[opendtv] Re: New Thread: What becomes of Legacy Analog Equipment
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 28 Nov 2007 11:00:48 -0500
Tom Barry wrote:
> Are we now assuming ATSC STB's or TV's will work indoors in urban
> canyons? I didn't know that was really proven yet with off the
> shelf equipment.
We know there is nothing in physics that prevents this. We know that
it's doable now in more or less easy fashion, most likely depending on
the quality of the tuner (i.e. independent of the specific modulation
scheme), using current state of the art demod.
8T-VSB today, in its basic wide mode, is about as far from the Shannon
limit as DVB-T2 wants to be. But 8T-VSB even today is not there as
reliably as DVB-T is in its current form is. Echo tolerance, and in
particular leading echo tolerance, is not as good as that of COFDM at
the same spectral efficiency setting.
So it's a mixed bag, but one that continued development of receivers,
without having to change the transmission standard, can address. Not a
bad place to be, really.
Eventually, perhaps, 8T-VSB may get to the point where the 2/3 fixed
convolutional FEC becomes a limiting factor. That's where receivers are
good enough that we could move to maybe 3/4 FEC, and get better than 3.3
b/s/Hz of spectral efficiency reliably. That would require a change to
the transmission standard, so it's as difficult to do as DVB-T2 is.
We're not there yet with 8T-VSB, but it could happen. For now,
concentrating on receivers makes sense.
Bert
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