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.Digital Modulation Techniques .For a listing of recent titles in the Artech House Telecommunications Library, turn to the back of this book. .Digital Modulation Techniques Fuqin Xiong .Library of Congress Cataloging-in-Publication Data Xiong, Fuqin. Digital modulation techniques / Fuqin Xiong. p. cm. - (Artech House telecommunications library) Includes bibliographical references and index. ISBN 0-89006-970-0 (alk. paper) 1. Digital modulation. I. Title. II. Series. TK5103.7.X65 2000 621.3815'36 - dc21 99-058091 CIP British Library Cataloguing in Publication Data Xiong, Fuqin Digital modulation techniques. - (Artech House telecommunications library) 1. Digital modulation I. Title 621.3'81536 ISBN 0-89006-970-0 Cover design by Igor Valdman © 2000 ARTECH HOUSE, INC. 685...

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Digital Modulation Techniques
For a listing of recent titles in the Artech House Telecommunications Library, turn to the back of this book.
Digital Modulation Techniques Fuqin Xiong
Library of Congress Cataloging-in-Publication Data Xiong, Fuqin. Digital modulation techniques / Fuqin Xiong. p. cm. - (Artech House telecommunications library) Includes bibliographical references and index. ISBN 0-89006-970-0 (alk. paper) 1. Digital modulation. I. Title. II. Series. TK5103.7.X65 2000 99-058091 621.3815'36 - dc21 CIP British Library Cataloguing in Publication Data Xiong, Fuqin Digital modulation techniques. - (Artech House telecommunications library) 1. Digital modulation I. Title 621.3'81536 ISBN 0-89006-970-0 Cover design by Igor Valdman © 2000 ARTECH HOUSE, INC. 685 Canton Street Norwood, MA 02062 All rights reserved. Printed and bound in the United States of America. No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without permission in writing from the publisher. All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capitalized. Artech House cannot attest to the accuracy of this information. Use of a term in this book should not be regarded as affecting the validity of any trademark or service mark. International Standard Book Number: 0-89006-970-0 Library of Congress Catalog Card Number: 99-058091 10 9 8 7 6 5 4 3 2 1
Contents Preface xiii Chapter 1. Introduction 1 1.1 Digital Communication Systems 1 1.2 Communication Channels 4 1.2.1 Additive White Gaussian Noise Channel 4 1.2.2 Bandlimited Channel 6 1.2.3 Fading Channel 7 1.3 Basic Modulation Methods 7 1.4 Criteria of Choosing Modulation Schemes 9 1.4.1 Power Efficiency 10 1.4.2 Bandwidth Efficiency 10 1.4.3 System Complexity 11 1.5 Overview of Digital Modulation Schemes 12 References 15 Chapter 2. Baseband Modulation (Line Codes) 17 2.1 Differential Coding 18 2.2 Description of Line Codes 22 2.2.1 Nonreturn-to-Zero Codes 25 2.2.2 Return-to-Zero Codes 25 2.2.3 Pseudoternary Codes (including AMI) 26 2.2.4 Biphase Codes (including Manchester) 27 2.2.5 Delay Modulation (Miller Code) 27 2.3 Power Spectral Density of Line Codes 28 2.3.1 PSD of Nonreturn-to-Zero Codes 30 2.3.2 PSD of Return-to-Zero Codes 34 2.3.3 PSD of Pseudoternary Codes 35 2.3.4 PSD of Biphase Codes 37 2.3.5 PSD of Delay Modulation 40 v
vi 2.4 Bit Error Rate of Line Codes 43 2.4.1 BER of Binary Codes 44 2.4.2 BER of Pseudoternary Codes 49 2.4.3 BER of Biphase Codes 54 2.4.4 BER of Delay Modulation 57 2.5 Substitution Line Codes 57 2.5.1 Binary N-Zero Substitution Codes 58 2.5.2 High Density Bipolar n Codes 60 2.6 Block Line Codes 62 2.6.1 Coded Mark Inversion Codes 63 2.6.2 Differential Mode Inversion Codes 69 2.6.3 mBnB Codes 71 2.6.4 mB1C Codes 74 2.6.5 DmB1M Codes 76 2.6.6 PFmB(m+1)B Codes 77 2.6.7 kBnT Codes 78 2.7 Summary 81 References 83 Chapter 3. Frequency Shift Keying 87 3.1 Binary FSK 87 3.1.1 Binary FSK Signal and Modulator 87 3.1.2 Power Spectral Density 92 3.2 Coherent Demodulation and Error Performance 95 3.3 Noncoherent Demodulation and Error Performance 98 3.4 M-ary FSK 102 3.4.1 MFSK Signal and Power Spectral Density 102 3.4.2 Modulator, Demodulator, and Error Performance 104 3.5 Demodulation Using Discriminator 115 3.6 Synchronization 121 3.7 Summary 121 References 122 Chapter 4. Phase Shift Keying 123 4.1 Binary PSK 123 4.2 Differential BPSK 129 4.3 M-ary PSK 136 4.4 PSD of MPSK 146 4.5 Differential MPSK 148 4.6 Quadrature PSK 154
vii 4.7 Differential QPSK 160 4.8 Offset QPSK 167 4.9 pi/4-QPSK 170 4.10 Synchronization 179 4.10.1 Carrier Recovery 179 4.10.2 Clock Recovery 183 4.10.3 Effects of Phase and Timing Error 186 4.11 Summary 187 4.12 Appendix 4A 190 References 192 Chapter 5. Minimum Shift Keying and MSK-Type Modulations 195 5.1 Description of MSK 196 5.1.1 MSK Viewed as a Sinusoidal Weighted OQPSK 196 5.1.2 MSK Viewed as a Special Case of CPFSK 201 5.2 Power Spectrum and Bandwidth 203 5.2.1 Power Spectral Density of MSK 203 5.2.2 Bandwidth of MSK and Comparison with PSK 204 5.3 Modulator 207 5.4 Demodulator 210 5.5 Synchronization 214 5.6 Error Probability 216 5.7 Serial MSK 219 5.7.1 SMSK Description 219 5.7.2 SMSK Modulator 221 5.7.3 SMSK Demodulator 223 5.7.4 Conversion and Matched Filter Implementation 227 5.7.5 Synchronization of SMSK 231 5.8 MSK-Type Modulation Schemes 231 5.9 Sinusoidal Frequency Shift Keying 236 5.10 Simon's Class of Symbol-Shaping Pulses 240 5.11 Rabzel and Pathupathy's Symbol-Shaping Pulses 247 5.12 Bazin's Class of Symbol-Shaping Pulses 250 5.13 MSK-Type Signal's Spectral Main Lobe 254 5.14 Summary 256 References 257 Chapter 6. Continuous Phase Modulation 259 6.1 Description of CPM 260 6.1.1 Various Modulating Pulse Shapes 261 6.1.2 Phase and State of the CPM Signal 265
viii 6.1.3 Phase Tree and Trellis, State Trellis 269 6.2 Power Spectral Density 272 6.2.1 Steps for Calculating PSDs for General CPM Signals 274 6.2.2 Effects of Pulse Shape, Modulation Index, and A Priori Distribution 276 6.2.3 PSD of CPFSK 277 6.3 MLSD for CPM and Error Probability 279 6.3.1 Error Probability and Euclidean Distance 281 6.3.2 Comparison of Minimum Distances 285 6.4 Modulator 286 6.4.1 Quadrature Modulator 286 6.4.2 Serial Modulator 292 6.4.3 All-Digital Modulator 295 6.5 Demodulator 297 6.5.1 Optimum ML Coherent Demodulator 297 6.5.2 Optimum ML Noncoherent Demodulator 301 6.5.3 Viterbi Demodulator 311 6.5.4 Reduced-Complexity Viterbi Demodulator 317 6.5.5 Reduction of the Number of Filters for LREC CPM 320 6.5.6 ML Block Detection of Noncoherent CPM 325 6.5.7 MSK-Type Demodulator 326 6.5.8 Differential and Discriminator Demodulator 330 6.5.9 Other Types of Demodulators 333 6.6 Synchronization 337 6.6.1 MSK-Type Synchronizer 337 6.6.2 Squaring Loop and Fourth-Power Loop Synchronizers 340 6.6.3 Other Types of Synchronizer 341 6.7 Gaussian Minimum Shift Keying 342 6.8 Summary 346 References 347 Chapter 7. Multi-h Continuous Phase Modulation 351 7.1 MHPM Signal, Phase Tree, and Trellis 351 7.2 Power Spectral Density 361 7.3 Distance Properties and Error Probability 366 7.4 Modulator 382 7.5 Demodulator and Synchronization 382 7.5.1 A Simple ML Demodulator for Multi-h Binary CPFSK 382
ix 7.5.2 Joint Demodulation and Carrier Synchronization of Multi-h CPFSK 388 7.5.3 Joint Carrier Phase Tracking and Data Detection of Multi-h CPFSK 392 7.5.4 Joint Demodulation, Carrier Synchronization, and Symbol Synchronization of M-ary Multi-h CPFSK 393 7.5.5 Synchronization of MHPM 398 7.6 Improved MHPM Schemes 399 7.6.1 MHPM with Asymmetrical Modulation Indexes 400 7.6.2 Multi-T Realization of Multi-h Phase Codes 401 7.6.3 Correlatively Encoded Multi-h Signaling Technique 401 7.6.4 Nonlinear Multi-h CPFSK 403 7.7 Summary 403 7.8 Appendix 7A 404 References 408 Chapter 8. Quadrature Amplitude Modulation 411 8.1 M-ary Amplitude Modulation 411 8.1.1 Power Spectral Density 412 8.1.2 Optimum Detection and Error Probability 414 8.1.3 Modulator and Demodulator for Bandpass MAM 418 8.1.4 On-Off Keying 421 8.2 QAM Signal Description 422 8.3 QAM Constellations 426 8.3.1 Square QAM 429 8.4 Power Spectral Density 432 8.5 Modulator 434 8.6 Demodulator 436 8.7 Error Probability 438 8.8 Synchronization 441 8.9 Differential Coding in QAM 448 8.10 Summary 454 8.11 Appendix 8A 455 References 457 Chapter 9. Nonconstant-Envelope Bandwidth-Efficient Modulations 459 9.1 Two-Symbol-Period Schemes and Optimum Demodulator 460 9.2 Quasi-Bandlimited Modulation 465 9.3 QORC, SQORC, and QOSRC 471 9.4 IJF-OQPSK and TSI-OQPSK 478
x 9.5 Superposed-QAM 490 9.6 Quadrature Quadrature PSK 498 9.7 Summary 515 References 515 Chapter 10. Performance of Modulations in Fading Channels 517 10.1 Fading Channel Characteristics 518 10.1.1 Channel Characteristics 518 10.1.2 Channel Classification 521 10.1.3 Fading Envelope Distributions 524 10.2 Digital Modulation in Slow, Flat Fading Channels 527 10.2.1 Rayleigh Fading Channel 527 10.2.2 Rician Fading Channel 531 10.3 Digital Modulation in Frequency Selective Channels 533 10.4 pi/4-DQPSK in Fading Channels 544 10.5 MHPM in Fading Channels 548 10.6 QAM in Fading Channels 554 10.6.1 Square QAM 555 10.6.2 Star QAM 558 10.7 Remedial Measures Against Fading 560 10.8 Summary 563 References 564 Appendix A. Power Spectral Densities of Signals 567 A.1 Bandpass Signals and Spectra 567 A.2 Bandpass Stationary Random Process and PSD 569 A.3 Power Spectral Densities of Digital Signals 572 A.3.1 Case 1: Data Symbols Are Uncorrelated 574 A.3.2 Case 2: Data Symbols Are Correlated 576 A.4 Power Spectral Densities of Digital Bandpass Signals 577 A.5 Power Spectral Densities of CPM Signals 580 References 586 Appendix B. Detection of Signals 589 B.1 Detection of Discrete Signals 589 B.1.1 Binary Hypothesis Test 589 B.1.2 Decision Criteria 590 B.1.3 M Hypotheses 594 B.2 Detection of Continuous Signals With Known Phases 596 B.2.1 Detection of Binary Signals 596 B.2.2 Decision of M-ary Signals 608
xi B.3 Detection of Continuous Signals With Unknown Phases 615 B.3.1 Receiver Structure 615 B.3.2 Receiver Error Performance 621 References 625 Glossary 627 About the Author 631 Index 633
Preface Digital modulation techniques are essential to many digital communication systems, whether it is a telephone system, a mobile cellular communication system, or a satellite communication system. In the past twenty years or so, research and development in digital modulation techniques have been very active and have yielded many promising results. However, these results are scattered all over the literature. As a result, engineers and students in this field usually have difficulty locating particular techniques for applications or for research topics. This book provides readers with complete, up-to-date information of all modulation techniques in digital communication systems. There exist numerous textbooks of digital communications, each of them containing one or more chapters of digital modulation techniques covering either certain types of modulation, or only principles of the techniques. There are also a few books specializing in certain modulations. This book presents principles and applications information of all currently used digital modulation techniques, as well as new techniques now being developed. For each modulation scheme, the following topics are covered: historical background, operation principles, symbol and bit error performance (power efficiency), spectral characteristic (bandwidth efficiency), block diagrams of modulator, demodulator, carrier recovery (if any), clock recovery, comparison with other schemes, and applications. After we fully understand the modulations and their performances in the A WGN channel, we will discuss their performances in rnultipath-fading channels. Organization of the book This book is organized into 10 chapters. Chapter 1 is an introduction for those requiring basic knowledge about digital communication systems, and modulation methods. Chapter 2 is about baseband signal modulation that does not involve a carrier. ... Xlll
Digital Modulation Techniques si v I t is usually called baseband signal formatting or line coding. Traditionally the term modzrlation refers to "impression of message on a carrier," however, if we widen the definition to "impression of message on a transmission medium," this format~ingis also a kind of modulation. Baseband modulation is important not only because i t is used in short distance data communications, magnetic recording. optical recording, etc., but also because i t is the front end of bandpass modulations. Chapters 3-4 cover classical frequency shift keying (FSK) and phase shift keying ( PSK) techniques, including coherent a nd noncoherent. These techniques are currently used in many digital communication systems, such as cellular digital telephone systems, and satellite communication systems. Chapters 5-7 are advanced phase modulation techniques which include minimum shift keying (MSK), continuous phase modulation (CPM), and multi-h phase modulation (MHPM). These techniques are the research results of recent years, and some of them are being used in the most advanced systems, for example, M SK has been used in NASA's Advanced Communications Technology Satellite (ACTS) launched in 1993, and the others are being perfected for future applications. Chapter 8 is about quadrature amplitude modulation ( QAM). Q AM schemes are widely used i n telephone modems. For instance, CCITT (Consultative Committee for International Telephone and Telegraph) recommended V .29 and V .33 modems use 16- and 128-QAM, reaching speeds of 9600 bps and 14400 bps respectively, over four-wire leased telephone lines. Chapter 9 covers nonconstant-envelope bandwidth-efficient modulation schemes. We will study eight schemes, namely, Q BL, QORC, SQORC, QOSRC, IJF-OQPSK, TSI-OQPSK, SQAM and Q ~PSK. hese schemes improve the power T spectral density with little loss in error probability. They are primarily designed for satellite communications. Chapter 10 first briefly introduces characteristics of channels with fading and multipath propagation. Then all modulations discussed i n Chapters 2-8 are examined under the fading-muhi path environment. Appendixes A and B are basic knowledge of signal spectra and classical signal detection and estimation theory. This book can be used as a reference book for engineers and researchers. I t also can be used as a textbook for graduate students. The material in the book can be covered in a half-year course. For short course use, the instructor may select relevant chapters to cover.
Acknowledgments First I would like to thank the reviewers and editors at Artech House, Ray Sperber, Mark Walsh, Barbara Lovenvirth, and Judi Stone, whose many critiques and suggestions based on careful reviews contributed to the improvement of the manuscript. I would like to thank Cleveland State University and Fenn College of Engineering for granting me the sabbatical leave in 1997 during which 1 wrote a substantial part of the book. I am grateful for the support and encouragement from many colleagues at the Department of Electrical and Computer Engineering. I a m grateful to N ASA Glenn Research Center for providing me with several research grants. Particularly, the grant for investigating various modulation schemes that resulted i n a report which was well received by N ASA engineers and researchers. Encouraged by their enthusiastic response to the report. I published the tutorial paper "Modem Techniques in Satellite Communications" in the l EEE Comnwzication Magazine, August 1 994. Further, encouraged by the positive response to the tutorial paper, I developed the idea of writing a book detailing all major modulation schemes. I would like to thank Professor Djamal Zeghlache of the Institut National des Telecommunications of France for his support and encouragement to the book. 1 would like to thank the Department of Electronics. City University of Hong Kong ( CUHK), and the Department of Electronics, Tsinghua University, Beijing, China for supporting m y sabbatical leave. Particularly, I would like to thank Professor L i Ping of C UHK for his suggestions to the book and Professor Cao Zhigang of Tsinghua for his support of the book writing. 1 am very grateful to the excellent education that I received from Tsinghua University and the University of Manitoba, Canada. Particularly, I would like to thank my doctoral program advisor, Professor Edward Shwedyk of the Department of Electrical and Computer Engineering, University of Manitoba, and Professor John B. Anderson of Electrical, Computer and Systems Engineering Department, Rensselaer Polytechnic Institute, who served in m y doctoral dissertation committee, for their guidance and encouragement. I also appreciate the support and suggestions from m y graduate students during the past a few years. Finally, the support and help for the book from my family are also deeply appreciated. Fuqin Xiong
Chapter 1 Introduction In this chapter we briefly discuss the role of modulation in a typical digital com- munication system, basic modulation methods, and criteria for choosing modulation schemes. Also included is a brief description of various communication channels, which will serve as a background for the later discussion of the modulation schemes. DIGITAL COMMUNICATION SYSTEMS 1 .1 Figure 1 .1 is the block diagram of a typical digital communication system. The mes- sage to be sent may be fiom an analog source (e.g., voice) or fiom a digital source (e.g., computer data). The analog-to-digital (AID) converter samples and quantizes the analog signal and represents the samples in digital form (bit 1 o r 0 . The source ) encoder accepts the digital signal and encodes it into a shorter digital signal. This is called source encoding, which reduces the redundancy hence the transmission speed. This in t urn reduces the bandwidth requirement of the system. The channel encoder accepts the output digital signal of the source encoder and encodes it into a longer digital signal. Redundancy is deliberately added into the coded digital signal so that some of the errors caused by the noise or interference during transmission through the channel can be corrected at the receiver. Most often the transmission is i n a high- frequency passband, the modulator thus impresses the encoded digital symbols onto a carrier. Sometimes the transmission is in baseband, the modulator is a baseband modulator, also called formator, which formats the encoded digital symbols into a waveform suitable for transmission. Usually there is a power amplifier following the modulator. For high-frequency transmission, modulation and demodulation are usually performed in the intermediate frequency (IF). If this is the case, a frequency up-convertor is inserted between the modulator and the power amplifier. If the IF is too low compared with the carrier frequency, several stages of carrier frequency con- versions are needed. For wireless systems an antenna is the final stage of the trans-
Digital Modulation Techniques 3 _, A/D Analog Source Power Modulator +, I source encoder -# encoder amplifier I , v Channel Source +, Channel* Low noise A nalog + amplifier DlA decoder Demodulator + + user decoder - I L-b-1 Digital Block diagram o f a typical digital communication system. Figure 1 . 1 mitter. The transmission medium is usually called the channel, where noise adds to the signal and fading and attenuation effects appear as a complex multiplicative fac- tor on the signal. The term noise here is a wide-sense term which includes all kinds of random electrical disturbance from outside or from within the system. The chan- nel also usually has a limited frequency bandwidth so that it can be viewed as a filter. In the receiver, virtually the reverse signal processing happens. First the received weak signal is amplified (and down-converted if needed) and demodulated. Then the added redundancy is taken away by the channel decoder and the source decoder recovers the signal to its original form before being sent to the user. A digital-to- analog (DIA) converter is needed for analog signals. The block diagram in Figure I . 1 is just a typical system configuration. A real system configuration could be more complicated. For a multiuser system, a mul- tiplexing stage is inserted before modulator. For a multistation system, a multiple access control stage is inserted before the transmitter. Other features like frequency spread and encryption can also be added into the system. A real system could be simpler too. Source coding and channel coding may not be needed i n a simple sys- tem. I n fact, only the modulator, channel, demodulator, and amplifiers are essential in all communication systems (with antennas for wireless systems). For the purpose of describing modulation and demodulation techniques and an-
Chapter I Introdttction @ld ?- - @ Channel ' W ter h(t) Modulator Demodulator , ' n(t) additive noise and interference Figure 1.2 Digital communication system model for modulation and demodulation alyzing their performance, the simplified system model shown in Figure 1.2 will be often used. This model excludes irrelevant blocks with regard to modulation so that relevant blocks stand out. However, recently developed modem techniques combine modulation and channel coding together. In these cases the channel encoder is part of the modulator and the channel decoder is part of the demodulator. From Figure 1.2, the received signal at the input of the demodulator can be expressed as where * denotes convolution. In Figure 1.2 the channel is described by three ele- ments. The first is the channel filter. Because of the fact that the signal s ( t ) from the modulator must pass the transmitter, the channel (transmission medium) and the re- ceiver before it can reach the demodulator, the channel filter therefore is a composite filter whose transfer function is where H T( f ), H c( f ), and H R (f ) are the transfer function of the transmitter, the channel, and the receiver, respectively. Equivalently, the impulse response of the channel filter is where hT(t), hc(t), and h R ( t )are the impulse responses of the transmitter, the chan- nel, and the receiver, respectively. The second element is the factor A ( t ) which is generally complex. This factor represents fading in some types of channels, such as mobile radio channel. The third element is the additive noise and interference term n ( t ) .W will discuss fading and noise in more detail in the next section. The channel e
Digital Modulation Techniques 4 model in Figure 1.2 is a general model. It may be simplified in some circumstances, as we will see in the next section. C OMMUNICATION CHANNELS 1.2 Channel characteristic plays an important role in studying, choosing, and designing modulation schemes. Modulation schemes are studied for different channels in order to know their performance in these channels. Modulation schemes are chosen or designed according to channel characteristic in order to optimize their performance. In this section we discuss several important channel models in communications. Additive White Gaussian Noise Channel 1.2.1 Additive white Gaussian noise (AWGN) channel is a universal channel model for analyzing modulation schemes. In this model, the channel does nothing but add a white Gaussian noise to the signal passing through it. This implies that the channel's amplitude frequency response is flat (thus with unlimited or infinite bandwidth) and phase frequency response is linear for all frequencies so that modulated signals pass through i t without any amplitude loss and phase distortion of frequency components. Fading does not exist. The only distortion is introduced by the AWGN. The received signal i n ( I . I ) is simplified to where n ( t )is the additive white Gaussian noise. The whiteness of n ( t )implies that it is a stationary random process with a flat power spectral density (PSD)for all frequencies. It is a convention to assume its PSD as This implies that a white process has infinite power. This of course is a mathemat- ical idealization. According to the Wiener-Khinchine theorem, the autocorrelation function of the AWGN is where & ( T ) is the Dirac delta function. This shows the noise samples are uncorrelated