CONSUMER ELECTRON ICs’ NEW ANGLES v

Special section: scoping out the industry’s geometric progress.

HDTV - What’s going on? High Definition Television, or HDTV,

J o h n G.N. Henderson David Sarnoff Research Center

circuits in popular con- sumer devices, the demands of HDTV surpass both of these products in di- versity of required technologies, magnit speed of the signal processing, and sh silicon.

The economic and signal envi which HDTV must fit dictates most of the tech- nology requirements; common sense imposes the rest. The first mandate is compatibility with existing National Television Standards Commit- tee (NTSC) broadcasts and home receivers. There are roughly 140 million such receivers in American homes. Economic and social consid- eration demand that they not be rendered in- stantly obsolete by a new standard. The Federal Communications commission (FCC) has wisely mandated compatibility th to the “chicken-or-egg” start-up problem of any new service - no on receivers for which signals are not available, and no one will broadcast si non-existent receiver population. Compatibility with existing mo allowed color television to survive initially sluggish sales. Desp compatibility imposes profoundly tough requirements on the sign signal processing of HDTV.

spectrum. HDTV requires more bandwidth than NTSC, especially I

The second mandate has been imposed by the finite av

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to be preserved. Exactly how much additional bandwidth is necessary to deliver a signal that is of “HDTV” quality is the subject of on-going research. But it is accepted that at least 9- 12 MHz per station will be required to deliver HDTV and support NTSC as compared with the present 6 MHz per station to deliver the present NTSC signal. The FCC has required that any Advanced TV system support compatibility and fit within the existing broadcast television VHF and UHF spectrum allocations. The implications are manifold.

At first blush, it appears that, within any local geographic area, there are many unusedTV channels, especially in the UHF band. However, especially along the crowded eastern seaboard, those seemingly “vacant” channels are preserved in order to simplify the design requirements on home receivers and antennas. Adjacent channels and image frequencies in the UHF band are not assigned. Re-use of the same frequency by another station (co-channel) is widely separated geographically. These rules must change if all stations that wish are to be able to deliver HDTV. New receiver designs must provide increased channel selectivity. And they must do so at a price that consumers will pay. Even with improved receivers, it will be difficult to provide all the new channels that will likely be sought for HDTV. Time must be allowed for phase-in of the new service if new channel allocations adversely affect the existing NTSC receiver population. Testina the abilitv of a new service to fit

temporal. Horiz horizontal resolution

r swift,” writes Brian ows that HDW. like n, will be introduced

with far less disruption to industry and the consumer than c w e n t hype would suggest. The real issues is not competitiveness, but the protection of en- trenched interests.

In the United States, the Federal Communications Commissions has de- manded that a HDW system marketed in the United States be compatible with existing domestic receivers. The most frequently proposed U.S. HDW stan- dard is based on 1050 scanning lines and a field rate of 59.94 - the same field rate and exactly double the number of scanning lines a s NTSC. It requires more than 30 megahertz of bandwidth and will require significant compression for transmission. The amount of bandwidth compression to be used is currently under discussion. The FCC will not likely to be able to recommend a delivery standard before 1992. So the soonest HDTV broadcasting could begin in the U.S. is 1993.

In Japan, as well a s North America, the current television standard is NTSC, which calls for 525 scanning lines per picture at a field rate of 59.94 per second. The HDW system being introduced in Japan, called Hi-Vision, is 1125/60, which means 1 125 scanning lines at a field rate of 60 times per second.

This 1 125/60 proposal requires a channel space, or bandwidth, of more than 30 megahertz - more than five times that allocated to conventional TV.

was by satellite, which uses a different area of the electromagnetic spectrum where more channel space is available. However, the consumer must purchase a special receiver and satellite antenna dish because the system is not compat- ible with existing satellite equipment.

In some European countries, the current TV standard is not NTSC but PAL or SECAM, which have 625 scanning lines and field rates of 50 per second. Each PAL or SECAM TV channel uses eight megahertz of bandwidth instead of the six megahertz required by NTSC. The proposed European standard, which is often referred to a s Eureka EU95, would require more than 30 megahertz for 1250 scanning lines at 50 fields per second.

Because the field rate is the same as PAL and the number of lines is exactly double, it will be possible to view the Eureka EU95 signal on existing European receivers. However, a converter box and a satellite antenna dish would be required. And, of course, picture quality would not be improved without a new HDTV receiver.

HDTV’s importance a s to i t s affect on the electronics industry has mixed reviews. Some feel that it is the greatest technology since the advent of color television. And not just as improved TV quality, but a s a medium which has limitless arenas such a s consumer TV’s, semiconductors, computers and defense products. Others, including the congressional Budget Office who issued a report back in August, feel that the markets are unlikely to be big enough to have the hoped-for effects; that HDTV will turn out to be nothing more than improved television.

So you see, the issue here is not developing the technology; but rather, how to implement the new technology within the realm of existing technology without disturbing existing social, economic and trade patterns.

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- Christine S. Vreeland I-_ - ~- ~ --.

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mensions meaningfully specified in MHz or in the number of black-white cycles that can be resolved per unit of picture width or height. Image resolution is also character- ized with vertical frequencies; in a line- scanned system, such as broadcast televi- sion, it is convenient to invoke the sam- pling operation inherent in scanning and dimension the vertical axis in cycles/pic- ture height (i.e., the number of scanning lines reduced by empirical factors related to the sampling process itself or to the interlaced nature of some scanning sys- tems). Television (and movie film) is also sampled in the temporal dimension in frames or fields/second.

Compatible color television (NTSC) ex- ploited the three-dimensional and sampled nature of monochrome television to hide a new color subcarrier. The subcar- rier produced color images on color re- ceivers but appeared in black and white with minimal artifacts on existing mono- chrome receivers. Early color receivers separated the monochrome luminance signal from the color information with a one-dimensional (horizontal) filter ap- proximation. More recent receivers, using comb filters, separate the signal using both horizontal and vertical dimensions and do the job more completely. They also preserve more of the original luminance bandwidth. Advanced TV receivers will filter in three dimensions, allowing better separation of chrominance and lumi- nance, and insertion and recovery of even more information (e.g., more resolution compatibly within the NTSC spectrum). Such three-dimensional filters must store frames of television video and will require several megabytes of random access memory.

HDTV signals, in their original form, require about 30 MHz of bandwidth. Straightforward transmission of such a signal would use 5-6 existing television channels and is completely impractical within the allowable spectrum. The HDTV signal must be compressed somehow for delivery by any existing medium. Various compression techniques and combina- tions are being studies. The existing NTSC spectrum can be packed more densely to include new signals. This ability offers

dramatic improvement in television im- ages, and can produce the wider aspect ratio (16:9 instead of NTSC’s 4:3) nor- mally associated with HDTV. But, it is unlikely that full HDTV resolution can be achieved by such means alone. However, improved NTSC signal could be aug- mented by information in a second chan- nel. The reception and combination of both channels would produce an HDTV image. If, as is likely, the practical prob- lems of two-channel reception and timing can be solved, this approach could pro- duce the best pictures, since a total of 12 MHz has been devoted to their transmis- sion. Another way to meet the compatibil- ity requirement would be to leave the existing NTSC channels as they are and deliver HDTV on a second, stand-alone channel. This method imposes the most severe compression requirements on the HDTV signal. Compression in both spatial and temporal dimensions could be re- quired. Much current research has been devoted to achieving compression ratios by using techniques that attempt to match the properties of the human visual system.

David Sarnoff Research Center

To date, though, no completely satisfac- tory result has been demonstrated publi- cally.

More obstacles await. “Normal” televi- sion reception today is plagued by trans- mission path degradations that could make HDTV meaningless. A common problem is multipath “ghost” images. Ghosts -- with path lengths such that their delay relative to the main signal exceeds about 0.5 microseconds - - manifest themselves a (generally distorted) repli- cas of the original signal displaced a dis- crete distance across the screen. Ghosts with shorter time delays (less than about 200 nanoseconds) show up as poor tran- sient response or “soft” edges rather than discrete echoes. Ghost cancellation will be required for HDTV receivers. Ghost can- cellation is best done at baseband, after demodulation, and will involve digital sig- nal processing. The fact that HDTV receiv- ers will be digital makes ghost cancelling systems and HDTV related symbiotically. Ghosts are detected using a transmitted training waveform whose original shape is stored in the receiver. The channel reflec-

tion filter that w filter can also hand1 delays over the rang econds to tens of measurement of the tion of the equalization filter coefficients must take place in reasonable time (less than a second) with computational power affordable in a TV receiver.

Cameras and displays must also be improved dramatically. For camera tech- nology, the problem is achieving the re- quired resolution at the light sensitivity production crews experts. Home displays are probably the more acute problem, because cost is so important. Displays must have high resolution; and, they must achieve it at a brightness and contrast level comparable to today’s TV picture tubes. Moreover, displays must be large if HDTV is to have meaning at normal TV viewing distances. NTSC pictures are in- tended for viewing at a distance of about five times the height of the picture. HDTV, with its higher resolution, is designed for viewing at about two times the picture height. Television is commonly viewed from across the room, say about ten feet away, which is about right for a large- screen set. For HDTV to be appreciated at the same viewing distance, the screen must be about five feet high, and it must be bright and of high contrast. Not incidently, it must be sold at a price people are willing to pay.

The foregoing discussion has focused on the video aspects of HDTV. But, HDTV is generally expected to include improved audio\ probably digital. Although “Com- pact Disc quality” is the phrase often used to describe HDTV’s audio goals, it is un- likely that Compact Disc’s 16-bit PCM will be transmitted because of the bandwidth it requires. Rather, some form of com- pressed digital audio will be selected, probably requiring a data rate no greater than 500 Kbits/second per stereo pair.

HDTV is a formidable challenge re- John G.N. Henderson is Head, Systems quiring application and creation of Technology Research, in the Teleuision Re- technologies on a scale not attempted search Center in Princeton, NJ. His present in electronics since color efforts focus on the Advanced Compatible Tele- television. The challenge is invigorat- vision system being developed by Sarnoff for

transmission o f HDN. Mr. Henderson holds ing, if daunting, but is in the best tradi- fourteen patents, He is president of the

ity, and manufacturing savvy that is 1989, tion Of high cost sensitiv- Consumer Electronic- Society of the /,FEE for

uniquely consumer electronics. +

Stated below are recommendations from the IEEE United States Activities’ committees on Communications and Information Policy and U.S. Competitive- ness. They deal with the introduction of HDTV in the United States.

+ The FCC should continue to foster a proactive, participatory effort that leads to clear decisions and to strive for a timetable that will allow a timely, but thoroughly considered, introduction of HDTV in the United States..

+ It is important to recognize that any consideration of HDTV must take a total systems approach to TV production, distribution, and delivery and not be limited merely to issues surrounding the TV receiver and spectrum allocation. Also, it is important to make a long-term view of technology, since once adopted, any new system can be expected to be in operation well into the next century.

+ Additional controlled and quantifiable tests are urgently required in order to put the perceived benefits of HDTV in perspective. These test results are an essential element in establishing the standard for HDTV.

+ The competitiveness of the U.S. television set manufacturing industry will not be materially aided by adopting a unique or an early U.S. standard. Therefore, U.S. competitiveness should not be a controlling factor in setting a HDTV standard, either in its makeup or timing of its adoption.

+ The FCC should, in a timely manner, produce a single set of standards for display, interface, and terrestrial broadcast. The display and interface standards should be capable of accommodating other delivery media and be consistent with the highest deliverable HDTV quality.

@ The standard adopted for terrestrial broadcasting should not be constrained by the current 6MHz broadcast channel bandwidth. Further tests and simulations can yield meaningful data to assist in making an informed decision regarding spectrum issues. Such tests should be carried out before adoption of a standard. In order that decisions not be delayed, some urgency should be given to the spectrum allocation questions.

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