[opendtv] Re: Let the games begin

  • From: "Bob Miller" <robmxa@xxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Mon, 13 Nov 2006 15:30:35 -0500

On 11/13/06, Manfredi, Albert E <albert.e.manfredi@xxxxxxxxxx> wrote:
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.


Who cares what can or cannot be done with DVB-T receivers. We are
talking about legacy 8-VSB receivers and whether it would be a good
idea to consider changing the US modulation and codec.

The one argument against doing so is the presence of legacy receivers.
These legacy receivers must be protected against obsolescence at all
cost was/is the mantra of 8-VSB supporters and even those who
belatedly agreed that other modulations were better but that because
of the LEGACY RECEIVER issue nothing could be done about it. We had to
stay the course no matter what the cost in bandwidth or how many
people would be disenfranchised from their OTA broadcast spectrum.

So in that light if you change or add to 8-VSB in some way to make it
better and that way also would seem to demand and allow for another
codec which IF USED would have the affect of making all legacy
receivers 909% obsolete then you open the issue of changing our
modulation and codec back up.

The question is then if legacy receivers will be made obsolete by the
use of MPEG4 AVC and A-VSB then why not look at all modulations which
would do the same thing. Maybe there is a better modulation.

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.

With the Chinese VSB we know that all legacy receivers would be made
obsolete but that all new receivers would work much better both mobile
and fixed. And of course if you consider the Chinese VSB solution you
might as well consider their DVB-TH also.

To go down the A-VSB road is not intellectually honest in my opinion.
It may however be politically correct in that we know that the powers
that be are too ignorant and to hear the truth to discombobulating.

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.

Bob Miller

> 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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