[opendtv] Re: Spectrum Repacking Looms for TV Broadcasters
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: "opendtv@xxxxxxxxxxxxx" <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 31 Mar 2010 15:14:09 -0500
Craig Birkmaier wrote:
> "Why would it not work with our ATSC signal?"
>
> Because the ATSC system was never designed to deal with SFNs.
Nor was COFDM!!
COFDM was designed to deal effectively against multipath distortion, just like
CDMA, but not for SFNs. SFNs were a "hey, look at this cool trick we can try"
afterthought. And as it turns out, 8K COFDM is not that good at it. And 2K
COFDM is very bad at it.
Why? Because the GIs you need for practical, cost-effective SFNs create the
need for a very dense mesh, or you have to eat into the spectral afficiency a
lot (like, 1/4 GI for 8K).
> We chose poorly!
I think we certainly would have chosen poorly if DVB-T2 had existed. And I also
think that most people don't think the SFN mantra through, when it comes to the
US TV broadcast model. Suddenly, SFNs are an absolute must-have, even though
they don't do much at all the way TV is set up in the US.
Bert
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