Introduction to wireless systems

I N H O II u n I ON Ỉ fl

W I R E L E S S S ï S T i m S

I'. i (I 11 il 11 il S h a n k a r

INTRODUCTION TO

WIRELESS SYSTEMS

R M.SHANKAR

Professor o f Electrical and Computer Engineering

Drexel University

JOHN W ILEY & SONS, INC.

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Library of Congress Cataloging-in-Publication Data

Shankar. P. M.

Introduction to wireless systems / P. M. Shankar,

p. cm.

Includes bibliographical references and index.

ISBN 0-471-32167-2 (cloth : alk. paper)

1. Wireless communication systems. 2. Mobile communication systems. I. Title.

TK5103.2 S517 2001

621.382—dc21

2001026251

Printed in the United States of America

10 9 8 7 6 5 4 3 2 1

To my parents,

Padmanabha Rao and Kanakabai Rao,

both former teachers,

who instilled in me the values o f education

and a strong commitment to teaching.

PREFACE

The field of wireless systems is expanding and moving toward becoming standard fare

of electrical engineering programs at the undergraduate level. This book addresses the

needs of the undergraduate students interested in learning the science and engineering

of wireless communications. Keeping this in view, the book’s purpose is to educate

undergraduate and first-year graduate students by providing the analytical tools, fun￾damental physics, communication theory, and other essentials.

The book is based on the course I developed at the undergraduate level at Drexel

University. Students taking a class based on this book are expected to have already

taken an introductory-level course in probability/random variables and also a course

in modulation techniques. These courses are required for students at the junior level of

the electrical engineering programs at most colleges and universities. For those stu￾dents who are not very familiar with this subject matter, some important basic topics

in these areas are presented in the appendices.

For the benefit of students and readers, each chapter ends with a summary of the

material covered in the chapter. The summary is detailed enough for students and the

instructor to go back and reread to reinforce the concepts. Chapters 2-6 have a number

of exercises that have to be completed using MATLAB. This strengthens the funda￾mental concepts and allows the students to practice the theory and techniques used in

mobile and wireless communication systems by varying the parameters and exploring

the resulting changes in the signals, waveforms, and other characteristic features of

wireless signals. This project-based focus will help the students absorb the lectures

through an interactive approach. These projects also demonstrate how and why mo￾bile systems operate, bringing out the nuances and subtleties of communication sys￾tems. Chapters 2 through 6 also contain example problems to demonstrate some of the

core concepts discussed. These examples are mostly numerical: the projects and exer￾cises are both analytical and numerical.

A very comprehensive list of references allows the students and other readers to

investigate and explore the topics discussed in the book.

Chapter 1 gives a brief overview and survey of the characteristic features of the

different wireless systems available.

Chapter 2 introduces the students to the issues and problems in the transmission

of wireless signals. The major topics of attenuation and fading are covered in detail.

Diagrams illustrating attenuation and computation of received power are given. The

topic of fading is covered in depth from a scattering approach, followed by the appli￾cation of the probability theory to derive results for Rayleigh. Rician, and lognormal

fading. Various statistical models of fading are described along with topics of hypoth￾esis testing to validate statistical models. The concept of dispersion is introduced us￾ing impulse response so that frequency-selective and flat fading can be explained. The

curves and figures were all generated using MATLAB. The origins of dispersion and

distortion are detailed in the appendices.

PREFACE V

Chapter 3 covers the topic of modems for wireless communications. Starting

with an overview of analog communication formats such as AM, FM, and FDM, the

area of digital communication is covered in detail. Topics of Nyquist pulse shaping,

analysis of receivers, orthogonal functions, and error probability calculations based on

signal constellations are presented. The concept of signal-to-noise ratio and the rela￾tionship to energy-to-noise ratio are explained in detail.

The different digital modulation techniques are presented. The two major tech￾niques, forms of QPSK and MSK (including GMSK), are covered in great detail, pro￾viding a complete theoretical basis for these major formats of mobile and wireless

communications. All the necessary derivations and explanations have been provided

along with block diagrams and curves. The waveforms for these different modulation

formats have been generated and are given. MATLAB was used for the generation of

the waveforms, and these programs can be made available to instructors.

Other A/-ary modulation schemes are also discussed. Comparison of the various

modulation formats is undertaken using Shannon’s theorem. The trade-off between

power and bandwidth efficiency is studied.

A number of background topics are presented in two of the appendices, one

dealing with topics in signals and systems, and the other dealing with topics in tele￾communications.

Chapter 4 covers cellular aspects of wireless communications. The effect of co￾channel interference (CCI) and techniques for its mitigation using sectored antennae

are described. Trunking efficiency is discussed, and a table of Erlang B probabilities is

provided. A detailed derivation of Erlang B and C probabilities is given in an

appendix.

The effect of fading in wireless communication systems is covered in Chapter 5.

The effect of randomness of the received signal and measures to overcome the in￾crease in bit error rate brought on by fading are described in detail. Improvements

brought on by different forms of diversity and diversity-combining methods are dis￾cussed. Detailed derivations and results for the effects of fading on the different mod￾ulation formats are presented. Methods to reduce the effects of frequency-selective

fading using equalizers are discussed.

The various multiple-access techniques used in wireless systems are presented

in Chapter 6. The three schemes, FDMA, TDMA, and CDMA, are described in terms

of their characteristic advantages and disadvantages. CDMA techniques are explored

in greater detail, going through both DS and FH techniques, along with the theoretical

development necessary to understand and appreciate the importance of the concepts.

Use of the RAKE receiver to achieve fading mitigation as a form of time diversity is

introduced. All the different wireless and mobile systems currently in use are re￾viewed and summarized in tabular form. A number of examples have been provided to

demonstrate the characteristics of CDMA-based systems.

Third-generation (3G) wireless communications are discussed with a review of

the characteristics of IMT 2000. Specifically, the unique features of cdma2000 are

presented along with comparisons with existing CDMA systems in North America

and W-CDMA, the parallel IMT 2000-based systems in Europe and Asia. A brief

overview of the new wireless paradigm, Bluetooth, is also given.

Three appendices are included. Appendix A covers topics in signals and systems

such as Fourier transforms and random variables. Appendix B covers topics in telecom￾munications, such as trunking theory, source coding, channel coding, orthogonal

v i PREFACE

frequency division multiplexing (OFDM), and eye patterns. Appendix C covers three topics

in wireless communications: dispersion, attenuation in PCS systems, and macrodiversity.

The solutions manual contains MATLAB programs for the project-based exercises

and will be available at the Wiley Web site, located on the back cover.

ACKNOW LEDGM ENTS

I would like to express my sincere thanks to a number of my colleagues and associates

who have provided encouragement and help with the preparation of this book. Of spe￾cial mention here are two of my colleagues at Drexel, Dr. Stan Kesler and Dr. Maja

Bystrom, who, despite their busy schedules, were kind enough to review some of the

chapters of the book. I received quite a bit of support at home as well. A number of di￾agrams were drawn by my daughter Raji, who, along with my wife, Rajakumari, spent

time reviewing the text for omissions, compiling the references, occasionally doing

the typing, and keeping track of my commitment to Wiley to submit the manuscript on

time. Indeed, the book has been a family project (as it should be), and I am very grate￾ful to my wife and my daughter for their patience, support, encouragement, and will￾ingness to help complete this project. Our family friend Ms. Maura Curran was

generous with her time, going through the text thoroughly to correct typographical

and grammatical errors.

The book would not have been possible without the strong support of Bill Zo￾brist, editor at Wiley, and his staff. Indeed, it was a pleasure working with Bill, who

was responsive and enthusiastic about this project. I am grateful to the local Wiley

representative, Dennis Laynor, for our initial discussion on the book proposal and for

his support throughout this process. I also would like to express my sincere apprecia￾tion of the reviewers of this book, whose suggestions were invaluable:

Brian D. Woemer, Virginia Tech

Gregory J. Pottie, University of California, Los Angeles

Prashant Krishnamurthy, University of Pittsburgh

Gerald Mitchell, University of Colorado

Alexander Haimovich, New Jersey Institute of Technology

Thomas Robertazzi, State University of New York at Stony Brook

Victor S. Frost, University of Kansas

John M. Shea, University of Florida

Bruce A. Black, Rose-Hulman Institute of Technology

P. M. Shankar

Philadelphia, PA

January 2001

CONTENTS

Preface ............................................................. iv

Acknowledgments ..........................................vii

CHAPTER 1 HISTORICAL OVERVIEW OF

WIRELESS SYSTEMS ......................................... 1

1.0 Overview ....................................................1

1.1 North American Cellular Systems ............ 1

1.2 Pan-European Cellular Systems ............... 4

1.3 Pacific Digital Cellular (PDC) Systems .. 4

1.4 Universal Mobile Telecommunication

Systems (UMTS)/Intemational Mobile

Telecommunications 2000 (IMT 2000) 5

1.5 Components of a Cellular System ............ 5

1.6 Summary .................................................... 7

Bibliography .....................................................8

CHAPTER 2 PROPAGATION

CHARACTERISTICS OF WIRELESS

CHANNELS ...................................................... 10

2.0 Introduction ................................................10

2.1 Attenuation .................................................12

2.1.1 Hata Model ....................................17

2.1.2 Lee’s Model .................................. 20

2.2 Indoor Propagation Models ..................... 22

2.2.1 Extra Large Zone ..........................22

2.2.2 Large Zone ....................................23

2.2.3 Middle Zone ................................. 23

2.2.4 Small Zone and Microzone ........ 24

2.3 Fading ........................................................ 24

2.3.1 Multipath Fading .......................... 24

2.3.2 Dispersive Characteristics of the

Channel ......................................28

2.3.3 Time-Dispersive Behavior of the

Channel ......................................34

2.3.4 Level Crossing and Average Fade

Duration .....................................37

2.3.5 Frequency Dispersion versus Time

Dispersion ............................... 39

2.4. Other Fading Models .............................. 40

2.4.1 Rician Fading ............................. 40

2.4.2 Lognormal Fading .........................41

2.4.3 Nakagami Distribution .................44

2.4.4 Suzuki Distribution ...................... 45

2.4.5 Summary of Fading ..................... 46

2.5 Testing of Fading Models .....................46

2.6 Power Units ................................................ 51

2.7 Summary .................................................... 52

Problems ........................................................... 53

CHAPTER 3 MODEMS FOR WIRELESS

COMMUNICATIONS ........................................57

3.0 Introduction ............................................... 57

3.1 Analog Modulation .................................. 58

3.1.1 Amplitude Modulation .................58

3.1.2 Angle Modulation ........................62

3.1.3 Comparison of Analog Modulation

Schemes .....................................65

3.2 Digital Modulation ................................... 67

3.2.1 Pulse Trains and Pulse Shaping ..68

3.2.2 General Analysis of Receivers ....77

3.3 Modems ....................................................86

3.3.1 Amplitude Shift Keying (ASK) ...87

3.3.2 Binary Phase-Shift Keying .......... 87

3.3.3 M-ary Modulation Schemes ....... 97

3.3.4 Constant Envelope Modulation

Techniques ................................ 109

3.4 General M-ary Modulation Schemes .... 125

3.4.1 M-ary Phase Modulation ........... 125

3.4.2 M-ary Quadrature Amplitude

Modulation (QAM) ..................126

3.5 Comparison of Modems for Wireless

Communications .................................. 128

3.5.1 Shannon's Theorem ....................128

3.5.2 Channel Capacity in Rayleigh

Fading ....................................... 131

3.6 Summary ..................................................132

Problems ........................................................ 134

CHAPTER 4 CELLS AND CELLULAR

TRAFFIC.......................................................................................138

4.0 Introduction ............................................. 138

4.1 Geometry of a Hexagonal Cell ............140

4.2 Co-Channel Interference (CCI) ............. 142

4.2.1 Special Cases of Co-Channel

Interference .............................. 144

4.3 CCI Reduction Techniques .................... 146

4.3.1 Directional Antenna Using Three

Sectors ......................................146

4.3.2 Directional Antenna Using Six

Sectors ......................................147

¡X

X CONTENTS

4.3.3. G eographical M odel w ith Several

Tiers o f Interferers ...................148

4.4 Cell Splitting .............................................. 149

4.5 M icrocells, Picocells, and Fiberoptic M obile

Systems .....................................................150

4.6 Coverage Area Estimation ......................152

4.7 Traffic Capacity and Trunking ...............156

4.8 Trunking Efficiency of Omni versus

Sectorized Antennae .............................161

4.9 Adjacent Channel Interference ..............162

4.10 Summary ...................................................165

Problems .............................................................166

CHAPTER 5 FADING MITIGATION IN

WIRELESS SYSTEMS ....................................... 168

5.0 Introduction ................................................ 168

5.1 Effects of Fading and the Concept of

Diversity ...................................................168

5.2 Other Signal Degradation Effects ......... 173

5.2.1 Effects o f Random Frequency

M odulation ................................174

5.2.2 Effects of Frequency-Selective

Fading and Co-Channel

Interference ................................175

5.3 Forms of Diversity ....................................178

5.3.1 Space or Spatial Diversity ........ 179

5.3.2 Angle Diversity ............................180

5.3.3 Frequency Diversity ....................180

5.3.4 Polarization Diversity ................ 180

5.3.5 Time Diversity .............................181

5.3.6 M ultipath Diversity .....................181

5.4 Diversity Combining M ethods .............. 182

5.4.1 Selection Com bining ..................182

5.4.2 M aximal Ratio Combining .......186

5.4.3 Equal G ain Combining ..............189

5.5 Performance Improvement from Diversity

in Terms of Reduced Bit Error Rate .. 191

5.6 M acroscopic Diversity .............................193

5.7 Equalization/ Frequency-Selective

Fading ......................................................... 194

5.7.1. Linear Transversal Equalizer ... 197

5.7.2 Nonlinear Equalizer .......................201

5.8 Summary ......................................... 204

Problems ...............................................................205

CHAPTER 6 MULTIPLE-ACC ESS

TECHNIQUES .......................................................207

6.0 Introduction .................................................. 207

6.1 Frequency Division M ultiple Access

(FDM A) ..................................................... 208

6.2 Time Division Multiple Access

(TDMA) .............................................210

6.3 Code Division Multiple Access

(CDMA) ............................................212

6.3.1 Description of a PN Code

Generator .............................. 214

6.3.2 Properties of Pseudonoise or

Pseudorandom Sequences .....215

6.3.3 Direct-Sequence Spread-Spectrum

Modulation ............................216

6.3.4 RAKE Receiver in DS-CDMA

Systems ................................. 220

6.3.5 Frequency-Hopping Spread￾Spectrum Technique ............. 221

6.3.6 Comparison of DS and FH

Systems ...................................222

6.4 Overview of Wireless Systems and

Standards .............................................224

6.4.1 Advanced Mobile Phone Systems

(AMPS) ...................................224

6.4.2 United States Digital Cellular

(IS 54) ....................................226

6.4.3 Japanese Digital System (JDC) 227

6.4.4 GSM ........................................... 227

6.5 North American Digital Cellular Systems

Based on CDMA ...............................228

6.5.1 Forward CDMA Channel ........228

6.5.2 Reverse CDMA Channel ...........229

6.5.3 Power Control in CDMA

Systems ................................. 229

6.5.4 Hand-off Procedure ..................230

6.5.5 Diversity in CDMA Systems .... 230

6.6 Comparison of Multiple-Access Systems

in Wireless Communications ............230

6.6.1 Capacity of CDMA Systems .... 232

6.6.2 Comparison of Features and

Standards ............................... 239

6.7 CDMA2000 .........................................240

6.8 Other New Developments: Bluetooth

Networks ...........................................245

6.9 Summary .............................................. 246

Problems .................................................... 247

APPENDIX A TOPICS IN SIGNALS AND

SYSTEMS ..................................................... 249

A. 1 Fourier Transforms ........................... 249

A.2 Linear Networks and Impulse

Response ........................................... 251

A.3 Orthogonal Functions .........................253

A.4 Probability, Random Variables and

Random Processes ............................ 256

A.4.1 Probability ................................. 256

CONTENTS Xi

A.4.2 Random Variables ..................... 259

A.4.3 Random Processes .................... 269

A.5 Noise in Communication Systems ..... 273

A.6 Power Spectra of Digital Signals ........ 273

APPENDIX B TOPICS IN COMMUNICATIONS

THEORY ........................................................ 277

B.l Orthogonal Frequency Division

Multiplexing .........................................277

B.2 Teletraffic Considerations .....................279

B.3 Coding .................................................... 282

B.3.1 Speech Coding ...........................282

B.3.2 Channel Coding .........................287

B.4 Synchronization ...................................... 291

B.4.1 Carrier Synchronization or Carrier

Recovery .................................. 292

B.4.2 Symbol Synchronization ...........292

B.5 Channel Capacity in Fading Channels 294

B.6 Intersymbol Interference and Eye

Patterns ...............................................295

B .7 Error Function .......................................297

APPENDIX C TOPICS IN ATTENUATION AND

FADING ..........................................................299

C .l Coherence Bandwidth and Coherence

Time .......................................................299

C. 1.1 Dispersion versus Distortion .... 301

C.2 Path Loss Models for Microcells and

PCS Systems .........................................303

C.2.1 Path Loss Calculations in PCS

Systems .................................... 303

C.3 Macrodiversity Systems ......................... 307

ACRONYMS.......................................................... 313

REFERENCES ...................................................317

CHAPTER

HISTORICAL OVERVIEW OF

WIRELESS SYSTEMS

1.0 OVERVIEW

The history of mobile communications is a long one. We can trace some of the earliest

uses of wireless systems to military, fire, and police communications. The equipment

used during these early days was relatively bulky; communication was in the simplex

mode. This was followed by what was known as Improved Mobile Telephone System

(IMTS), which allowed full-duplex provision. Owing to the very small number of

available channels, the IMTS system was inadequate for providing service to customers

waiting to gain access. The situation did not improve until the concepts of cellular

systems were developed. Though cellular technology started with analog systems,

mobile telephone providers have ushered in new developments incorporating digital

technology and making it possible to cover large geographical regions and to provide

access to a large number of users. At the time these developments were taking place in

North America, Europe and Japan were also in the forefront of new developments in

mobile and wireless systems and standards. This almost simultaneous progress across

the world has made it possible to provide mobile telephone access to an ever-increasing

population. But competing standards within North America and around the world,

coupled with claims of superior performance of one standard over others, make it

difficult for the ordinary customer to choose wisely. Even though these multiple

standards and systems coexist in the United States, Europe has promoted a single

standard, which is being increasingly adopted by the rest of the world. It is necessary

for us to understand the natural growth of these multiple standards and systems to fully

appreciate where we are today, where we came from, and how far we have come.

We will briefly look at the progress and deployment of cellular systems around

the world, starting with the North American cellular systems.

1.1 NORTH AMERICAN CELLULAR SYSTEM S

There are several cellular systems operating within North America. These include the

Advanced Mobile Phone System (AMPS) and the American Digital Cellular System,

based on Interim Standard 54 (IS 54) and Interim Standard 95 (IS 95).

The idea of “cellular communications,” conceived and developed at AT&T Bell

Laboratories, was the first major step in what we now regard as the modem era of

wireless communications. With the idea of splitting a geographical region into cells

and reusing some of the channels over and over again, it was demonstrated that the

1