[opendtv] "It can't be done"
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Thu, 28 Dec 2006 09:49:47 -0500
At 1:47 PM -0800 12/26/06, Dale Kelly wrote:
IMO, Bert does indeed have a grasp of signal and receiver dynamics which
impact DTV reception and does also generally understand issues related to
SFNs. However, he nor you have ever dealt with the practical and financial
aspects of designing an RF system that is FCC compliant and which can
overcome such difficult coverage problems. However, if your maps had the
necessary information, he could likely give it a good start.
Obviously Bert has no interest in the challenge. His pre-conceived
notions about the viability of SFNs versus continuing to waste
valuable spectrum with the current high powered ATSC big stick
approach are keeping him from using his imagination and engineering
skills.
So be it. The challenge was a good natured attempt to get Bert
thinking about alternatives to the failing U.S. OTA broadcast system.
I would add that Dale also seems to be looking at all of this via a
rear-view mirror. But I believe Dale may be more open to innovative
new solutions, if he can get past the age old problem of "we tried
that and it didn't work.
A brief aside. Several times during my career, I have confronted what
i consider to be one of the major roadblocks to innovation and
progress, as it relates to designing any kind of product or
infrastructure. There is a built in (and highly biased) database in
most engineers/companies/industries, which springs from real world
experience. The response one hears is typically something like: we
tried that years ago and it can't be done. Every industry builds up
such a legacy mind set, which makes it difficult to solve problems in
new and innovative ways.
I experienced this at the Grass Valley Group when I helped to lead
the team that built the Model 100. The hardest task was to overcome
all of the things that various people around the project said could
not be done. Perhaps the best single example was the need to change
the company colors - prior to the Model 100 every switcher was Grass
Valley beige, with DS (diaper shit) orange silk screens. The most
useful new feature was the ability to get the entire video path onto
a single board, so that video alignment was simplified, and we could
do a switcher alignment via a board exchange.
Helping companies to develop the new computer-based tools that now
dominate video production was a much more difficult undertaking. Here
we were fighting the way things were always done, and an analog
mindset, that was not open to the idea that we are just processing
rasters of samples, not analog waveforms complete with sync, blanking
and subcarrier. The shift to digital technology re-wrote the
rulebook. Many things that could not be done, were quite easy when we
started manipulating pixels.
The same is true for the biggest laggards of them all, TV
broadcasters. They still don't understand that they are in the
business of managing data. They haven't a clue that they have all the
technology they need to compete effectively, developing relationships
with viewers rather than audiences. And the worst aspect of this is
what Dale identified in his post. The need to keep an outdated
government bureaucracy happy, rather than working to get rid of it
and the excess baggage that keeps broadcasters from using the
spectrum to develop a competitive OTA service.
I fully understand where Dale is coming from. I enjoyed great success
in my career, acting as the expediter to help companies overcome some
of these mental hurdles. That is, until I got involved in the U.S.
DTV process. For the past 14 years I have been amazed at the power of
key industry players to block and delay, and to throw logic and good
engineering principles to the wind. Eventually I let go, after
beating my head into a wall too many times. At least now I have the
satisfaction of beating a nail or two, and actually building things
that work.
I ask Dale, and others to simply consider alternatives, without the
legacy bias that say you can't do that. When OTA broadcasting dies
someone will come behind and do it. Actually, companies are already
starting to do it. But they are highly constrained, due to the lack
of spectrum available to build new digital broadcast infrastructure
that can provide a viable option to the broadcast and multichannel
oligopoly that has us stuck in the past today.
So please consider the possibilities, without the constraints of
legacy thinking.
As a starting point, I did a bit of research yesterday into some
basic OFDM design constraints. The best resource I found is a pdf
White paper published by MediaFlo, the Qualcom subsidiary that is
building out an OFDM-based mobile TV infrastructure in recovered
700Mhz spectrum.Here is the link:
http://www.qualcomm.com/mediaflo/news/pdf/MediaFLO_SFN_Whitepaper.pdf
The paper is highly informative, and includes several maps detailing
how the network will be built in several areas of the country. One
interesting take away is that it will take only 30 transmission sites
to completely cover the NE corridor, and this includes both national
channels and local channels in several markets. You can zoom in on
the maps and see exactly how they plan to do it.
Based on this document, it appears that they are using a cell spacing
of 27.7 km, or about 17.7 miles. Keep in mind that this is designed
to provide a base and enhancement layer for fixed, portable and
mobile reception in a six MHz channel. I consider this to be the
worst case scenario - but it serves as an excellent example of what
broadcasters COULD do. Given this spacing, it appears that Dale's
market could be served with 5-6 transmission sites, probably two a
bit closer together to provide optimal service in the more populous
Santa Barbara area. My guess is that this would leave only a few
isolated pockets where On-channel repeaters would be needed to fill
in terrain blocked areas.
This should be enough to get things moving on a useful discussion.
I'll add more ideas as we develop this thread.
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