[opendtv] Re: U.S. mobile TV spec in the works
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 11 Apr 2007 11:21:23 -0400
John Shutt wrote:
> 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.
Everything is a matter of degree. The same can be said for COFDM at
64-QAM. It too can be received by mobile devices, within certain limits.
Does that mean you don't need the other constellations or DVB-H? But
certainly, I would agree that you make do with standard 8-VSB as much as
you can, including by adding a diversity antenna. And it looks like
newer receivers, including the rumored 6th gen, are getting better.
> Remember, E-VSB did little or nothing to deal with dynamic
> echoes, hence Samsung's A-VSB and their "pseudo-training"
> sequences.
I just don't think this is so hard to do. I'm glad Al responded with
some of his ideas, and I think there are many other ways of achieving
better training and consequently better symbol sync, once you've
accepted that you can allocate some of the bandwidth for this purpose.
I already described the possibility of using turbo coding for the data
streams. How about adding a sync segment that only the new portable
receivers would use? This could follow immediately after the existing
one, to allow for some 1023-symbol sequence that Al, Doug, and CB have
suggested, or one or more new sync segments could be added elsewhere in
the 313-segment frame. And, of course, these additional segments could
also be used for time slicing.
All of these options could retain backward compatibility with existing
receivers for all the data streams, possibly with the only penalty being
the b/s capacity of the 6 MHz channel. And they can be added by the
pound. Meaning, you can create many levels of additional robustness.
Bert
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