[opendtv] Re: U.S. mobile TV spec in the works
- From: "Allen Le Roy Limberg" <allimberg@xxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 11 Apr 2007 09:27:45 -0400
Robust transmission schemes that are backward compatible in the sense that
they include a component that can be usefully received by legacy DTV
receivers are certainly possible. At various times I have proposed three
such systems myself.
One system used two-dimensional Reed-Solomon coding with the conventional
lateral R-S coding being augmented by transverse R-S coding sent in data
segments interspersed with those of ordinary 8VSB. Decoding would use
cross-interleaved R-S decoding. This is similar to CIRC used in disks.
Another system (12, 8) linear-block-codes ordinary 8VSB bytes with the
parity bits being transmitted in data segments interspersed with those of
ordinary 8VSB. The linear block coding corrects isolated bit errors and
locates byte errors for the Reed-Solomon coding, so its correction
capabilities are doubled. Code rate is 2/3 that of ordinary 8VSB.
Classical turbo coding of the Z-sub-1 and Z-sub-2 bits of ordinary 8VSB has
a code rate 1/3 that of ordinary 8VSB and is usefully received by legacy DTV
receivers.
The hard fact is that over-the-air broadcasters have not banded together to
fund research and development of robust transmission schemes by an R&D lab
like Lucent, but instead have expected consumer electronics manufacturers to
do this. There are more promising businesses for consumer electronics
manufacturers to invest in.
If ATSC was serious about developing a robust transmission scheme, it would
have developed a set of technical specifications and guaranteed acceptance
of any proposed standard that met those specifications and did not disrupt
too many legacy DTV receivers. As it is, those in the DTV industry that do
not desire to see a successful robust transmission adopted have the power to
block any useful proposal.
Al Limberg
----- Original Message -----
From: "John Shutt" <shuttj@xxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Tuesday, April 10, 2007 6:40 PM
Subject: [opendtv] Re: U.S. mobile TV spec in the works
> Bert,
>
> Now I understand what you meant by "backwards compatible." Interesting
> idea, but I guess I don't have enough imagination to envision a scheme
other
> than retransmission of redundant data that could do what you propose.
>
> I mean, if a mobile device could decode the same stream that legacy
decoders
> could, there wouldn't be a need for a more robust coding or modulation
> scheme. And if the mobile devices couldn't decode the legacy stream, then
> whatever "enhancements" aimed at mobile devices would be a de facto
> simulcast of the data, would it not?
>
> It has been my experience that there is a very narrow window where you can
> recover only some of the 8VSB data that might be improved with redundant
> data. Usually either you can demod and decode the entire bitstream, or
you
> get nothing. That cliff edge thing. At least that's what I've seen
playing
> around with a portable antenna and a bitstream analyzer. Redundant data
is
> useless if you can't recover the transport stream.
>
> It would seem simpler to me to just have a regular stream aimed at fixed
> displays, and a robust stream in an enhanced modulation scheme with lower
> resolution video suitable to portable and mobile devices, simulcast in the
> same channel.
>
> Remember, E-VSB did little or nothing to deal with dynamic echoes, hence
> Samsung's A-VSB and their "pseudo-training" sequences.
>
> John
>
> ----- Original Message -----
> From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
>
> > Another is where the robust stream is decodable by all receivers, even
> > if legacy receivers don't benefit from any extra robustness. That is
> > what I would describe as "backward compatible."
>
>
>
>
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