[opendtv] Re: Backward Compatibility of Robust DTV Transmissions
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Tue, 7 Nov 2006 18:27:26 -0500
John Shutt wrote:
>> Hmmm. Since blind equalization works best with a strong
>> signal, why wouldn't it help these legacy receivers if the
>> 8-VSB transmissions included some variable number of "bogus"
>> segments, each of which is, for example, always modulated at
>> 100 percent (i.e. all large amplitude symbols)?
>
> Because if you did this, then you would be eating into the
> precious 19.4 Mbps payload of ATSC.
That was a given. I mentioned that at the end. There is no free lunch.
However, the amount of reduction in spectral efficiency is in principle
adjustable.
> Also, you'd violate the data interleaver which worked so
> diligently to make sure that there was equal energy in each
> symbol,
No, I think you'd create a less flat spectrum, but that's the
*randomizer's* function you'd be messing with, not the interleaver. The
interleaver is used to overcome impulse noise, and these bogus 8-VSB
segments would not have to worry about that. They wouldn't carry real
data, so nothing they have would ever reach the MPEG decoder.
Maybe a segment here, a segment there would not overly unflatten the
spectrum.
> But the Samsung does play tricks with the interleaver so that
> a recurring pattern of symbols occurs periodically, and these
> are the pseudo-training signals used by the A-VSB receiver.
http://www.tvtechnology.com/features/On-RF/2006.06.14-f_Doug_Lung.shtml
That's A-VSB, which does not provide added robustness for legacy
receivers. So it's out of scope of your original question. But that's a
cool column. Shows a lot of people working to make things better.
Bert
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