[opendtv] Re: France goes DTV
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: "OpenDTV (E-mail)" <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 7 Feb 2005 18:50:35 -0500
Bob Miller wrote:
[XM Radio and Sirius]
> > But you don't see those systems using COFDM for their
> > long range coverage. Just for the local gap fillers.
>
> Just for the local gap fillers? Which cover 95% of
> their customers 99% of the time.
No.
Just the local gap fillers. Meaning in urban downtown
canyon areas, tunnels, under bridges, etc.
> > From the perspective of a transmitter wanting to
> > operate as close as possible to saturation, e.g. in
> >a satellite, 16-QAM is no different from 4-VSB.
>
> Weirdness! COFDM can use 16-QAM, 64-QAM or QPSK that
> does not mean that COFDM is not different than those.
Of course it's different. COFDM is multicarrier, has
multiple unsuppressed carriers, has guard intervals.
If you don't comprehend the difference between n-QAM
and COFDM, then you might as well lump n-VSB in there
with the rest of them. They're all variations on
similar concepts, when all is said and done.
> 16-QAM is different from 4-VSB.
In terms of spectral efficiency and quantity of
amplitude levels used (which matters to satellite
transmitters), they are identical. They differ in
the bits carried per symbol and the symbol rate,
but it all comes out in the wash.
I was trying to get across the idea that what
XM Radio and Sirius use for the bulk of their
coverage areas is far more n-VSB-like than it is
COFDM-like.
> Well the latest Chinese test say that COFDM has
> a 2.5 db advantage in power so if true there
> goes your "long range".
What I saw was 15 dB of C/N required for DMB-T,
which is identical to 8-VSB. Possibly, if you
had the details, you could explain what those
numbers actually represented. E.g., specific
scenarios, modes of COFDM or DMB-T used, and
what specific 8-VSB receiver was being used. What
you provided was simply not enough info.
> I wish I could convey the derisive dismissive
> tone on the phone that 8-VSB is treated
Everybody has his pet system. Problem is, too
many people have a vested interest in *not*
telling the whole story, and too many others
simply prefer to evangelise rather than
understand what's going on.
Bert
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