Communication Systems

446 Pages·1968·19.981 MB·English

by  B. P. Lathi

COMMUNICATION SYSTEMS
lt.- )
By the Some Author
S|GNALS, SYSTEMS AND COMMUNTCATTON (t965)
I
I
I
COMMUNICATION
SYSTEMS
B. P. LATHI
Professor of Electrical Engineering
Bradley University
Wiley & Sons, lnc.
John
New York . London ' SydneY
r
20 19 18 17 16'ls 14'13 12 11
Copyright G) f968 by John lViloy & Sons, Inc'
All Righta Resorved
Reproduction or translation of any part of this work beyond that
peimitted by Sections 107 or lO8 ofthe 1976 United States Copy-
iigt, R., without the permission of the copyright owner is unlaw-
fJ. R"qr".,, for permission or further information should be
addressed to rhe Permissions Department, John Wiley & Sons' Inc'
rsBN 0 47r 51832 I
Librrry of Congress Catalog Caril Number: 6t-ll008
Print€at in tho Uniterl Statos of Americc
Preface
The purpose of this book is to introduce the student to communication
systems and the broad prihciples of modern communication theory
at an early stage in the undergraduate curriculum. It begins with the
study of speciflc communication systems and gradually develops the
underlying role of the signal-to-noise ratio and the bandwidth in
limiting the rate of information transmission.
Since the book is intended for an introductory course, it was
necessary to ignore many of the finer points regarding the power
density spectra of random processes. The student is introduced to
the concept of the power density spectrum of nonrandom signals.
This concept, is then extended to random signals without any formal
development. A rigorous treatment, of random processes is deemed
unnecessarily distracting in such an introductory course, for it
would defeat its very purpose. After completing this course, a
student can then fruitfully undertake a rigorous course in communi-
cation theory using statistical concepts.
Throughout the book, the stress is on a physical appreciation of the
concepts rather than mathematical manipulation. fn this respect the
book closely follows the philosophy of my earlier book, S,ignals,
Systems and, Communicat'ion. Wherever possible, the concepts and
results are interpreted intuitively. The basic concepts of information
theory are not introduced. as axioms but are developed heuristically.
PREFACE
Commun'i,cation Bystems can be used for a semester or a quarter by
judiciously choosing the topics. Any of the following four combina-
tions of chapters will form a well balanced first course in communi-
cation systems.
$
2ut''
r-2-3-4-5-6-7-8-9
\o
-td
)0
Other combinations will no doubt prove suitable in some cases.
Chapter I (Signal Analysis) is essentially a review. The f,'ourier series
is introduced as a representation of a signal in orthogonal signal
space. This is done because of the growing importance of geometrical
representation of signals in communication theory. This aspect, how-
ever, is not essential for the material covered in this book. Thus the
student may skip the first 30 pages (Sections 1.1 through I.3).
The book is self-contained and there are no prerequisites whatsoever.
No knowledge of probability theory is assumed on the part, of students.
The modicum of probability theory that is required in Chapter 9 (on
digital communication) is developed in that chapter.
I would like to thank Mr. fvar Larson for assisting me in proof-
reading, Professors J. L. Jones and R,. B. Marxheimer for helpful
suggestions, and Professor Philip Weinberg, the department head, for
making available to me the time to complete this book. I am also
pleased to acknowledge the assistance of Mrs. Evelyn Kahrs for typing
the manuscript.
B. P. Lersr
Peori,a, Illi,nois
Januarg, 7968
Contents
I SIGNAL ANALYSIS
l.I
Analogy between Vectors
Signals
and 3
1.2
Some Examples of Orthogonal
X'unctions 2l
1.3
Representation of a Periodic Function
by the Fourier Series over the
Entire Interval (-o < I < oo) 29
1.4
The Complex Fourier
Spectrum
30
I.5
Representation of an Arbitrary
X'unction over the Entire fnterval
(-.o,
oo): The tr'ourier
Transform
36
1.6
Some Remarks about the
Function
Continuous Spectrum 40
L.7
Time-Domain and Frequency-
Domain Representation of
Signal
a 42
1.8
Existence of the tr'ourier
Transform
43
vI
)
Viii
CONTENTS
I.9
X'ourier Transforms of Some
Functions
Useful 44
f .t0 Singularity X'unctions 46
1.11 X'ourier Transforms Involving
fmpulse Functions 52
l.l2
Some Properties of the Fourier
Transform
63
1.13 Some Convolution
Relationships
82
1.14 Graphical Interpretation of
Convolution
83
1.15 Convolution of a Function with a
Function
Unit Impulse 86
l.16 Theorem
The Sampling 89
2 TRANSMISSION OF SIGNALS
AND POWER DENSITY
ilt
SPECTRA
2.1
Signal Transmission through
Linear Systems lll
2.2 The Filter Characteristic of
Linear Systems ll3
2.3 Distortionless Transmission Il5
2.4 Filters
Ideal 117
2.5
Causality and Physical Realizability:
Criterion
The Paley-Wiener l2O
2.6
Relationship between the
Time
Bandwidth and the Rise 122
2.7 The Energy Density Spectrum 125
2.8 The Power Density Spectrum 130
3 COMMUNICATION SYSTEMS:
AMPLITUDE MODULATIO N !48
3.1 X'requency Division Multiplexing
Multiplexing
and Time Division 149
3.2 Amplitude Modulation: Suppressed
Carrier Systems (AM-SC) I50
tx
CONTENTS
3.3 Amplitude Modulation with Large
(AM)
Carrier Power 167
3.4 Single Sideband Transmission
(ssB)
r78
3.5 Effects of Frequency and Phase
Detection
Errors in Synchronous 186
3.6 Carrier Reinsertion Techniques of
Detecting Suppressed Carrier
Signals
191
3.7 Comparison of Various
AM Systems 195
3.8 Vestigial Sideband Transmission 196
3.9 Frequency Division
Multiplexing
200
COMMUNTCATION SYSTEMS:
ANGLE MODULATION 210
4.1 X'M
Narrowband 214
4.2 FM
Wideband 216
4.3 Multiple Frequency
Modulation 223
4.4 Modulation
Square Wave 225
4.5
Linear and Nonlinear
Modulation 228
4.6
Some Remarks on Phase
Modulation
229
4,7 Power Contents of the Carrier and
the Sidebands in Angle-Modulated
Carriers
230
4.8 Noise-ReductionCharacteristics of
Modulation
Angle 231
4.9 Generation of FM Signals 232
4.I0 Demodulation of FM Signals 236
COMMUNICATION SYSTEMS:
PULSE MODULATION 241
5.1 Pulse-Amplitude Modulation 241
5.2 Other X'orms of Pulse
Modulation
251
CONTENTS
5.3 Time Division Multiplexing 254
5.4
Bandwidth Required for Trans-
Signals
mission of PAM 286
5.5
Comparison of Frequency Division
Multiplexed and Time Division
Multiplexed Systems 259
6
NOISE 2U
6.1 Noise
Shot 265
6.2 Noise
Thermal 274
6.3
Noise Calculations: Single Noise
Source
279
6.4
Multiple Noise Sources: Superposition
of Power Spectra 281
6.5 Equivalent Noise Bandwidth 287
6.6 Amplifier
Noise Figure of an 288
6.7
Experimental Determination of a
Figure
Noise 298
6.8
Power Density and Available
Density
Power 300
6.9 Effective Noise Temperature 803
0
6.f Noise Figure in Terms of
Available Gain 303
6.11 Stages
Cascaded 806
6.L2 The Cascode Amplifier Btt
Appendix. Proof of the Generalized
Nyquist Theorem 3f l
7 PERFORMANCE OF COM.
MUNICATION SYSTEMS 3t8
7.1 Bandpass Noise Representation Bf 8
7.2
Noise Calculations in Communication
Systems
325
7.3
Noise in Amplitude-Modulated
Systems
326
7.4
Noise in Angle-Modulated
Systems
335
7.5 Noise in Pulse-Modulated Systems 349