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Fundamentals of Digital Television Transmission. Gerald W. Collins, PE Copyright  2001 John Wiley & Sons, Inc. ISBNs: 0-471-39199-9 (Hardback); 0-471-21376-4 (Electronic) FUNDAMENTALS OF DIGITAL TELEVISION TRANSMISSION FUNDAMENTALS OF DIGITAL TELEVISION TRANSMISSION GERALD W. COLLINS, PE GW Collins Consulting A Wiley-Interscience Publication JOHN WILEY & SONS, INC. New York ž Chichester ž Weinheim ž Brisbane ž Singapore ž Toronto Designations used by companies to distinguish their products are often claimed as trademarks. In all instances where John Wiley & Sons, Inc., is aware of a claim, the product names appear in initial capital or ALL CAPITAL LETTERS. Readers, however, should contact the appropriate companies for more complete information regarding trademarks and registration. Copyright  2001 by John Wiley & Sons, Inc. All rights reserved. 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ISBN 0-471-21376-4 This title is also available in print as ISBN 0-471-39199-9. For more information about Wiley products, visit our web site at www.Wiley.com. To God who created the electromagnetic force and the law that governs its operation in communications systems and To my beautiful wife Wilma who, after 39 years of marriage, still wonders why I’m thinking about my work! CONTENTS Preface xi Acknowledgments xiii 1 Digital Television Transmission Standards 1 ATSC terrestrial transmission standard, vestigial sideband modulation, DVB-T transmission standard, ISDB-T transmission standard, channel allocations, antenna height and power, MPEG-2 2 Performance Objectives for Digital Television 21 System noise, external noise sources, transmission errors, error vector magnitude, eye pattern, interference, cochannel interference, adjacent channel interference, analog to digital TV, transmitter requirements 3 Channel Coding and Modulation for Digital Television 43 Data synchronization, randomization/scrambling, forward error correction, interleaving, inner code, frame sync insertion, quadrature modulation, 8 VSB, bandwidth, error rate, COFDM, flexibility, bandwidth vii viii CONTENTS 4 Transmitters for Digital Television 67 Precorrection and equalization, up conversion, precise frequency control, RF amplifiers, solid-state transmitters, RF amplifier modules, power supplies, power combiners, Wilkinson combiner, ring combiner, starpoint combiner, cooling, automatic gain or level control, ac distribution, transmitter control, tube transmitters, tube or solid-state transmitters, performance quality, retrofit of analog transmitters for DTV 5 Radio-Frequency Systems for Digital Television 98 Constant-impedance filter, output filters, elliptic function filters, cavities, channel combiners 6 Transmission Line for Digital Television 117 Fundamental parameters, efficiency, effect of VSWR, system AERP, rigid coaxial transmission lines, dissipation, attenuation, and power handling, higher-order modes, peak power rating, frequency response, standard lengths, corrugated coaxial cables, wind load, waveguide, bandwidth, waveguide attenuation, power rating, frequency response, size trade-offs, which line? waveguide or coax? pressurization 7 Transmitting Antennas for Digital Television 150 Antenna patterns, elevation pattern, mechanical stability, null fill, azimuth pattern, slotted cylinder antennas, gain and directivity, power handling, antenna impedance, bandwidth and frequency response, multiple-channel operation, types of digital television broadcast antennas, antenna mounting 8 Radio-Wave Propagation 199 Free-space propagation, distance to the radio horizon, refraction, multipath, ground reflections, surface roughness, effect of earth’s curvature, Fresnel zones, linear distortions, diffraction, fading, undesired signal, field tests, Charlotte, North Carolina, Chicago, Illinois, Raleigh, North Carolina CONTENTS ix 9 Test and Measurement for Digital Television 245 Power measurements, average power measurement, calorimetry, power meters, peak power measurement, measurement uncertainty, testing digital television transmitters Symbols and Abbreviations 251 Index 261 PREFACE Many engineers familiar with analog television broadcast systems are now faced with designing, operating, and maintaining digital television systems. A major reason for this introductory book is to make the transition from analog to digital television broadcasting as painless as possible for these engineers. The emphasis is on radio-frequency (RF) transmission, those elements of the system concerned with transmitting and propagating the digitally modulated signal. I begin with the digital signal as it emerges from the transport layer and end with the RF signal as it arrives at the receiver. The emphasis is on factors affecting broadcast system performance. The scope of this book is necessarily limited; some topics, such as studio- to-transmitter links and receivers are not covered. It is intended as a self-study resource by the broadcast system engineer, as well as a reference for the design engineer, system engineer, and engineering manager. An index is included to make it a more useful resource for future reference. It may be used as a text for a formal training class. Most people would agree that a useful engineering tool must include some mathematics. For this reason, and to make the presentation as clear as possible, concepts have been described verbally, mathematically, and in many cases, graphically. The mathematics used include algebra, trigonometry, and a small amount of calculus. For those not interested in the mathematical formulation, the charts and graphs should be sufficient to grasp the key points. For those who wish to probe further, extensive footnotes are provided. These not only provide much more detail but are my attempt to give credit to the many workers who have brought digital television to its present state of maturity. Even with ample footnotes, I may have failed to give credit to all who deserve it. This is by no means intentional; the references included are simply those sources of which I am aware. xi xii PREFACE To the extent possible I have used the mathematical symbols most commonly used for the quantities discussed. However, the literature for the many subsystems comprising a digital television transmission system use common symbols to represent a large number of the quantities. To avoid confusion, I have added subscripts and used alternative type fonts to distinguish such quantities where necessary. When I found it necessary to use a nonstandard symbol, I attempted to make the relationship between the quantity and its symbol as intuitive as possible. To the extent that information was available to me, I have discussed the American ATSC, the European DVB-T system, and Japan’s ISDB-T system. My personal experience and library are heavily biased in the direction of the ATSC and DVB-T systems, however, a fact that will readily be apparent to the reader. The information presented should not be considered an endorsement of a specific system for any particular country or group of countries. There are many factors to be considered when selecting a transmission system, not all of which are determined by performance parameters such as transmitter peak-to-average ratio or threshold carrier-to-noise ratio. These include the type of network, program and service considerations, and the extent of the use of mobile receivers, as well as language, industrial policy, and other issues. The information presented is factual to the best of my understanding. Readers are left to draw the appropriate conclusions for their applications. My personal design background is in antennas, analog transmitter systems, passive RF components, and propagation. When the transition to digital television began, it became necessary to educate myself with regard to digital modulation techniques, system design, and testing. This has required collaboration with many experts and the study of many reports and papers. This book is the result of that effort. If in some respect the presentation of any topic is incomplete, I take full responsibility. The implementation of digital television is a process that will continue for many years to come. The transition periods will take up to 15 years in some countries. The process will not start in Japan until after 2003. In the United States the transition period has started and is mandated to be short. However, stations whose initial channel is outside the core spectrum will be required to move to a core channel after the transition. Those whose analog and digital channel is inside the core will be permitted to chose their permanent channel. It is hoped that this book will be helpful to those who are designing and implementing these systems, both now and in the future. J ERRY COLLINS December 1999 ACKNOWLEDGMENTS I most certainly do not claim originality for much of the material included in this book. In fact, the story of digital television builds on the many contributions of workers since the beginning of radio and television transmission. Rather, this book represents the result of my own attempt to understand and manage the development of digital television broadcast equipment since 1989. I am especially grateful to my former colleagues and the management of Harris Corporation Broadcast Division for their outstanding efforts. Together we participated in the process of developing digital television standards, designing equipment, and testing broadcast systems. It is to them that I owe so very much. In naming some, I’m sure I will miss some important contributors. However, I must mention the very beginning of our work when Bob Plonka, Jim Keller, I, and others worked with Charlie Rhodes of the ATTC to develop the RF test bed by which the proponent transmission systems were tested. Bob and Jim have continued their work developing, implementing, and testing new designs and production equipment for Harris. Charlie’s name is almost synonymous with DTV transmission. As soon as it was clear that the 8 VSB system would be the standard for the United States, I involved others in my R&D group in the development of the first series of 8 VSB exciters. These fine engineers included Dave Danielsons, Ed Twitchell, Paul Mizwicki, Dave Nickell, Dave Blickhan, Bruce Merideth, and Joe Seccia. The system engineering skills of Bob Davis were vital. We started the work on power amplifier development soon after the exciter. This could not have been accomplished without the able contributions of the engineers at our sister facility in Cambridge, England, under the leadership of Dave Crawford and Barry Tew. Dmitri Borodulin joined us in Quincy, Illinois for xiii [...]... adjust OFDM Byte-wise Trellis interleaver coder modulator Energy dispersal R/S coder Delay adjust Delay adjust Byte-wise Trellis interleaver coder Null R/S packets Figure 1- 12 Block diagram of ISDB-T channel coding 16 DIGITAL TELEVISION TRANSMISSION STANDARDS TABLE 1- 1 Frame Duration (ms) versus Mode and Guard Interval Ratio Guard Interval Ratio 1 4 1 8 1 16 1 32 Mode 1 2 3 64.26 12 8.52 257.04 57.83 11 5.67... are reserved; 92 of these symbols may be a continuation of the PN63 sequence The last 12 of these symbols are duplicates of the last 12 symbols of the preceding data segment 4 511 symbols 63 63 63 24 10 4 4 Figure 1- 7 Field sync for the ATSC system (From ATSC DTV Standard A/53, Annex D; used with permission.) 8 DIGITAL TELEVISION TRANSMISSION STANDARDS In addition to providing a means of synchronizing... Collins, PE Copyright  20 01 John Wiley & Sons, Inc ISBNs: 0-4 71- 3 919 9-9 (Hardback); 0-4 71- 213 76-4 (Electronic) 1 DIGITAL TELEVISION TRANSMISSION STANDARDS A great deal of fear, uncertainty, and doubt can arise among engineers with an analog or radio-frequency (RF) background at the mere mention of digital transmission systems Engineers sometimes fall into the trap of believing that digital systems are fundamentally... 1 16 1 32 Mode 1 2 3 64.26 12 8.52 257.04 57.83 11 5.67 2 31. 34 54.62 10 9.24 218 .46 53. 01 106.03 212 .06 transmission mode and the length of the guard interval These relationships are summarized in Table 1- 1 The frame duration doubles from mode 1 to mode 2 and doubles again from mode 2 to mode 3 Modes 1, 2, and 3 are defined for 10 8, 216 , and 432 OFDM carriers per segment, respectively The packets comprising... exciter To PA 4 DIGITAL TELEVISION TRANSMISSION STANDARDS The digital input signal to the ATSC transmission system is a synchronous serial MPEG1 -2 transport stream at a constant data rate of 19 .39 Mb/s This serial data stream is comprised of 18 7-byte MPEG data packets plus a sync byte The payload data rate is 19 .2895 Mb/s The payload may include encoded packets of digital video, digital audio, and/or... and radiating the on-channel signal 1. 00 0.90 0.80 0.70 Magnitude 0.60 0.50 0.40 0.30 0.20 0 .10 0.00 0.00 1. 00 2.00 3.00 4.00 Relative frequency (MHz) Figure 1- 10 Transmitted spectrum, 8 VSB 5.00 6.00 DVB-T TRANSMISSION STANDARD 11 DVB-T TRANSMISSION STANDARD The European Telecommunications Standards Institute has adopted a set of standards for digital broadcasting of television, sound, and data services... complete DVB-T signal has been generated at the output of the modulator The remainder of a transmitting system exists for the purposes of upconverting Upper skirt 3.75 0.00 3.80 3.85 3.90 −5.00 Relative level (dB) 10 .00 15 .00 −20.00 −25.00 −30.00 −35.00 −40.00 −45.00 Relative frequency (MHz) Figure 1- 11 Typical COFDM spectrum 3.95 4.00 14 DIGITAL TELEVISION TRANSMISSION STANDARDS to the desired channel,... the active OFDM carriers Detailed operation of the symbol interleaver depends on the number of carriers generated, whether 2048 ( 211 ) in the 2k mode or 819 2 ( 213 ) in the 8k mode Some of the carriers are used to transmit reference information for signaling purposes (i.e., to select the parameters related to the transmission mode) The number of carriers available for data transmission is 17 05 in the... consisting of eight amplitude levels, four positive and four negative The signal is often displayed in a two-dimensional I–Q or constellation diagram, as shown in Figure 1- 9 This is a graphical representation of the orthogonal I and Q components of the modulated waveform, plotted in X–Y or rectangular Q −7 −5 −3 1 1 3 5 7 Figure 1- 9 I–Q diagram for 8 VSB signal I 10 DIGITAL TELEVISION TRANSMISSION. .. or part of a program or service After channel coding, these data groups become OFDM 1 segments Each OFDM segment occupies 14 of the channel bandwidth This arrangement allows for both broadband and narrowband services For example, a single HDTV service might occupy 12 of the OFDM segments, with the thirteenth used for sound and data.3 Alternatively, multiple SDTV programs might occupy the 12 OFDM segments . Fundamentals of Digital Television Transmission. Gerald W. Collins, PE Copyright  20 01 John Wiley & Sons, Inc. ISBNs: 0-4 71- 3 919 9-9 (Hardback); 0-4 71- 213 76-4 (Electronic) FUNDAMENTALS OF DIGITAL. review of the manuscript and his constructive comments. Fundamentals of Digital Television Transmission. Gerald W. Collins, PE Copyright  20 01 John Wiley & Sons, Inc. ISBNs: 0-4 71- 3 919 9-9. beginning of radio and television transmission. Rather, this book represents the result of my own attempt to understand and manage the development of digital television broadcast equipment since 19 89.