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Mr. Charles Pantuso
Vice-President, HD Vision. Dallas, Texas
July 17, 1999
Dale,
I do not know enough about the issues myself. People who I respect are on the side of 8-VSB, and someone who used to be the Director of Engineering for Sinclair said to me that he has other motives, but I have not personally confirmed it. If he is right, ultimately we will change, but it won't be worth it. HD will be dead. What we really need now is more marketing confusion.
Charlie
Mr. Mark Schubin
Consulting Engineer
July 17, 1999
Like Mike, I, too, have been told, by people I respect, that 8-VSB reception can be dramatically improved, and I eagerly await seeing that improvement.
Unlike Mike, I do not think the problem is restricted to indoor reception, nor do I think cable TV and satellite TV are cures for the indoor reception problem. Let me start with those alternative delivery mechanisms:
- Satellite TV - Both houses of Congress have passed bills authorizing local-into-local satellite transmission. Both say that if a satellite service provider provides any local transmission it must eventually provide all stations in that market. Yet no satellite service provider has any plans to provide all local stations in any market, and the bills do not make any provision for DTV. Satellite programming is typically carried at around 3 Mbps; DTV is over 19 Mbps. Barring some major technology change, satellites are not going to solve the DTV-reception problem, even if and when they approach the requisite household penetration.
- Cable TV - There is no must-carry requirement for DTV. There may never be. I have a DTV receiver hooked to my cable system. Through it, I can get HBO and WCBS-DT. I cannot get WNYW-DT, the Fox DTV station broadcasting in my area, because my cable system has chosen not to carry it. As with satellites, there is a big bandwidth problem for cable TV to carry DTV, at least during the transition period, when they will have to provide both NTSC and DTV carriage (requirements for any simulcasting don't begin until 2003).
- Combined, satellite and cable TV U.S. household penetration do not yet satisfy the requirements of the Balanced Budget Act of 1997 in terms of shutting down NTSC, and that's not even considering their cariage of DTV (as would be required under the act).
- I live in a 17-story apartment building. It is higher than some buildings on either side, but it still does not have line of site to the WCBS-DT and WNYW-DT transmitting antennas. It is likely that an antenna on my building's roof, even on a tall mast, would not solve my DTV reception problems.
- As Professor William Schreiber has pointed out, in a survey he performed more than half of all U.S. TVs currently rely on antenna reception -- even many in cable households.
- As the Sinclair tests in Baltimore pointed out, there are DTV reception problems outdoors as well as indoors.
I am perfectly willing to be optimistic. Perhaps someday improvements to 8-VSB will solve all antenna-reception problems. Perhaps someday DTV must-carry regulations combined with increased cable-TV and/or satellite-service penetration will bring DTV to homes without need for antenna-reception improvements.
TODAY, this is not true.
TTFN,
Mark
Permission granted to publish this as long as the date is included.
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William Schreiber
Professor, MIT, Retired
July 17, 1999
Complexity: A COFDM decoder is no more complex than a VSB decoder, as clearly demonstrated by the hardware now available in Europe and the equipment used by Sinclair in its current demonstration. COFDM does require a Fourier transform, but its equalizer is much simpler than the one in VSB, and that, perhaps, is the reason the two have similar complexity.
There is no evidence that increasing the complexity of the VSB receiver would make it work any better. The VSB people have had 4 years to develop their
system.
As far as I know, there have been no tests that showed markedly superior performance by VSB when compared with a modern COFDM receiver. Robust (i.e., reception as easy as with NTSC on an indoor antenna) reception of DTV is an absolute necessity for a successful introduction of DTV in the US, in my opinion. As I have pointed out, more than half the NTSC receivers in the US use antennas.
If DTV receivers remain at $3000 for more than a year or so, DTV will fail in any event.
No doubt both types of receivers can and will be improved with additional development. It is also true that I cannot now give a bullet-proof theoretical showing that COFDM will always be better than VSB. However, having worked extensively with computer simulation of COFDM, and having seen how its performance depends on elements that have no parallel in VSB, I doubt very much that the two will ever be equal. VSB has no equivalent of the guard interval, by means of which intersymbol interference disappears. While it is true that equalization produces the same loss of SNR in both systems, in COFDM it is possible to ignore noisy carriers, taking advantage of the fact that some carriers have their SNR increased by the echoes. |
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