[opendtv] Re: 20050627 Mark's Monday Memo
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 6 Jul 2005 18:03:02 -0400
Dale Kelly wrote:
> I seem to recall that the E8-VSB improvement is not
> backward compatible, (though it will not harm normal
> EVSB DTV reception in older receiver) and it was
> approved by ATSC to be used as a "fall back" audio
> service*. I believe that only Zenith's newest 5G product
> supports this service. Am I wrong?
I agree with the above, although I didn't know that the
ATSC only approved E8-VSB it for audio. (But that would
also be just a pen and ink change to fix.)
> An advantage of COFDM is that the more robust modes are
> compatible in *all* receivers.
>
> *Note: I doubt that this is restriction enforceable.
In principle, yes. In practice, who knows.
But this isn't a huge problem either. As long as there is
a large number of receivers out there sans E8-VSB, all a
station would have to do is transmit two dumbed-down
streams when they are servicing the main antenna. Those
lucky enough to have E8-VSB capability would more easily
ride through the weak signal period.
John S already said that 2.5 Mb/s was acceptable for
SDTV. So let's take a worst-case scenario. Assume Wayne
Bretl meant that the 1/4 rate E8-VSB provided the
extra 6 dB of margin. Send an SDTV stream of, say, 2.6
Mb/s over that 1/4 rate channel, and you're left with 7.2
Mb/s for the wide stream. This would allow the legacy
receivers to keep working as long as they're not too far
away, and the new receivers would have a choice of
quasi-HD if they're within range of the backup antenna,
or the robust channel if they're too far away.
If the 1/2 rate E8-VSB is deemed robust enough, you get
even better service.
Bert
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