Digital Transmission Systems DAVID R. SMITH Chief, Transmission System Development Division Defense Communications Engineering Center Associate Professorial Lecturer Department of Electrical Engineering and Computer Science George Washington University LIFETIME LEARNING PUBLIC AT IONS ~ SPRINGER SCIENCE+BUSINESS MEDIA, LLC Production Management: Bernie Scheier & Associates Designer: Rick Chafiar Copy Editor: Don Yoder Illustrator: John Foster Compositor: Science Typographers, Inc. © 1985 by Springer Science+Business Media New York Originally published by Wadsworth, Inc. in 1985 Softcover reprint of the hardcover 1st edition 1985 All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transcribed, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher. 1 2 3 4 5 6 7 8 9 10--88 87 86 85 Library of Congress Cataloging in Publication Data Smith, David R. (David Russell), 1945- Digital transmission systems. Includes index. 1. Digital communications. I. Title. TK5103.7.S65 1985 621.38 84-27049 ISBN 978-1-4757-1187-5 ISBN 978-1-4757-1185-1 (eBook) DOI 10.1007/978-1-4757-1185-1 To my wife, Carolyn, and our children Christy, Stacy, Allison, and Andrew. Preface In the development of telecommunication networks throughout the world, digital transmission has now replaced analog transmission as the predominant choice for new transmission facilities. This trend began in the early 1960s when the American Telephone and Telegraph Company first introduced pulse code modulation as a means of increasing capacity in their cable plant. Since that time, digital transmission applications have grown dramatically, notably in the United States, Canada, Japan, and Western Europe. With the rapidity of digital transmission developments and imple mentation, however, there has been a surprising lack of textbooks written on the subject. This book grew out of my work, research, and teaching in digital transmission systems. My objective is to provide an overview of the subject. To accomplish this end, theory has been blended with practice in order to illustrate how one applies theoretical principles to actual design and imple mentation. The book has abundant design examples and references to actual systems. These examples have been drawn from common carriers, manufac turers, and my own experience. Considerable effort has been made to include up-to-date standards, such as those published by the CCITT and CCIR, and to interpret their recommendations in the context of present-day digital transmission systems. The intended audience of this book includes engineers involved in development and design, system operators involved in testing, operations, and maintenance, managers involved in system engineering and system planning, and instructors of digital communications courses. For engineers, managers, and operators, the book should prove to be a valuable reference v Vi • PREFACE because of its practical approach and the insight it provides into state-of the-art digital transmission systems. In the classroom the book will allow the student to relate theory and practice and to study material not covered by other textbooks. Theoretical treatments have been kept to a minimum by summarizing derivations or simply stating the final result. Moreover, by consulting the extensive list of references given with each chapter the interested reader can explore the theory behind a particular subject in greater detail. Even so, to gain from this book the reader should have a fundamental knowledge of communication systems and probability theory. The organization of this book follows a natural sequence of topics: • Chapter 1: Historical background and perspective on worldwide dig ital transmission systems • Chapter 2: System design including services to be provided, parame ters used to characterize performance, and means of allo cating performance as a function of the service, media, and transmission equipment • Chapter 3: Analog-to-digital conversion techniques, starting with the most commonly used technique, pulse code modulation, and ending with specialized voice coders • Chapter 4: Time-division multiplexing using both asynchronous and synchronous techniques • Chapter 5: Baseband transmission including coding, filtering, equaliza tion, and scrambling techniques • Chapter 6: Digital modulation, starting with binary (two-level) forms and generalizing to M-ary forms, showing comparisons of error performance, bandwidth, and implementation com plexity • Chapter 7: Digital transmission over the telephone network, from voice-channel modems for low data rates to wideband modems for high data rates • Chapter 8: Digital cable systems for twisted-pair, coaxial, and optical fibers, showing design and performance • Chapter 9: Digital radio systems including propagation and interfer ence effects, radio equipment design, and link calculations • Chapter 10: Digital network timing and synchronization, describing fundamentals of time and frequency and means of network synchronization • Chapter 11: Testing, monitoring, and control techniques used to measure and maintain system performance • Chapter 12: Assessment of the future of digital transmission services and technology, together with a look at the emerging integrated services digital network (ISDN) PREFACE • Vii The material presented in Chapters 3 through 8 has been used for a graduate course in digital communications at George Washington Univer sity. The contents of the entire book form the basis for a short course on digital transmission, also offered by George Washington University. David R. Smith Acknowledgment I first wish to acknowledge the support of my colleagues at the Defense Communications Agency, especially K. R. Belford, J. J. Cormack, W. A. Cybrowski, B. S. McAlpine, T. L. McCrickard, J. L. Osterholz, M. J. Prisutti, D. 0. Savoye, D. 0. Schultz, P. S. Selvaggi, S. Soonachan, and H. A. Stover. My graduate students at George Washington University used early versions of chapters of this book and made many helpful contributions. Participants in numerous short courses offered encouragement and sug gested improvements. I am indebted to all those who have taken my courses and at the same time helped me with the writing of this book. I would like to pay special thanks to Dr. Heinz Schreiber of Grumman Aerospace Corporation and the State University of New York, who care fully reviewed the entire manuscript and provided many valuable com ments. In writing a book of this size, I have made considerable use of the open literature, especially the IEEE Transactions on Communications, the Bell System Technical Journal, and proceedings of various technical conferences. In describing standards applicable to digital transmission systems, I have extracted from the reports and recommendations of the CCIR and CCITT. * Finally, I would like to express my thanks to Linda Thomas who diligently typed the original and revised versions of the manuscript. *The reproduction in this book of material taken from the publications of the International Telecommunications Union (ITU), Place des Nations, 1211 Geneva 20, Switzerland, has been authorized by the ITU. ix Contents Preface v Acknowledgment ix 1 Introduction to Digital Transmission Systems 1 1.1 Historical Background 1 1.2 Present-Day Digital Transmission 4 1.3 Digital Transmission Standards 8 1.4 Digital vs. Analog Transmission 10 1.5 A Simplified Digital Transmission System 12 1.6 Summary 13 2 Principles of System Design 17 2.1 General Plan 17 2.2 Transmission Services 19 2.3 Hypothetical Reference Circuits 26 2.4 Performance Objectives 31 2.5 Summary 59 3 Analog-to-Digital Conversion Techniques 63 3.1 Introduction 63 3.2 Pulse Code Modulation 64 3.3 Differential PCM and Delta Modulation 89 3.4 Comparison of OM, DPCM, and PCM 104 3.5 Voice Coders (Vo coders) 114 3.6 Summary 120 xi Xii • CONTENTS 4 Time-Division Multiplexing 127 4.1 Introduction 127 4.2 Frame Synchronization 131 4.3 Pulse Stuffing 152 4.4 Multiplexing of Asynchronous Data 168 4.5 Digital Multiplex Hierarchies 171 4.6 Statistical Multiplexing and Speech Interpolation 181 4.7 Summary 184 5 Baseband Transmission 189 5.1 Introduction 190 5.2 Types of Binary Coding 190 5.3 Power Spectral Density of Binary Codes 198 5.4 Error Performance of Binary Codes 203 5.5 Pulse Shaping and Intersymbol Interference 207 5.6 Multilevel Baseband Transmission 210 5.7 Partial Response Coding 212 5.8 Eye Patterns 221 5.9 Equalization 223 5.10 Data Scrambling Techniques 228 5.11 Summary 235 6 Digital Modulation Techniques 239 6.1 Introduction 239 6.2 Binary Amplitude-Shift Keying (ASK) 245 6.3 Binary Frequency-Shift Keying (FSK) 248 6.4 Binary Phase-Shift Keying (BPSK) 251 6.5 Comparison of Binary Modulation Systems 254 6.6 M-ary FSK 256 6.7 M-ary PSK 260 6.8 Quadrature Amplitude Modulation (QAM) 266 6.9 Offset QPSK (OQPSK) and Minimum-Shift Keying (MSK) 270 6.10 Quadrature Partial Response (QPR) 275 6.11 Summary 279 7 Digital Transmission Over the Telephone Network 283 7.1 Introduction 283 7.2 Frequency-Division Multiplex (FDM) 284 7.3 Transmission Parameters 290 7.4 Conditioning 294 7.5 Voice-Band Modems 296 7.6 Wideband Modems 300 7.7 Transmultiplexers 305