[opendtv] Re: Seeing Ghosts on a Single Frequency Network

From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
To: "opendtv@xxxxxxxxxxxxx" <opendtv@xxxxxxxxxxxxx>
Date: Wed, 16 Feb 2011 16:35:47 -0600
Craig Birkmaier wrote:

> You are correct that it is possible to squeeze things closer together
> by reducing the effective coverage area for a transmitter and by
> creatively using low power transmitters to fill in the gaps.

In fact, Wash/Balt and NYC do share the same big stick frequencies, and the 
market between the two, Phildelphia, is assigned the same frequencies for LPTV. 
You can't hope for much better reuse of frequencies if you used SFNs to cover 
Wash/Balt and NYC. I see that you persist in not believing this, but all you 
have to do is go to the FCC web site on TV, and see for yourself.

If there were some rationale that permitted the NYC and Wash/Balt coverage to 
be reduced in area, then the big sticks from these two markets could be reduced 
in power, or HAAT, or both, and the Philadelphia LPTV towers could be increased 
in power, HAAT, or both.

To support mobility, you need (a) a scheme that is good with dynamic echo, and 
(b) you need C/N ratios closer to 25 dB throughout the market (to retain the 
b/s used in fixed service). But that is a different discussion. The discussion 
before was only about spectral efficiency. I would have no problem agreeing 
that spectral efficiency must go down if you want to support mobility. If for 
no other reason, because in order to create that greater signal power density, 
you are forcing yourself to create a larger interference zone at the 
boundaries, before that same frequency can be reused. This is true for both 
SFNs or big sticks supplemented by DOCRs.

> The ideal solutions seems to be a small number of transmitters that
> are properly masked to control emission within a market. And ATSC
> does not work well for this,

Depends. For single market coverage, I think the ideal solution is the big 
stick assisted by small sticks. This allows you to keep the spectral efficiency 
higher than the true SFN. If you are a regional broadcaster, or severely 
limited in the max allowable ERP (like Italy), this would likely not even be an 
option. But in a single market without draconian ERP restrictions, you could 
get by with much lower GIs in COFDM, and even make it work with 8-VSB. But of 
course, you need receivers that withstand dynamically changing echo (easy with 
COFDM, and should be doable even with regual non-M/H 8-VSB).

> People commute between markets in the NE corridor every day. But this
> is NOT a justification for having the signals from one market spilling
> into another.

Sorry, we have been around and around this for too many years. I totally 
disagree. People that live in the communities between these cities shop in one, 
the other, or both markets all the time. This should be so obvious.

Bert
 
 
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[opendtv] Re: Seeing Ghosts on a Single Frequency Network

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