[opendtv] Re: China writes its own digital TV standard
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 5 Jul 2006 10:27:47 -0400
John Shutt wrote:
> The ATSC has codified E-VSB in it's specifications, but
> the FCC has yet to adopt those specifications into the
> rules.
>
> FWIW, all Zenith VSB demodulator chips and receivers
> ever sold have the ability to receive and decode 16-VSB,
> 4T-VSB, and 2T-VSB in addition to the usual 8T-VSB.
>
> That is not the same as E-VSB or A-VSB, but 4T and 2T
> was once suggested by Zenith as alternate transmission
> modes that lowered the C/N requirements even more, but
> were never adopted by the ATSC. AFAIK LG/Zenith chipsets
> still contain these legacy modulation modes.
Very interesting. I knew that Zenith had proposed the simpler
constellations, but I didn't know they were supporting them. Annex D
Section 5.5.2.3 of A/53E shows a lot of "reserved" settings for the 24
bits assigned to VSB Mode in the training segment, and that's probably
what they were meant to be used for. (Only 8T-VSB and 16-VSB are used,
although the document says 8-VSB rather than 8T-VSB.)
But the holy grail is the Shannon limit. The closer you get to that,
IMO, the more interesting it is. 2T-VSB or 4T-VSB, with no improvement
in training or FEC, doesn't get you any closer to the Shannon limit. So
I'm all for a more interesting approach (but not the endless wait!).
Bert
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