PROBABILITY, RANDOM 
VARIABLES, AND 
STOCHASTIC PROCESSES 
FOURTH EDITION 
Athanasios Papoulis  < 
University Professor 
Polytechnic University 
s. Unnikrishna Pillai 
Professor of Electrical and Computer Engineering 
Polytechnic University 
Boston  Burr Ridge, IL  Dubuque, IA  Madison, WI  N~w York  San Francisco  St.  Louis 
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PROBABIUTY. RANDOM VARIABLES, AND STOCHASTIC PROCESSES. FOUR11:l EDmoN 
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Library of Congress Cataloging-ln.PubJication Data 
Papoulis. Atbanasios. 1921-
Probability, random variables. and stochastic processes I Atbanasios Papoulis. 
S. Unnikrishna PlIlai. - 4th ed. 
p.em. 
Includes bibliographical references and index. 
ISBN 0-07-366011-6 -
1. Probabilities.  2. Random variables.  3. Stochastic processes.  l. Pillai. S. U~bna, 1955 -. 
ISBN 0-07-112256-7 (ISE) 
II. TIde. 
QA273 .P2 
5 19.2---dc21 
2002 
2001044139 
CIP 
INTERNATIONAL EDmON ISBN 0-07-112256-7 
Copyright C 2002. Exclusive rights by The McGraw-Hill Companies, Inc .. for manufacture and export. This 
book cannot be re-exported from the country to which it is sold by McGraw-Hut. The International Bdition is 
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CONTENTS 
Preface 
PART I  PROBABILITY AND RANDOM VARIABLES 
Chapter!  The Meaning of Probability 
1-1  Introduction  I  1-2  The Definitions  I  1-3  Probability 
and Induction  I  1-4  Causality Versus Randomness 
Chapter 2  The Axioms of Probability 
2-1  Set Theory  I  2-2  Probability Space  I  2-3  Conditional 
Probability  I  Problems 
Chapter 3  Repeated Trials 
3-1  Combined Experiments  I  3-2  Bernoulli 
Trials  I  3-3  Bernoulli's Theorem and Games of 
Chance  I  Problems 
Chapter 4  The Concept of a Random Variable 
4-1  Introduction  I  4-2  Distribution and Density 
Functions  I  4-3  Specific Random Variables  I  4-4  Conditional 
Distributions  I  4-5  Asymptotic Approximations for Binomial 
Random Variable  I  Problems 
ChapterS  Functions of One Random Variable 
5-1  The Random Variable g(x)  I  5-2  The Distribution  " 
of g(x)  I  5-3  Mean and Variance  I  5-4  Moments  I 
5-5  Characteristic Functions  I  Problems 
Chapter 6  Two Random Variables 
6-1  Bivariate Distributions  I  6-2  One Function of Two Random 
Variables  I  6-3  Two Functions of Two Random 
Variables  I  6-4  Joint Moments  I  6-5  Joint Characteristic 
Functions  I  6-6  Conditional Distributions  I  6-7  Conditional 
Expected Values  I  Problems 
ix 
1 
3 
15 
46 
72 
123 
169 
vi  CONTENTS 
Chapter 7  Sequences of Random 'Variables 
7-1  General Concepts  /  7-2  Conditional Densities, 
Characteristic Functions, and Normality  I  7-3  M~ Square 
Estimation  I  7-4  Stochastic Convergence and Limit 
Theorems  I  7-5  Random Numbers: Meaning and 
Generation  I  Problems 
Chapter 8  Statistics 
8-1  Introduction  I  8-2  Estimation  I  8-3  Parameter 
Estimation  I  8-4  Hypothesis Testing  I  Problems 
PART II  STOCHASTIC PROCESSES 
Chapter 9  General Concepts 
9-1  Definitions  I  9-2  Systems with Stochastic Inputs  I 
9-3  The Power Spectrum  I  9-4  Discrete-Time Processes  I 
Appendix 9A  Continuity, Differentiation, Integration  I 
Appendix 9B  Shift Operators and Stationary 
Processes  I  Problems 
Chapter 10  Random Walks and Other Applications 
10-1  Random Walks  I  10-2  Poisson Points and Shot 
Noise  I  10-3  Modulation  I  10-4  Cyclostationary 
Processes  I  10-5  Bandlimited Processes and Sampling 
Theory  I  10-6  Deterministic Signals in Noise  I  10-7  Bispectra 
and System Identification  I  Appendix lOA  The Poisson Sum 
Formula  I  Appendix lOB  The Schwarz Inequality  I  Problems 
Chapter 11  Spectral Representation 
11-1  Factorization and Innovations  I  11-2  Finite-Order Systems 
and State Variables  I  11-3  Fourier Series and Karhunen-Loeve 
Expansions  I  11-4  Spectral Representation of Random 
Processes  I  Problems 
Chapter 12  Spectrum Estimation 
12-1  Ergodicity  I  12-2  Spectrum 
Estimation  I  12-3  Extrapolation and System 
Identification  I  12-4  The GeQeral Class of Extrapolating Spectra 
and Youla's Parametrization  I  Appendix  12A  Minimum-Phase 
Functions  I  Appendix 12B  All-Pass Functions  I  Problems 
Chapter 13  Mean Square Estimation 
13-1  Introduction  I  13-2  Prediction  I  13-3  Filtering and 
Prediction  I  13-4  Kalman Filters  I  Problems 
Chapter 14  Entropy 
14-1  Introduction  I  14-2  Basic Concepts  I  14-3  Random 
Variables and Stochastic Processes  I  14-4  The Maximum 
Entropy Method  I  14-5  Coding  I  14-6  Channel 
Capacity  I  Problems 
243 
303 
371 
373 
435 
499 
523 
580 
629 
Chapter 15  Markov Chains 
CONTENTS  vii 
695 
15-1  InlI'Oduction  I  15-2  Higher Transition Probabilities and the 
Chapman-Kolmogorov Equation  I  15-3  Classification of 
StaleS  I  15-4  Stationary Distributions and Limiting 
Probabilities  I  IS-S  Transient States and Absorption 
Probabilities  I  15-6  Branching Processes  I  Appendix 15A 
Mixed Type Population of Constant Size  I  Appendix.  ISB 
Structure of Periodic Chains  I  Problems 
Chapter 16  Markov Processes and Queueing Theory 
16-1  Introduction  I  16-2  Markov Processes  I  16-3  Queueing 
Theory  I  16-4  Networks of Queues  I  Problems 
Bibliography 
Index 
773 
835 
837 
PREFACE 
The fourth edition of this book has been updated significantly from  previous editions. 
arid it includes a coauthor. About one-third of the content of this edition is new material, 
and these additions are incorporated while maintaining the style and spirit of the previous 
editions that are familiar to many of its readers. 
The basic outlook and approach remain the same: To develop the subject of proba
bility theory and stochastic processes as a deductive discipline and to illustrate the theory 
with basic applications of engineeling interest. To this extent. these remarks made in the 
first edition are still valid: "The book is written neither for the handbook-oriented stu
dents nor for the  sophisticated few  (if any)  who can learn  the  subject from  advanced 
mathematical texts.  It is written for the majority of engineers and physicists who have 
sufficient maturity to appreciate and follow a logical presentation .... There is an obvi
ous lack of continuity between the elements of probability as presented in introductory 
courses, and the sophisticated concepts needed in today's applications .... Random vari
ables.  transformations, expected values, conditional densities,  characteristic functions 
cannot be  mastered  with  mere  exposure. These concepts  must be  clearly defined  and 
must be developed, one at a time,  with sufficient elaboration." 
Recognizing these factors,  additional examples are added for further clarity, and 
the new topics include the following. 
Chapters 3 and 4 have ul)dergone substantial rewriting.  Chapter 3 has a detailed 
section on Bernoulli's theorem and games of chance (Sec.  3-3), and  several examples 
are presented there including the classical gambler's ruin problem to stimulate student 
interest. In Chap. 4 various probability distributions are categorized and illustrated, and 
two kinds of approximations to the binomial distribution are carried out to illustrate the 
connections among some of the random variables. 
" 
Chapter 5 contains new examples illustrating the usefulness of characteristic func
tions  and  moment-generating functions  including the  proof of the DeMoivre-Laplace 
theorem. 
Chapter 6 has  been  rewritten  with  additional  examples,  and  is  complete  in  its 
description of two random variables and their properties. 
Chapter 8 contains a new Sec. 8-3 on Parameter e6Eimation that includes key ideas 
on minimum variance unbiased estimation, the Cramer-Rao bound, the Rao-Blackwell 
theorem, and the Bhattacharya bound. 
PREFACE 
. In  Chaps.  9  and  la, sections  on  Poisson  processes  are  further  expanded  with 
additional results. A new detailed section on random walks has also been added. 
Chapter 12 includes a new subsection describing the parametrization of the class 
of all admissible spectral extensions given a set of valid autocorrelations. 
Because of the importance of queueing theory, the old material has undergone com
plete revision to the extent that two new chapters (15  and  16) are devoted to this topic. 
Chapter 15 describes Markov chains, their properties, characterization, and the long-term 
(steady state) and transient behavior of the chain and illustrates various theorems through 
several  examples.  In  particular,  Example  15-26  The  Game  of Tennis  is  an  excellent 
illustration of the theory to analyze practical applications, and the chapter concludes with 
a detailed  study of branching processes,  which have important applications  in queue
ing theory.  Chapter 16 describes Markov processes and queueing  theory starting with 
the Chapman-Kolmogorov equations and concentrating on the birth-death processes to 
illustrate markovian queues.  The treatment,  however,  includes  non-markovian queues 
and machine servicing problems, and concludes with an introduction to the network of 
queues. 
The material in this book can be organized for various one semester courses: 
•  Chapters 1 to 6:  Probability Theory (for senior andlor first-level graduate students) 
•  Chapters 7 and 8:  Statistics and Estimation Theory (as a follow-up course to Proba
bility Theory) 
•  Chapters 9 to  11: Stochastic Processes (follow-up course to Probability Theory.) 
•  Chapters 12 to 14: Spectrum Estimation and Filtering (follow-up course to Stochastic 
Processes) 
•  Chapters  15  and  16:  Markov  Chains  and Queueing  Theory  (follow-up  course  to 
Probability Theory) 
The authors would like to thank Ms.  Catherine Fields Shultz, editor for electrical 
and computer engineering at McGraw-Hill Publishing Company, Ms. Michelle Flomen
hoft and Mr. John Griffin, developmental editors, Ms. Sheila Frank, Project manager and 
her highly  efficient team,  and Profs.  D.  P.  Gelopulos, M.  Georgiopoulos,  A.  Haddad, 
T. Moon, 1. Rowland, C. S. Tsang, J. K. Tugnait, and O. C. Ugweje, for their comments, 
criticism, and guidance throughout the period of this revision. In addition, Dr.  Michael 
Rosse, several colleagues at Polytechnic including Profs. Dante Youla, Henry Bertoni, 
Leonard Shaw and Ivan Selesnick, as well as students Dr. Hyun Seok Oh. Mr. Jun Ho Jo. 
and Mr. Seung Hun Cha deserve special credit for their valuable help and encouragement 
during the preparation of the manuscript. Discussions with Prof.  C. Radhakrishna Rao 
about two of his key theorems in statistics and other items are also gratefully acknowl
edged. 
Athanasios PapouIis 
S. Unnikrishna Pillai