[opendtv] Re: PR: Enhanced AC-3 Audio Specifications Serve Multiple Applications

  • From: "John Shutt" <shuttj@xxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Fri, 9 Apr 2004 08:46:57 -0400

Bert,

I specifically and for a very good reason said "demonstrated at the 2000
NAB."

The LP (high capacity) stream was received on the convention floor using a
Radio Shack double bow tie set top antenna, albeit carefully aimed, while
the Nokia Mediascreen toured every nook and cranny in the Greater Las Vegas
Area to receive the HP (robust) stream. (There was some controversy about
passive repeaters in the convention hall or active repeaters in the DVB
booth, but I think those were proved false.)  No 8-VSB was receivable on the
convention floor at all.

Implementations of DVB-T in Great Britain are at much lower ERPs than are
allocated here, thus the difference in performance.  Also, Great Britain has
not yet attempted to use HM modulation at all.  Their Freeview deployment of
DVB, like the onDigital network it is built upon, calls for a broadcast
model where the collective bits of several broadcast channels are used in
aggregate to deliver a multi-channel service, so HM is less attractive in
that situation.

It is perfectly acceptable to have a fragile LP stream targeted at huge
immovable HDTV screens, and a second stream targeted at portable and mobile
use.  What I find more and more every day with practical ATSC reception of
our own station, is that it is not so great to have one system that is fixed
for one application and has no flexibility at all.  And I am perfectly aware
that the original ATSC standard was specifically designed to deliver the
maximum number of bits to a fixed outdoor antenna, and it fulfilled it's
design criteria.

It was just the wrong criteria.

Cheers,

John Shutt

----- Original Message ----- 
From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>

> The European implementations of non-HM DVB-T have not been
> able to use such high spectral efficiency effectively. And
> worse, this combination is even less robust than it would
> appear, when it is transmitted in an HM channel. It requires
> a theoretical 24.5 dB of C/N for successful decoding in
> Rayleigh fading, and 21 dB in a Gaussian channel.

 
 
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