[opendtv] Re: Let the games begin

  • From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Wed, 8 Nov 2006 13:03:52 -0500

Tom Barry wrote:

> It appears that after FEC overhead in order to get mobile or good
> multi path reception it would only have 4-5 mbps of payload. Did I
> understand that correctly? If so then it obviously doesn't do
> anything for HDTV reception since with MPEG-2 that is certainly
> not enough for HD.

You are looking at the turbo coding option, with 1/2 or 1/4 rate, which
is by far the most onerous. It seems to me that you can use the SRS
option to achieve good training in rapidly shifting echo, and still have
plenty of good HDTV space available. And backward compatibility.

> But I guess A-VSB is really only for mobile.

I don't see that in the presentation. It's also for fixed reception.

> Can anybody say what throughput can be expected for mobile
> reception on a 6 mhz channels using the various DVB or OFDM
> options? Is A-VSB competitive here?

I see it as a more adjustable form of HM than COFDM offers. Meaning, the
robust channel can be tuned to much lower bit rates than 4.5 Mb/s,
leaving more room for HDTV, and the robust channel can also provide for
very competitive C/N margins compared with COFDM.

Look at the numbers. A 1/4 rate turbo-coded channel (but still using
8-VSB symbols), with single antenna, gives you 4.5 dB of C/N. This is
similar to HM COFDM, QPSK in otherwise 16-QAM. But it's better than HM
QPSK in 64-QAM. And with diversity antennas, you're down to the 1.7 dB
C/N, but I don't have the COFDM numbers to compare that to. Overall, I'd
say competitive, and that's what makes it interesting.

---- quote -----
---- /quote ---

> Is Raleigh channel performance something we need in gen-x receivers
> to handle dynamic multi path properly?

That and more. Rayleigh means that there is no dominant path. An example
is Brazil E. I thought that 5th gen receivers were actually okay in this
department. In any event, using the SRS technique should certainly help
here, and that's fully backward compatible.

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