[opendtv] Re: Opinion: Mobile TV's New Free Market Economy
- From: Mark Aitken <maitken@xxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Sat, 21 Mar 2009 09:33:08 -0400 (EDT)
C/N margin is but one (1) of the requirements to receive a signal...many other
'factors' determine an ability to provide service...and many of THOSE are NOT
technical.
It is not always the best technology that wins...
Mark
the Mark who knows that just 'good enough' is sometimes what we end up with
----- Original Message -----
From: "Albert E Manfredi" <albert.e.manfredi@xxxxxxxxxx>
To: opendtv@xxxxxxxxxxxxx
Sent: Friday, March 20, 2009 4:43:25 PM (GMT-0500) America/New_York
Subject: [opendtv] Re: Opinion: Mobile TV's New Free Market Economy
Tom Barry wrote:
> I do not have access to DVB/COFDM to test. Do you now
> believe that you can get equivalent after-FEC throughput
> (spectral efficiency) with 8vsb using non-directional
> antennas at the same power and spectrum width?
With 8T-VSB set up as it is in A/53, we get 3.23 b/s/Hz (calculated as
described below). That is better than just about all deployed DVB-T
setups, in some cases by just a tad.
The most spectrally efficient COFDM used in DVB-T that I know of would
be the French 64-QAM, 2/3 FEC, 1/32 GI mode, which offers 24.13 Mb/s. To
be completely fair about expressing this in b/s/Hz, I'll use the total
channel bandwidth, not the actual bandwidth used by the signal. Which
will favor COFDM in 8K mode, because it's shoulders are steeper than
those of 8-VSB, meaning it can fill in more of the 8 MHz channel than
8-VSB can fill of its 6 MHz channel.
So in 8 MHz of RF bandwidth, 24.13 Mb/s comes out to 3.02 b/s/Hz. In
that mode, the C/N margin required in a gaussian channel is 16.5 dB.
8T-VSB provides 19.39 Mb/s in 6 MHz, or 3.23 b/s/Hz, for 15.2 dB of C/N
in a gaussian channel.
Now, I'm sure that most DVB-T receivers out there now are better at this
than most 8T-VSB receivers are, but I know that I can take my DB4
antenna downstairs, in the den, indoors, and wave it around the room,
and receive a solid signal for at least some of the broadcast channels.
I happened to try this on the local Fox 5 station, which fortuitously is
one of the stations that gives me a strong signal. I know for a fact
that other stations won't allow this sort of behavior, though, e.g. the
Baltimore stations. Still, the Fox 5 transmitter is more than 12 miles
away as the crow flies, and I'm down in a valley.
Honestly, I believe that today there are far more interesting and
intriguing things to wonder about in the future of TV distribution, than
modulation standard.
Bert
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