One other little problem with legacy receivers and the future/present needs of the US DTV spectum. Doug Lung in "China's new DTV Standard and DOCRs" brings up the troubling need for DOCRs. He thinks they are required for a successful OTA HDTV future. http://www.tvtechnology.com/pages/s.0001/t.456.html And then he mentions that "Engineering these systems to reduce interference to older DTV receivers, however, will not be easy." How about receivers that are being installed in all TV sets today? Are they designed to work with DOCRs? The more we stay the course the more ridiculous the idea of protecting legacy receivers becomes. But as soon as we cut them loose it then makes sense to upgrade to the latest modulation and codec. Bob Miller On 11/13/06, Bob Miller <robmxa@xxxxxxxxx> wrote:
On 11/13/06, Manfredi, Albert E <albert.e.manfredi@xxxxxxxxxx> wrote: > Bob Miller wrote: > > > There is no argument in Europe over their modulation. Only > > discussion over how to get from SD to HD. The UK will > > upgrade from their 2K to 8K and most of their receivers > > are ready for that. > > I think you are missing what has to happen in the UK. > > Yes, the newer receivers should have no trouble going from 2K to 8K, the > older ones will go dark. > > But why the move to 8K? 8K does not add spectral efficiency by itself. > > The move to 8K is to tolerate more echo range. And the reason they need > to tolerate more echo range is to install SFNs. And the reason they need > to install SFNs is that they need to migrate from 16-QAM to 64-QAM to > support the HD bit rate, and don't want to go to high power big sticks > in doing so. They want to use low power big sticks instead. > > So the move to HDTV is not so simple. And, besides that, they still need > to broadcast the SD simulcasts, assuming they want shows to be available > to SD and HD viewers alike, as we do here. > > > For example the VSB modulation that the Chinese will not > > use is only another step up the ladder from A-VSB. The > > difference is that with A-VSB we have the argument that it > > could be used in such away that all legacy receivers could > > theoretically receive all broadcast while we know that in > > reality it will be used in such a way as to make all > > legacy receivers obsolete. > > The Chinese VSB scheme is probably better at high spectral efficiency > settings than 8-VSB, although proper LG prototype-like receivers are > apparently very good anyway. And could be made better, e.g. by doing the > Viterbi and Reed Solomon FEC differently and by improving the way > training is done. But I doubt the Chinese system is any better at the > very robust modes than A-VSB. When you get close to the Shannon limit, > as A-VSB does with diversity antenna, the message is that you can't do a > whole lot better. > > Why this apparent need to consider A-VSB to be a pointless kludge? > > Bert If we are saying that in the US broadcasters will enthusiastically embrace and use A-VSB with MPEG2 then maybe it is not a pointless kludge, just a pointless and inefficient one. If, as i suspect however, broadcasters would only embrace A-VSB if they plan on using it with all the bandwidth and with MPEG4 for all but the required SD MPEG2 program then it is indeed an unnecessary kludge and still inefficient. And at that point, the point where all legacy receivers are for all intents and purposes made obsolete, it would make all the sense in the world to consider changing to a better modulation and codec. Or you could argue that even if all broadcasters only sent the required one SD program in MPEG2 that that alone would justify staying the course with 8-VSB/A-VSB forever. Forever is a long time. The way we do things in this country the next correct time to chance modulations and codecs will be the day that 87% of the public has legacy receivers a percentage of which can benefit from A-VSB. We have to wait for that moment to screw the most people the most. More likely is that most of us will continue to pay little to no attention to OTA. Everyone will have a receiver in their big DTV sets and the fact that you can actually possibly receive something with it will be a trivia question on Jeopardy. One which any one under 30 won't get. Bob Miller
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