[opendtv] Re: Let the games begin
- From: "Albert Manfredi" <bert22306@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Sat, 11 Nov 2006 16:38:19 -0500
Bob Miller qrote:
Listen, lets get real. If any broadcaster was to seriously
consider using A-VSB what would they do with it?
Lets say they use it to simulcast their regular programming
in a robust mode so it is receivable for almost everyone.
Are they going to adhere to MPEG2 in this 1.5 Mbps
robust channel?
One use would be a Moviebeam-like service, which could use any compression
technique they wanted. And it wouldn't even have to be video info,
necessarily. Could be any ancillary service at even very low bit rates.
Another use could be a simulcast at lower bit rate when doing transmitter
maintenance, using a lower power secondary transmitter. John Shutt's idea.
New receivers in the market area could continue to receive the program even
in the fringe areas.
Other uses could be service to handheld appliances, which again would use
any compression algorithm they want, at this point, since it doesn't exist
yet, and a small fraction of the total 6 MHz. And the rest could be regular
8-VSB.
In the UK, Italy, and Germany (and I'm not certain about France for SD
service), in essence what they did was to transmit everything in their
equivalent of A-VSB, i.e. 16-QAM and 1.8 b/s/Hz spectral efficiency, to
support low power transmitters. And they also use more translators than we
do here, per area of coverage. (But in the UK, they want to go back to
64-QAM for HDTV. And in France, HDTV is also 64-QAM, but limited range due
to low power and no SFNs.)
I doubt it. I think we break company with compatibility right
there. Yes A-VSB is backward compatible in theory but not in
practice.
I don't know what you mean. For one thing, A-VSB allows any fraction of the
total 6 MHz to be transmitted as A-VSB. It's not all or nothing. For
another, in the SRS mode, any receiver can use the transmissions, even if
they don't benefit from the extra roubustness. So it is backward compatible
in that sense. Even in STS mode, as I showed you, you can mix that with
regular 8-VSB or with A-VSB in SRS mode.
If I were a broadcaster and resigned to live with 8-VSB and A-VSB I
would go full A-VSB with one SD MPEG2 program using minimal bits
and use the rest with MPEG4 all at 1/2.
You can play all sorts of games. In Europe, when HDTV comes in play, they
all want to crank up the b/s/Hz as much as possible. There is a lesson in
there somewhere.
It would seem that we should be doing our utmost to stop the
injection of more of these legacy receivers into the OTA
bloodstream instead of offering a subsidy for doing so.
I don't entirely disagree. But I still think that it's much more fun to see
robust receivers being developed that use the full 3.3 b/s/Hz than to use
the crutch of lower spectral efficiency.
What do you think the Chinese did to COFDM, by the way? By putting the
training sequence in what used to be the GI gap, and allowing use of turbo
codes, don't you think they did much the same thing to COFDM as A-VSB does
to 8-VSB? Sounds like a similar design mods to me.
Bert
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