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

  • From: Craig Birkmaier <craig@xxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Wed, 16 Feb 2011 08:53:45 -0500

At 3:09 PM -0600 2/15/11, Manfredi, Albert E wrote:
In a parallel universe where Baltimore and NYC are smaller market areas and geographically closer together, even with big sticks, the two cities could STILL share the same frequencies. You must have misinterpreted the fact that these big sticks are so far apart as meaning that they must be. I can guarantee you, reduce power, and they don't need to be. The proof of what I'm saying is that the frequencies ARE shared, even among adjacent markets, even when big sticks are used. 

Bert
Perhaps this is just a semantic issue. If you reduce the HAAT and power levels, even with a single carrier system like ATSC, you no longer are using "big sticks." it is all about how far the signals travel, and how much these signals interfere with use of the same frequency in adjacent markets.
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. 

But there is a major problem here.
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, ESPECIALLY if the primary market is serving mobile devices, which "IS" the future for broadcasters. On the other hand, it has already been demonstrate that with COFDM, a market like New York can be effectively covered with 4-5 transmitters. I would note that in any market there will still be locations where low power on channel repeaters may be needed, for example in Grand Central Station or the New York subway system.
Didn't you understand my point? The reason why Balt/DC and NYC high power big sticks are 200 miles apart is because that's what geography dictated. It's not because that's the nature of big sticks. Even if someone misled you when they were trying deperately to support some argument of theirs years ago, you can't continue to repeat the same tired old slogans without an occasional review of the facts, right?
No the reason they are this far apart is because at the height and power levels used, it is not feasible to reuse these channels in markets that lie between Baltimore and New York. Geography did not dictate this, PHYSICS dictate this, although ducting across the ocean that lies between adds to the problem at some frequencies.
Baltimore and Washington are indeed separate markets, but there are many people who live in areas between the two that work in the other market. Places like Laurel and Columbia MD. There are even many people who live in Baltimore who take the train daily to Washington for work. So like it or not, the coverage has to overlap. If this were done with SFNs, coverage would still have to overlap, so the SFN frequencies would still have to be different. Just like the big stick frequencies are different.
And there are additional TV markets between Baltimore and DC, like Annapolis. te
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. I could just as easily say that if I live in New York I should be able to receive DC stations, because I spend three days a week riding Amtrack or the Air Shuttle to do work in Washington.
What we are talking about here is a service that is totally dependent on advertisers, many of which are LOCAL advertisers who serve only a segment of the larger TV market, and have no interest at all in reaching adjacent markets. Cable gives them the ability to reach these sub markets; you on the other hand want to get rid of localism and move to regional broadcasting.
I'm not saying one business model is better than the other; it is clear, however, that the current broadcasting business model is broken and needs to be made relevant again. I personally believe that hyper localism is the path for any service that hopes to get advertising messages to consumers on their mobile devices. If broadcasters don;t do something about this to compete, then mobile broadband will put the final nail in broadcaster's coffins. 




 We disagree. Yes, there are many ways to slice and dice this debate. But
 the big sticks cause unnecessary problems, especially with respect to
 out of market emissions.
So would SFNs, when the boundaries between markets are poorly defined and need a lot of overlap. 

Scale Bert.
We are talking about reducing the overlap areas to a few miles from a hundred miles or more. And we can use directional transmitters with emission masks to further reduce these interferrence zones.
It's really simple. I can build a big stick system, with perhaps some carefully placed and aimed low power DOCRS if need be, and achieve coverage of the market area with zero guard interval. Your SFN, if it is to be at all reliable, MUST include a sizeable GI. In practice, 1/8 or 1/4, which decreases spectral efficiency by 12.5 to 25 percent. Therefore, all else equal, your spectral efficiency, in a single-market SFN scenario, is lower than my big stick system.s 

Your solution is good for fixed receivers, not so good for mobile reception.
And you are failing to consider how much white space is needed to make your system work... 



It's really very simple. "There is no such thing as a free lunch."


Yup.

And there is no such thing as Free TV either...
It is a question of creating a rational regulatory policy and developing appropriate technologies that maximize spectral reuse, and therefore maximize the potential of this scarce resource. 

Regards
Craig


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