[opendtv] Re: Interview: ARE MANY TRANSMITTERS BETTER THAN ONE?
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Wed, 19 Sep 2007 08:50:07 -0400
At 11:12 AM -0400 9/18/07, Manfredi, Albert E wrote:
I'm not sure where you're going with this. It sounds like in terms of
the SFN argument alone, it's six of one and half a dozen of the other.
The cost of deploying SFNs is a wash, if you assume synchronization to
be required in both cases.
Where I am going with this in ~1994.
The advisory committee, the FCC and the ATSC were all focused on a
DTV transmission system based on the "Big Stick" model employed for
NTSC. This was the easiest approach for the FCC to deal with, and the
cheapest route for broadcasters. There was NO INTEREST in SFNs in
1994 when COFDM was being evaluated, however, this was being promoted
by the DVB folks as a major advantage of their system. So an economic
argument was created to mitigate this advantage...
"It's an interesting feature, but economically prohibitive to deploy
because of the need for telco land lines to feed the transmitters."
Somehow, the economic argument used in the 1994 time-frame turned out
to be completely wrong. So now, 13 years later the ATSC has figured
out how to make SFNs work and it is economically viable and
politically correct to talk about SFNs.
Are you saying that he should have included the example of passively
synchronized, small area SFNs, with either two towers or one big stick
and a few much smaller ones?
No. I am saying that it was already obvious that there would be
multiple technologies available to solve the synchronization problem
in 1994, thus the economic argument against DVB was questionable at
best. To be fair, there were other issues as well. For example,
there were purported advantages in using an 8K carrier system versus
a 2K system, but it took a decade for the 8k version to become
economically practical.
When you are designing a standard that is to be used for decades, you
need to have a decent grasp of where the enabling technologies are
going to come from. This is true for DVB, ATSC, et al.
You have been a staunch supporter of the big stick approach,
predicting that the equalization problems would be solved. It took
more than a decade, but it turns out that you were right.
I could also add that we provided input to the Advisory committee
about the trends in enabling technologies, which were largely
ignored. These predictions also turned out to be true. So it all
boils down to how technology is misused to gore someone else's Oxen.
This effectively forced COFDM to be compared with ATSC using
only single high powered transmitters. In this comparison, many
of the advantages of the COFDM approach are lost.
Which is exactly the right analysis. The passively synchronized, small
area SFNs, for which COFDM would have the clear advantage, require
dialing down spectral efficiency, and are not very effective in covering
huge OTA markets. As we have in the US. So it is very appropriate, IMO,
to consider whether the benefits outweight the liabilities.
Right analysis, but your conclusion is wrong. SFNs DO NOT "dial down"
spectral efficiency; they SIGNIFICANTLY enhance it.
As we have discussed MANY times before, there are some areas in the
U.S. where markets are isolated and the "Big Stick" approach is the
best solution. There are ALSO many markets in the U.S. that are
closely co-located, where the BIG Stick approach causes severe
market-into-market interference, forcing large chunks of spectrum to
lie fallow to protect the channels that are being used. This reduces
spectral efficiency by nearly half.
As you are no doubt aware, attempts to use these white spaces have
been challenged at every turn to protect a distribution
infrastructure that is used by less than 15% of the population. If
this spectrum were used properly, broadcasters could offer at least
20 multiplexes in every market, which in turn, would allow them to
compete effectively with cable and DBS.
But this is not the U.S. way...
Here, the spectrum is used to provide the political cover so that
broadcasters can gain additional compensation from competitors for
content that is advertiser supported and delivered in the free and
clear via their Big Sticks.
Now that synchronization is more practical, using GPS rather than
perfectly measured transmission lines, more useful SFNs can be installed
in both systems. Which makes the two more similar, and further pushes
into the past all the silly debates about COFDM vs 8-VSB.
Not really.
Funny how we could not disenfranchise first generation receivers, but
now it is perfectly acceptable to develop channel compatible
enhancements to the ATSC standard that will require new receivers
for the new services. If we had gone with DVB, we would have all of
the needed modes of operation from the outset, and using these modes
would not disenfranchise exsiting receivers.
Regards
Craig
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