[opendtv] Re: Price comparison
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: "OpenDTV (E-mail)" <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 10 Jan 2005 13:31:53 -0500
I had written:
> This means that in principle, barring the legacy
> problems this would cause, DVB-T could rely more on
> equalizers and less on guard intervals for robust
> reception, which means they could tune transmitters
> to the smallest 1/32 GI, and they could therefore
> closely match the spectral efficiency of 8-VSB.
John Shutt wrote:
> Or exceed it? 64-QAM, 7/8 code rate, 1/32 guard
> interval =3D 23.751 Mbps in 6 MHz.
Well, sure, because you've essentially removed any
convolutional FEC. 7/8 is next to nothing. But then
the channel becomes more vulnerable to errors.
Since 64-QAM and 8-VSB offer exactly the same
b/s/Hz, introducing any GI at all can only reduce
b/s/Hz. The GI is used to avoid depending on high
tech equalizers.
Now introduce high tech equalizers after the fact,
and the GI won't help anymore. But there's no
reason to believe that COFDM could get by with
less FEC, when you've done this.
Bert
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