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Home , Analog signal, Analog television

4.5 Mbps Data Compatibly Transmitted in 6 MHz Analog

Walter S. Ciciora, Ph.D. Technology Consultant Southport Connecticut [email protected]

Abstract television transmission in its Report & Order (R & O), “ Transmission Within has a long the Portion of Television Broadcast future. Cable will service these large and Station Transmissions”, in MM docket No. important markets for may years to come. 95-42. This R & O amends FCC rules to The compatible inclusion of digital data in allow ancillary data within the video portion analog television will increase the value of the spectrum which must continue of the NTSC in four formats. to serve analog receivers. This data can be used for inputs to and for ANALOG REQUIEM? set top boxes which implement “push technology” information services. The It might be assumed that this FCC’s technology described makes possible in action in allowing systems which add data to excess of 4.5 Mbps of data carriage in an analog television is too late to be of analog 6 MHz signal while not interfering commercial value. With the emphasis on with the normal analog reception of , DTV, some might television. Data is hidden in a signal in consider analog television’s demise quadrature with the video carrier, imminent. This is hardly the case! of the sound carrier, and use of the VBI. This has The recent adoption of an accelerated sufficient capacity to convey one, two, or schedule for DTV deployment in the US has even three MPEG compressed signals to caused some in the popular press to suggest implement the “Compatible Digital that the sole surviving technology for Upgrade”. terrestrial domestic will be INTRODUCTION digital and that analog NTSC will rapidly fade away. There are several reasons this The National Bureau of Standards, may not happen at all and even more reasons NBS, first proposed data embedded in why the notion of an accelerated schedule television signals in 1970 for the purpose of may not be realistic. distributing accurate time information nation- wide. While that effort did not succeed, it The deployed base of NTSC television spawned the system for the receivers in the United States is huge. More hearing impaired which in turn led to . than 250 million receivers plus another 175 More recent efforts to embed data in analog million VCRs --- all of which are exclusively television signals led to the formation of the analog NTSC --- exist in about 100 million National Data Broadcasting Committee in American television households. 1993 and its consideration of systems by Additionally, Americans purchase about 25 several proponents. On June 28, 1996, the million receivers and about 15 million VCRs Federal Communications Commission (FCC each year. The Half Life of these receivers is or the Commission) approved digital data on the order of 12-15 years! If the average transmission in the video portion of broadcast television receiver is a 19” model, it’s approximately 15 inch wide screen will be contained in a cabinet about 18” wide. All of It will take at least three years of the existing U.S. TVs set side by side would availability at market for any uptick of stretch 71,100 miles, several times around the consumer acceptance to materialize. Given earth. And 7,100 miles worth of new sets are the optimistic schedule of 40 top market sold in the US each year – more than enough stations on the air with digital signals by mid to go coast to coast a couple of times! VCRs 1999, the migration won’t be a national rush are in about half that quantity and would but rather a market by market crawl. stretch about half that distance again. Color TV suffered for thirteen years The American viewing public has yet to from its introduction in 1954 until the full be exposed to broadcast DTV. Broadcasters color prime time of NBC’s 1967 season. have yet to ascertained a viable business plan Only then did the marketplace favorably for the new capital expenditures. Early respond. It should be noted that monochrome predictions by the Consumer TV was a great improvement over . Manufacturers Association, CEMA, of the Color TV is a lesser improvement over Electronic Industries Association, EIA, monochrome TV. The High Definition project first DTV receivers to have a cost of Television, HDTV, flavor of DTV is a still around $5,000. New VCRs will be required lesser improvement over color TV. Digital as well. These will be at least $1,000. The “standard definition” television, SDTV, may consumer’s willingness to spend such be no improvement at all to a good analog unprecedented sums on a large scale for NTSC signal! television has not been tested. There is the promise of digital set top adapters which Surprisingly, there is very little talk of, consumers may purchase to obtain the digital HDTV. Most of the broadcaster interest programming on their existing receivers. seems to be in SDTV. So the offering to These will be around the cost of cable set top consumers is not better TV, but more TV. boxes, but with a retailer’s profit margin That may not be an attractive trade off for the added in. This will make cable’s $400 box high costs of the new television receivers and cost at least $500. What motivation would VCRs. drive consumers to spend this kind of money to get this programming? If they can afford While the FCC is postulating the return it, they already have cable or DBS. If they of analog broadcast spectrum, it has no can’t afford cable or DBS, they certainly authority to forbid cable from continuing to can’t afford to purchase an expensive digital serve the huge installed base of analog TVs set top box or and multi-thousand and VCRs. Such a vast marketplace cannot dollar digital TV receiver. Will those who be ignored. Cable will continue to service concern themselves with the plight of the this important audience. economically disadvantaged allow this ripe From the broadcaster’s point of view, it cause to pass? How can the government take will be politically unacceptable to be denied away the utility of one of the disadvantageds’ access to analog television receivers if cable only sources of entertainment and operators continue to have that market place. information? The politics of this situation have not yet been seriously weighed. Long From the consumers’ point of view, it range business plans in such an environment will be politically unacceptable to cannot be credible. disenfranchise the consumer’s . Consider the furor raised over the problems of cable’s set top box and the potential interference with features of television The Compatible Digital Cable Upgrade receivers. Imagine rendering the television useless and requiring the purchase of an Cable’s migration plans expensive new digital receiver or a digital set usually do not include comprehensive top box adapter! replacement of all analog channels because of the horrific expense of the digital set top THE MOTIVATIONS boxes. Instead, a hybrid service, part analog, part digital is planned. Two approaches are Why at this late date when it appears possible. The first expands and that everyone is talking about digital uses most or all of the new bandwidth for television is there a reason to be interested in digital services. This entails considerable embedding digital data in analog signals? construction expense and may not be practical for smaller systems or in tight economic times. Clearly, if analog television is not going In the second approach, there is the intention to disappear quickly, there is a strong of converting a few of the channels to digital motivation to maximize the utility of the and leaving the remainder as analog. In this spectrum which must continue to be allocated strategy, the channels converted to digital will to serving the existing market of analog have previously been occupied by low television receivers and VCRs. penetration services. Subscribers wishing to continue with those services will need a digital The Broadcaster’s Opportunity set top box. If these subscribers take no new There are a number of opportunities for services, just the ones they had previously broadcasters. During the period of transition, taken, their costs go up considerably while when an analog and a digital channel are there is no increase in revenue. Subscribers available, the digital capacity of the analog who do not wish the new advanced services channel should not lie fallow. It could be put will not receive a new digital set top box. to good economic use. However, they will lose programming previously carried on the analog channels If a is hidden in the analog which are converted to digital. This can be a signal, the value of the spectrum increases. serious loss for low capacity cable systems. Not only does the spectrum continue to serve those who cannot afford new receivers or Techniques which hide the data in the adapters, but it also serves those who can are an attractive alternative for make such a purchase. The electronics for the carriage of digital signals. Since television digital reception is complimentary to that tuners are relatively inexpensive, multiple needed to access digital signals hidden in tuners can be provided so that data can be analog. When a digital receiver or set top collected from more than one channel. That box is not accessing a digital part of the data can then be assembled to provide the spectrum, most of those same circuits can be MPEG streams needed to create new synthetic extracting the digital signal out of the analog channels. Statistical can be used signal at little additional cost. to advantage. In this approach, all of the analog channels are preserved for those who The broadcaster may find this double are satisfied with the existing service. The value of the existing spectrum to be a existing analog subscribers will notice no compelling political reason for retaining it difference other than the advertising programs when the appointed time for surrendering it promising more programming if they add arrives. digital services to their existing analog service. Only those willing to pay for more deliver digital video or services. will incur the extra cost of the new set top These can result in an expansion of broadcast box. or cable capacity without interference to ordinary analog reception. In recent years the metaphor of the “Chicken and the Egg” has given way to The data can be used with personal “Field of Dreams” concept of “Build it and computers, special television sets or set top they will come”. Each equally points up how boxes or versions of the “net ”. progress is frequently suppressed by When computers and computer adapters for codependent events. “Build it and they will television receivers are used, there are two come” requires an act of faith which is modes: “pull” and “push”. The “pull” mode difficult for those who have to sign checks. is the traditional approach where sites While there will be some building, the are accessed and data retrieved. This requires process is helped along considerably if the a two way connection. The “push” approach methods of construction are cost effective. can be implemented in a one way system. Here, the user indicates his fields of interest It will be some time before any and the data is retrieved from the data stream meaningful penetration of receivers for the and loaded into storage. It then is displayed. DTV format emerge. It is axiomatic that In a two way , “push” can be these receivers will be compatible analog supplemented with web site access for more television. The need to support NTSC will details. be so important that a non NTSC compatible DTV receiver is not expected to be a starter A related application involves in the US market. While the receiver is tuned . This is the inclusion of data in to an analog channel, the digital circuits are the broadcast television signal for use with a idle. The Compatible Digital Upgrade allows personal computer. The most aggressive such those circuits to be put to use to provide a implementation is Intercast whose main data stream for other purposes. This sharing partners include Intel and NBC. HyperText of resources gives extra value to the Markup Language (HTML) formatted Web investment in . pages are delivered in the VBI of the television signal. HTML is a method of The Compatible Digital Upgrade can be linking information. Highlighted words or the bridge between the massive installed base phrases can be “clicked on” and relevant of NTSC hardware and the yet unproved information appears on the screen. In some DTV Service. The building blocks that make cases, this is achieved by going to another up a DTV receiver are intrinsically location in the same document. In still other compatible with the needs of the Compatible cases, data from another document is Digital Upgrade. A high quality , good displayed. In other cases, locations on the and an MPEG engine World Wide Web are automatically accessed provide an ideal environment to support the and information retrieved. A personal Compatible Digital Upgrade. computer with a television tuner receives the signals and displays the video in a small Applications window. The rest of the screen displays the HTML pages. The computer’s hard disk can There are a variety of applications for capture and store pages of interest. Since data in analog signals. Data can be supplied HTML pages are around 50 Kbytes each and as just data. Alternatively, if sufficient most personal computers come with at capacity is available, data can be used to least a 1 GB hard drive, capacity is not a carry data. The data carrying capacity of a problem. In a major application of this cable system is just huge! technology, the pages downloaded pertain closely to the video programming. When HIDING DATA IN ANALOG SIGNALS several hundred pages are downloaded, the access speed is governed by the hard disk, not A few years ago, the question was a modem. In affect, the server is built into the asked if it was possible to hide enough data in personal computer! However, a high speed an analog video signal to allow carriage of a data link keeps the contents of the hard drive separate digital video signal. At first, the fresh and yields a fast response to a new prospects seemed dim. There are at least two inquiry for information. The HTML nature of reasons for this. First, it was thought that 5 or the pages makes accessing different parts of 6 Mb/s would be required for a digital the data downloaded easy and familiar to any television signal. Secondly, the early analysis Web surfer. The HTML can include was based on binary signals; i.e. signals with embedded links to related Web sites accessed just two logic levels. with the computer’s regular phone or cable Subsequently, several things happened. modem. Access to these sites is automatic. First it became clear that MPEG encoding has Cable vs Broadcast Data improved dramatically so that fewer Mb/s are required for good quality results. Secondly, Since cable’s spectrum is much more the use of multi-level coding makes it possible well behaved than the broadcast spectrum, to convey multiple bits simultaneously. several significant advantages accrue. A time Advanced tuner technology makes it possible domain equalizer may not be necessary. If one to consider two or more tuners in a receiver to is included, it may have relaxed specifications extract data from more than one channel leading to lower cost. There is no “airplane simultaneously. Lastly, very sophisticated flutter”, i.e. Doppler effect from approaching processing is affordable in receivers. This or receding aircraft. Because the spectrum is processing allows compensation for problems better behaved, less error detection and introduced by extra data signals. correction is required for a given level of performance. This was well demonstrated in Data Under Visual the Advanced Television Grand Alliance’s The new approach involves a data modulation scheme. While 8-VSB is used for signal which is double amplitude broadcast, 16-VSB was developed for cable modulated onto suppressed carrier which is in allowing two HDTV signals in 6 MHz on quadrature phase with the picture carrier. If cable. 16-VSB does not have twice the data both the video signal and the new data signal capacity of 8-VSB. The doubling of payload were normal double sideband, they could be comes because 16-VSB requires significantly separated with synchronous detectors by less data protection. If this same approach is conventional methods. Since the television applied to the techniques proposed for data signal is not all double sideband, but vestigial carriage in analog television signals, more of sideband, a television receiver includes a the raw data capacity can be harvested for Nyquist slope filter to properly weight the payload purposes. This approach has not been upper and lower video around the well explored and offers a significant carrier so that the correct amplitude is opportunity. An additional advantage is available for detection. A Nyquist filter is one cable’s availability of multiple channels to which has an anti-symmetric characteristic about a critical which is called the Nyquist frequency. The exact shape of the synchronous or similar behaving filter is not specified, only that it is anti- which inherently is immune to quadrature symmetric about the critical frequency. The components, the added data signal will be receiver manufacture has some latitude in the essentially ignored. implementation of this filter. The pre-shaping of the added data The Nyquist filter is a serious problem signal is done with a compensation network for a double sideband signal which is which includes a Nyquist filter representative modulated onto a quadrature carrier. In the of those found in the population of receivers course of its normal functions, this filter exposed to the added data signal. In the event would convert a plain double sideband that the population consists of a mixture of modulated signal (with opposite sidebands differently shaped Nyquist filters, a composite equal in amplitude to each other) into a double signal optimizing the result can be sideband signal with asymmetrical sidebands. implemented either with a parallel Vector analysis reveals that when the two configuration of Nyquist filters fed with signal sidebands are symmetrical, there is only a strengths in proportion to the numbers of the resultant signal in phase with the carrier. respective filters in the population or with a Conversely, when the two sidebands are not Nyquist filter designed to optimize the result symmetrical, there is an additional component using standard filter synthesis techniques. in quadrature with the carrier. This newly formed asymmetrical sideband set would have In order to maintain a relationship that an undesired component in phase with the allows synchronous detection to separate the video carrier which would cause interference. data signal from the video signal, the data Stated another way, even though the new signal should be limited to the frequency sideband set was initially placed on a region over which the Nyquist filter operates. suppressed carrier which is in quadrature to This is + 750 kHz around the visual carrier. the picture carrier at the origination point of Two level data will accommodate 1.5 Mb/s of the signal, after being operated on by the throughput. However, the signal to receiver’s Nyquist filter, a detector extracting environment required to present acceptable the video signal would “see” unwanted pictures will support better than two level components from the new sidebands. data. Four levels of data will allow two Consequently, quadularity would not be simultaneous bits of data for 3.0 Mb/s of preserved between the visual carrier and the throughput. While higher data rates may be added data signal. possible, the signal levels required make the problem of avoiding interference with the This problem can be averted by video very difficult. Since going to three properly shaping the spectrum of the added simultaneous bits would involve data signal so that when it passes through the discriminating eight levels of signal, the point receiver’s Nyquist filter, a double sideband of diminishing returns may have been reached. spectrum in quadrature with the visual carrier and possessing equal amplitude sidebands will The addition of a data signal in be obtained. Under these conditions, there quadrature with the video carrier will will be minimal cross coupling of the modulate the envelope of the resulting signal. quadrature signal’s energy to the receiver’s If the receiver’s detector is not a pure video detector. Therefore the receiver’s synchronous detector, that is, if it exhibits detector will respond essentially only to the sensitivity to the envelope of the resulting video signal. If the receiver utilizes a signal, the data signal will contaminate the video. The problem is that there is a huge signal quality environments. In an NTSC population of receivers already in existence (type M system) the highest chroma whose performance must not be seriously utilized are 5.43 MHz above the impacted. lower band edge. This is arrived at by the visual carrier being 1.25 MHz above the lower The solution to this problem is the band edge, the chroma being 3.58 introduction of abatement signals to counter MHz above the visual carrier and the highest the impact of the data. Since the phenomena frequency chroma sidebands extending up to are non-linear, the optimum abatement 600 kHz above the chroma subcarrier (1.25 + strategies will involve non-linear techniques. 3.58 +0.6 = 5.43). If it is desired to maintain A couple of year’s of intensive development the sanctity of this spectrum, the aural data, 8 work has resulted in successful techniques for level, 1.5 Mb/s signal will be implemented. achieving this goal. Just as in the MPEG model, the expensive processing is done at the With four level data under visual point of signal origination. The receiver contributing 3.0 Mb/s and eight level under circuits are very cost-effective. aural contributing another 1.5 Mb/s, a total of 4.5 Mb/s is achieved. Data Under Aural Other Data Resources Additional information may also be added on the aural carrier of the NTSC Neither the data under visual nor the television format. This is achieved through data under aural interferes with Vertical of the aural carrier Blanking Interval (VBI) data transmission. which is already frequency modulated by the Approximately another half Mb/s can be TV audio and BTSC signals. The first caveat achieved in that manner. There are other is that the AM modulation may not be full methods for hiding data under consideration depth without corrupting the aural program by others. Some of these methods can be information. The allowable depth of employed along with these methods to achieve modulation is limited by the worst signal to still greater total capacity. noise ratio to be encountered in the service area of the broadcasts. To be approximately The combined data capacity per analog equivalent in both program material and data channel is a significant resource which should performance at the FCC “Grade B” contour a not be ignored. The electronics for extracting downward modulation depth of about one half that data is very cost effective. It is a trivial (6 dB) which corresponds to 33% cost addition to a digital set top box or modulation is appropriate, but other values personal computer mother board. It is well can be used. At this depth of modulation within the customary prices paid for personal multilevel data signals may be employed computer after-market plug in cards. increasing the data carrying capacity of the channel. Modern television receivers When two or more adjacent channels generally perform with full limiting when are simultaneously utilized, statistical receiving noisy video signals. multiplexing techniques can be employed to pack still more programming into the analog More efficient use of the available spectrum. spectrum is achieved by multilevel encoding of data. In the aural data system, 2, 4, 8, and even 16 levels are appropriate for different THE AUTHOR Industry Association (EIA) for eight years. He has served on several industry standard-setting Dr. Ciciora is a technology consultant committees. He currently co-chairs the Cable specializing in , Consumer Consumer electronics Compatibility Advisory Electronics, and . He serves Group to the Federal Communications on several Boards of Directors, Technology Commission and its Decoder Interface Advisory Boards, and does expert witness work. subcommittee.

Most recently he was Vice President of Walt is a Fellow of three engineering Technology at Time Warner Cable. Walt joined societies the IEEE, the SMPTE, and the SCTE. American Television and Communications, the Other memberships include Tau Beta Pi, Etta predecessor to Time Warner Cable, in December Kappa Nu, and Beta Gamma Sigma. of 1982 as Vice President of Research and Development. Prior to that he was with Zenith Current interests center on competitive Electronics Corporation, starting in 1965. He was technology, the consumer electronics interface Director of Sales and Marketing, Cable Products, with cable, Digital Video Compression, from 1981 to 1982. Earlier at Zenith he was Interactive Television, Multimedia, and High Manager, Electronic System Research and Definition Television. Development specializing in Teletext, Videotext and Video Signal Processing with emphasis on Walt received the 1987 NCTA Vanguard digital television technology and ghost canceling Award for Science and Technology and was for television systems. named "1990 Man of the Year" by CED magazine. CED also named him "1993 Man of the Year". He has ten patents issued, two more He was the Fall 1994 Levenson Memorial allowed but not yet issued and several more Lecturer at the National Cable Television Center pending. He has presented over two hundred at Penn State. papers and published about a hundred, two of which have received awards from the Institute of Walt has a Ph.D. in Electrical and Electronic Engineers (IEEE). His from Illinois Institute of Technology (IIT) dated papers have been translated into Japanese, 1969. The BSEE and MSEE are also from IIT. Chinese, German and Spanish. Walt wrote a He received an MBA from the University of monthly columns for Communications Chicago in 1979. He has taught Electrical Engineering and Design (CED) magazine and for Engineering in the evening division of IIT for Communications Technology (CT) magazine for seven years. three years each. Hobbies include helping his wife with her He currently serves on the Executive horses, reading, wood working, photography, Committee of the Montreux Television skiing, and a hope to someday become more active Symposium. He was a member of the board of in amateur radio (WB9FPW). directors of the Society of Cable Telecommunications Engineers (SCTE) for six Walter S. Ciciora, Ph.D. years. He was inaugural Chairman of the 45 Hulls Farm Road Technical Advisory Committee of CableLabs for Southport CT 06490-1027 four years and Chairman of the National Cable Phone: 203-259-5183 Television Association (NCTA) Engineering 203-259-0556 Committee also for four years. He was president [email protected] of the IEEE Consumer Electronics Society for two years and is a past chairman of the IEEE International Conference on Consumer Electronics. He chaired the Joint Engineering Committee of the NCTA and the Electronic