[opendtv] Re: Let the games begin

  • From: "Albert Manfredi" <bert22306@xxxxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Tue, 14 Nov 2006 21:24:25 -0500

Craig Birkmaier wrote:

You COULD say that this is similar to DVB, however, with DVB additional
training signals are not needed, and you DO CHANGE the modulation
parameters to deal with robustness, but these configuration changes
are fully compatible with legacy receivers.

I agree that in DVB-T, the additional robust modes had already been pre-ordained, and that is a big advantage. Also there is still an advantage to multicarrier schemes: they are more adept at surviving deep and narrow nulls. But a diversity antenna is very successful at solving that particular problem for single carrier schemes, luckily.

Other than that, it fundamentally comes out to the same thing. The Chinese seem to think so too, by going to fancy training sequences *with COFDM*, instead of relying on the guard interval. You say that DVB-T doesn't "need" the fancier training sequences, but in fact they have hundreds of training sequences in their hundreds of active carriers (8K), and DVB-T uses other bandwidth-robbing techniques such as the empty GI, which empty space 8-VSB does not rely on. So really, no big diff once the scheme is in place.

So I think the big difference is that in DVB-T, the more robust modes were already there. If you really want to know how the schemes compare, just check how far you are from the Shannon limit in each mode. That's the bottom line.

What the Shannon equation tells us is that changing modulation or changing error correction are means to same end. Shannon doesn't mandate anything about either technique.


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