[opendtv] Re: FCC Gives Official Nod to DTS

  • From: Albert Manfredi <albert.e.manfredi@xxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Sat, 6 Dec 2008 17:29:52 -0500

John Shutt wrote:
> Very nice explanation, but you barely scratched the
> surface of dynamic echo, which is still the Achilles'
> Heal of ATSC, and why ATSC needs M/H to perform
> decently in a mobile environment. DVB-T on the other
> hand, deals with dynamic echo in exactly the same way
> it deals with static echo, therefore as long as the
> guard interval and FEC is sufficient, it just works.
True enough.
On the other hand, don't forget that there's more that can be done with ATSC 
"as is," before saying that you absolutely must have M/H to fix a particular 
As far as I'm concerned, when you're trying to make something that you're 
handed over work better, the way to tackle the problem effectively is to make 
the best use of its own assets. What you're given with 8T-VSB is a scheme of 
frequent, short duration symbols, well scrambled to look random. So capitalize 
on that aspect, instead of crying about it.
As Doug has explained in the past, one way to tackle dynamic echo is to exploit 
the fact that the ATSC spectrum very soon appears flat as a pancake. A receiver 
that adjusts its equalizer based on that flatness, over very short time 
intervals possible with 8-VSB, and also uses the periodic, well-known symbol 
patterns to set absolute levels, should do very, very well in terms of dynamic 
echo tolerance. Even without the additional training offered by M/H.
I wouldn't expect such a scheme to be in all respects better than M/H, 
obviously, but it could match regular DVB-T, at 64-QAM, and it wouldn't have to 
trade away any spectral efficiency at all. And it would be compatible with 
existing transmitted 8T-VSB.
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