[opendtv] Re: Let the games begin
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 13 Nov 2006 10:27:23 -0500
Craig Birkmaier wrote:
>> Well, then that's a completely different discussion, isn't
>> it. We were talking about the technical aspects of A-VSB,
>> not how some particular broadcasters might want to use it.
>
> No it's the same discussion Bert. It really does not matter
> what kind of decoders are in the legacy receiver, if it
> cannot understand the A-VSB bits.
>
> Any receiver designed to understand SRS and STS, can also
> be designed to use new codecs. But there is NOTHING you can
> do to take advantage of these new tools in legacy receivers.
There is also NOTHING you can do for legacy DVB-T receivers to take
advantage of DVB-H, or to take advantage of HDTV. And yet, no one would
argue that DVB-H and HDTV are incompatible with DVB-T. They are,
instead, compatible post-facto additions to the standard.
Exactly as A-VSB is to ATSC.
> From this perspective, those in Europe who want to invest
> in an HD capable display will have the option of buying a
> new STB that delivers multiple services. Or they can invest
> in portable and handheld devices that take advantage of
> other new services.
>
> Meanwhile here in the U.S., consumers will be able to invest
> in new receivers that may actually improve reception of DTV,
> including HDTV programming, however, this will come at a
> cost in quality to the programming that is staved for
> bandwidth like HDTV. Or they may be able to buy devices that
> will receive A-VSB broadcasts, that do not need HDTV image
> quality.
In Europe, in order to maintain compatibility with SDTV sets and not
reduce SD programming choices, HDTV is having to be transmitted on new
dedicated frequencies. Which in practice means that HDTV choices will be
more scarce. And in order to fit HDTV in the multiplexes, a reduction of
robustness is going to be required, as the HDTV multiplexes go to 64-QAM
vs the 16-QAM used for SD.
Over here, the HDTV choices are already available, but the more robust
options are not yet. So, opposite what Euro DTT is doing, the US model
started with HDTV and then adds the robust modes, potentially usable for
SD streams.
>> I'm saying, that 1.5 Mb/s, using let's say A-VSB in 1/4 rate
>> STS mode, does not in any way make the remaining 13 Mb/s less
>> robust or incompatible with all existing receivers. And, of
>> course, that is only the worst case example.
>
> No Bert, that's the BEST CASE example, or at least very close
> to it. We may learn that we can reduce the SRS overhead
> slightly, but it will clearly reduce the overall payload
> significantly.
STS 1/4 rate is "worst case" in the sense that it removes more legacy
8-VSB compatible bandwidth than any other A-VSB mode.
SRS, instead, can be tuned to whatever level of robustness you want. Add
one byte at a time of training sequence, if you want, until you achieve
the required robustness. And the remining payload remains compatible
with legacy receivers.
It is intellectually dishonest, there is no other word for it, to
pretend that A-VSB is incompatible with 8-VSB.
Bert
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