[opendtv] Re: PR: Enhanced AC-3 Audio Specifications Serve Multiple Applications
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Thu, 8 Apr 2004 17:04:06 -0400
John Shutt:
> I also equate E-VSB to DVB-T HM, but in concept only. ATSC=20
> takes a bigger
> hit in the high capacity bitstream to provide the robust=20
> stream than DVB-T
> HM does.
>=20
> For every Mbps of robust in ATSC, you subtract 2 Mbps from=20
> the standard
> stream. So for 4 Mbps of robust ATSC you get 11 Mbps of=20
> standard stream.
>=20
> For DVB-T, the mode that was demonstrated in Las Vegas=20
> (almost exactly) 4
> years ago at NAB 2000 had 13.6 Mbps in the LP stream and 4.5=20
> Mbps in the HP
> stream.
Except that I wouldn't put too fine a point on these
differences. If you want to do HM in a 6 MHz channel, with
~13 Mb/s in the LP channel, you need to use 64-QAM, 3/4 FEC,
and 1/16 GI in the LP channel.
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.
So in practice, to allow at least some indoor reception of
the LP channel in real installations, you'd want to tune
down the LP parameters. I doubt you'll do much better
either way.
Bert
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