[opendtv] Re: Let the games begin
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Fri, 10 Nov 2006 15:30:14 -0500
Craig Birkmaier wrote:
>> Let's compare. You can transmit 4.5 Mb/s over normal 8-VSB
>> with 15 dB of C/N margin, and send along HDTV or a couple
>> or three of SDTV channels to boot, not just one NTSC.
>
> Really? Can you provide the parameters to do this? By my
> calculations, you would use the entire 6 MHz channel to send
> 4.5 Mbps of robust data - and that would leave ZERO room for
> SDTV or HDTV.
Of course I can.
Okay, to play it safe, a Moviebeam service on plain old 8-VSB might only
give people permission to join if they can measure, say, 17 to 20 dB of
margin at a minimum. That is probably more comparable to the 40 dB they
are now requiring for NSTC Dotcast. And, of course, this service can
afford to contract LG or Samsung for "proper" 5th gen boxes. The good
ones.
Done. Craig. That gives you 19.39 - 4.5 = 14.89 Mb/s left over for HDTV
or multicast SDTV, or even one HDTV and one SDTV channel.
> In the example used in the paper I referenced, the high
> quality 8-VSB payload is reduced by ~4.5 Mbps to accommodate
> SRS and ONE 1.5 Mbps robust channel.
The most robust A-VSB service layers a 1/4 rate turbo code over the
existing 2/3 rate Viterbi, which means that a *very* robust 1.5 Mb/s
still leaves:
19.39 - (1.5 * 4) = 13.39 Mb/s of normal 8-VSB, for a few SD multicasts.
Or, in a pinch, even 720 at 24p HDTV.
This would apply to a Moviebeam service that wanted access to
subscribers way outside of any HDTV reception range. So a completely
different scenario from the limited Dotcast situation.
> You get on a slippery slope real quick trying to compare
> these standards.
Not really. The only real difference is that COFDM figured out all these
alternate modes ahead of time, while 8-VSB is doing it after the fact.
But after all is said and done, both would end up being flexible in
similar ways.
To someone who just crawled out of a cave after 25 years, they will just
look like two different ways of doing pretty much the same things.
Bert
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