[opendtv] Re: From Broadcast Engineering - WRAL tests mobile DTV
- From: Albert Manfredi <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Fri, 8 Aug 2008 21:23:55 -0400
John Shutt wrote:
> 8-VSB's threshold C/N ratio changes with the number of
> equalizer taps engaged to cancel out multipath.
>
> In a challenging environment, the 3 dB 'advantage' of ATSC
> goes away.
Not really, John. The 3 dB advantage was in a gaussian channel, comparing
gaussian threshold levels. COFDM and 8-VSB both degrade to an extent in more
challenging channels. The only problem is, the DVB-T documents give model
results to indicate what one can expect, e.g. the 18 dB of C/N margin increases
to 22 dB in the rayleigh channel they modeled, but the ATSC documentation does
not give such numbers.
However, if you look at the CRC results, you can get those numbers, in the
different Brazil profiles. And the differences seem to hold up reasonably well
with the newer generation receivers (to the extent a comparison can be made).
Check it out.
Bert
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