[opendtv] Re: (No Date: Tue, 28 Sep 2004 10:30:37 -0400

  • From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
  • To: "OpenDTV (E-mail)" <opendtv@xxxxxxxxxxxxx>
  • Date: Fri, 8 Oct 2004 20:21:24 -0400

Bob Miller wrote:

> If Germany and the UK chose a lower data rate for
> a more robust reception fine. They can with COFDM.
> But they could have chosen a higher data rate with
> COFDM than the 19.34 Mbps of 8-VSB and still be more
> robust than 8-VSB as was demonstrated in Congress in
> 2000

I see I didn't address this particular comment directly
as it deserves to be (or maybe not).

At the ~19 Mb/s level, in 6 MHz, and with the severe
Brazil E profile, the new 8-VSB receivers were capable
of solid reception with 25 dB of C/N (actually 24.8 dB
for the Linx receiver, and I didn't see anything as
precisely stated for the LG). To respond to Mark
Aitken's concern, yes, this includes symbol sync. Not
just tracking a signal, but reaquiring.

According to ETSI EN 300 744, the Rayleigh fading
performance of COFDM at this bit rate is 21.7 dB of
C/N. But the Rayleigh profile in that document isn't
Brazil E. The CRC testing reported in 2003 claimed
that at the time of the test, the COFDM receiver
managed to receive two 0 dB signals (one 0 dB echo)
with 31 dB of C/N. And this is not Brazil E either.
I would expect that COFDM receiver to be of 2002
vintage.

Going just on this information alone, therefore,
one has to conclude that what you saw in 2000 is
irrelevant to this discussion. But more to the
point, it leaves open the question of how these
systems compare today. It's entirely possible,
even likely, that today 8-VSB beats COFDM in certain
indoor scenarios, and doubtless vice versa, at the
~19 Mb/s level in 6 MHz (3.3 b/s/Hz).

I'd guess that COFDMS will beat any of these new
ATSC receivers with dynamic echo, e.g. people
walking around smartly especially in the signal path,
but it's very possible that 8-VSB beats COFDM where
the signal is weak and dynamic echo not too severe.
It's an intriguing question which you dismiss in
a most unconvincing manner.

So yes, you can tune COFDM for even higher spectral
efficiency, but you'll make it more vulnerable than
8-VSB if you do this. I don't see where E8-VSB
would allow for more spectral efficiency, because
it looks like the 2/3 trellis is the weakest one
permitted. You'd have to either go to 16-VSB and
fuss with adding trellis coding, or you'd have to
allow for something like 3/4 or 5/6 rate trellis,
to get anything better than 19.39 Mb/s for a
terrestrial n-VSB system. Where we are today,
that would make no sense at all.

Bert
 
 
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