本书对通信系统的基础理论和关键环节进行了深入分析，
力图让学生在讨论中领会通信的精髓。
本书特点
演示通信理论主要内容的MATLAB实验。
新兴数字技术的延伸，如数字用户线（DSL）、无载波幅度/相位调制（CAP）及离散多音（DMT）等。
数十个将理论与实际通信系统相结合的实例。
通过精心组织，系统地指导学生学习从脉冲调制到带通数据传输、从随机过程到差错控制编码等知识。
全书以深入浅出的语言向学生传授了深奥的概念。
Preface
Electrical engineering education has undergone some radical changes during the past couple of decades and continues to do so. A modern undergraduate program in electrical engineering includes the following two introductory courses:
    ▲ Signals and Systems, which provides a balanced and integrated treatment of continuous-time and discrete-time forms of signals and systems. The Fourier transform (in its different forms), Laplace transform, and z-transform are treated in detail. Typically, the course also includes an elementary treatment of communication systems.
    ▲  Probability and Random, Processes, which develops an intuitive grasp of discrete and continuous random variables and then introduces the notion of a random process and its characteristics.
Typically, these two introductory courses lead to a senior-level course on communication systems.
    The fourth edition of this book has been written with this background and primary objective in mind. Simply put, the book provides a modern treatment of communication systems at a level suitable for a one- or two-semester senior undergraduate course. The emphasis is on the statistical underpinnings of communication theory with applications.
 The material is presented in a logical manner, and it is illustrated with examples, with the overall aim being that of helping the student develop an intuitive grasp of the theory under discussion. Except for the Background and Preview chapter, each chapter ends with numerous problems designed not only to help the students test their understanding of the material covered in the chapter but also to challenge them to extend this material. Every chapter includes notes and references that provide suggestions for further reading. Sections or subsections that can be bypassed without loss of continuity are identified with a footnote.
    A distinctive feature of the book is the inclusion of seven computer experiments using MATLAB. This set of experiments provides the basis of a “Software Laboratory”, with each experiment being designed to extend the material covered in the pertinent chapter. Most important, the experiments exploit the unique capabilities of MATLAB in an instructive manner.
    The Background and Preview chapter presents introductory and motivational material, paving the way for detailed treatment of the many facets of communication systems in the subsequent 10 chapters. The material in these chapters is organized as follows:
    ▲ Chapter 1 develops a detailed treatment of random, or stochastic, processes, with particular emphasis on their partial characterization (i.e., second-order statistics). In effect, the discussion is restricted to wide-sense stationary processes. The correlation properties and power spectra of random processes are described in detail. Gaussian processes and narrowband noise feature prominently in the study of communication systems, hence their treatment in the latter part of the chapter. This treatment naturally leads to the consideration of the Rayleigh and Rician distributions that arise in a communications environment.
    ▲ Chapter 2 presents an integrated treatment of continuous-wave (CW) modulation (i.e., analog communications) and their different types, as outlined here:
    (i) Amplitude modulation, which itself can assume one of the following forms (depending on how the spectral characteristics of the modulated wave are specified):
        ? Full amplitude modulation
        ? Double sideband-suppressed carrier modulation
        ? Quadrature amplitude modulation
        ? Single sideband modulation
        ? Vestigial sideband modulation
    (ii) Angle modulation, which itself can assume one of two interrelated forms:
        ? Phase modulation
        ? Frequency modulation
The time-domain and spectral characteristics of these modulated waves, methods for their generation and detection, and the effects of channel noise on their performances are discussed.
    ▲ Chapter 3 covers pulse ,-nodulation and discusses the processes of sampling, quantization, and coding that are fundamental to the digital transmission of analog signals. This chapter may be viewed as the transition from analog to digital communications. Specifically, the following types of pulse modulation are discussed:
    (i) Analog pulse modulation, where only time is represented in discrete form; it embodies the following special forms:
        ? Pulse amplitude modulation
        ? Pulse width (duration) modulation
        ? Pule position modulation
The characteristics of pulse amplitude modulation are discussed in detail, as it is basic to all forms of pulse modulation, be they of the analog or digital type.
    (ii) Digital pulse modulation, in which both time and signal amplitude are represented in discrete form; it embodies the following special forms:
        ? Pulse-code modulation
        ? Delta modulation
        ? Differential pulse-code modulation
In delta modulation, the sampling rate is increased far in excess of that used in pulse code modulation so as to simplify implementation of the system. In contrast, in differential pulse-code modulation, the sampling rate is reduced through the use of a predictor that exploits the correlation properties of the information-bearing signal.
    (iii)  MPEG/audio coding standard, which includes a psychoacoustic model as a key element in the design of the encoder.
    ▲ Chapter 4 covers baseband pulse transmission, which deals with the transmission of pulse-amplitude modulated signals in their baseband form. Two important issues are discussed: the effects of channel noise and limited channel bandwidth on the performance of a digital communication system. Assuming that the channel noise is additive and white, this effect is minimized by using a matched filter, which is basic to the design of communication receivers. As for limited channel bandwidth, it manifests itself in the form of a phenomenon known as intersymbol interference. To combat the degrading effects of this signal-dependent interference, we may use either a pulse shaping fitter or correlative encoder/decoder; both of these approaches are discussed. The chapter includes a discussion of digital subscriber lines for direct communication between a subscriber and an Internet service provider. This is followed by a derivation of the optimum linear receiver for combatting the combined effects of channel noise and intersymbol interference, which, in turn, leads to an introductory treatment of adaptive equalization.
    ▲ Chapter 5 discusses signal-space analysis for an additive white Gaussian noise channel. In particular, the foundations for the geometric representation of signals with finite energy are established. The correlation receiver is derived, and its equivalence with the matched filter receiver is demonstrated. The chapter finishes with a discussion of the probability of error and its approximate calculation.
    ▲ Chapter 6 discusses passband data transmission, where a sinusoidal carrier wave is employed to facilitate the transmission of the digitally modulated wave over a band-pass channel. This chapter builds on the geometric interpretation of signals presented in Chapter 5. In particular, the effect of channel noise on the performance of digital communication systems is evaluated, using the following modulation techniques:
    (i) Phase-shift keying, which is the digital counterpart to phase modulation with the phase of the carrier wave taking on one of a prescribed set of discrete values.
    (ii) Hybrid amplitude/phase modulation schemes including quadrature-amplitude modulation (QAM), and carrierless a amplitude/phase modulation (CAP).
    (iii) Frequency-shift keying, which is the digital counterpart of frequency modulation with the frequency of the carrier wave taking on one of a prescribed set of discrete values.
    (iv) Generic multichannel modulation, followed by discrete multitone, the use of which has been standardized in asymmetric digital subscriber lines. In a digital communication system, timing is everything, which means that the receiver must be synchronized to the transmitter. In this context, we speak of the receiver being coherent or noncoherent. In a coherent receiver, provisions are made for the recovery of both the carrier phase and symbol timing. In a noncoherent receiver the carrier phase is ignored and provision is only made for symbol timing. Such a strategy is dictated by the fact that the carrier phase may be random, making phase recovery a costly proposition. Synchronization techniques are discussed in the latter part of the chapter, with particular emphasis on discrete-time signal processing.
    ▲ Chapter 7 introduces spread-spectrum modulation. Unlike traditional forms of modulation discussed in earlier chapters, channel bandwidth is purposely sacrificed in spread-spectrum modulation for the sake of security or protection against interfering signals. The direct-sequence and frequency-hop forms of spread-spectrum modulation are discussed.
    ▲ Chapter 8 deals with multiuser radio communications, where a multitude of users have access to a common radio channel. This type of communication channel is well represented in satellite and wireless communication systems, both of which are discussed. The chapter includes a presentation of link budget analysis, emphasizing the related antenna and propagation concepts, and noise calculations.
   ▲ Chapter 9 develops the fundamental limits in information theory, which are embodied in Shannon＇s theorems for data compaction, data compression, and data transmission. These theorems provide upper bounds on the performance of information sources and communication channels. Two concepts, basic to formulation of the theorems, are (1) the entropy of a source (whose definition is analogous to that of entropy in thermodynamics), and (2) channel capacity.
    ▲ Chapter 10 deals with error-control coding, which encompasses techniques for the  encoding and decoding of digital data streams for their reliable transmission over noisy channels. Four types of error-control coding are discussed:
    (i) Linear block codes, which are completely described by sets of linearly independent code words, each of which consists of message bits and parity-check bits. The parity-check bits are included for the purpose of error control.
    (ii) Cyclic codes, which form a subclass of linear block codes.
    (iii) Convolutional codes, which involve operating on the message sequence continuously in a serial manner.
    (iv) Turbo codes, which provide a novel method of constructing good codes that approach Shannon＇s channel capacity in a physically realizable manner. Methods for the generation of these codes and their decoding are discussed.
    The book also includes supplementary material in the form of six appendices as follows:
    ▲ Appendix 1 reviews probability theory.
    ▲ Appendix 2, on the representation of signals and systems, reviews the Fourier transform and its properties, the various definitions of bandwidth, the Hilbert transform, and the low-pass equivalents of narrowband signals and systems.
    ▲ Appendix 3 presents an introductory treatment of the Bessel function and its modified form. Bessel functions arise in the study of frequency modulation, noncoherent detection of signals in noise, and symbol timing synchronization.
    ▲ Appendix 4 introduces the confluent hypergeometric function, the need for which arises in the envelope detection of amplitude-modulated signals in noise.
    ▲ Appendix 5 provides an introduction to cryptography, which is basic to secure communications.
    ▲ Appendix 6 includes 12 useful tables of various kinds.
    As mentioned previously, the primary purpose of this book is to provide a modern treatment of communication systems suitable for use in a one- or two-semester undergraduate course at the senior level. The make-up of the material for the course is naturally determined by the background of the students and the interests of the teachers involved. The material covered in the book is both broad and deep enough to satisfy a variety of backgrounds and interests, thereby providing considerable flexibility in the choice of course material. As an aid to the teacher of the course, a detailed solutions manual for all the problems in the book is available from the publisher.

Acknowledgments
    I wish to express my deep gratitude to Dr. Gregory J. Pottie (University of California, Los Angeles), Dr. Santosh Venkatesh (University of Pennsylvania), Dr. Stephen G. Wilson (University of Virginia), Dr. Gordon Stuber (Georgia Institute of Technology), Dr. Venugopal Veeraralli (Cornell University), and Dr. Granville E. Ott (University of Texas at Austin) for critical reviews of an earlier version of the manuscript and for making numerous suggestions that have helped me shape the book into its present form. The treatment of the effect of noise on envelope detection presented in Chapter 2 is based on course notes made available to me by Dr. Santosh Venkatesh, for which I am grateful. I am grateful to Dr. Gordon Stuber for giving permission to reproduce Figure 6.32.
    I am indebted to Dr. Michael Moher (Communications Research Centre, Ottawa) for reading five chapters of an earlier version of the manuscript and for making many constructive comments on turbo codes. I am equally indebted to Dr. Brendan Frey (University of waterloo, Ontario) for his invaluable help in refining the material on turbo codes, comments on low-density parity-check codes, for providing the software to plot Fig. 9.18, and giving me the permission to reproduce Figures 10.27 and 10.33. I am grateful to Dr. David Conn (McMaster University, Ontario) for his critical reading of the Background and Preview Chapter and for making suggestions on how to improve the presentation of the material therein.
    I also wish to thank Dr. Jean-Jacque Wrerner (Lucent Technologies, Holmdel), Dr. James Mazo (Lucent Technologies, Murray Hill), Dr. Andrew Viterbi (Qualcom, San Diego), Dr. Radford Neal (University of Toronto, Ontario), Dr. Yitzhak (Irwin) Kalet (Technion, Israel), Dr. wralter Chen (Motorola), Dr. John Cioffi (Stanford University), Dr. Jon Mark (University of wraterloo, Ontario), and Dr. Robert Dony (University of Guelph, Ontario), I thank them all for their helpful comments on selected sections in the book. Corrections and suggestions for improvements to the book made by Dr. Donald wunsch II (University of Missouri) are also appreciated.
    I am grateful to my graduate student Mathini Sellathurai (McMaster University) for performing the computer experiments in the book, and Hugh Pasika (McMaster University) for many useful comments on the Background and Preview Chapter and for doing the computations on some graphical plots in the book. Proofreading of the page proofs by Mathini Sellathurai and Alpesh Patel is much appreciated.
    I am particularly grateful to my editor at wiley, Bill Zobrist, for his strong support and help throughout the writing of the book. I am indebted to Monique Calello, Senior Production Editor at Wiley, for her tireless effort in overseeing the production of the book in its various stages. I thank Katherine Hepburn for advertising and marketing the book. I thank Karen Tongish for her careful copyediting of the manuscript, Katrina Avery for her careful proofreading of the page proofs, and Kristen Maus for composing the index of the book.
    Last but by no means least, as always, I am grateful to my Technical Coordinator, Lola Brooks, for her tireless effort in typing the manuscript of the book. I also wish to record my gratitude to Brigitte Maier, Assistant Librarian, and Regina Bendig, Reference Librarian, at McMaster University, for helping me on numerous occasions in tracing references for the bibliography.