[opendtv] Re: Letter to TV Technology
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Tue, 9 Oct 2007 16:08:21 -0400
John Shutt wrote:
> I believe that Bob's point was that Sinclair's petition to the
> FCC to permit COFDM did not ask the FCC to ban 8-VSB, and
> Sinclair offered to replace on a one-for-one basis DVB-T STBs
> for ATSC STBs for every viewer in their markets.
First of all, I wonder how long it will take for some to stop living in
the past.
The main problem with that idea is that the coverage is different for
the two schemes. Sinclair was happy to keep power levels down for COFDM,
so as not to change the FCC planning factors, but that would have meant
problems for those living in fringe areas.
As we saw, the planning factors for 8T-VSB do differ from what at least
one COFDM country uses, by more than just a couple of dB by the way. So
it's not like this is a complete non-issue. And also, I've now seen
first hand that the 15 dB C/N requirement for 8T-VSB is not some
theoretical number that doesn't really work. It's a real number,
measured many times in many venues.
What I don't understand is this. We have seen that the newest DTT scheme
out there, the Chinese scheme, has gone to a design that is half-way
between the COFDM approach and the single-carrier approach. The Chinese
system goes for equalizers and training sequences, much like 8T-VSB
does, to benefit from the lower C/N margin requirement. (The training
sequence is longer, and it uses a different convolutional FEC as well.)
So why are we still complaining like nothing changed for the past 9
years? Clearly, all of that is in the past and the world has moved
beyond. If the ATSC today should put out an RFP for a next gen 8T-VSB,
surely it would not be to go COFDM a la DVB-T today. Oh yeah, even DVB-T
is moving beyond.
As to using a new codec, even DVB-T is not madating AVC *except for* the
new, incompatible, HDTV streams. Countries like New Zealand have the
luxury of specifying AVC and HDTV from the start, because they are
starting years behind. And even New Zealand will face another transition
problem, as soon as DVB-T2 comes to pass. So they are not immune by any
means.
None of this is cause for monotonous complaints. It's just the way
things are.
Bert
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