[opendtv] Re: New Thread: What becomes of Legacy Analog Equipment

  • From: "Bob Miller" <robmxa@xxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Wed, 28 Nov 2007 11:50:29 -0500

Do what you will with receivers. You can't make legacy recievers work with
MPEG4 and when you come to the point that you want to dump all current
receivers to implement a better codec it only makes sense to switch to the
best modulation also.

If that is a super duper 8-VSB no problem.

At the moment broadcasters are contemplating going with a mobile variant of
8-VSB that could use most of the 6 MHz channel and I would think they would
use MPEG4. While technically and legally OK it is not in the spirit of
maintaining compatibility with legacy receivers. That spirit which was used
to derail allowing a COFDM based modulation 8 years ago when there were very
few legacy receivers to cry about. If it was true then it is far more true
today.

If broadcasters actually get to the point of using something like AVSB with
most of their 6 MHz channel I think they may be the first to say this is
crazy and suggest starting over.

At that point there will be few early adopters still using OTA 8-VSB since
they only can get one SD channel on it and they will have all migrated to
cable or satellite. We will be down to the non voting poor demographic lot
relying on OTA, maybe ONE% or so, who no one thought about in this
transition so far anyway. With out the vocal early adopters and with
possible a new and large mobile TV voting population with good demographics
who are happy with mobile offering from others, it might be easy for
broadcasters to suggest a switch in modulation and codec.

And maybe well before 2012. Maybe in 2010.

Bob Miller


On Nov 28, 2007 11:00 AM, Manfredi, Albert E <albert.e.manfredi@xxxxxxxxxx>
wrote:

> Tom Barry wrote:
>
> > Are we now assuming ATSC STB's or TV's will work indoors in urban
> > canyons? I didn't know that was really proven yet with off the
> > shelf equipment.
>
> We know there is nothing in physics that prevents this. We know that
> it's doable now in more or less easy fashion, most likely depending on
> the quality of the tuner (i.e. independent of the specific modulation
> scheme), using current state of the art demod.
>
> 8T-VSB today, in its basic wide mode, is about as far from the Shannon
> limit as DVB-T2 wants to be. But 8T-VSB even today is not there as
> reliably as DVB-T is in its current form is. Echo tolerance, and in
> particular leading echo tolerance, is not as good as that of COFDM at
> the same spectral efficiency setting.
>
> So it's a mixed bag, but one that continued development of receivers,
> without having to change the transmission standard, can address. Not a
> bad place to be, really.
>
> Eventually, perhaps, 8T-VSB may get to the point where the 2/3 fixed
> convolutional FEC becomes a limiting factor. That's where receivers are
> good enough that we could move to maybe 3/4 FEC, and get better than 3.3
> b/s/Hz of spectral efficiency reliably. That would require a change to
> the transmission standard, so it's as difficult to do as DVB-T2 is.
> We're not there yet with 8T-VSB, but it could happen. For now,
> concentrating on receivers makes sense.
>
> Bert
>
>
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