[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

> 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

> 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.


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.

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