[opendtv] Re: Let the games begin

  • From: "Bob Miller" <robmxa@xxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Sun, 12 Nov 2006 17:36:07 -0500

On 11/11/06, Albert Manfredi <bert22306@xxxxxxxxxxx> wrote:
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.

I didn't spell it out but all the conversations I have been privey to
suggest that broadcasters would be using MPEG4 with any A-VSB robust
mode which makes all current receivers incompatible.

If you have all of 1.5 Mbps who is going to use MPEG2 with that? So
you can say that A-VSB is backward compatible with all current
receivers while in fact using it in an incompatible way. Which BTW is
how I think most of the spectrum will be used, incompatibly.

Bob Miller

>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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