directions as a result of multipath propagation. This depends on terrain conditions and local buildings and structures, causing the received signal power to fluctuate randomly as a function of distance. Fluctuations on the order of 20 dB are common within the distance of one wavelength (I λ). This phenomenon is called fading. One may think this signal as a product of two variables. The first component, also referred to as the short-term fading component, changes faster than the second one and has a Rayleigh distribution. The second component is a long-term or slow-varying © 2002 by CRC Press LLC quantity and has lognormal distribution [17, 25]. In other words, the local mean varies slowly with lognormal distribution and the fast variation around the local mean has Rayleigh distribution. A movement in a mobile receiver causes it to encounter fluctuations in the received power level. The rate at which this happens is referred to as the fading rate in mobile communication literature  and it depends on the frequency of transmission and the speed of the mobile. For example, a mobile on foot operating at 900 MHz would cause a fading rate of about 4.5 Hz whereas a typical vehicle mobile would produce the fading rate of about 70 Hz. 220.127.116.11 Doppler Spread The movement in a mobile causes the received frequency to differ from the transmitted frequency because of the Doppler shift resulting from its relative motion. As the received signals arrive along many paths, the relative velocity of the mobile with respect to various components of the signal differs, causing the different components to yield a different Doppler shift. This can be viewed as spreading of the transmitted frequency and is referred to as the Doppler spread. The width of the Doppler spread in frequency domain is closely related to the rate of fluctuations in the observed signal . 18.104.22.168 Delay Spread Because of the multipath nature of propagation in the area where a mobile is being used, it receives multiple and delayed copies of the same transmission, resulting in spreading of the signal in time. The root-mean-square (rms) delay spread may range from a fraction of a microsecond in urban areas to on the order of 100 µsec in a hilly area, and this restricts the maximum signal bandwidth between 40 and 250 kHz. This bandwidth is known as coherence bandwidth. The coherence bandwidth is inversely proportional to the rms delay spread. This is the bandwidth over which the channel is flat; that is, it has a constant gain and linear phase. For a signal bandwidth above the coherence bandwidth the channel loses its constant gain and linear phase characteristic and becomes frequency selective. Roughly speaking, a channel becomes frequency selective when the rms delay spread is larger than the symbol duration and causes intersymbol interference (ISI) in digital communications. Frequency-selective channels are also known as dispersive channels whereas the nondispersive channels are referred to as flat-fading channels. 22.214.171.124 Link Budget and Path Loss Link budget is a name given to the process of estimating the power at the receiver site for a microwave link taking into account the attenuation caused by the distance between the transmitter and the receiver. This reduction is referred to as the path loss. In free space the path loss is proportional to the second power of the distance; that is, the distance power gradient is two. In other words, by doubling the distance between the transmitter and the receiver, the received power at the receiver reduces to one fourth of the original amount. For a mobile communication environment utilizing fading channels the distance power gradient varies and depends on the propagation conditions. Experimental results show that it ranges from a value lower than two in indoor areas with large corridors to as high as six in metal buildings. For urban areas the path loss between the base and the cell site is often taken to vary as the fourth power of the distance between the two . Normal calculation of link budget is done by calculating carrier to noise ratio (CNR), where noise consists of background and thermal noise, and the system utility is limited by the amount of this noise. However, in mobile communication systems the interference resulting from other mobile units is a dominant noise compared with the background and man-made noise. For this reason these systems are limited by the amount of total interference present instead of the background noise as in the other case. In other words, the signal to interference ratio (SIR) is the limiting factor for a mobile communication system instead of the signal to noise ratio (SNR) as is the case for other communication systems. The calculation of link budget for such interference-limited systems involves calculating the carrier level, above the interference-level contributed by all sources . © 2002 by CRC Press LLC 1.2.3 Multiple Access Schemes The available spectrum bandwidth is shared in a number of ways by various wireless radio links. The way in which this is done is referred to as a multiple access scheme. There are basically four principle schemes. These are frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), and space division multiple access (SDMA) [29–40]. 126.96.36.199 Frequency Division Multiple Access Scheme In an FDMA scheme the available spectrum is divided into a number of frequency channels of certain bandwidth and individual calls use different frequency channels. All first-generation cellular systems use this scheme. 188.8.131.52 Time Division Multiple Access Scheme In a TDMA scheme several calls share a frequency channel . The scheme is useful for digitized speech or other digital data. Each call is allocated a number of time slots based on its data rate within a frame for upstream as well as downstream. Apart from the user data, each time slot also carries other data for synchronization, guard times, and control information. The transmission from base station to mobile is done in time division multiplex (TDM) mode whereas in the upstream direction each mobile transmits in its own time slot. The overlap between different slots resulting from different propagation delay is prevented by using guard times and precise slot synchronization schemes. The TDMA scheme is used along with the FDMA scheme because there are several frequency channels used in a cell. The traffic in two directions is separated either by using two separate frequency channels or by alternating in time. The two schemes are referred to as frequency division duplex (FDD) and time division duplex (TDD), respectively. The FDD scheme uses less bandwidth than TDD schemes use and does not require as precise synchronization of data flowing in two directions as that in the TDD method. The latter, however, is useful when flexible bandwidth allocation is required for upstream and downstream traffic . 184.108.40.206 Code Division Multiple Access Scheme The CDMA scheme is a direct sequence (DS), spread-spectrum method. It uses linear modulation with wideband pseudonoise (PN) sequences to generate signals. These sequences, also known as codes, spread the spectrum of the modulating signal over a large bandwidth, simultaneously reducing the spectral density of the signal. Thus, various CDMA signals occupy the same bandwidth and appear as noise to each other. More details on DS spread-spectrum may be found in Reference . In the CDMA scheme, each user is assigned an individual code at the time of call initiation. This code is used both for spreading the signal at the time of transmission and despreading the signal at the time of reception. Cellular systems using CDMA schemes use FDD, thus employing two frequency channels for forward and reverse links. On forward-link a mobile transmits to all users synchronously and this preserves the orthogonality of various codes assigned to different users. The orthogonality, however, is not preserved between different components arriving from different paths in multipath situations . On reverse links each user transmits independently from other users because of their individual locations. Thus, the transmission on reverse link is asynchronous and the various signals are not necessarily orthogonal. It should be noted that these PN sequences are designed to be orthogonal to each other. In other words, the cross correlation between different code sequences is zero and thus the signal modulated with one code appears to be orthogonal to a receiver using a different code if the orthogonality is preserved during the transmission. This is the case on forward-link and in the absence of multipath the signal received by a mobile is not affected by signals transmitted by the base station to other mobiles. On reverse link the situation is different. Signals arriving from different mobiles are not orthogonalized because of the asynchronous nature of transmission. This may cause a serious problem when the base station is trying to receive a weak signal from a distant mobile in the presence of a strong signal from a © 2002 by CRC Press LLC nearly mobile. This situation where a strong DS signal from a nearby mobile swamps a weak DS signal from a distant mobile and makes its detection difficult is known as the “near–far” problem. It is prevented by controlling the power transmitted from various mobiles such that the received signals at the base station are almost of equal strength. The power control is discussed in a later section. The term wideband CDMA (WCDMA) is used when the spread bandwidth is more than the coherence bandwidth of the channel . Thus, over the spread bandwidth of DS-CDMA, the channel is frequency selective. On the other hand, the term narrowband CDMA is used when the channel encounters flat fading over the spread bandwidth. When a channel encounters frequency-selective fading, over the spread bandwidth, a RAKE receiver may be employed to resolve the multipath component and combine them coherently to combat fading. A WCDMA signal may be generated using multicarrier (MC) narrowband CDMA signals, each using different frequency channels. This composite MC-WCDMA scheme has a number of advantages over the single-carrier WCDMA scheme. It not only is able to provide diversity enhancement over multipath fading channels but also does not require a contiguous spectrum as is the case for the single-carrier WCDMA scheme. This helps to avoid frequency channels occupied by narrowband CDMA, by not transmitting MC-WCDMA signals over these channels. More details on these and other issues may be found in Reference  and references therein. 220.127.116.11 Comparison of Different Multiple Access Schemes Each scheme has its advantages and disadvantages such as complexities of equipment design, robustness of system parameter variation, and so on. For example, a TDMA scheme not only requires complex time synchronization of different user data but also presents a challenge to design portable RF units that overcome the problem of a periodically pulsating power envelope caused by short duty cycles of each user terminal. It should be noted that when a TDMA frame consists of N users transmitting equal bit rates, the duty cycles of each user is 1/N. TDMA also has a number of advantages . 1. A base station communicating with a number of users sharing a frequency channel only requires one set of common radio equipment. 2. The data rate, to and from each user, can easily be varied by changing the number of time slots allocated to the user as per the requirements. 3. It does not require as stringent power control as that of CDMA because its interuser interference is controlled by time slot and frequency-channel allocations. 4. Its time slot structure is helpful in measuring the quality of alternative slots and frequency channels that could be used for mobile-assisted handoffs. Handoff is discussed in a later section. It is argued in Reference  that, though there does not appear to be a single scheme that is the best for all situations, CDMA possesses characteristics that give it distinct advantages over others. 1. It is able to reject delayed multipath arrivals that fall outside the correlation interval of the PN sequence in use and thus reduces the multipath fading. 2. It has the ability to reduce the multipath fading by coherently combing different multipath components using a RAKE receiver. 3. In TDMA and FDMA systems a frequency channel used in a cell is not used in adjacent cells to prevent co-channel interference. In a CDMA system it is possible to use the same frequency channel in adjacent cells and thus increase the system capacity. 4. The speech signal is inherently bursty because of the natural gaps during conversation. In FDMD and TDMA systems once a channel (frequency and/or time slot) is allocated to a user, that channel cannot be used during nonactivity periods. However, in CDMA systems the background noise is roughly the average of transmitted signals from all other users and thus a nonactive period in speech reduces the background noise. Hence, extra users may be accommodated without the loss of signal quality. This in turn increases the system capacity. © 2002 by CRC Press LLC 18.104.22.168 Space Division Multiple Access The SDMA scheme also referred to as space diversity uses an array of antennas to provide control of space by providing virtual channels in angle domain . This scheme exploits the directivity and beamshaping capability of an array of antennas to reduce co-channel interference. Thus, it is possible that by using this scheme simultaneous calls in a cell could be established at the same carrier frequency. This helps to increase the capacity of a cellular system. The scheme is based on the fact that a signal arriving from a distant source reaches different antennas in an array at different times as a result of their spatial distribution, and this delay is utilized to differentiate one or more users in one area from those in another area. The scheme allows an effective transmission to take place between a base station and a mobile without disturbing the transmission to other mobiles. Thus, it has the potential such that the shape of a cell may be changed dynamically to reflect the user movement instead of currently used fixed size cells. This arrangement then is able to create an extra dimension by providing dynamic control in space [39, 40]. A number of chapters in this book deal with various aspects of antenna array processing. 1.2.4 Channel Reuse The generic term channel is normally used to denote a frequency in FDMA system, a time slot in TDMA system, and a code in CDMA system or a combination of these in a mixed system. Two channels are different if they use different combinations of these at the same place. For example, two channels in a FDMA system use two different frequencies. Similarly, in TDMA system two separate time slots using the same frequency channel is considered two different channels. In that sense, for an allocated spectrum the number of channels in a system is limited. This limits the capacity of the system to sustain simultaneous calls and may only be increased by using each traffic channel to carry many calls simultaneously. Using the same channel again and again is one way of doing it. This is the concept of channel reuse. The concept of channel reuse can be understood from Fig. 1.2. Figure 1.2a shows a cluster of three cells. These cells use three separate sets of channels. This set is indicated by a letter. Thus, one cell uses set A, the other uses set B, and so on. In Fig. 1.2b this cluster of three cells is being repeated to indicate that three sets of channels are being reused in different cells. Figure 1.3 shows a similar arrangement with cluster size of seven cells. Now let us see how this helps to increase the system capacity. Assume there are a total of F channels in a system to be used over a given geographic area. Also assume that there are N cells in a cluster that use all the available channels. In the absence of channel reuse this cluster covers the whole area and the capacity of the system to sustain simultaneous calls is F. Now if the cluster of N cells is repeated M times over the same area, then the system capacity increases to MF as each channel is used M times. The number of cells in a cluster is referred to as the cluster size, the parameter 1/N is referred to as the frequency reuse factor, and a system using a cluster size of N sometimes is also referred to as a system using N frequency reuse plan. The cluster size is an important parameter. For a given cell size, as the cluster size is decreased, more clusters are required to cover the given area leading to more reuse of channels and hence the system capacity increases. Theoretically, the maximum capacity is attained when cluster size is one, that is, when all the available channels are reused in each cell. For hexagonal cell geometry, the cluster size can only have certain values. These are given by N = i 2 + j 2 + ij, where i and j are nonnegative integers. The cells using the same set of channels are known as co-channel cells. For example, in Fig. 1.2, the cells using channels A are co-channel cells. The distance between co-channel cells is known as co-channel distance and the interference caused by the radiation from these cells is referred to as co-channel interference. For proper functioning of the system, this needs to be minimized by decreasing the power transmitted by mobiles and base stations in co-channel cells and increasing the co-channel distance. Because the transmitted power normally depends on the cell size, the minimization of co-channel interference requires a minimum co-channel distance; that is, the distance cannot be smaller than this minimum distance. © 2002 by CRC Press LLC A B C A B C A C A C FIGURE 1.2 B B (a) A cluster of three cells. (b) Channel reuse concept using a three-cell cluster. In a cellular system of equal cell size, the co-channel interference is a function of a dimensionless parameter known as co-channel reuse ratio Q. This is a ratio of the co-channel distance D and the cell radius R, that is, Q = D R For hexagonal geometry, Q = 3N It follows from these equations that an increase in Q increases the co-channel distance and thus minimizes the co-channel interference. On the other hand, a decrease in Q decreases the cluster size N and hence maximizes the system capacity. Thus, the selection of Q is a trade-off between the two parameters, namely, the system capacity and co-channel interferences. It should be noted that for proper functioning of the system, the signal to co-channel interference ratio should be above a certain minimum value . © 2002 by CRC Press LLC B G A C E D B G A C G A C D FIGURE 1.3 B F E D B F G A C D F E F E (a) A cluster of seven cells. (b) Channel reuse concept using a seven-cell cluster. 1.2.5 Cellular Configuration A cellular system may be referred to as a macrocell, a microcell, or a picocell system depending on the size of cells. Some characteristics of these cellular structures are now described. 22.214.171.124 Macrocell System A cellular system with its cell size of several kilometers is referred to as macrocell systems. Base stations of these systems transmit several watts of power from antennas mounted on high towers. Normally there is no line of sight (LOS) between the base station and mobiles and thus a typical received signal is a combination of various signals arriving from different directions. The received signal in these systems experience spreading of several microseconds because of the nature of propagation conditions. 126.96.36.199 Microcell Systems As cells are split and their boundaries are redefined, their size becomes very small. At a radius less than about a kilometer, the system is referred to as a microcell system. In these systems a typical base station transmits less than 1 W of power from an antenna mounted at a few meters above the ground and normally an LOS exists between the base and a mobile. Cell radius in microcell systems is less than a kilometer giving rms delay spread on the order of few tens of nanoseconds compared with a few micoseconds for macrocell systems. This impacts on the maximum data rate a channel could sustain. For microcell systems maximum bit rate is about 1 Mbps compared with that of about 300 kbps for macocell systems . Microcell systems are also useful in providing coverage along roads and highways. Because the antenna height is normally lower than the surrounding buildings the propagation is along the streets and an LOS © 2002 by CRC Press LLC exists between the base and a mobile. When a mobile turns a corner, sometimes a sudden drop in received signal strength is experienced because of loss of LOS. Depending on how antennas are mounted on intersections and corners, various cell plans are possible. More details on these aspects may be found in Reference  and references therein. 188.8.131.52 Picocell Systems When cell sizes are reduced below about 100 m covering areas such as large rooms, corridors, underground stations, large shopping centers, and so on, cellular systems are sometimes referred to as picocell systems with antennas mounted below rooftop levels or in buildings. These in-building areas have different propagation conditions than those covered by macrocell and microcell systems, and thus require different considerations for developing channel models. Details on various models to predict propagation conditions may be found in Reference . Sometimes the picocell and microcell systems are also referred to as cordless communication systems with the term cellular identifying a macrocell system. Mobiles within these smaller cell systems are called cordless terminals or cordless phones [1, 6, 42]. Providing in-building communication services using wireless technology, based on cell shapes dictated by floors and walls, is a feasible alternative and offers many advantages. It is argued in Reference  that radio frequencies in 18-GHz band are ideal for such services because these do not penetrate concrete and steel structures, eliminating the problem of co-channel interferences. These frequencies offer huge bandwidth and require millimeter size antennas that are easy to manufacture and install. 184.108.40.206 Overlayed System Small cell systems make very efficient use of the spectrum, allowing large frequency reuse resulting in an increased capacity of a system. However, these are not suitable for all conditions because of their large handoff requirement. A system of mixed cells with the concept of overlaying is discussed in References [41, 44–46]. In this system a hierarchy of cells is assumed to exist. A macrocell system is assumed at the top of the hierarchy with smaller cells systems at its bottom. A mobile with high mobility is assigned to a macrocell system whereas the one with a low mobility, to smaller cell systems. A design incorporating various combinations of different multiple access schemes reflects the ease of handoff and other traffic management strategies. A space division multiple access scheme has an important role to play in this concept, with various beams placed at the bottom of the hierarchy. 1.2.6 Channel Allocation and Assignment Various multiple access schemes discussed in a previous section are used to divide a given spectrum into a set of disjoint channels. These channels are then allocated to various cells for their use. Channel allocation may be carried out using one of the three basic schemes, namely, fixed channel allocation, dynamic channel allocation, and hybrid channel allocation . 220.127.116.11 Fixed Channel Allocation Schemes In fixed channel allocation schemes a number of channels are allocated to a cell permanently for its use such that these channels satisfy certain channel reuse constraints as discussed in the previous section. In its simplest form the same number of channels are allocated to each cell. For a system with uniform traffic distribution across all cells, this uniform channel allocation scheme is efficient in the sense that the average call blocking probability in each cell is the same as that of the overall system. For systems where the distribution is not uniform, the call blocking probability differs from cell to cell, resulting in the call being blocked in some cells when there are spare channels available in other cells. This situation could be improved by allocating channels nonuniformally as per the expected traffic in each cell or employing one of many prevailing channel borrowing schemes. One of these is referred to as a static borrowing scheme where some channels are borrowed from cells with light traffic and allocated to those with heavy traffic. Rearrangements of channels between cells are performed periodically to meet the variation in traffic load. In this scheme the borrowed channels stay with the new cell until reallocated. There are other temporary borrowing schemes where a cell that has used all its channels is allowed to © 2002 by CRC Press LLC borrow a free channel from a neighbor provided it does not interfere with existing calls. The borrowed channel is returned to the original cell once the call is complete. Some temporary borrowing schemes allow any channel from a cell to be borrowed, whereas in others only nominated channels are allowed to be borrowed. Many borrowing strategies are available for selecting a channel, ranging from a simple scheme to pick the first available channel that satisfies the co-channel distance constraints to the one that performs an exhaustive search to select a channel that yields maximum signal to interference ratio and minimizes the future probability of call blocking. 18.104.22.168 Dynamic Channel Allocation Schemes Fixed channel allocation schemes discussed thus far are simple to implement and are generally useful for relatively stable traffic conditions. These schemes are not very efficient for fast changing user distribution because they are not designed to adapt to short-term variations in traffic conditions. Dynamic channel allocation schemes are most suited for such situations. In these schemes channels are not allocated to various cells but are kept in a central pool and are assigned to calls as they arrive. At the completion of a call the assigned channel is released and goes back to the pool. The process of channel assignment involves working out a cost of assigning a channel to a call and a channel with the minimum cost is chosen for the purpose. The various channel assignment schemes differ in the way the cost function is selected using various parameters of interest such as reuse distance, SIR ratio, probability of call blocking, and so on. Some schemes base their assignment only on the current traffic conditions in the service area whereas the others take the past and the present conditions into account. Dynamic channel assignment schemes may be implemented centrally where a central controller assigns the channels to calls from the pool. The central controller is able to achieve very efficient channel assignment but requires high overhead. The channel assignment may also be implemented in a distributed manner by base stations where calls are originated. The channel implementation by base stations requires less overhead than that required by a central controller and is more suitable for microcell systems. The distributed channel assignment schemes can be divided into two categories. In one case each base station keeps detailed status information about current available channels in its neighborhood by exchanging status information with other base stations. The schemes in this category may provide near optimum allocation but pay a heavy price in terms of increased communication with other base stations, particularly in heavy traffic. The other category of distributed channel assignment schemes uses simple algorithms that rely on mobiles to measure signal strength to decide the suitability of a channel. 22.214.171.124 Hybrid Channel Allocation Schemes The fixed channel allocation schemes are efficient under uniformly distributed heavy traffic. On the other hand, the dynamic channel allocation schemes perform better under low traffic conditions with varying and nonuniformly distributed loads. The hybrid channel allocation schemes maximize advantages of both these schemes by dividing channels into fixed and dynamic sets. The channels in fixed sets are allocated as per fixed channel allocation strategies and those in the other set are free to be assigned to calls in a cell that has used all its allocated channels. The channels in this set are assigned as per the dynamic channel allocation procedures. Apparently, no optimum ratio of channels are assigned to two sets and the design parameter is dependent on local traffic conditions. More details on these and related issues may be found in Reference  and references therein. 1.2.7 Handoff It is common for a mobile to move away from its servicing base station while a call is in progress. As the mobile approaches the cell boundary, the strength and quality of the signal it receives starts to deteriorate. At some stage, near the cell boundary, it receives a stronger signal from a neighboring base station than it does from its serving base station. At this point the control of the mobile is handed over to the new base station by assigning a channel belonging to the new cell. This process where a radio channel used by a mobile is changed, is referred to as handoff or handover [41, 44, 48–50]. When handoff is between two base stations as described earlier, it is referred to as intercell handoff. On the other hand, when handoff is between © 2002 by CRC Press LLC two channels belonging to the same base stations, it is referred to as intracell handoff. The situation arises when the network, while monitoring its channels, finds a free channel of better quality than that used by a mobile and decides to move the mobile to this new channel to improve the quality of channels in use. Sometimes, the network rearranges channels to avoid congestion and initiates intracell handoff. Handoff is also necessary between different layers of overlayed systems consisting of microcells and macrocells. In these systems, the channels are divided into microcell channels and macrocell channels. When a mobile moves from one microcell to another and there is no available channel for handoff, a macrocell channel is used to meet the handoff request. This avoids the forced termination of a call. Later if a channel becomes available at an underlayed microcell, then the macrocell channel may be released and a microcell channel is assigned to the call by initiating a new handoff. Forced termination of a call in progress is undesirable and to minimize it a number of strategies are employed. These include reserving channels for handoff, using channel assignment schemes that give priority to a handoff request over new calls, and queuing the handoff request. The channel reservation and handoff priority scheme reduce the probability of forced termination by increasing the probability of blocking new calls. The queuing schemes are effective when handoff requests arrive in groups and there is a reasonable likelihood of channel availability in the near future. The handoff is initiated when the quality of current channels deteriorates below an acceptable threshold or a better channel is available. The channel quality is measured in terms of bit-error rate (BER), received signal strength, or some other signal quality such as eye opening of radio signal that indicates signal to interference plus noise ratio. For handoff initiation the signal strength is used as an indication of the distance between the base and the mobile. For this reason, a drop in signal strength resulting from Rayleigh fading is normally not used to initiate handoff and some kind of averaging is used to avoid the problem. In some systems the roundtrip delay between mobile and base is also used as an indication of the distance. The measurement of various parameters may be carried out either at the mobile or at the base. Depending on where the measurements are made and who initiates the handoff, various handoff implementation schemes are possible including network-controlled handoff, mobile-controlled handoff, and mobile-assisted handoff. 126.96.36.199 Network-Controlled Handoff In network-controlled handoff, each base station monitors the signal strength received from mobiles in their cells and makes periodic measurements of the received signal from mobiles in their neighboring cells. The MSC then initiates and completes the handoff of a mobile as and when it decides. The decision is based on the received signal strength at the base station serving the mobiles and base stations in neighboring cells. Because of its centralized nature, the collection of these measurements generates a large network traffic. This could be reduced to an extent by making measurements less frequently and by not requiring the neighboring base station to send the measurements continually. However, this reduces the accuracy. The execution of handoff by this method takes a few seconds and for this reason the method is not preferred by microcellular systems where a quick handoff is desirable. 188.8.131.52 Mobile-Controlled Handoff Mobile-controlled handoff, is a highly decentralized method and does not need any assistance from the MSC. In this scheme a mobile monitors signal strength on its current channel and measures signals received from the neighboring base stations. It receives BER and signal strength information from its serving base stations about uplink channels. Based on all this information, it initiates the handoff process by requesting the neighboring base for allocation of a low interference channel. The method has a handoff execution time on the order of 100 ms and is suitable for microcell systems. 184.108.40.206 Mobile-Assisted Handoff In mobile-assisted handoff methods, as the name suggests, a mobile helps the network in the handoff decision making by monitoring the signal strength of its neighboring base stations and passing them to © 2002 by CRC Press LLC MSC via its serving base station. The handoff is initiated and completed by the network. The execution time is on the order of 1 s. 220.127.116.11 Hard Handoff and Soft Handoff Handoff may be classified into hard handoff and soft handoff. During hard handoff the mobile can communicate only with one base station. The communication link gets broken with the current base station before the new one is established and there is normally a small gap in communication during the transition. In the process of soft handoff, the mobile is able to communicate with more than one base station. It receives signals from more than one base station and the received signals are combined after appropriate delay adjustment. Similarly, more than one station receives signals from mobiles and the network combines different signals. This scheme is also known as macroscopic diversity and is mostly employed by CDMA systems. Hard handoff, on the other hand, is more appropriate for TDMA and FDMA systems. It is also simple to implement compared with soft handoff. However, it may lead to unnecessary handoff back and forth between two base stations when the signals from two base stations fluctuate. The situation may arise when a mobile, currently being served for example by Base 1 receives a stronger signal, from say Base 2 and is handed over to Base 2. Immediately after that it receives a stronger signal from Base 1 compared to that it receives from Base 2, causing a handoff. This phenomenon, known as the ping-pong effect, may continue for some time and is undesirable because every handoff has a cost associated with it requiring network signaling of varying amount for authentication, database updates, circuit switching, and so on. This is avoided by using a hysteresis margin such that the handoff is not initiated until the difference between the signal received from the two base stations is more than the margin. For example, if the margin is ∆ dB then the handoff is initiated when the signal received by the mobile from base 2 is ∆ dB more than that from Base 1. More details on various handoff implementation issues may be found in References [41, 48, 49] and references therein. 1.2.8 Cell Splitting and Cell Sectorization Each cell has a limited channel capacity and thus could only serve so many mobiles at a given time. Once the demand in that cell exceeds this limit the cell is further subdivided into smaller cells, each new cell with its own base station and its frequency allocation. The power of the base station transmitters is adjusted to reflect the new boundaries. The power transmitted by new base stations is less than that of the old one. The consequence of the cell splitting is that the frequency assignment has to be done again, which affects the neighboring cells. It also increases the handoff rate because the cells are now smaller and a mobile is likely to cross cell boundaries more often compared with the case when the cells are big. Because of altered signaling conditions, this also affects the traffic in control channels. Cell sectorization is referred to the case when a given cell is subdivided into several sectors and all sectors are served by the same base station. This is normally done by employing directional antennas such that the energy in each sector is directed by separate antennas. This has the effect of increased channel capacity similar to cell splitting. However, it uses the same base station and thus does not incur the cost of establishing new base stations associated with the cell splitting. This helps in reducing the cochannel interference because the energy is directed in the direction of the sector that does not cause interference in the co-channel cells, particularly in co-channel cells in the opposite direction to the sector. As in the case of cell splitting, this also affects the handoff rate. 1.2.9 Power Control It is important that a radio receiver receives a power level that is enough for its proper function but not high enough for this level to disturb other receivers. This is achieved with maintaining constant power level at the receiver by transmitter power control. The receiver controls the power of the transmitter at the other end. For example, a base would control the power transmitted by mobile phones and vice versa. © 2002 by CRC Press LLC It is done by a receiver monitoring its received power and sending a control signal to the transmitter to control its power transmission as required. Sometimes a separate pilot signal is used for this purpose. Power control reduces the near–far problem in CDMA systems and helps to minimize the interference near the cell boundaries when used in forward-link [32, 33]. 1.3 First-Generation Systems These systems use analog frequency modulation for speech transmission and frequency shift keying (FSK) for signaling, and employ FDMA to share the allocated spectrum. Some of the popular standards developed around the world include Advanced Mobile Phone Service (AMPS), Total Access Communication System (TACS), Nordic Mobile Telephone (NMT), Nippon Telephone and Telegraph (NTT) and C450. These systems use two separate frequency channels, one for base to mobile and the other for mobile to base for full duplex transmission . 1.3.1 Characteristics of Advanced Mobile Phone Service AMPS system uses bands of 824 to 849 MHz for uplink and 869 to 894 MHz for downlink transmission. This spectrum is divided into channels of 30-kHz bandwidth. In a two-way connection two of these channels are used. A pair of channels in a connection is selected such that channels used for uplink and downlink transmission are separated by 45 MHz. This separation was chosen so that inexpensive but highly selective duplexers could be utilized. A typical frequency-reuse plan in this system either uses clusters of 12 cells with omnidirectional antennas or 7-cell clusters with three sectors per cell. There are a total of 832 duplex channels. Of these, 42 are used as control channels and the remaining 790 channels are used as voice channels. The control channels used for downlink and uplink transmission are referred to as forward control channels (FCC) and reverse control channels (RCC), respectively. Similarly, voice channels are referred to as forward voice channels (FVC) and reverse voice channels (RVC). Each base continuously broadcasts FSK data on FCC and receives on RCC. A mobile scans all FCCs and locks on an FCC with the strongest signal. Each mobile needs to be locked on an FCC signal to receive and send a call. Base stations monitor their RCCs for transmission from mobiles that are locked on the matching FCCs. 1.3.2 Call Processing When a mobile places a call, it transmits a message on RCC consisting of destination phone number, its mobile identification number, and other authorization information. The base station monitoring an RCC receives this information and sends it to the MSC. The MSC in turn checks the authentication of the mobile; assigns a pair of FVC and RVC, a supervisory audio tone (SAT), and a voice mobile attenuation code (VMAC); and connects the call to a public switched telephone network (PSTN). The mobile switches itself to the assigned channels. The SAT is used to ensure the reliable voice communication and the VMAC is used for power control. The SAT is an analog tone of 5970, 6000, or 6030 Hz. It is transmitted during a call on both FVC and RVC. It is superimposed on voice signal and is barely audible to the user. It helps the mobile and the base to distinguish each other from co-channel users located in nearby cells. It also serves as a handshake between the base station and the mobile. The base transmits it on FVC and the mobile retransmits it on RVC after detection. If the SAT is not detected within 1 s, both the mobile and the base stop transmission. A call to a mobile originating at a PSTN is processed by the MSC in a similar fashion. When a call arrives at an MSC, a paging message with mobile identification number (MIN) is sent out on FCCs of every base station controlled by the MSC. A mobile terminal recognizes its MIN and responds on RCC. The MSC assigns a pair of FVC and RVC, SAT and VMAC. The mobile switches itself to the assigned channel. © 2002 by CRC Press LLC TABLE 1.1 Parameters of Some First-Generation Cellular Standards Parameters Tx Frequency (MHz) Mobile Base Station Channel bandwidth (kHz) Spacing between forward and reverse channels (MHz) Speech signal FM deviation Control signal data rate (kbps) Handoff decision is based on AMPS C450 NMT 450 NTT TACS 824–849 869–894 30 450–455.74 460–465.74 20 453–457.5 463–467.5 25 925–940 870–885 25 890–915 935–960 25 45 10 10 55 45 ±12 ±5 ±5 ±5 ±9.5 10 Power received at base 5.28 Round-trip delay 1.2 Power received at base 0.3 Power received at base 8 Power received at base While a call is in progress on voice channels, the MSC issues several blank-and-burst commands to transmit signaling information using binary FSK at a rate of 10 kbps. In this mode, voice and SAT are temporarily replaced with this wideband FSK data. The signaling information is used to initiate handoff, to change mobile power level, and to provide other data as required. The handoff decision is taken by the MSC when the signal strength on RVC falls below threshold or when the SAT experiences interference level above a predetermined value. The MSC uses scanning receivers in nearby base stations to determine the signal level of a mobile requiring handoff. The termination of a call by a mobile is initiated using a signaling tone (ST). ST is a 10-kbps data burst of 1 and 0 s. It is sent at the end of a message for 200 ms indicating “end-of-call.” It is sent along with SAT and indicates to the base station that the mobile has terminated the call instead of the call dropping out or prematurely terminating. It is sent automatically when a mobile is switched off. 1.3.3 Narrowband Advanced Mobile Phone Service, European Total Access Communication System, and Other Systems A narrowband AMPS (N-AMPS) was developed by Motorola to provide three 10-kHz channels using FDMA in a 30-kHz AMPS channel. By replacing one AMPS channel by three N-AMPS channels at a time, the service providers are able to increase the system capacity by three times. It uses SAT, ST, and blank-and-burst similar to AMPS. Because it uses 10-kHz channels, FM deviation is smaller compared with AMPS and hence it has a lower signal to noise plus interference ratio (SNIR) resulting in degradation of audio quality. It has taken measures to compensate this degradation. The European Total Access Communication Systems (ETACS) is identical to AMPS except that it uses 25-kHz wide channels compared with 30-kHz channels used by AMPS. It also formats its MIN differently to AMPS to accommodate different country codes in Europe. Parameters for some other popular analog systems are shown in Table 1.1. 1.4 Second-Generation Systems In contrast to the first-generation analog systems, second-generation systems are designed to use digital transmission and to employ TDMA or CDMA as a multiple access scheme. These systems include North American dual-mode cellular system IS-54, North American IS-95 systems, Japanese Personal Digital Cellular (PDC) systems, and European GSM and DCS 1800 systems. GSM, DCS 1800, IS-54, and PDC systems use TDMA and FDD whereas IS-95 is a CDMA system and also uses FDD for a duplexing technique. Other parameters for these systems are shown in Table 1.2. In this section a brief description of these systems is presented . © 2002 by CRC Press LLC TABLE 1.2 Parameters of Some Second-Generation Cellular Standards Parameters TX frequencies (MHz) Mobile Base station Channel bandwidth (kHz) Spacing between forward and reverse channels (MHz) Modulation Frame duration (ms) IS-54 GSM IS-95 PDC 824–849 869–894 30 kHz 45 890–915 935–960 200 kHz 45 824–849 869–894 1250 kHz 45 940–956 and 1429–1453 810–826 and 1477–1501 25 kHz 30/48 π/4 DQPSK 40 GMSK BPSK/QPSK 4.615 20 π/4 DQPSK 20 1.4.1 United States Digital Cellular (Interim Standard-54) United States Digital Cellular (IS-54) is a digital system and uses TDMA as a multiple access technique compared with AMPS, which is an analog system and uses FDMA. It is referred to as a dual-mode system because it was designed to share the same frequency, frequency-reuse plan, and base stations with AMPS. It was done so that the mobile and base stations can be equipped with AMPS and IS-54 channels within the same equipment to help migrate from an analog to a digital system and simultaneously to increase system capacity. In this system each frequency channel of 30 kHz is divided into six time slots in each direction. For full-rate speech, three users equally share six slots where two slots are allocated per user. For half-rate speech, each user only uses one slot. Thus, the system capacity is three times more than that of the AMPS for full-rate speech and double that for the half-rate speech. This system also uses the same signaling (FSK) technique as that of AMPS for control whereas it uses π/4 DQPSK for the voice. It was standardized as IS-54 by the Electronic Industries Association and Telecommunication Industry Association (EIA/TIA) and was later revised as IS-136. The revised version has digital control channels (DCCs) that provide an increased signaling rate as well as additional features such as transmission of point-to-point short messages, broadcast messages, group addressing, and so on. As was discussed in the previous section, AMPS has 42 control channels. The IS-54 standard specifies these as primary channels and additional 42 channels as secondary channels. Thus, it has twice the control channels as that of AMPS and is able to carry twice the control traffic in a given area. The secondary channels are not monitored by AMPS users and are for the exclusive use of IS-54 users. Each time slot in each voice channel has one digital traffic channel (DTC) for user data and digitized speech and three supervisory channels to carry control information. A full duplex DTC consists of forward DTC to carry data from the base station to the mobile and reverse DTC to carry data from the mobile to the base station. The three supervisory channels are coded digital verification color code (CDVCC), slow associated control channel (SACCH), and fast associated control channel (FACCH). The CDVCC is a 12-b message transmitted every slot containing 8-b color code number between 1 and 255. The 12-b message is generated using shortened Hamming code. It has a similar function to SAT in AMPS. A station transmits this number on CDVCC channels and expects a handshake from each mobile that must retransmit this value on a reverse voice channel. If the number is not returned within a specified time, the time slot is relinquished. The SACCH is a signaling channel and carries control information between base and mobile while a call is in progress. It is sent with every slot carrying information about power level change, handoff, and so on. Mobiles use this channel to send signal strength measurement of neighboring base stations so that the base may implement mobile-assisted handoff (MAHO). The FACCH is a second signaling channel to carry control information when the call is in progress. It does not have a dedicated time during each slot as is the case for CDVCC and SACCH. It is similar to © 2002 by CRC Press LLC blank-and-burst in AMPS and replaces speech data when used. It carries call release instructions, MAHO, and mobile status requests. 1.4.2 Personal Digital Cellular System The PDC system, established in Japan, employs TDMA technique. It uses three time slots per frequency channel and has a frame duration of 20 ms. It can support three users at full-rate speech and six halfrate speech users similar to IS-54. It has a channel spacing of 25 kHz and uses π/4 DQPSK modulation. It supports a frequency-reuse plan with cluster size four and uses MAHO. 1.4.3 Code Division Multiple Access Digital Cellular System (Interim Standard-95) This CDMA digital system uses CDMA as a multiple access technique and occupies the same frequency band as that occupied by AMPS; that is, the forward-link frequency band is from 869 to 894 MHz and the reverse-link band is from 824 to 849 MHz. Forward-link and reverse-link carrier frequencies are separated by 45 MHz. Each channel in IS-95 occupies a 1.25-MHz bandwidth and this is shared by many users. The users are separated from each other by allocating 1 of 64 orthogonal spreading sequences (Walsh functions). The user data are grouped into 20-ms frames and are transmitted at a basic user rate of 9600 bps. This is spread to a channel chip rate of 1.2288 Mchip/s giving a spreading factor of 128. RAKE receivers are used at both base station and mobiles to resolve and combine multipath components. During handoff the standard allows for base station diversity whereby a mobile keeps link with both the base stations and combines signals from both the stations to improve signal quality as it would combine multipath signals. In forward-link a base station transmits simultaneously to all users using 1 of 64 spreading sequences for each user once the user data are encoded using a half-rate convolution code and are interleaved. All signals in a cell are also scrambled using a PN sequence of length 215 to reduce the co-channel interference. During the scrambling process the orthogonality between different users is preserved. The forward channel consists of 1 pilot channel, 1 synchronization channel, up to 7 paging channels, and up to 63 traffic channels. The pilot channel transmits higher power than other channels and is used by mobiles to acquire timing for forward channel and to compare signal strength of different base stations. It also provides phase reference for coherent detection. The synchronization channel operates at 1200 bps and broadcasts a synchronization message to mobiles. The paging channels are used to transmit paging messages from the base station to mobiles and to operate at 9600, 4800, or 2400 bps. The traffic channels support variable data rate operating at 9600, 4800, 2400, and 1200 bps. On reverse channels, mobiles transmit asynchronously to the base, and orthogonally between different users in a cell is not guaranteed. A strict control is applied to the power of each mobile so that a base station receives constant power from each user, thus eliminating the near–far problem. Power control command is sent by the base to mobiles at a rate of 800 bps. The reverse channels are made up of access channels and reverse traffic channels. The reverse channels contain up to 32 access channels per paging channel, operate at 4800 bps, and are used by mobiles to initiate communication with base and to respond to paging messages. The reverse traffic channel is a variable data rate channel and operates similar to the forward channels at 9600, 4800, 2400, and 1200 bps. 1.4.4 Pan European Global System for Mobile Communications The “Groupe Special Mobile” was established in 1982 to work toward the evolution of digital system in Europe, and its work now has become the Global System for Mobile (GSM) Communications system. Two frequency bands have been allocated for this system. The primary band is at 900 MHz and the © 2002 by CRC Press LLC 15 26 Frequency (kHz) 200 Time (ms) FIGURE 1.4 GSM multiple access. secondary band is at 1800 MHz. The description here mainly concerns the primary band. It has been divided into two subbands of 25 MHz each, separated by 20 MHz. The lower band is used for uplink and the upper band is used for downlink. Operators are assigned a portion of the spectrum for their use. The carrier frequencies are separated by 200 kHz. This gives the total number of frequency channels over the 25-MHz band as 124. The first carrier is at 890.2 MHz, the second one is at 890.4 MHz, and so on. These carriers are numbered as 0, 1, 2 and so on, respectively. Similarly, 374 different carriers are allocated in the secondary band, which is 75 MHz wide. 18.104.22.168 Multiple Access Scheme GSM employs a combination of TDMA and FDMA schemes with slow frequency hopping. GSM transmission takes place by modulating a bundle of about 100 b known as a burst. A burst occupies a finite duration in time and frequency plane. The center frequency of these bursts is 200 kHz apart and these are 15/26 ms in duration. The duration of these bursts is the time unit and is referred to as burst period (BP). Thus, time is measured in BP. When this burst is combined with slow frequency hopping, a typical transmission appears as shown in Fig. 1.4. The hopping sequence is selected randomly using a PN sequence. A channel is defined by specifying which time slot it may use for transmit burst. That means specifying time instant and specific frequency. Time slots of a channel are not contiguous in time. All time slots are numbered and the description of a channel sent to the mobile by the base refers to this numbering scheme. The numbering is cyclic and each time slot is uniquely identified in this cycle, which is about 3.5 h (3 h 28 min 53 s, and 760 ms). Many types of channels are defined in GSM, and each are cyclic. The simplest cycle is of 8 BP. This cycle of eight time slots is also called a slot, which is 60/13 ms in duration. The duration of the BP is chosen such that 26 slots equal to 120 ms, which is a multiple of 20 ms to obtain synchronization with other networks such as the Integrated Services Digital Network (ISDN). A full dedicated channel is thus cyclic in 120 ms and uses 26 slots. Note that each slot is made up of eight time slots of 15/26 ms known as BP. Out of these 26 slots, 24 slots are used for traffic burst, 1 slot is used for control burst, and 1 slot is not used. The transmission between the uplink and the downlink is not independent. Transmission in uplink follows the downlink reception by 3 BP later. When the mobile is far from the base, the mobile advances its transmission from the reception to compensate the propagation delay. Hopping sequences in the uplink and the downlink are also related. The hopping sequence in the uplink direction is derived from the one in the downlink direction in by adding 45 MHz. © 2002 by CRC Press LLC 22.214.171.124 Common Channels These channels do not carry traffic and are organized based on a cycle of 51 slots (51 × 8 BP). This cycle is deliberately chosen differently from 26 slots of traffic channels so as not to have a common divider between the two. This allows mobiles in a dedicated channel to listen to synchronization channels (SCHs) and frequency correction channels (FCCHs) of the surrounding cells, which helps mobiles to stay in synchronization. Each SCH and FCCH uses 5 slots in a 51-slot cycle with SCH following FCCH 8 BP later. This helps mobiles to find SCH once it has located FCCH. The other downlink common channels defined include BCCH for broadcasting and PAGCH for paging. For uplink, a channel RACH is defined. 126.96.36.199 Burst Format The quantum of transmission in GSM is 1 BP, which is 7500/13 s in duration and is occupied by about (156 + 1/4) b. In GSM several burst formats have been defined and these are used for different purposes. Access burst is used in uplink direction from the mobile to the base during the initial phase. This is the first access of the mobile to the base. The burst has constant amplitude for the period of 87 b. The structure of the burst consists of 7 b of tail followed by 41 b of training sequence, 36 b of information, and 3 b of tail on the other side. A single training sequence is specified for this burst. The access burst is the first burst from the mobile to the base and contains required demodulation information for the base. The S burst is similar to the access burst but it is transmitted from the base to the mobile. It is the first burst from the base and has 64 training sequence bits surrounded by 39 information bits and 3 tail bits. The training sequence is unique and chosen so that the mobile knows which sequence the base has chosen. The F burst enables the mobile to find and demodulate the S burst. All of its 148 b are set to zero, resulting in a pure sine wave of 1625/24 kHz. The normal burst is used for all other purposes. Its amplitude stays constant covering 147 b. It has 26 training sequence bits surrounded by 58 information bits and 3 tail bits. Eight different training sequences have been specified to distinguish co-channel signals. For more details on the GSM system, see, for example, Reference . 1.4.5 Cordless Mobiles The first generation analog cordless phones were designed to communicate with a single base station, effectively replacing telephone cord with a wireless link to provide terminal mobility in a small coverage area such as a house or an office. The aim of the second-generation digital cordless system is to use the same terminal in residential as well as public access areas such as offices, shopping malls, train stations, and so on to receive and to originate calls. The cordless systems differ from cellular systems in a number of ways. Their cell size is small, typically less than half a kilometer, and their antenna elevation is low. These are designed for low-speed mobiles, typically on foot, and provide coverage in specific zones instead of continuous wide-area coverage provided by cellular systems. Cordless handsets transmit very low power. A typical average transmitted power is about 5 to 10 mW compared with a few hundred milliwatt for cellular handsets . Most of the cordless systems use TDD as duplexing techniques compared with FDD employed by cellular systems. Some of the popular digital cordless standard include CT2, a British standard; digital European cordless telecommunication (DECT) standard; personal handyphone system (PHS) of Japan, and personal access communication service (PACS) of the United States. Some of the parameters of these systems are compared in Table 1.3. More details on these may be found in Reference  and references therein. 1.5 Third-Generation Systems The third-generation systems aim to provide a seamless network that can provide users voice, data, multimedia, and video services regardless of their location on the network: fixed, cordless, cellular, © 2002 by CRC Press LLC TABLE 1.3 Digital Cordless System Parameters Parameter Frequency (MHz) Channel spacing (kHz) Duplexing Channel rate (kbps) Transmitted power (mW) Average Peak Frame duration (ms) Channels per carrier CT2 DECT PACS PHS 864–868 1880–1900 1895–1918 100 TDD 72 1728 TDD 1152 1850–1910 and 1930–1990 300 FDD 384 5 10 2 1 10 250 10 12 25 200 2.5 8 300 TDD 384 10 80 5 4 satellite, and so on. The networks support global roaming while providing high-speed data and multimedia applications of up to 144 kbps on the move and up to 2 Mbps in a local area. Third-generation systems are currently being defined by both the International Telecommunications Union (ITU) and regional standardization bodies. Globally, the ITU has been defining third-generation systems since the late 1980s through work on the IMT-2000 system, formerly called the Future Public Land Mobile Telecommunications Service (FPLMTS) . The ITU is now in the process of seeking candidate technologies to be evaluated in accordance with agreed guidelines . The European proposal for IMT-2000 is known as the Universal Mobile Telecommunications System (UMTS) — see discussions in References [54–57] — and is being defined by the European Telecommunications Standards Institute (ETSI), which has been responsible for UMTS standardization since the 1980s. Although UMTS will provide significant changes for customers and technologies, systems will be deployed within a short time frame. Japan plans to launch its UMTS network in the year 2001; and the United Kingdom wants its UMTS radio interface working alongside enhanced GSM networks by the year 2002, with a fully working UMTS network operating by 2005. Third-generation networks are planned for the United States sometime between 2003 and 2005 . Additional updates on IMT-2000 developments in the Asia Pacific Region can be found in References [59–62]. IMT-2000 defines systems capable of providing continuous mobile telecommunications coverage for any point on the earth’s surface. Access to IMT-2000 is via either a fixed terminal or a small, light, portable mobile terminal (MT) . Several different radio environments are utilized to provide the required layers of coverage. These range from very small indoor picocells with high capacity, through to terrestrial micro- and macrocells, to satellite megacells. IMT-2000 recommendations aim to maximize commonality between the various radio interfaces involved, to simplify the task of developing multimode terminals for the various operating environments . In this section some salient features of IMT-2000 are discussed [4, 5]. 1.5.1 Key Features and Objectives of International Mobile Telecommunications-2000 The key features and objectives of IMT-2000 include  1. Integration of current first- and second-generation terrestrial and satellite-based communications systems into a third-generation system 2. Ensuring a high degree of commonality of design at a global layer 3. Compatibility of services within IMT-2000 and with fixed networks 4. Ensuring high quality and integrity of communications, comparable to the fixed network 5. Accommodation of a variety of types of terminals including pocket-size terminals 6. Use of terminals worldwide 7. Provision for connection of mobile users to other mobile users or fixed users © 2002 by CRC Press LLC 8. 9. 10. 11. 12. Provision of services by more than one network in any coverage area Availability to mobile users of a range of voice and nonvoice services Provision of services over a wide range of user densities and coverage areas Efficient use of the radio spectrum consistent with providing service at acceptable cost Provision of a framework for the continuing expansion of mobile network services and for the access to services and facilities of the fixed network 13. Number portability independent of service provider 14. Open architecture that accommodates advances in technology and different applications 15. Modular structure that allows the system to grow as needed 1.5.2 International Mobile Telecommunications-2000 Services IMT-2000 supports a wide range of services, including those based on the fixed telecommunication network and those that are specific to mobile users. Services are available in a variety of environments ranging from dense urban situations, including high intensity office use, through to suburban and rural areas . The actual services obtained by a user depend on the capabilities of their terminal, their subscribed set of services, and the services offered by the relevant network operator and service provider . Global roaming users have access to at least a minimum set of services comprising voice telephony, selection of data services, and indication of other services available. IMT-2000 also provides services to fixed users and if required, can provide rapid and economical implementation of wide-area communications, which is particularly relevant to developing countries . The general service objectives of IMT-2000 are to  1. Provide a wide range of telecommunication services to mobile or stationary users by means of one or more radio links 2. Make these services available for mobile terminals located anywhere (subject to economic constraints) 3. Provide for flexibility of service provision 4. Promote flexible introduction of services 5. Ensure that a user is provided with an indication of service availability 6. Provide access to voice telephony 7. Provide access to a selection of data services 8. Provide services that depend on terminal type, location, and availability from the network operator 9. Provide a temporary or permanent substitute to fixed networks in rural or urban areas under conditions approved by the appropriate national or regional regulation authority The general service requirements of IMT-2000 are to provide 1. 2. 3. 4. Validation and authentication procedures to facilitate billing and accounting based on ITU-T X509 Additional layer of security for mobile telecommunications services Privacy of location of a roaming user when desired by the called or calling party Quality of service comparable with that of fixed networks The general access requirements are as follows: 1. For access to fixed networks, IMT-2000 may be either an adjunct to, or an integral part of, the PSTN/ISDN. 2. For global use, IMT-2000 should allow international operation and automatic roaming of terminals. 3. For maritime and aeronautical use, operation should be facilitated to the extent permitted by the relevant regulatory body. 4. For satellite operation, IMT-2000 should facilitate direct and indirect satellite operation. The first phase of IMT-2000 provides several telecommunications services, most of which are based on ITU-T E and F series recommendations. © 2002 by CRC Press LLC Network services — These services are provided by IMT-2000 : 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. Voice telephony (ITU-T E105) Program sound Message handling (ITU-T F400) Teletex (ITU-T F200) Paging (open loop, closed loop, user acknowledged) Telefax (ITU-T F160 and F180) Point to multipoint Data Video services using MPEG derived algorithms  Short messages Location monitoring Multimedia Supplementary services — The following services may be provided by IMT-2000: 1. Separation of answering from alerting: Currently, the alerting function resides in the same device used for answering. In IMT-2000, the alerting device may be a pager and the answering device may be a terminal of the user’s choice. 2. Advice of charging: Parties to a call should be able to receive charging information before, during, and after the call. 1.5.3 Planning Considerations In defining IMT-2000, several factors required consideration: radio access, spectrum requirements, security, network issues, and regulatory environments. 188.8.131.52 Radio Access IMT-2000 provides access, by means of one or more radio links, to a wide range of services in a wide variety of operating environments. High data rates are required to provide users with the necessary quality of service for multimedia communications, ranging from a few tens of kilobits per second for image transfer, to a couple of hundreds of bits per second for peak Internet transfers, to 2 Mbps for video. The bearers for IMT-2000 are therefore defined as 384 kbps for full area coverage and 2 Mbps for local area coverage. It is essential to optimize third-generation techniques to cater for variable bit rate and packet capabilities because many multimedia applications are packet oriented. Similarly, multimedia support implies flexibility to handle services with different bit rates and Eb/N0 requirements . The mode of delivery is via either terrestrial or satellite-based radio links, with the possibility of incorporating two or more radio