[opendtv] Re: Bolivia TV standard mystery
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Thu, 21 Dec 2006 16:33:00 -0500
Craig Birkmaier wrote:
> I don't think we are talking about systems that use a dense
> mesh like cellular telephony. The synchronized main
> transmitters will do the major portion of the work, using a
> fraction of the power now assigned for ATSC transmission.
I'm glad that Ian spoke up, to put things in perspective. And it's
interesting to see that Craig can agree with Ian and yet disagree with
me. There must be something either in what Ian described, or in what
I've been describing, that isn't getting across.
The dense mesh of towers would be required to create the sharp contour
you keep advocating. Of course, if you give up on that idea, then
everything becomes more reasonable. To create the sharp contour, you
need lots of low power sticks at the edges. And it is specifically at
the edges of the coverage area that your small sticks are the most
problematic, *if* they are on the same channel as the main transmitter.
So the idea of using small sticks to create your fine contour is exactly
what won't work well.
The practical reality of lowering the power of the big stick and then
expecting small sticks at the edge to provide service to the market area
fringes is that you'll have to resort of translators. Otherwise, even
with the best of SFNs, you'll create areas of very bad reception. This
is even with synchronization. The reason is the large distance between
towers and the variability of signal propagation caused by all manner of
factors, including terrain and weather. You'd just be asking for
persistent coverage problems, especially toward the fringe.
Of course, using on-channel gap fillers within the coverage pattern of
the big stick will be easier to implement. And for 8-VSB, the lower the
power of the gap fillers the better, as the CRC demoed in Ottawa back in
2003.
> The on-channel repeater infrastructure will be unique to each
> market based on topography, terrain blocking, and location of
> pockets of population. Even here, we are probably talking
> about "tens" not "hundreds" or"thousands" of repeaters.
That's a completely different matter. Filling in where there are holes
in coverage is an obvious application of OCRs, but has nothing to do
with creating the sharp contours you advocate.
Bert
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