WIRELESS INFORMATION NETWORKS€¦ · PART I INTRODUCTION TO WIRELESS NETWORKS 1 1 Overview of Wireless Networks 3. 1.1 Introduction, 3 1.2 Network Architecture and Design Issues,

WIRELESS INFORMATIONNETWORKS

Second Edition

KAVEH PAHLAVANALLEN H. LEVESQUE

A JOHN WILEY & SONS, INC., PUBLICATION

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Second Edition

KAVEH PAHLAVANALLEN H. LEVESQUE

A JOHN WILEY & SONS, INC., PUBLICATION

Copyright 2005 by John Wiley & Sons, Inc. All rights reserved.

Published by John Wiley & Sons, Inc., Hoboken, New JerseyPublished simultaneously in Canada

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To those from whom we learned,to those we taught, and

to those we love

CONTENTS

Preface xi

PART I INTRODUCTION TO WIRELESS NETWORKS 1

1 Overview of Wireless Networks 3

1.1 Introduction, 31.2 Network Architecture and Design Issues, 61.3 Key Trends in Wireless Networking, 201.4 Outline of the Book, 21

Questions, 22

2 Evolution of the Wireless Industry 23

2.1 Introduction, 232.2 Three Views of the Wireless Industry, 292.3 Three Generations of Cellular Networks, 322.4 Trends in Wireless Technologies, 43

Questions, 49

PART II CHARACTERISTICS OF RADIO PROPAGATION 51

3 Characterization of Radio Propagation 53

3.1 Introduction, 533.2 Multipath Fading and the Distance–Power Relationship, 553.3 Local Movements and Doppler Shift, 643.4 Multipath for Wideband Signals, 663.5 Classical Uncorrelated Scattering Model, 723.6 Indoor and Urban Radio Propagation Modeling, 81

Questions, 86Problems, 87Projects, 89

4 Modeling and Simulation of Narrowband Signal Characteristics 93

4.1 Introduction, 93

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viii CONTENTS

4.2 Modeling Path Loss and Slow Shadow Fading, 964.3 Doppler Spectrum of Fast Envelope Fading, 1104.4 Statistical Behavior of Fast Envelope Fading, 1224.5 Simulation of Fast Envelope Fading, 126


5 Measurement of Wideband and UWB Channel Characteristics 149

5.1 Introduction, 1495.2 Time-Domain Measurement Techniques, 1515.3 Frequency-Domain Measurement Techniques, 1715.4 Advances in Frequency-Domain Channel Measurement, 180

Questions, 197Problems, 198Project, 200

6 Modeling of Wideband Radio Channel Characteristics 205

6.1 Introduction, 2066.2 Wideband Time-Domain Statistical Modeling, 2086.3 Wideband Frequency-Domain Channel Modeling, 2346.4 Comparison Between Statistical Models, 2436.5 Ray-Tracing Algorithms, 2456.6 Direct Solution of Radio Propagation Equations, 2616.7 Comparison of Deterministic and Statistical Modeling, 2636.8 Site-Specific Statistical Model, 265

Appendix 6A: GSM-Recommended Multipath PropagationModels, 270Appendix 6B: Wideband Multipath Propagation Models, 272Questions, 274Problems, 275Projects, 277

PART III MODEM DESIGN 279

7 Narrowband Modem Technology 281

7.1 Introduction, 2827.2 Basic Modulation Techniques, 2847.3 Theoretical Limits and Practical Impairments, 3077.4 Traditional Modems for Wide-Area Wireless Networks, 3127.5 Other Aspects of Modem Implementation, 328


8 Fading, Diversity, and Coding 341


CONTENTS ix

8.2 Radio Communication on Flat Rayleigh Fading Channels, 3438.3 Diversity Combining, 3478.4 Error-Control Coding for Wireless Channels, 3538.5 Space-Time Coding, 3638.6 MIMO and STC, 365


9 Broadband Modem Technologies 377

9.1 Introduction, 3789.2 Effects of Frequency-Selective Multipath Fading, 3809.3 Discrete Multipath Fading Channel Model, 3849.4 Adaptive Discrete Matched Filter, 3899.5 Adaptive Equalization, 3939.6 Sectored Antennas, 4059.7 Multicarrier, OFDM, and Frequency Diversity, 4119.8 Comparison of Traditional Broadband Modems, 4219.9 MIMO in Frequency-Selective Fading, 423

Appendix 9A: Analysis of the Equalizers, 425Questions, 428Problems, 429Projects, 431

10 Spread-Spectrum and CDMA Technology 435

10.1 Introduction, 43510.2 Principles of Frequency-Hopping Spread Spectrum, 43910.3 Principles of Direct-Sequence Spread Spectrum, 44410.4 Interference in Spread-Spectrum Systems, 46410.5 Performance of CDMA Systems, 476

Questions, 494Problems, 495

PART IV SYSTEMS ASPECTS 499

11 Topology, Medium Access, and Performance 501

11.1 Introduction, 50111.2 Topologies for Local Networks, 50311.3 Cellular Topology for Wide-Area Networks, 50611.4 Centrally Controlled Assigned Access Methods, 52111.5 Distributed Contention-Based Access Control, 537

Questions, 572Problems, 573Project, 576

12 Ultrawideband Communications 581


x CONTENTS

12.2 UWB Channel Characteristics, 58412.3 Impulse Radio and Time-Hopping Access, 58912.4 Direct-Sequence UWB, 59512.5 Multiband OFDM, 599


13 RF Location Sensing 607

13.1 Introduction, 60713.2 RF Location-Sensing Techniques, 61113.3 Modeling The Behavior of RF Sensors, 61913.4 Wireless Positioning Algorithms, 626


14 Wireless Optical Networks 639

14.1 Introduction, 63914.2 Implementation, 64114.3 Eye Safety, 64314.4 IR Channel Characterization and Data-Rate Limitations, 64414.5 Modulation Techniques for Optical Communications, 65314.6 Multiple Access and Data Rate, 659

Questions, 661

15 Systems and Standards 663

15.1 Introduction, 66315.2 GSM, GPRS, and EDGE, 66415.3 CDMA and HDR, 67415.4 Other Historical Systems, 67915.5 Wireless LANs, 68215.6 Speech Coding in Wireless Systems, 685

Questions, 687

References 689

Index 713

About the Authors 721

PREFACE

The first edition of this book, published in 1995, was the first textbook to provide acomprehensive introduction to the field of wireless information networks. That bookpresented wireless networking as the enabling communications technology of the 1990sand beyond. Now, only a decade later, mobile and portable telephones and wirelessdata services are a familiar part of our daily lives, as the twenty-first century witnesseswidespread deployment of wireless networks, which has revolutionized the conceptof communication and information processing for business, professional, and privateapplications. The field of wireless communications continues to experience unprece-dented market growth, as evidenced by over 1.5 billion cellular telephone subscribersworldwide and the rapid increase in the size of the wireless local area network mar-ket for office, home, and public access applications. The initial growth in the marketfor second-generation cellular products and services spurred important new initiativestoward the development and deployment of third-generation cellular networks. Morerecently, attention has been focused on location-aware broadband ad hoc wirelessnetworks as the foundation for the next generation of wireless networking technology,which is expected to enable systems of geographically dispersed sensors. The emergingwireless sensor and ad hoc networks are expected to interconnect numerous terminalswith a variety of data-rate requirements with traditional multimedia Internet networksto create a worldwide communication medium among RFID tags, a variety of sensors,home appliances, and small robotic devices.

These developments were all part of a major paradigm shift in the world of telecom-munication, a shift away from nearly exclusive reliance on wired networks to an eraof “tetherless” communications based largely on wireless technology, and a shift inthe computer industry toward integration of high-performance distributed computingand portable devices in a pervasive mobile computing environment. We adopted thetitle Wireless Information Networks in 1995 as an encompassing name intended toinclude all applications related to evolving wireless networks in the telecommunica-tion and computer industries, and that book provided comprehensive coverage of thesignal processing and system engineering aspects of this field. Given the tremendousgrowth of the industry in both its signal processing and systems engineering aspects,it becomes increasingly difficult to treat all the important topics in a single volume.With that in mind, in 2002 the lead author published a new book, Principles of WirelessNetworks—A Unified Approach, coauthored by Prashant Krishnamurthy, which is morefocused on systems engineering aspects, and began preparing this second edition ofthe original book, with more emphasis on signal processing topics. The objective of

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xii PREFACE

Principles of Wireless Networks is to provide a systems engineering treatment that canbe taught to both electrical and computer engineering (ECE) and computer sciencestudents in undergraduate or first-year graduate courses. This second edition of Wire-less Information Networks places greater emphasis on signal processing and is moresuitable for ECE graduate students and possibly senior undergraduate students.

At the emergence of the wireless industry in late 1980s and early 1990s, all telecom-munication enterprises that were involved in traditional wired communications servicesand product development made major investments in wireless technology. Computercompanies invested in wireless communications to add mobile computing and ad hocnetworking features to the laptop, handheld, notepad, and other portable computingdevices that are coming into increasingly pervasive use. Later, large corporations, asend users, included wireless components in their network infrastructures to extend theaccessibility of their networks to their traveling personnel. Military agencies devel-oped location-aware ad hoc sensor networks for use in tactical environments, as wellas portable devices that place a large amount of computational power in the handsof the foot soldier operating in urban fighting scenarios. Today, almost all compa-nies in engineering disciplines other than telecommunications are entering the wirelesscommunications business, for applications such as in-vehicle networking or home net-working, and are now a part of this wireless revolution. All of this means that thereare a great many engineers, computer science specialists, and managers with a varietyof interests who are faced with having to educate themselves in this area. This majornew emphasis on wireless communications has also spurred a renewed emphasis onthe teaching of principles of wireless communications in colleges and universities.This second edition is designed to provide students, engineers, and scientists with anintroduction to the major signal processing aspects of wireless networks.

The book is written from a systems engineering perspective, by which we mean thatthe various technical topics are presented in the context of ongoing development ofspecific new systems and services, as well as key recent developments in national andinternational spectrum allocations and standards. Our method of presentation is to orga-nize the myriad of emerging wireless technologies into logical categories that reflectthe variety of perspectives that users have toward different networks and services.The book addresses the major segments of wireless technology: first-, second-, andthird-generation wide-area cellular networks, wireless local area networks (WLANs),and wireless personal area networks (WPANs), with special attention to the emerginglocation-aware broadband wireless sensor and ad hoc networks. Although the bookcovers technology applicable to a wide range of wireless systems, as in the first edi-tion, particular attention is given to indoor wireless communications, an area that isnot treated in great depth in most other books.

In writing the book, we have endeavored to bring together treatments of all themajor topics to be considered in the design of wireless information networks, but haveavoided the presentation of detailed mathematical derivations that are available in othertexts. In each instance, we have tried to provide the motivation for various wirelesssystem design choices in the context of overall system considerations. We believe thatthis is an effective approach to training systems engineers, who should have an overallperspective of an entire system as well as a working knowledge of how to apply theresults of specific research to an engineering problem.

The first edition of the book has been used as a graduate-level textbook in uni-versities throughout the world. It has also been used as a reference book for indoor

PREFACE xiii

radio communication research programs at DARPA and the National Science Foun-dation and for indoor radio channel modeling for WLAN and WPAN standardizationactivities such as IEEE 802.11n and IEEE 802.15.3. Being the first comprehensivetextbook on wireless networks, the first edition has served many of today’s leadingresearchers as a key resource in gaining a comprehensive understanding of the impor-tant issues related to wireless communications. As a result, in this second edition wehave tried to maintain the comprehensive treatment and have included major tech-nical developments that have emerged since publication of the first edition, such asultrawideband communications, wireless positioning, space-time coding, multiple-inputmultiple-output antennas, orthogonal frequency-domain multiplexing, interference can-cellation, and multiuser detection. Therefore, we have increased the number of chaptersfrom 12 to 15 to include ultrawideband communications and wireless positioning intwo new chapters and to expand the modem design chapters from three to four. Somereaders of the first edition indicated that certain problem sets were overly difficult.Thus, in this edition we have added a number of simpler problems and have turnedsome of the more difficult ones into projects with expanded explanations, to make themeasier to understand. As in the first edition, the questionnaire format is used to empha-size the importance of having a general understanding of the overall system at hand andof the rationale behind key engineering design choices. The traditional problem setsare exercises for derivation and understanding of the detailed mathematical analysisof various concepts. Projects provide more detailed exercises, usually involving com-puter simulations or extensive analysis of data. We have directed these problems andprojects toward application-oriented issues. This approach provides students with anunderstanding of the issues, motivates them to use the computer as a tool in the learningprocess, and shifts their viewpoint toward real-world engineering problems rather thanmathematical drills. We believe that this approach is essential for the proper trainingof engineers for productive careers in the market-driven telecommunication industry,where simple ideas and added features will often generate greater revenues than willthe latest technical inventions.

This edition of the book covers four categories of topics, organized into four parts.In Part I of the book, Chapters 1 and 2, we provide an overview of major categories ofwireless communications and outline the user and market perspectives toward variouswireless systems and services. Then we review briefly the current state of developmentof wireless and mobile communications systems, including the important issues ofspectrum administration and standards.

In Part II, Chapters 3 through 6, we describe the characteristics of radio propa-gation, as well as measurement and simulation methods used in evaluating existingthird-generation cellular, WLAN, and WPAN systems and emerging location-awarebroadband wireless ad hoc networks. We provide a detailed description of time- andfrequency-domain statistical channel modeling techniques and their application to pop-ular standards such as GSM, IEEE 802.11, and IEEE 802.15. We also describe theray-tracing algorithm and give a brief overview of direct solution of the radio propa-gation equations.

In Part III, Chapters 7 through 10, we discuss wireless modem design technolo-gies. We begin in Chapter 7 with a description of traditional narrowband modemtechnologies and issues arising in their application to radio channels. In Chapter 8we address fading, diversity, and coding in relation to the analysis and performanceevaluation of wireless modems. In this chapter we also introduce the concepts of

xiv PREFACE

multiple-input multiple-output and space-time coding, which are gaining considerableattention as techniques to be used in modem design. Chapter 9 is devoted to broadbandmodem technologies, including equalization techniques, smart antenna techniques, andorthogonal frequency-division multiplexing (OFDM). Chapter 10 is devoted to spread-spectrum techniques and code-division multiple-access techniques for direct-sequenceand frequency-hopping systems.

Part IV, Chapters 11 through 15, is devoted to network access and system aspects.Chapter 11 treats network access methods and provides a comprehensive descriptionof voice-oriented assigned access and data-oriented random access techniques anddiscusses performance evaluation methods as well. Chapter 12 is devoted to ultra-wideband (UWB) communications. In this chapter we discuss the detailed behaviorof UWB channels and describe impulse radio, multiband OFDM, and direct-sequenceUWB techniques being considered by IEEE 802.15 for the next generation of WPANapplications. Chapter 13 is devoted to RF location-sensing techniques, the foundationfor wireless positioning and indoor geolocation science. We discuss RF channel behav-ior in the context of positioning applications and describe the popular received signalstrength systems used in WLAN positioning as well as the time-of-arrival techniquesused for more accurate positioning. These chapters provide a comprehensive under-standing of the emerging technologies for implementation of wireless sensor and adhoc networks. Chapter 14 is the same as Chapter 10 of the first edition and provides theprinciples of infrared communications. Chapter 15, devoted to systems and standards,is a revision of the concluding chapter of the first edition.

The book can be used in its entirety for a first- or second-year graduate course inwireless communications networks in electrical and computer engineering curricula. Aspreparation for such a course, students should have an understanding of the elementsof probabilistic signal and system analysis and some background in the principles ofmodulation and coding. This material is taught at the Worcester Polytechnic Institute(WPI) and the University of Oulu in Finland as a 14-week course meeting three hoursper week. The first two chapters are taught in the first week, Chapters 3 to 6 in the nextfive weeks, Chapters 7 to 10 in four weeks, and Chapters 12 and 13 in two weeks.The remaining two weeks can be spent on other topics selected by the instructoror on student presentations, followed by course exams. Weekly assignments includeanswering selected questions and solving a few selected problems at the end of thechapter. In addition, students are asked to do three of the projects throughout the course.The material in some chapters is covered completely, whereas material in other chaptersis covered with more emphasis on the concepts and less emphasis on the details ofmathematical derivations. To cover all chapters of the book in full detail, a two-semestercourse format is advisable, although most of the material might be covered in a fast-paced one-semester course with selective omission of the more specialized topics. Withappropriate selection of topics, the book can also be used at the undergraduate level.An extensive list of references is included, which will be especially helpful to theindividual reader using the book for self-study or reference purposes.

Much of the material in the first edition and part of the material in the secondedition was drawn from the published work of the lead author and his students in theCenter for Wireless Information Network Studies (CWINS) at WPI. We are pleased toacknowledge students’ contributions to advancing the understanding of wireless chan-nels and networks. In particular, we thank Dr. Steven Howard, Dr. Rajamani Ganesh,Dr. Ker Zhang, Dr. Ganning Yang, Dr. Thomas Sexton, Dr. Mitch Chase, Timothy

PREFACE xv

Holt, Dr. Aram Falsafi, Glen Bronson, Joseph Meditz, Dr. Mudhafar Hassan Ali, andDr. Sheping Li, whose contributions were helpful in the preparation of the first editionof the book. In addition, we would like to express our appreciation to Dr. PrashantKrishnamurthy, Dr. Xinrong Li, Dr. Ali Zahedi, Jeff Feigin, Dr. Aram Falsafi, Dr.Robert Tingley, Hamid Hatami, Bardia Alavi, Emad Zand, Muzafer Kannan, NayefAlsindi, Mohammad Heidari, Leon Teruo Metreaud, and other recent affiliates of theCWINS Laboratory, as well as Dr. Mika Ylianttila and Juha-Pekka Makela of the Uni-versity of Oulu, who have directly or indirectly helped the lead author to extend hisknowledge in this field and shape his thoughts for preparation of the second editionof the book. We owe special thanks to the National Science Foundation, DARPA, andthe United States Department of Defense, to TEKES, Nokia, Sonera, and the FinnishAir Force in Finland, and to many other companies and research organizations whosesupport of the CWINS program at WPI enables graduate students and the staff ofCWINS to pursue continuing research in this important field. A substantial part of thenew material in this second edition has flowed out of these sponsored research efforts.

Much of the writing of the lead author in this second edition was accomplished whileteaching and carrying out research at the University of Oulu, Finland, as well as duringhis sabbatical at Olin College of Engineering, Needham, Massachusetts. He would liketo express his deep appreciations to the University of Oulu, Olin College, and WorcesterPolytechnic Institute for providing him with these opportunities. In particular, he thanksProfessor Pentti Leppanen of the University of Oulu for his continual encouragementand creative administrative support, and Professor Matti-Latva-aho of the Universityof Oulu and Dr. Sassan Iraji of Nokia Research Center for fruitful discussions oncurrent developments in spread-spectrum and CDMA technologies. He also thanksDavid Kerns, provost of Olin College, for providing him the opportunity to spend thefall 2004 semester at Olin. Also, he thanks Professor Fred Looft, head of the WPI ECEDepartment, and WPI provost John Carney for their support of a sabbatical leave forwork on this second edition.

The lead author would also like to express his deep appreciation to Dr. Phillip Bello,Professor John Proakis, and Dr. Jerry Holsinger, through whom he has increased thedepth of his understanding of the theory and practice of telecommunications, and toProfessor James Matthews for introducing him to the field of radio communications.

His coauthor would like to express appreciation to his many colleagues at GTE(now Verizon) who during his industrial career helped in many ways in his work inmobile and cellular communications. He would also like to thank Professors John Orrand Fred Looft and provost John Carney for providing him with the opportunity forgraduate teaching and participation in CWINS research activities at WPI.

Most of all, the authors are indebted to their families for their patience and supportthroughout this long and challenging project.

K. P.A. H. L.

PART I

INTRODUCTION TO WIRELESSNETWORKS

Part I consists of two chapters that provide an introduction to wireless network tech-nologies and standards. These chapters cover the market sectors and describe incentivesfor the use of wireless networks by the telecommunications and computer industriesand the military.

Chapter 1: Overview of Wireless Networks

In this chapter we provide an overview of wireless information networks. We describethe basic elements of a wireless network and the key technical issues to be consideredin the design of these networks. We also discuss the market sectors that constitute thewireless industry and the trends apparent in voice- and data-oriented networks. In thefinal section of the chapter we outline the remaining chapters of the book.

Chapter 2: Evolution of the Wireless Industry

In this chapter we consider the evolution of wireless networking technology, which hasbeen built upon developments occurring not only in the telecommunications industrybut also in the computer industry, as communications and computer technologies havedrawn closer together. Many observers see the wireless industry as one that has inte-grated radio science with communications and computer technologies. Thus, beforedelving into details of radio propagation and signal processing—the primary focusof this book—it is useful to consider the wireless industry from the separate view-points of the telecommunications and computer industries, which is the approach wetake in this chapter. We also discuss briefly the view of an important user commu-nity, military ground forces, which have had a long history of reliance on wirelesscommunications networks.

Wireless Information Networks, Second Edition, by Kaveh Pahlavan and Allen H. LevesqueCopyright 2005 John Wiley & Sons, Inc.

1

1OVERVIEW OF WIRELESS NETWORKS

1.1 Introduction1.1.1 Elements of a Wireless Network1.1.2 Key Technical Issues for Wireless Networks1.1.3 Four Market Sectors

1.2 Network Architecture and Design Issues1.2.1 Network Architectures1.2.2 Wireless Versus Wired Networks1.2.3 Elements of a Wireless Network Architecture1.2.4 Technical Aspects of a Wireless Infrastructure1.2.5 Technical Aspects of the Air Interface

1.3 Key Trends in Wireless Networking1.3.1 Voice-Oriented Networks1.3.2 Data-Oriented Networks1.3.3 Where Is the Complexity?

1.4 Outline of the BookQuestions

1.1 INTRODUCTION

The second half of the twentieth century witnessed enormous transformations in elec-tronic communications, including the development of data transmission over legacytelephone networks, the introduction of packet-data networks, the development ofhigh-speed local area networks (LANs), and the development of mobile wirelesscommunications networks, most notably cellular networks, paging systems, and evenmobile satellite systems. By the start of the current century, cellular and paging serviceshad come into widespread use in support of business communications and personalcommunications as well. The early analog cellular networks were rapidly supplantedby digital networks affording increased traffic capacity and capable of supporting anexpanding menu of data-oriented services. In this first decade of the new century, we

Wireless Information Networks, Second Edition, by Kaveh Pahlavan and Allen H. LevesqueCopyright 2005 John Wiley & Sons, Inc.

3

4 OVERVIEW OF WIRELESS NETWORKS

are seeing rapidly increasing interest in higher-rate forms of wireless data communi-cation, including multimedia transmission to and from portable phones, and wirelessaccess to the Internet from laptop computers. The technology underlying these wirelesscommunications developments is the specific focus of this book.

The worldwide growth of the wireless communications industry has been trulyphenomenal. At this writing, there are more than 1 billion cellular telephone usersthroughout the world, and the aggregate annual revenue of the wireless industry exceedsthe revenues of the wired-telephone service industry. About 10 years ago, Internetaccess began expanding from the business environment to include the home envi-ronment, and this soon generated annual revenues comparable to those of traditionaltelephone service and wireless service. Currently, the information exchange industry,defined to include both wired and wireless phone services as well as Internet access,enjoys annual revenues of several trillion dollars and is by far the largest industry inthe world.

Underlying this rapid development of all communications services and networks hasbeen the ongoing evolution of digital technology, particularly large-scale integrationand microprocessor chip technology. The digital revolution enabled transformation ofthe core of a traditional telephone network to a digital infrastructure providing greaterreliability, increased capacity, and an ever-widening array of services to customers.About 10 years ago, digital technology began to have an impact on mobile wirelessservices and networks, increasing network capacities and capabilities as well as low-ering the cost and increasing the battery life of mobile devices. An interesting andimportant aspect of the burgeoning worldwide wireless communications industry hasbeen the rebirth of wireless LAN (WLAN) technology, driven by the steadily increas-ing popularity of laptop computers, the demand for wireless Internet access, and theexpanding deployment of wireless access points on campuses and, increasingly, inpublic commercial venues.

Many of the wireless technology developments of the past decade have focusedon improved physical (PHY) layer and medium access control (MAC) layer designs.The technical core of these protocol layers comprises digital signal processing (DSP)techniques and technology, to which most of this book is directed.

In this chapter we provide an overview of wireless information networks. Wedescribe the basic elements of a wireless network and the key technical issues tobe considered in the design of these networks. We also discuss the market sectorsconstituting the wireless industry and the trends apparent in voice- and data-orientednetworks. In the final section of the chapter we outline the remaining chapters ofthe book.

1.1.1 Elements of a Wireless Network

An information network is an infrastructure that interconnects telecommunicationdevices to provide them with means for exchanging information. Telecommunicationdevices are terminals that allow users to run applications that communicate with otherterminals through the information network infrastructure. The basic elements of aninformation network infrastructure are switches or routers that are connected by point-to-point links. Switches include fixed- and variable-rate voice-oriented circuit switches,low-speed (X.25) and high-speed (frame relay) data-oriented packet switches (routers),and ATM switches. The point-to-point links include a variety of fiber links, coaxialcables, twisted-wire pairs, and wireless connections.

INTRODUCTION 5

To support transmission of voice, data, and video, several wired information networkinfrastructures have evolved throughout the past century. Wireless networks allow amobile telecommunication terminal to access these wired information network infras-tructures. At first glance it may appear that a wireless network is only an antenna siteconnected to one of the switches in the wired infrastructure, enabling a mobile terminalto be connected to the backbone network. In reality, in addition to the antenna site,a wireless network may also need its own mobility-aware switches and base stationcontrol devices in order to support mobility, that is, enabling a mobile terminal tochange its point of connection to the network. Thus, a wireless network has a fixedinfrastructure with mobility-aware switches and point-to-point connections, similar toother wired infrastructures, as well as antenna sites and mobile terminals.

Important examples of wireless networks are cellular telephone networks and wire-less Internet access networks, which we discuss in greater detail in Section 1.2. There,we show how these networks extend the structure and services of existing wired net-works to support either voice- or data-oriented wireless services

1.1.2 Key Technical Issues for Wireless Networks

As we can see in the two examples mentioned above, a wireless network includes notonly the wireless terminals and radio-frequency (RF) links to fixed antennas, but alsonetwork elements and functions needed to support both interoperation with the existingfixed-wired networks and mobility for the wireless user. The set of characteristics of thewireless connection between the mobile terminal and a base station, including all thePHY- and MAC-layer details of access method, modulation, coding, and transmissionformats, is commonly referred to as the air interface. Thus, we can say that the keytechnical issues for wireless networks are networking issues and air-interface designissues. Although these two sets of issues are not totally independent of each other, theyare largely independent and can be treated separately. As we shall see in subsequentsections of the book, the networking issues relate primarily to interoperability betweenthe wireless and wired infrastructures and to support of user mobility. On the otherhand, air-interface issues relate primarily to the quality of service provided to wirelessusers and to efficiency in the use of available RF bandwidth.

1.1.3 Four Market Sectors

The market for wireless networks has evolved within four different segments that canbe divided logically into two classes: the voice-oriented market and the data-orientedmarket. The voice-oriented market has evolved around wireless connection to the publicswitched telephone network. These services evolved further into local and wide areamarkets. The local voice-oriented market is based on low-power, low-mobility deviceswith a higher quality of voice, including cordless telephone, personal communicationservices (PCSs), wireless private branch exchanges, and wireless Telepoint. The voice-oriented wide-area market evolved around cellular mobile telephone services usingterminals with higher power consumption, comprehensive coverage, and lower qualityof voice. Figure 1.1a compares several features of these two sectors of the voice-oriented market.

The wireless data-oriented market evolved around the Internet and computer-communication network infrastructure. Data-oriented services can be divided into local


Tariff

Intelligentnetwork

Servicequality

Power consumption

Coverage

Cellular Phone

Cordless Phone and PCS

(a) (b)

Mobile Data

WLAN/WPAN

Users per network

Compatibilitywith LANs

Data rate

Size/powerconsumption

Mobility

Coverage

Mobility

FIGURE 1.1 Wireless market sector comparisons: (a) voice-oriented networks; (b) data-oriented networks.

broadband and ad hoc markets on the one hand, and wide-area mobile data markets onthe other. The wide-area wireless data market provides Internet access for mobile users.Local broadband and ad hoc networks include wireless LANs and wireless personalarea networks (WPANs) that provide high-speed Internet access. The local and adhoc networks will also support evolving ad hoc wireless consumer product markets.Figure 1.1b illustrates several differences among the local- and wide-area wirelessdata networks.

1.2 NETWORK ARCHITECTURE AND DESIGN ISSUES

Next we describe the principal system architectures for wireless networks and outlinethe key design issues that must be addressed in the design of these networks. Thesearchitectures and design issues are dealt with in detail in the remainder of the book.

1.2.1 Network Architectures

Here we consider two prominent examples of wireless networks: cellular telephoneand wireless Internet.

Cellular Telephone. Figure 1.2 depicts wireless telephone service as an extension ofthe familiar public-switched telephone network (PSTN). The PSTN, designed to providewired telephone services, is augmented with a wireless fixed infrastructure to supportcommunication with mobile terminals. The mobile terminals communicate with thewireless fixed infrastructure via RF links to fixed antennas, each antenna connected toor integral with a base station. The PSTN infrastructure comprises switches, point-to-point connections, and computers used for operation and maintenance of the network.

The fixed infrastructure of the cellular telephone service has its own mobility-awareswitches, point-to-point connections, and other hardware and software elements that

NETWORK ARCHITECTURE AND DESIGN ISSUES 7

PSTN Infrastructure

Cellular TelephoneInfrastructure

X

X X

X

M-X

PSTN Switches Switches with mobility support

FIGURE 1.2 Cellular telephone infrastructure as an extension of the PSTN.

are needed for operation and maintenance of the mobile network. A wireless telecom-munication device (e.g., a cordless telephone) can connect to the PSTN infrastructureby replacing the wire attachment with radio transceivers. However, for the wirelessdevice to change its point of connection, switches in the PSTN must be able to supportmobility. Switches in the PSTN infrastructure were not originally designed to supportmobility. To solve this problem, a cellular telephone service provider adds its ownfixed infrastructure with mobility-aware switches. The fixed infrastructure of the cellu-lar telephone service provider is an interface between the base stations and the PSTNinfrastructure that implements the functionality to support mobility. Just as a wiredtelephone service network needs added infrastructure to allow a mobile telephone toconnect to the PSTN, a wireless data network needs its own added infrastructure tosupport wireless Internet access. Consider the next example.

Wireless Internet. Figure 1.3 shows the traditional wired data infrastructure togetherwith an additional wireless data infrastructure that allows wireless connection to theInternet. The traditional data network consists of routers, point-to-point connections,and computers for operation and maintenance. The elements of a wireless networkinclude mobile terminals, access points, mobility-aware routers, and point-to-pointconnections. This new infrastructure has to implement all the functionalities needed tosupport mobility.

The difference between the cellular telephone and wireless Internet examples isthat the wireless network in Fig. 1.2 is a connection-based voice-oriented network,whereas the wireless network in Fig. 1.3 is a connectionless data-oriented network. Aconnection-oriented operation needs a setup procedure to connect the communicatingterminals, and after the connection is established, a certain quality of service (QoS) isguaranteed to the user throughout the communication session. In connectionless opera-tion there is no setup procedure and terminals are always connected to the network, inthe sense that the communication session remains intact, but the QoS is not guaranteed.Instead, each protocol data unit (e.g., datagram or packet) is communicated betweennetwork access points on a best-effort basis. Common examples of connectionless pro-tocols are the Internet Protocol (IP) and the User Datagram Protocol (UDP), both of


Fixed components for awireless datainfrastructure

Internet Infrastructure

R

R R

R

Internet Routers

M-R

Routers with mobility support

LAN

WLAN

FIGURE 1.3 Wireless connectivity to the Internet.

which are used to support the Transmission Control Protocol (TCP), a transport-layerconnection-oriented protocol, which in turn supports higher-layer protocols such asHypertext Transfer Protocol (HTTP) and Simple Mail Transfer Protocol (SMTP). TCPis connection-oriented because a TCP session is set up and maintained for the fullduration of a higher-layer session such as a Web-access session.

1.2.2 Wireless Versus Wired Networks

There are a number of fundamental differences between wired and wireless networks,essentially all stemming from the inherent characteristic of wireless communications(i.e., the replacement of fixed subscriber equipment connections by radio links). Thisfreedom from the wired “tether” provides enormous advantages for customers ofcommunications services but also introduces some new problems not encountered intraditional wired networks.

Perhaps the most important characteristic of wireless networking is that a radiolink connecting the user’s device to a wired network infrastructure is inherently lessreliable than a fixed wired connection. This characteristic should be obvious and will befamiliar to users of cellular phones who have experienced signal breakup and droppedconnections on cellular phone calls. This inherent relative unreliability of radio linksleads to a need for considerably more complexity in the physical-layer design than isrequired in traditional wired networks. Also, there is a need for connection managementtechniques as part of the solution to the radio-link reliability problem.

Another important characteristic of wireless communications is the fundamental lim-itation on the availability of frequency spectrum. For systems that operate in licensedfrequency bands (cellular telephone service is the primary example), each serviceprovider operates its network within a fixed band of frequencies, and means mustbe provided to manage the sharing of allocated bandwidth among a large number ofusers. Furthermore, as the service provider’s subscriber volume grows, there must be


means for expanding the overall capacity of the service network in an efficient mannerto accommodate the growth in demand for service.

The bandwidth limitation problem also gives rise to the need for complexity in thedesign of source coding techniques (speech coding in the case of voice service, andother compression techniques in the case of multimedia transmission) so as to reducethe amount of bandwidth needed for each user channel signal while maintaining aprescribed level of signal quality as perceived by the user.

A very practical issue for users of mobile wireless devices is the necessary relianceon batteries, with the need for periodic recharging. This issue has led to the cleverapplication of power management techniques in the design of mobile devices, so as toextend talk time and recharging cycles.

The inherent advantage of wireless networking—mobility for the user—adds com-plexity to the network design to manage changing the connection point to the fixednetwork infrastructure, including changes over both small and large geographical areas.This calls for greater complexity in registration and call routing techniques than areneeded in wired networks, and a need for the use of both permanent and temporaryaddressing to support mobility.

Finally, the use of wireless transmission creates a vulnerability of the user’s com-munications to eavesdropping and fraudulent intrusion into the network. Because ofthese problems, considerable attention has been given to providing security and privacyfor wireless communications networks. Security provisions include such techniques asauthentication to prevent unauthorized access to networks. Privacy provisions includethe encryption of transmitted digital streams to prevent eavesdropping.

1.2.3 Elements of a Wireless Network Architecture

It is useful to consider the elements of a wireless network in four categories: services,infrastructure, protocols, and network engineering.

Services. From the perspective of the user of the network, the principal aspect ofthe network is the service or set of services the network is designed to support. Infact, the various industry efforts that lead to interoperability standards invariably beginwith agreements among participants as to the array of services to be provided by theintended network standard, and considerable attention is given to the detailed featuresof those services and the specific ways in which the user’s equipment will interact withthe network in the operation of the service. Of course, the basic types of services arevoice and data services.

In some networks, the voice services might comprise a menu of selectable digitaldata rates, the higher data rates providing a higher received voice quality at the costof higher bandwidth requirement, accompanied by an appropriate tariff differential.

Data services may be provided in various forms, the simplest, called data-bearerservice, being simple transport of data with minimal specification of data format at themobile data port. Data service offerings might include a choice of transparent (T) ornontransparent (NT) data in either synchronous (clock-driven) or nonsynchronous(start/stop character-driven) formats. Transparent data service will employ forward-error correction coding at a fixed transmission rate in the channel. Nontransparentservice will employ error-detection coding and retransmission of faulty data blocksso as to ensure greater accuracy in the delivered user data. Other options might


include circuit-switched (connection-oriented) data versus packet (connectionless) ser-vice. Other, application-specific data services, such as Group-3 Facsimile service, willtypically be offered with a set of optional data rates.

Short messaging service (SMS) is available in many cellular networks for trans-mission and reception of short text messages displayed on a small screen. The SMSmessages are embedded in the control channels of the cellular network, which enablesrapid delivery. A service that is growing rapidly, called text messaging, is built onSMS. As the demand for wireless multimedia service grows, data services are beingprovided at increasingly high data rates.

System Infrastructure. Provisioning of the various services in a wireless networkin turn places requirements on hardware and software that must be included in theelements connecting the wireless service customer with the fixed networks. We needto consider two categories of system elements: the mobile terminal and the fixedwireless infrastructure that makes connection with the fixed network.

The mobile terminal is the user’s device for sending and receiving signals over awireless link. For a user requiring only basic voice service, the mobile terminal is thefamiliar cellular phone, nowadays probably a CDMA digital phone in the United Statesor a GSM phone in Europe and many other regions of the world. Many cellular phonesare designed with a standardized data port for connecting to a portable computer orother data terminal. In supporting data connectivity, the cellular phone is function-ing as a wireless modem interfacing baseband data (e.g., ASCII-formatted) with thewireless network. Currently, this wireless modem function is typically implementedin a circuit card to be plugged into a socket on a laptop computer, or even a cardalready mounted inside the laptop. As wireless networks evolve to support increasingcapability for multimedia transmission, a variety of new mobile devices are appearingin the marketplace to support sending and receiving multimedia images.

Signals from the mobile user terminal arrive at an antenna that provides an RFinterface to the fixed wireless infrastructure, and that infrastructure in turn providesan interface to the fixed wired infrastructure. In the case of cellular systems, the fixedwired infrastructure will typically be a public-switched telephone network (PSTN) ora public-switched data network (PSDN). In the case of WLAN systems, the fixednetwork will typically be a wired Ethernet LAN in an office building, office complex,or university campus.

In the case of cellular systems, the fixed wireless infrastructure includes antennas,radio base stations (BSs), mobile switching centers (MSCs), and terrestrial lines (typi-cally, coaxial cable or optical fiber) to make connections among BSs and MSCs as wellas between MSCs and the PSTN. The fixed wireless infrastructure will also includecomputers and a variety of instrumentation needed for operation and maintenance ofthe cellular network. All of the equipment and software in place, from the antennas tothe PSTN connections, will be owned and operated by the cellular service provider.Currently, a cellular service company might have to deploy 50 to 100 BSs to providesatisfactory signal coverage over a major metropolitan area.

Functional partitioning between network equipment elements may vary from onemanufacturer’s equipment to another’s, but in current cellular networks, the BS willtypically include not only RF transmission and reception equipment but also speechcoder/decoders (codecs). In such a configuration, all transmissions between the BSand the PSTN are in digital form. In such a configuration, the BS will also typically


include interworking functions (IWFs), also called modem emulators, to modulate anddemodulate the data streams in support of wireless data services. The MSCs includemobile-aware switches that provide for the setup and routing of call connections toand from mobile terminals and also handle the hand-off of call connections from oneBS to another as mobile users move about the cellular service area. The MSCs alsoinclude the other hardware and software elements that are needed for mobile networkoperation, maintenance, and troubleshooting.

Wired Backbones for Wireless Networks. Since wireless networks depend heavilyon the wired infrastructures to which they connect, in this section we provide a briefoverview of the important wired infrastructures. The most commonly used wired infras-tructures for wireless networks are PSTN, Internet, and hybrid fiber coax (HFC),originally designed for voice, data, and cable TV distributions applications, respec-tively. Figure 1.4 provides an overall picture of these three networks and how theyrelate to other wired and wireless networks. (A more detailed discussion of this topiccan be found in [Pah02a].)

The main sources of information transmitted through telecommunication devicesare voice, data, and video. Voice and video are analog in nature, whereas data trafficis digital. The dominant voice application is telephony, that is, a bidirectional sym-metric real-time conversation. To support telephony, telephone service providers havedeveloped a network infrastructure that establishes a connection for a telephone call

HFC

InternetWireless

DataLAN

WLAN

PDN

Public Switched TelephoneNetwork (PSTN)

Cellular Infrastructure

PBX

FIGURE 1.4 Interconnection of PSTN, Internet, and HFC.


during the dialing process and disconnects it after completion of the conversation. Thisnetwork is referred to as the public switched telephone network (PSTN). As shown atthe top of Fig. 1.4, the cellular telephone infrastructure provides wireless access to thePSTN. Another network attached to the PSTN is the private branch exchange (PBX),a local telephone switch owned privately by a business enterprise. This private switchallows privacy and flexibility in implementing additional services in an office environ-ment. The PSTN physical connection to homes is twisted-pair wiring that is also usedfor broadband xDSL services. The core of the PSTN is a huge digital transmissionsystem that allocates a 64-kb/s channel for each direction of a telephone conversa-tion. Other network providers often lease the PSTN transmission facilities needed tointerconnect their nodes.

The infrastructure developed for video applications is cable television, shown in thelower part of Fig. 1.4. This network broadcasts wideband video signals to residentialpremises. A cable goes from an end office to a residential neighborhood, and allcustomers are fed from the same cable. The set-top boxes leased by cable companiesprovide selectivity of channels, depending on the customer’s service subscription. Theend offices, where groups of distribution cables arrive, are connected to one anotherwith fiber lines. For this reason, the cable TV network is also called hybrid fiber coax(HFC). Nowadays, cable distribution is also used for broadband residential accessto Internet.

The data network infrastructure was developed for bursty data applications andevolved into the Internet, which supports Web access, e-mail, FTP, and Telnet appli-cations as well as multimedia (voice, video, and data) sessions with a wide variety ofsession characteristics. The middle part of Fig. 1.4 shows the Internet and its relationto other data networks. From a user point of view, data-oriented networks are alwaysconnected, but they use the transmission resources only when a burst of informationis to be transferred. Sessions of popular data communications applications such asWeb browsing or FTP are often asymmetric, and a short upstream request burst resultsin downstream transmission of a large amount of data. Symmetric sessions such asIP telephony over data networks (termed voice over IP, or VoIP) are also becomingpopular, providing an alternative to traditional telephony. Residential Internet accessis a logical access that is physically implemented on other media, such as cable TVwiring or copper telephone lines. Distribution of the Internet in office areas is usuallythrough Ethernet local area networks (LANs). Wireless LANs in offices are usuallyconnected to the Internet through the wired LANs. Nowadays all other private datanetworks (PDNs), such as those used by banks or airline reservation agencies, arealso connected to the Internet. The Internet also serves as the backbone for wirelessdata services.

Protocol Layering. Wireless communications networks, and cellular networks in par-ticular, must accomplish many complex functions in order to establish call connectionsto and from mobile users, to implement the services to which each user has subscribed,to manage user authentication, and to provide mobility for wireless user terminals. Aswe have noted above, these tasks are performed in a number of mobile and fixed ele-ments. At the same time, these networks must provide smooth interoperability amonghardware and software elements supplied by a variety of manufacturers. In complexsystems such as these, designers have found it beneficial to organize systems designsaccording to the concepts of protocol layering. Perhaps the best known model for

Documents

WIRELESS INFORMATION NETWORKS€¦ · PART I INTRODUCTION TO WIRELESS NETWORKS 1 1 Overview of Wireless Networks 3. 1.1 Introduction, 3 1.2 Network Architecture and Design Issues,