CODING AND MODULATION FOR DIGITAL TELEVISION

Transcription

1 CODING AND MODULATION FOR DIGITAL TELEVISION

2 MULTIMEDIA SYSTEMS AND APPLICATIONS SERIES Consulting Editor Borko Furht Florida Atlantic University Recently Published Titles: CELLULAR AUTOMATA TRANSFORMS: Theory and Applications in Multimedia Compression, Encryption, and Modeling, by Olu Lafe ISBN: COMPUTED SYNCHRONIZATION FOR MULTIMEDIA APPLICATIONS, by Charles B. Owen and Fillia Makedon ISBN: STILL IMAGE COMPRESSION ON PARALLEL COMPUTER ARCHITECTURES, by Savitri Bevinakoppa ISBN: INTERACTIVE VIDEO-ON-DEMAND SYSTEMS: Resource Management and Scheduling Strategies, by T. P. Jimmy To and Babak Hamidzadeh ISBN: MULTIMEDIA TECHNOLOGIES AND APPLICATIONS FOR THE 21st CENTURY: Visions of World Experts, by Borko Furht ISBN: INTELLIGENT IMAGE DATABASES: Towards Advanced Image Retrieval, by Yihong Gong ISBN: BUFFERING TECHNIQUES FOR DELIVERY OF COMPRESSED VIDEO IN VIDEO-ON-DEMAND SYSTEMS, by Wu-chi Feng ISBN: HUMAN FACE RECOGNITION USING THIRD-ORDER SYNTHETIC NEURAL NETWORKS, by Okechukwu A. Uwechue, and Abhijit S. Pandya ISBN: MULTIMEDIA INFORMATION SYSTEMS, by Marios C. Angelides and Schahram Dustdar ISBN: MOTION ESTIMATION ALGORITHMS FOR VIDEO COMPRESSION, by Borko Furht, Joshua Greenberg and Raymond Westwater ISBN: VIDEO DATA COMPRESSION FOR MULTIMEDIA COMPUTING, edited by Hua Harry Li, Shan Sun, Haluk Derin ISBN: REAL-TIME VIDEO COMPRESSION: Techniques and Algorithms, by Raymond Westwater and Borko Furht ISBN: MULTIMEDIA DATABASE MANAGEMENT SYSTEMS, by B. Prabhakaran ISBN:

3 CODING AND MODULATION FOR DIGITAL TELEVISION by Gordon Drury Garik Markarian Keith Pickavance KLUWER ACADEMIC PUBLISHERS NEW YORK, BOSTON, DORDRECHT, LONDON, MOSCOW

4 ebook ISBN Print ISBN Kluwer Academic Publishers New York, Boston, Dordrecht, London, Moscow All rights reserved No part of this ebook may be reproduced or transmitted in any form or by any means, electronic, mechanical, recording, or otherwise, without written consent from the Publisher Created in the United States of America Visit Kluwer Online at: and Kluwer's ebookstore at:

5 Contents Preface 1. AN INTRODUCTION TO TELEVISION 1. Television History 2. The History of Radio 3. Television Standards 3.1 Introduction 3.2 Colour NTSC, PAL and SECAM 3.3 The MAC Family 3.4 W-MAC 3.5 HD-MAC 3.6 MUSE 3.7 Enhanced PAL (E-PAL) 3.8 PALPlus 3.9 High Definition TV 4. Emergence of DTV 4.1 Broadcasting 4.2 Computing 5. The Business of TV 5.1 The Infrastructure of Broadcasting 5.2 Regulation 5.3 Commercial Matters 6. Digital Broadcasting Standards 6.1 Administration of Technical Standards 6.2 European approach DVB 6.3 North America 6.4 Japan 2. BASIC PRINCIPLES OF DIGITAL TV BROADCASTING 1. Why Digital 2. Digital Coding of existing TV signals 3. The Compression Process ix

6 vi CODING AND MODULATION FOR DIGITAL TELEVISION 4. ISO/IEC MPEG-1 and Beyond MPEG2 MPEG-4, 7 and Conditional Access Interactive TV Modulation and Error Control The Future MODULATION TECHNIQUES IN DIGITAL TV BROADCASTING Principles and Basic Definitions of Digital Modulation Phase Shift Keying Modulation Techniques Definition and Major Parameters Binary Phase Shift Keying Quadrature Phase Shift Keying Phase Shift Keying With Increased Spectral Efficiency Quadrature Amplitude Modulation Definitions and Major Parameters Methods of Generating and Detecting QAM Vestigial Sideband Modulation Basic Principles Vestigial Sideband Modulation for ATSC Transmission System Orthogonal Frequency Division Multiplexing (OFDM) History of OFDM Basic Principles of OFDM Spectrum Shaping of the OFDM Signals Developing OFDM Modems Demodulation of the Received Signals Definition of the Optimum Receiver Correlation Receiver Synchronisation Systems Introduction Maximum Likelihood Estimate Criteria for Carrier Recovery Systems Basic Carrier Recovery System Enhanced Carrier Recovery System for High-Order QPSK 87 Carrier Recovery System for QPSK 87 Carrier Recovery for 8-PSK Modulation 88 Carrier Recovery for 16-PSK 88 Implementation Consideration Clock Recovery Systems 91 Squaring Clock Recovery Technique 92 Early-Late Clock Recovery System 92 Zero Crossing Clock Recovery 93 Synchroniser 94

7 Contents vii 4. ERROR CONTROL CODING IN DIGITAL TV BROADCASTING Basic Elements of Error Control Coding Block Codes Introduction 95 Groups 96 Rings Polynomial Rings 99 Finite Fields 100 Linear Dependence and Independence 101 Subspaces 102 Polynomial Rings Finite Fields Polynomial Representation 106 Reducing Polynomials modulo another polynomial Linear Block Codes The Generator Matrix and Parity Check Matrix Hamming Codes Decoding Linear Codes 116 Syndrome Decoding Cyclic Codes Matrix Notation of Cyclic Codes Decoding of Cyclic Codes 123 Syndrome Decoding Reed-Solomon Codes Encoding Reed-Solomon Codes Reed-Solomon Decoders Convolutional Codes Shift Register Representation Time Domain Approach The Generator Matrix Transform Domain Approach Polynomial Matrix Representation The case k > Systematic and Non-Systematic Convolutional Codes Distance Properties Graphical Representation 143 Tree Diagram 143 Trellis Diagram Encoder State Diagram Decoding of Convolutional Codes Optimal Decoding Maximum Likelihood Decoding Practical Encoders Catastrophic Encoders State Diagrams when k > Viterbi Decoding Soft Decision Viterbi Decoding 160

8 viii CODING AND MODULATION FOR DIGITAL TELEVISION 8. Punctured Convolutional Codes Interleaving and deinterleaving Block Interleavers Convolutional Interleavers Trellis Coded Modulation Pragmatic Trellis Coded Modulation EXISTING STANDARDS FOR DIGITAL TV BROADCASTING Major DVB Standards DVB-S Standard DSNG Standard DVB-C Standard DVB-T Standard Advanced Television System Committee [ATSC] Terrestrial Integrated Services Digital Broadcasting [ISDB-T] North American Cable Standard - Data Over Cable Service Interface Specifications [DOCSIS] FUTURE TRENDS IN DIGITAL TELEVISION Estimation of system performance Modulation Techniques for Future DTV Systems Mu1ti-Dimensional Modulation Formats Minimum Shift Keying Continuous Phase Modulation Schemes An Alternative Approach Soft Output Decoding Techniques Turbo Codes 216 Turbo Convolutional Codes 216 Turbo Block Codes Other Iterative Decoding 225 Soft Input Soft Output Convolutional codes 225 Soft Input Soft Output Block Codes 226 References 229 Index 247

9 Preface For over 50 years analogue TV systems, such as NTSC, PAL and SECAM, have proved to be very rugged and reliable, providing reasonable quality pictures and audio even in severe environments. However, the world s consumers paid a high price for the diversity of analogue broadcasting standards. The division of the world television services between NTSC, PAL and SECAM built substantial barriers not only between the different continents, but also between countries of the same continent. The latest advances of technology attempt to remove this diversity by providing the transmission of digital television (DTV) signals in the same bandwidth, currently used by the analogue signal. Such a transmission can offer improved quality video and audio reception, with none of the usual impairments seen in analogue transmission, e.g. multi-path, white noise, etc. The main benefit of such developments is the possible addition of extra services that can be offered. There are two major directions for the development of DTV: (i) To deliver an increased number TV programmes of standard definition in the existing bandwidth - the approach taken by Digital Video Broadcasting (DVB) in Europe; (ii) Broadcasting of high definition television (HDTV) programmes in the existing bandwidth - the approach taken by American Telecommunications Standard Committee (ATSC) in the United States of America and in Australia. Both standards are based on the use of the MPEG-2 compression algorithm (the second generation source coding algorithm developed by the Moving Pictures Expert Group) with the major differences being in the types of error control coding and digital modulation schemes chosen for a particular environment. Furthermore, with the introduction of new DTV systems and services (e.g. interactive TV, video broadcasting in third generation mobile telephones, etc) these differences become more and more apparent. The main aim of this book is to provide the reader with a comprehensive description of all error control coding and digital modulation techniques used

10 x CODING AND MODULATION FOR DIGITAL TELEVISION in the DTV. The book commands a potentially wide audience including both undergraduate and postgraduate students, broadcasting and communication engineers, researchers, marketing managers, regulatory bodies, governmental organisations and standardisation institutions of the digital television industry. It also will be useful to everybody who wishes to discover the advantages of digital TV and the power of channel coding in delivering these advantages. The classroom market will be such that the book can show not only the theory of the subject at hand but connects all the theory to achieved practical aspects and provides the reader with a glimpse at what the future holds in the subject. Immediately the book will provide the reader with the knowledge that all the theory of communications can be brought together in a concise and clear manner proving it to be one of the most important fields in society today. In the book the reader will find the relevant elements from the expansive theory of channel coding and how the transmission environment dictates the choice of error control coding and digital modulation schemes. These will be presented in such a way that both the mathematical integrity and understanding for engineers will be combined in a complete form and supported by a number of practical examples. In addition, the book will contain descriptions of the existing standards, and will provide a valuable source of corresponding references. As DTV is a very young and dynamic field of communications engineering, the book also will include the description of the latest techniques which could find application in the future DTV systems. These include the concept of softin-soft-out decoding, turbo-coding and cross-correlated quadrature modulation to name but a few, which will have a prominent future in improving efficiency of the future DTV systems. The digital broadcasting standards provide the state-of-the-art at the current time and shall remain in use for many years. The expertise gained in developing one scheme is used and further developed for new schemes and standards. Thus in the future the book will provide a basis for probably all DTV schemes in existence, thus proving its warrant for inclusion in any relevant person s library. The organisation of the book is summarised below: 1. INTRODUCTION: In this Chapter we will present the brief history of DTV and describe the regional differences and the correspondingly the relevant standards. This will include the European digital video broadcasting (DVB) project, North American HDTV and Japanese multiple sub-nyquist sampling encoding (MUSE) and (enhanced television) systems (EDTV). 2. BASIC PRINCIPLES OF DIGITAL TV BROADCASTING: This Chapter will explain the rationale for developing DTV, explain the role of the MPEG-2 compression algorithm and describe the necessity for using different error control coding and digital modulation formats for different environments. We also briefly discuss the role of conditional access (CA) in protecting broadcaster s

11 revenues. Finally we will look at the wider feature of the interactive digital TV, what is in use today and what the viewer can expect to obtain from such a facility. 3. MODULATION TECHNIQUES IN DIGITAL TV BROADCASTING: In this Chapter we will present the theoretical background of the major digital modulation formats and describe all the modulation techniques used in the DTV. These include the following: (i) phase shift keying (PSK) modulation used in the digital satellite broadcasting (QPSK) and digital satellite news gathering (8PSK); (ii) quadrature amplitude modulation (QAM), used in the cable systems (MQAM, M=16,64,,256), digital satellite news gathering (16QAM) and terrestrial broadcasting (hierarchical QAM); (iii) vestigial side band modulation (VSB) used in ATSC HDTV system; (iv) orthogonal frequency division multiplexing (OFDM) used in the terrestrial broadcasting systems. In addition, the Chapter will describe the corresponding demodulation, and symbol and carrier recovery techniques. 4. ERROR CONTROL CODING IN DIGITAL TV BROADCASTING: This Chapter will include theoretical background of the error control coding, presented in a thorough but comprehensible manner. It will describe the basic principles of block and convolutional codes and thoroughly explain the two major error control codes used in DTV: (i) Reed-Solomon block codes and (ii) convolutional codes. Furthermore, the state-of-the art decoding algorithms for these codes will be presented, supported by a number of worked examples. Finally, the principles of trellis coded modulation (TCM) and pragmatic trellis coded modulation (PTCM) will be shown to further evolve the use of error control codes in channel coding. 5. EXISTING STANDARDS IN DIGITAL TV BROADCASTING: In this Chapter we will present the existing DTV standards on channel coding and modulation and show how the channel environment dictates the use of the particular schemes. This will include the full range of DVB standards (DVB- S, DVB-T, DVB-C, DSNG, LMDS, MMDS, RCS, RTS), the ATSC HDTV standard, the Japanese standard and the DOCSIS cable standard used in the USA. 6. FUTURE TRENDS IN DIGITAL TELEVISION In this Chapter we show that despite all the advantages of modem DTV, the efficiency of the current systems is far from the theoretical Shannon limit. We present an easy way to calculate the Shannon efficiency of any DTV system and compare the efficiencies of the different systems we have met up to this point. After identifying the gap between the theoretical limit and the efficiency of the current standards, we suggest a number of different techniques that could be used to close the gap. This includes not only a feasibility study of some particular techniques, xi

12 xii CODING AND MODULATION FOR DIGITAL TELEVISION for example turbo-codes and the soft-output Viterbi algorithm (SOVA), but also recommendations to avoid the limitation of these techniques, for example the error floor of turbo-codes. 7. REFERENCES: In this Section we will present an up to date bibliography which will include most of the important and relevant papers in the field. Gordon Drury Garik Markarian Keith Pickavance