[opendtv]
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Thu, 7 Jul 2005 16:59:56 -0400
John Shutt wrote:
> If the FCC adopts ATSC A/53C in it's entirety as law, as
> they have with A/53B, then yes, it can be enforced. Or
> at least amendment 1 paragraph 5.6.1 can be enforced:
>
> "Limits have been defined for the maximum bitrate in the
> Enhanced (E-VSB) service.
>
> "At all times, the quality of video in the main stream
> shall be equal to or better than the equivalent program
> in the Enhanced stream. In the event that the
> programming is different in the main and Enhanced streams,
> a higher resolution format is deemed to be higher quality.
>
> "Additionally, during premium programming times, the
> maximum bitrate in the enhanced (EVSB) stream shall be 3
> Mbps out of the total 19.4 Mbps channel capacity."
That text, IIRC all of it, was also there in the previous
candidate standard. It's logical, I think. EVSB is meant to
be a hierarchical modulation sort of service rather than a
complete replacement of the 19.3 Mb/s channel. And even
then, the ATSC seems to think it's okay to cut the capacity
down to 8.5 or 4.3 Mb/s total, off prime time.
The nice thing about E8-VSB is the way it permits very
narrow robust channels to be created, taking away as little
as possible from the wide stream capacity. It gives a lot
of granularity in that way. On the other hand, it does not
allow for fine tuning of the robustness of the whole 6 MHz
band. That could have been done by directly changing the
FEC used in the band, but such a scheme would not have been
backward compatible. EVSB had to be layered over the 8-VSB,
2/3 trellis, and RS[208,188] FEC that was already there.
Anyway, it's still IMO well suited to the task you
suggested. But here too, some field trials would be nice.
Bert
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