[opendtv] Re: ITV calling for temporary spectrum for transition to HDTV

  • From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Mon, 28 May 2007 19:17:15 -0400

Craig Birkmaier wrote:

>> The multiplexes they have now are good for 15.6 Mb/s or so.
>> If they go to 64-QAM, they will be able to increase that to
>> 22 Mb/s, assuming they want to go with the SFN idea (still
>> 2/3 FEC, but reducing the GI to 1/8).
>
> These numbers are not correct. The 16QAM multiplexes deliver
> 18 Mbps and the 64QAM multiplexes deliver 24 Mbps:

Possibly for 16-QAM, if the existing 16-QAM multiplexes use only a 1/32
GI, and 3/4 FEC. This could indeed be how these 16-QAM multiplexes are
set up in the UK.

But clearly not for 64-QAM, *if* they intend to use SFNs. The 24.13 Mb/s
is only available with /32 GI, when 2/3 code FEC is used. It would be
very hard to deploy SFNs with only a 1/32 GI. The towers would have to
be no more than about 4 miles apart all told. When SFNs are deployed in
other countries, the GI is increased to 1/8. With the FEC set to 2/3, as
it is for 64-QAM in Freeview, a GI of 1/8 results in 22.12 Mb/s.

This site:

http://www.ukfree.tv/fullstory.php?storyid=1107051058

explicitly mentions the FEC code used in each mode. It does not mention
going to SFNs for 64-QAM. So that's the missing piece.

> These numbers will increase when the system converts to 8K
> carriers and higher power levels.

Says who?

> You can be certain that everything will convert to H.264.

That's the second migration I was talking about. All existing receivers
would need to be replaced to provide HDTV over Freeview without adding
spectrum.

Bert
 
 
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