Modern Digital and Analog Communication Systems [2 ed.] 0195105001, 9780195105001

Table of contents :
1. Introduction
2. Analysis and Transmission of Signals
Part I. Signal Analysis
Part II. Signal Transmission
3. Digital Communication Systems
4. Modulation
Part I. Amplitude (Linear) Modulation
Part II. Angle (Exponential) Modulation
5. Probability Theory and Random Processes
Part I. Probabiltiy Theory
Part II. Random Processes
6. Behavior of Communication Systems in the Presence of Noise
Part I. Analog Systems
Part II. Digital Systems
7. Optimum Signal Detection
8. An Introduction to Information Theory
9. Error Correcting Codes
Appendix.
Index.

Citation preview

MODERN DIGITAL AND ANALOG COMMUNICATION SYSTEMS !

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Digitized by the Internet Archive in

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http://www.archive.org/details/moderndigitalanaOOIath

Uploaded to library genesis by M.Talaat Electronics and Electrical Communications Engineering Al Azhar University in Cairo

Modern Digital

and

Analog Communication Systems

The Oxford

Series in Electrical Engineering

M. E. Van Valkenburg, Senior Consulting Editor Adel S. Sedra, Series Editor, Electrical Engineering Michael R. Lightner, Series Editor, Computer Engineering

ALLEN AND HOLBERG, CMOS Analog Circuit Design BOBROW, Elementary Linear Circuit Analysis, 2/e BOBROW, Fundamentals of Electrical Engineering, 2/e CAMPBELL, The Science and Engineering of Semiconductor Fabrication CHEN, Linear System Theory and Design CHEN, System and Signal Analysis, 2/e COMER, Digital Logic and State Machine Design, 3/e COMER, Microprocessor Based System Design COOPER AND McGlLLEM, Probabilistic Methods of Signal and System Analysis, 2/e GhaUSI, Electronic Devices and Circuits: Discrete and Integrated HOUTS, Signal Analysis in Linear Systems JONES,

Introduction to Optical Fiber Communication Systems

KENNEDY, Operational Amplifier Circuits: Theory and Application KuO, Digital Control Systems, 3/e

LASTMAN AND SlNHA, Microcomputer-Based Numerical Methods for Science and Engineering LATHI, Modern

Digital

and Analog Communications Systems,

2/e

LEVENTHAL, Microcomputer Experimentation with the IBM PC LEVENTHAL, Microcomputer Experimentation with the Intel SDK-86 LEVENTHAL, Microcomputer Experimentation with the Motorola MC6800 ECB McGlLLEM AND COOPER, Continuous and Discrete Signal and System Analysis, 3/e NAVON, Semiconductor Microdevices and Materials PAPOULIS,

Circuits

and Systems:

RAMSHAW AND Van

A

Modern Approach

HeeSWIJK, Energy Conversion

SadIKU, Elements of Electromagnetics,

SCHWARZ,

2/e

Electromagnetics for Engineers

SCHWARZ AND OLDHAM, Electrical Engineering: An Introduction, 2/e SEDRA AND SMITH, Microelectronic Circuits, 3/e SlNHA, Control Systems STEFANI, SAVANT, AND HOSTETTER, Design of Feedback Control Systems, 3/e

VAN VaLKENBURG, Analog Filter Design VRANESIC AND ZaKY, Microcomputer Structures WARNER AND GrUNG, Semiconductor Device Electronics WASSER AND FLYNN, Introduction to Arithmetic for Digital Systems Designers WOLOVICH,

Robotics: Basic Analysis and Design

YARIV, Optical

Electronics, 4/e

Modern Digital

and

Analog Communication Systems SECOND EDITION

B. P.

LATHI

CALIFORNIA STATE UNIVERSITY, SACRAMENTO

New

York Oxford Oxford University Press 1995

Oxford University Press

New

Oxford Athens

York

Bangkok Bombay Cape Town Dar es Salaam Delhi Florence Hong Kong Istanbul Karachi Kuala Lumpur Madras Madrid Melbourne Auckland

Calcutta

Mexico City Nairobi Paris Tokyo Toronto

Singapore

Taipei

and associated companies

in

Ibadan

Berlin

© 1989, 1983 by B. P. Lathi

Copyright

Published by Oxford University Press, 198 Madison Avenue,

Oxford

Inc.,

New York, New York 10016

a registered trademark of Oxford University Press

is

No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior permission of All rights reserved.

Oxford University

Press.

Library of Congress Cataloging-in-Publication Data Lathi, B.

P.

(Bhagwandas Pannalal) digital and analog communication systems/

Modern 2nd

B. P. Lathi-

ed.

cm.

p.

—(Oxford series in

electrical engineering)

Includes bibliographical references and index.

ISBN 0-19-510500-1

(cl

:

acid-free paper)

Telecommunication systems. 3. Statistical communication theory. TK5101.L333 1995 621.382— dc20 1.

2. I.

Digital communications. Title.

II.

Series.

95-37440

CIP

9

8

7 6

5

4

3

Printed in the United States of America

on

acid-free

paper

To Professor R.

A

pioneer

W. Hamming

in

Information Sciences and Systems

whose writings are

full

of insights.

Contents Preface 1

2

xi

INTRODUCTION 1.1

Communication system

1.2

Analog and

1.3

The signal-to-noise communication

digital

Modulation

I:

I

12

14

AND TRANSMISSION OF SIGNALS

Signal Analysis

16

16

Periodic signal representation h\ Fourier scries

29

2.3

Some

2.4

The sampling theorem

43

properties of the Fourier transform

64

Signal Transmission

72

5

Distortionless transmission through a linear system

6

Signal distortion over a channel

The S The 9 The 10 The 7

bandwidth and

Problems

DIGITAL

72

82

the rate of pulse transmission

energ) spectral density

93

power power

103

spectral densit\

spectral densit) ot noise

I

15

117

References

3.1

17

Exponential representation of nonperiodic signals: The 1-ouner transform

II:

rate ol

9

Randomness, redundancy, and coding

2.2

3

4

channel bandwidth and the

ratio, the

1.5

2.

Part

2

messages

1.4

ANALYSIS Part

1

117

COMMUNICATION SYSTEMS

Conversion modulation

o\

132

analog signals to digital form: Pulse code and Delta 1

34

1

viii

COM Ms I

;

2

!

J

1

4

Digital multiplexing

Line coding

156

Ui2

Pulse shaping

178

3.5 Scrambling

194

The regenerative repeater

3.6

196

3.7 Detection error probability 3.8

\1

-an communication

3.9 Digital carrier systems

Appendix

3.1

Equalizer tap setting computations

Problems

MODULATION Part

222

Amplitude

I:

212

214 214

References

4

203

206 209

(Linear)

Modulation

222

222 Baseband and carrier communication modulation: double sideband (DSB) 223 Amplitude 4.3 (AM) 234 Amplitude modulation 243 4.4 Amplitude modulation: single sideband (SSB) 4.5 Effects of frequency and phase errors in synchronous demodulation 253 4.6 260 Amplitude modulation: vestigial sideband (VSB) 266 4.7 Digital carrier systems 268 4.8 Interference and noise in AM systems 274 4.9 The superheterodyne AM receiver 4.10 Television 277 290 4. Frequency-division multiplexing 4.1

4.2

1

Part

1

II:

4. 12

Angle (Exponential) Modulation

The concept of generalized angle and angle modulation

4.13 Bandwidth of angle-modulated waves 4. 14

294

Generation of

FM Waves 317 FM

294

300

312

4.15 Demodulation of

4.16 Interference and noise in angle-modulated systems 4.17 The FM receiver 337 4.18 Transmission media 4.19 Optical communication

Appendix

4.1

340 344

Phase-lock loop analysis

346

350

References

Problems 5

325

351

PROBABILITY THEORY

AND RANDOM PROCESSES

Parti: Probability Theory

367

5.

Introduction to the theory of probability

5.2

Random

377 averages (means)

variables

5.3 Statistical

397

368

367

1

1

CONTENTS

5.4

The

theorm 407

Partl

II: II.

M Random I

\

1 1

406

central-limit

Correlation I

I

l

I

i

I

Processes »J C33C3 I

I

111 411

».

I

i*

41 rom random variable to random m pixx process ...^ ,v...v. ». a The ul power spectral w^ densirj ol random process >K 4>4 Mulunlc random processes Multiple orocesses 434 I

5.7 5

8

5

'>

transmission

ol

random processes through

5.10 Bandpass random processes 5.11

Optimum

rhe Wienei Hopl

filtering

Problems

Part

I:

435

systems

450

filter

BEHAVIOR OF COMMUNICATION SYSTEMS NOISE

linear

441

453 453

References

6

420

.

IN

THE PRESENCE OF

465

Analog Systems

465

Baseband systems 466 Amplitude-modulated systems 468 477 Vngle-modulated systems 6.4 Pulse-modulated systems 494 6

I

6

2

6.5

Part

II:

6 6

Optimum preemphasis-deemphasis systems Digital

Systems

Optimum

510

threshold detection:

6.7 A/-ar\ communication -

Synchronization

The binar) ease

Problems

I

549

OPTIMUM SIGNAL DETECTION

558

7.2

Geometrical representation of signals: The signal space 565 The Gaussian random process

7.3

The optimum

7.1

receiver

7.4 Equivalent signal sets

7.6 Other useful performance criteria

Appendix References

Problems

604 605

Gram-Schmidt orthogonalization

7.1

6 3 1

8.1

Measure of information

v

Source encoding

619

620

625

8.3 Error-tree communication over a nois) channel 8.4

609

o\ a vector set

612

AN INTRODUCTION TO INFORMATION THEORY 2

559

570 597

7.5 Nonwhite (colored) channel noise

8

51

536

550 550

References

7

505

The channel capacity of

a discrete

63

memoriless channel

635

X

(

DMI MS Channel capacity oi a continuous channel Practical communication systems in the light equation 66 References 668 Problems 668 s 5

8

()

643 Shannon's

oi

1

9

ERROR-CORRECTING CODES 9.

I

Introduction

674

9.2 Linear block codes 9.3 Cyclic codes

674

677

684

9.4 Burst-error-detecting and -correcting codes

692

9.5 Interlaced codes for burst- and random-error correction

694 9.7 Comparison of coded and uncoded systems References 705 Problems 705 9.6 Convolutional codes

A 711 A.l Trigonometric identities Appendix

A. 2 Series expansion 711 A. 3 Summations 712 A. 4 Indefinite integrals

Index

715

712

711

702

693

Preface The stud) of communication systems can be divided into two distinct areas 1.

2.

The

How communication How the) perform in

systems work the presence ol noise

two areas, in turn, requires specific tools To Stud) the first area, must he familiar with signal analysis (Fourier techniques), and to study

studs of these

the students

the second area, a basic understanding of probability theorv

is

essential.

For a meaningful comparison of various communication systems, it is necessar) to have some understanding of the second area. For this reason most instructors feel that the study of communication systems is not complete unless both oi the areas are covered reasonably well. As one o\ my colleagues put it. "I cannot imagine teaching communication systems without teaching their behavior in the presence of noise."

Most of

material to be covered

whelming:

The

However, it poses one serious problem: the enormous. The two areas along with their tools are over-

us will agree with this sentiment.

it

is

is

difficult to

cover

this material in

depth

in

current trend in teaching communication systems

one course is

to stud) the tools

m

early

chapters and then proceed with the study of the two areas of communication. Because too

much

time

is

spent

in

the beginning in studying the tools (without

much mo-

two proper areas of communication. Consequently, teaching a course in communication sv stems poses a real dilemma. The second area (statistical aspects) of communication theory is a degree harder than the first area, and it can be properly understood only if the first area is well assimilated. One of the reasons for the problem is our attempt to cover both areas at the same time tivation), there

is

little

time

left

to study the

The students are forced to grapple with the statistical aspects while also trving to become familiar with how communication systems work. This practice is most unsound pedagogically because it violates the basic fact that one must learn to walk before one can run. The ideal solution would be to offer two courses in sequence, the first course dealing w ith how communication systems function and the second course dealing with statistical aspects and noise. But

competing courses,

it

is

difficult to

in the

squeeze

in

many commu-

present curriculum, with so

two basic courses

in

the

nications area.

There it is

is.

however, a way out of this difficulty. A careful examination shows that go into probabilistic aspects (at least in the first course) in

really not necessary to

xi

xii

PRLFACE

order to study comparative behavior

in

the presence of noise.

analog

In

commu-

nication systems, the noise can be treated as an interference, and using a Rayleigh

model

to represent noise as a

sum of

sinusoids,

it

is

possible to find the noise output

from these interfering sinusoids. This model uses the frequency domain description (the power spectral density) of noise and permits the derivation of noise power outputs and signal-to-noise ratios, and the discussion of the relative merits ot various systems without requiring any statistical description of noise. The additional advantage of this approach is that, here, the power of a signal is a time average rather resulting

than an ensemble average.

Time averages are much more direct and easier for the course. The concept of ensemble averages is rather

students to understand in a

first

confusing to a beginner.

appreciation requires a level of maturity that

Its

able to expect from an average undergraduate in the very

systems. Also, in digital communication systems,

if

we

first

course

in

unreason-

is

communication

consider threshold detection,

the error probability depends only on the difference of strengths of pulses to be

distinguished.

The

relative

performance of various schemes (such as on-off, polar,

bipolar, etc.) can be determined with ease. For example, for the (that is, the

same

error probability),

we can show,

same noise immunity

without any recourse to

statistical

concepts, that the on-off or bipolar requires two times the power needed for the polar

scheme. Even the determination of error probability, which amounts

to

determining

some value, requires only a modest Thus to study the comparative behavior

the probability that the noise amplitude will exceed

discussion of the probability density function.

of communication systems (digital and analog)

by and

large, to avoid statistical concepts

in the

presence of noise,

and ensemble averages.

I

it

is

possible,

have found

this

most appropriate way of dealing with the dilemma mentioned earlier. The first four chapters in this book follow precisely this philosophy. These chapters treat in depth how digital and analog communication systems work and how they behave in the presence of noise in the manner discussed above. Thus, they form a sound, well-rounded, comprehensive survey course in communication systems that is within the reach of an average undergraduate and that can be taught in three to four semester hours. Once the students have mastered the first four chapters, they are ready for an in-depth treatment of statistical concepts in communication theory. Chapters 5 through 9 provide such a treatment and are appropriate for advanced undergraduates to be the

or graduate students.

Chapter

1

introduces the students to a panoramic view of communication systems.

All the important concepts of communication theory are explained qualitatively in a heuristic

way. This gets the students deeply interested and they are encouraged

study the subject. Because of this

momentum,

to

they are motivated to study the tool of

signal analysis in Chapter 2. Signal distortion caused by various types of channel

imperfections

is

also discussed in this chapter. Chapter 3 deals with digital

nication systems, including the digital transmission of analog signals

(PCM

commu-

and DM).

Chapter 4 discussed linear and exponential (or angle) modulation of a carrier by analog as well as digital signals. Chapter 5 is a reasonably thorough treatment of the theory of probability and random processes. This

is

the second tool required for the study of

communication systems. Every attempt is made to motivate the students and sustain their interest through this chapter by providing applications to communications prob-

PREFACE

xiii

lems wherever possible. Chapter 6 discusses the behavior of communication systems presence of noise this tunc using ensemble averages Optimum signal de-

—

in the

discussed

Chapter

and information theor\ is introduced in Chapter X. m Chapter 9. Analog pulse modulation systems such as PAM, PPM. and are deem phasized in comparison to digital schemes (PCM and DM) because the applications tection

is

in

Finally, error-control coding

is

7.

discussed

PWM

of the former in communications are hard to find. The digital schemes are used u ulek

now and receives

will be

used even more uidek

in

the future.

share of deemphasis tor a sound reason.

its

KM

Tone-modulated

also

Since angle modulation

is

nonlinear, the conclusions derived from tone modulation cannot be blindly applied to

modulation by other baseband signals

In tact, these

conclusions are misleading

many instances. For example, in the literature PM gets short shrift as to FM, a conclusion based on tone-modulation analysis.* It is shown and 6

PM

that

this reason,

is, in fact,

tone-modulated

the comparison In

my

superior to

o\'

earlier

FM

with

FM

FM

in

Chapters 4

for all practical cases (including audio). For

deemphasized and more space

is

in

being inferior

is

devoted

PM

to

and

PM.

books {Signals, Systems and Communication, Wiley, 1965 and had devoted a great deal of space and effort

Communication Sxstcms, Wiley. 1968). to signal-vector analogy. In

I

terms of the time available, signal-vector analog)

.

despite

which we can now ill afford due to the addition of several new areas to communication. For this reason, in the present book, the signal-vector analogy is omitted and the study of signal space is postponed to Chapter 7. Chapters 2. 4. 5. and 6 each have two parts. Each of these chapters could easily have been split into two separate chapters. I have avoided this temptation for a good reason. When a subject is fragmented into too many chapters, beginning students are confused and bewildered by the proliferation of seemingly endless topics and they fail to see the interrelationship between them. On the other hand, it is easy to see the whole when it is divided into fewer but well-defined parts. The situation is similar to a visit to a big mansion. When a first-time visitor sees many rooms, he is confused and bewildered and fails to see the wholeness of the mansion. But if a guide carefully divides the mansion into fewer but more well-defined areas such as living area, its

charm,

is

a luxury

sleeping area, recreation area, etc.,

and

its

relationship to the

One

of the aims

in

least a less intimidating

whole

much

it is

easier to grasp the purpose of each

writing this book has been to

make

learning a pleasant or at

experience for the student by presenting the subject

understandable, and logically organized manner. Every effort has been

an insight

—

theoretical

rather than just an understanding

wherever possible.

results

clarification of abstract results.

would make

*

all

mv

toils

Another reason given

to a value less than

signals.

it.

It

room

structure.

Even

—

in a clear,

made

to give

as well as heuristic explanations of

Many examples

are

provided for further

a partial success in achieving

my

stated goal

worthwhile.

for the alleged inferiority of

has been

shown

in

Chapter 4

PM

is

that the

that this

is

phase deviation has to be restricted

simply not true of bandlimited analog

PREFACE

xiv

It

a pleasure to

is

acknowledge

during the preparation of this book.

the assistance received

Many

from several individuals

students have helped

me

to prepare illustra-

Dave Lewis, Yu/o Yano (computer generated plots), Ron Taylor and Arnel Guanlao (editing). I am indebted to Professor Warren Smith and Mahlon Heller for contributing some items to the problem sets in this edition. thank Professors Rudolph Engelbrecht and Zhang Su-Wen for pointing out some typographical errors in the first edition. Thanks are also due to three anonymous reviewers for their helpful comments. tions

and

to proofread.

I

would

particularly like to mention

I

Finally,

I

owe

a debt of gratitude to

my

my

family:

Anjali and Pandit for their patience and understanding.

my

wife Rajani,

A

children

mere "thank you"

cannot make up for the hardships they suffered on account of

this

really

book. B. P. Lathi

A Note

to Instructors

This book can be used for a variety of undergraduate and graduate level courses in

communications systems and theory. With a judicious selection of topics, the book can be used for a one or two-semester (or quarters) sequence in the area of communication. Sufficient material is included to allow flexibility in adopting the book for a variety of courses. I.

Some

possible options are suggested below:

Undergraduate courses which do not require probability theory 1. A survey course in communication systems: Chapters 1, 2. 3, and 4

(3 to

4 semester-hours or 4 to 6 quarter-hours). Sections dealing with noise (Sees. 2.10, 3.6, 4.7, and 4. 16) can be omitted,

if

so desired, without loss

of continuity. 2.

Modulation theory and noise calculations: Chapters

2,

1,

and 4

(3

semester-hours or quarter-hours). 3.

Digital communications: Chapters

1,

2,

and

3,

and possibly 9 (2

to 3

semester-hours or 3 to 4 quarter-hours). II.

Advanced undergraduate or Statistical theory

2.

Analog communication of

graduate-level courses

of communication: Chapters 5 and 6 or 5, 6, and

1.

in noise:

Chapters

1, 2,

4 (review),

5,

7.

and Part

I

6.

3.

Digital communications: Chapters

4.

Information theory and coding: Chapters 8 and

1, 2,

3 (review), 5, Part 9.

II

of 6, and 7.

Introduction

This book examines communication b\ electrical signals.

In the past,

messages have

been carried by runners, carrier pigeons, drum beats, and torches. These schemes

were adequate for the distances and "data rates" of the age. In most parts of the world, these modes of communication have been superseded by electrical communication systems* that can transmit signals over

and galaxies) and Electrical

at the

speed of

communication

will alleviate the

energy

crisis

is

much

longer distances (even to distant planets

light.

reliable

and economical: communication technology

by trading information processing for

use of energy resources.

Some examples:

nicated face-to-face

meetings or conferences, often requiring

in

a

more

Important discussions now mostl) travel,

rational

commuwill

in-

creasingly use "teleconferring." Similarly, teleshopping and telebanking will provide services by electronic

news

*

communication, and newspapers

services.

With the exception of the postal service!

will be replaced

by

electronic-

2

l

M-M'IIK

1

IMK( MH

(

HON

COMMUNICATION SYSTEM

1.1

II shows three examples of communication systems. A typical communication system can he modeled as shown in Fig. 1.2. The components ol a commuFigure

nication system arc as follows:

The source a teletype

originates the message, such as a

message, or data.

If

the data

is

human

nonelectrical

voice, a television picture,

(human

voice, teletype mes-

must be converted by an input transducer into an trical waveform referred to as the baseband signal or the message signal. The transmitter modifies the baseband signal for efficient transmission.* sage, television picture),

Figure 1.1

*The

Some examples

it

of

communication systems.

transmitter consists of one or

more of

the following subsystems: a preemphasizer. a sampler, a

quantizer, a coder, and a modulator. Similarly, the receiver filter,

and a deemphasizer.

elec-

may

consist of a demodulator, a decoder, a

C

_.

-

Q.

s

_-

= A r 3 n _

*~v

w

*

o

^

\j

a 2£

— _> **

^

_

w

~

,1

•J

e f

'->

BO

2i

7

:-»

55

E

s -

J5

—y

*-'

-

c od

X.

o B C M -

—

M -

^ k

u.

s

-

— E y c ed k_

—

a

—

'

r,

*

.

'j

-

>

^-

E E c

~

u

r


.

t.

then

if /(f) is

all

the sine terms in

an odd function oi

the cosine terms in the series vanish {aH

-

t.

for all n).

its

Fourier series vanish

then the constant term and

Moreover, the computation

of nonvanishing coefficients requires integration over only half the period. The proof is

relatively simple (see Prob. 2.1-1).

EXAMPLE

2.2

Find the Fourier series for the rectangular pulse train k(t) shown the period

is

=

T. f

T

1

and

.

to

in

Fig. 2. 4a.

Here

= 2w/ = 2- T

x

kit)

a

-

= i

a„

bn

^

+

a

=

—2 Tto

=

kit) dt i

=

+ bn

t

-

J

A

,

cos

nto,.t

at

=

—

(2.11a)

2A

.

sin

nirr

-^-

(2.11b)

T

:

A

\

J

— Trn

]-r/ J-t/2

t

I

:

-

r-

sin nto

Adt =

\

i

:

i

—2 r h

cos nto

a,,

-

sin nto

j

dt

=

:

Hence x

k(t)

= C +

2 n=\

C

"

cos (nu)^

+

dn)

(2,,2a)

22

(HMMIKJ

TRANSMISSION

-\NM>i SIS -\\[)

sin

2 lim 7—0

T

(

\

n-T — /

(f) /177T\

~z)

5

(2.14b)

T The

last result

sin

follows from the use of [/Hospital's rule to obtain

x

lim

* In fact

any odd multiple of tt. ^This also follows from Eq. (2.6). -tan [0/(-2/A/3)] = -tt. '

If

a?

= -2/4/3

and

b,

=

0.

then C?

= 2A/3« and

ft.

=

24

IMMMIKJ \S\ns|s

\\[) |k\\s\Mss|