Digital and Analog Communication Systems

618 Pages·1979·16.85 MB·English

by  K. Sam Shanmugan

DIGITAL AND ANALOG
COMMUNICATION SYSTEMS
K. SAM SHANMUGAM
Wichita State University
John Wiley & Sons
New York I Chichester I Brisbane / Toronto
Copyright © 1979, by John Wiley & Sons, Inc.
All rights reserved. Published simultaneously in Canada.
Reproduction or translation of any part of
this work beyond that permitted by Sections
107 and 108 of the 1976 United States Copyright
Act without the permission of the copyright
owner is unlawful. Requests for permission
or further information should be addressed to
the Permissions Department, John Wiley & Sons.
Library of Congress Cataloging in Publication Data:
Shanmugam, K. Sam.
Digital and analog communication systems.
Includes bibliographical references and index.
1. Telecommunication.
2. Digital communications.
3. Information theory.
4. Signal theory (Tf.!iecommunication) I. Title.
TK5101.S445 621.38 78-26191
Printed in the United States of America
10 9 8 7 6 5 4 3 2 1
To
Radha,
Kannon, and
Ravi

PREFACE
With the increasing importance of digital communication, there is a need for a
communication theory text that emphasizes the basic aspects of ~nformation
theory, discrete modulation techniques, and coding theory at a level ap
propriate for advanced undergraduates and first-year graduate students. The
purpose of this book is to present an introductory level treatment of digital
and analog communication systems with an emphasis on digital com
munication systems.
A study of communication systems covers many varied aspects-from the
mathematical and statistical abstraction of information theory, modulation
theory, and coding theory, to the electronic considerations associated with the
building of functional blocks to perform various signal processing tasks. I
have attempted to present in this book a unified treatment of these many
diverse aspects of communication systems.
Throughout the book we consider the process of electrical communication
as consisting of a sequence of signal processing operations. Each functional
block in the system performs a specifi<; signal processing operation. For each
functional block, we define the input/output requirements and the parameters
we have at our disposal. We derive expressions that relate the performance of
each functional block to its parameters and use these relationships to optimize
the design of the functional block. While we occasionally present examples of
physical blocks (or circuits) that correspond to specific functional blocks, less
emphasis is placed on this aspect of the problem-namely, the physical
realization of functional blocks. The major reasons for neglecting this prob-
vii
viii Preface
lem are: (1) specific circuits and devices become obsolete in a short time due
to rapid technological developments, and (2) the design of circuits could be
taught better in a circuit design course rather than in a communication
systems course.
The material presented in this book is arranged into three study areas: a
review section, the study of digital communication systems, and the study
of analog communication systems. The review section (Chapters 2 and 3)
covers signal models, systems analysis, random variables, and random pro
cesses. A cursory treatment of modulation and demodulation techniques and
signal-to-noise ratios are included in the review. These topics are covered in
detail in later chapters.
Chapters 4, 5, 8, and 9 deal with the analysis and design of digital
communication systems. Chapter 4 presents information theory and its im
plications for digital communication systems. Discrete pulse and carrier wave
modulation schemes are discussed in Chapters 5 and 8. Finally, basic ideas in
coding theory are dealt with in Chapter 9.
Analog communication systems are discussed in Chapters 6 and 7. Base
band analog signal transmission and continuous wave (CW) modulation tech
niques for analog signal transmission are covered in Chapter 6. The effect of
noise in CW modulation schemes is discussed in Chapter 7. This chapter also
contains a comparison of various CW modulation schemes.
Finally, Chapter 10 deals with digital transmission methods for analog
signals. Sampling, quantizing, and encoding of analog signals for transmission
over digital systems are described here.
It is assumed that the student has some knowledge of circuit analysis and
linear systems analysis. Prior exposure to Fourier transforms, random vari
ables, and random processes would be helpful, but not essential. With this
background, it should be possible to organize and teach several possible
courses out of this text. First, this book can be used, as a whole, for a
two-semester course on digital and analog communication systems. It is also
possible to teach a one-semester course on digital and analog communication
systems by covering Chapters 2 and 3 rapidly and selecting materials from
Chapters 5, 6, 7, and 8. Finally, an elective course in digital communication
systems may be taught using the material in Chapters 4, 5, 8. 9, and 10.
Selective double coverage of topics in the book will allow the instructor
considerable flexibility in structuring these courses.
Considerable effort has been made to present material at such a level that
there is consistent progression from concepts to design considerations
without getting mired in too much theoretical details. Proofs of theorems and
statements are included only when it is felt that they contribute sufficient
insight into the problem being addressed. Proofs are omitted when they
Preface ix
involve lengthy theoretical discourse of material at a level beyond the scope
of this text. In such cases, outlines of proofs with adequate references to
outside material is presented so that the ambitious reader can labor through
the details.
Each chapter contains a number of examples and problems. The examples
and problems cover practical and theoretical aspects of analysis and design of
communication systems. An instructor's manual giving complete solutions to
the problems is available from the publisher on request.
ACKNOWLEDGMENTS
I am indebted to many people for their advice, assistance, and contributions
to the development of this text. First, I wish to thank the Air Force
Communication Service and the U.S. Air Force Rome Air Development
Center for their support of my research activities in the field of com
munication systems. Several problems and concepts presented in this text
came out of these research activities and I am deeply indebted to these and
other agencies, including the National Science Foundation, NASA, and the
Department of Energy, for their research support.
Several individuals have read the manuscript and their comments have
helped me considerably to improve the accuracy and clarity of the text. I am
pleased to acknowledge the assistance of Professor Arthur M. Breipohl,
University of Kansas, and Professor M. Lal, Wichita State University, who
supplied many helpful suggestions while teaching from the earlier drafts of
the manuscript. The comments and suggestions from the reviewers, Profes
sors Arthur M. Breipohl (University of Kansas), R. Frank Quick, Jr. (Car
negie Mellon University), Robert A. Gabel (University of Colorado), and
Gene A. Davenport, Editor, John Wiley and Sons, have also been very
helpful. I am also grateful to my graduate students, J. M. Naik, Art Frankowski,
and Mark A. Miller for proofreading the final manuscript.
I also wish to thank the staff and administration of the College of Engineer
ing at Wichita State University for providing me with typing and other help in
the earlier stages of the development of the manuscript. In particular, I wish
to thank Marta Manny who typed the entire manuscript in expert fashion, not
once, but several times.
Finally, I am grateful to my wife and children for their patience and
understanding during the time I devoted to writing this book.
K. Sam Shanmugam

CONTENTS
1 INTRODUCTION 1
1.1 Model of a Communication System 2
1.2 Elements of a Digital Communication System 4
1.2.1 Information Source 5
1.2.2 Source Encoder/Decoder 6
1.2.3 Communication Channel 7
1.2.4 Modulator 8
1.2.5 Demodulator 9
1.2.6 Channel Encoder/Decoder 10
1.2.7 Other Functional Blocks 11
1.3 Analysis and Design of Communication Systems 12
1.3.1 Analysis of Communication Systems 12
1.3.2 Design of Communication Systems 12
1.4 Organization of the Book 14
2 SYSTEMS AND SIGNAL ANALYSIS 16
2.1 Systems and Signals 17
2.1.1 Classification of Sig nals 17
2.1.2 Classification of Systems 20
2.2 Signal Representation Using Fourier Series 21
2.2.1 Complex Exponential Fourier Series 21
2.2.2 Fourier Series Representation of Periodic Signals 22
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xii Contents
2.3 Signal Representation Using Fourier Transforms 26
2.3.1 Fourier Transform Representation of Aperiodic Sig-
nals 26
2.3.2 Fourier Transform of Periodic Power Signals 30
2.3.3 Transform Theorems 31
2.4 Power Spectral Density 36
2.5 System Response and Filters 41
2.5.1 Impulse Response, Step Response, and Time Domain
Analysis 41
2.5.2 Transfer Function and Frequency Domain Analysis 42
2.5.3 Effect of Transfer Function on Spectral Densities 43
2.5.4 Real and Ideal Filters 43
2.6 Spectral Analysis of Modulation and Demodulation Opera-
tions 47
2.6.1 Analysis of a Linear Modulation System 47
2.7 Spectral Measurements and Computations 50
2.7.1 Spectrum Analyzer 50
2.7.2 Numerical Computation of Fourier series Coefficients 51
2.7.3 Numerical Computation of Fourier Transforms 54
2.8 Summary 55
References 57
Problems 58
3 RANDOM SIGNAL THEORY 68
3.1 Introduction 68
3.2 Introduction to Probabilities 70
3.2.1 Definitions 70
3.2.2 Probabilities of Random Events 70
3.2.3 Joint and Conditional Probabilities 72
3.3 Discrete Random Variables 74
3.3.1 Probability Mass Functions 74
3.3.2 Statistical Averages 76
3.3.3 Examples of Probability Mass Functions 77
3.4 Continuous Random Variables 79
3.4.1 Probability Density Functions and Statistical Aver-
ages 79
3.4.2 Examples of Probability Density Functions 80
3.4.3 Transformation of Random Variables 83
3.5 Random Processes 86
3.5.1 Definitions and Notations 88