[opendtv] Re: White spaces and 700MHz D Block could be part of new US spectrum plan

  • From: Craig Birkmaier <craig@xxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Mon, 28 Sep 2009 08:59:51 -0400

At 5:45 PM -0400 9/26/09, Albert Manfredi wrote:
Yes, but first you need to understand the environment we are talking about, compared with your WiFi or even 3G examples, that don't apply here.

In this instance, the desired signal is often a whole lot weaker than the intruding opportunistic signal would be. Instead in your examples, the signal looking for access will end up being one of the strongest ones in that slice of spectrum.

That's the point Bert. The goal is to provide signals that sufficiently exceed the threshold for reliable service. Unfortunately the big stick approach does not provide this. Instead it provides some areas of a market with signals that are too strong and can overload a receiver, some areas where the signal strength is in the range needed to provide reliable service, and some areas where the signal is marginal or insufficient to achieve reliable reception.

ONLY the last one is susceptible to interference from devices sharing the spectrum that use auto-detection, and even here it is possible to augment auto-detection with GPS and database driven choices about available channels.

The 3G example is actually quite good. At my home there is a variable level of service from AT&T via their 3G network. This is influenced by capacity issues for the network and RF variations that affect the signal strength. If I install a microcell, two things happen:

1. The local radio link in the microcell with be significantly stronger than the AT&T network signal, but only in a small geographic area in and around my home.

2. Shifting traffic to a wired VOIP network reduces congestion on the AT&T wireless 3G network.

So the real issue here is whether white space devices will interfere with inadequate RF signals from the local broadcasters. IF they do, the real issue is not the failure of the auto-detection capability of the white space device, but the failure of the broadcaster to provide an adequate RF signal in the same physical environment. The solution is for broadcasters to think in terms of distributed transmission networks that provide a consistent level of RF signal throughout their coverage area, not to rely on protection of weak signals from interference, or worse, to tie up large chunks of spectrum as guard bands for big stick broadcast services.

In the process of building distributed networks, broadcasters will gain two major benefits:

1. freeing up more spectrum for reuse, both by broadcasters and white space devices;

2. Providing the ability to provide unique services to sub-markets within their coverage areas. That is, to segment some of the bits for localizened services that can be different from cell to cell (but not necessarily adjacent cells.

If we reduce power levels for everyone, we free up significant chunks of spectrum fro new services within the market, and this could be the difference that allows broadcasting to survive.

The TV white space usage is much more similar to someone wanting to use the GPS spectrum. Would you trust an auto-detection scheme to share that? I very much doubt it.

A very poor analogy from an RF perspective. GPS relies on direct line of sight to devices using very low transmission power levels. Broadcast relies on line of sight for a portion of the audience, high power levels and transmission antennas to overcome geographic blockage, and reflections to serve areas where line-of-sight is not possible. AND broadcast relies on protected white spaces to allow distant reception at very low RF levels. As I said, this is "horse and buggy" technology from an RF perspective.

It just so happens that today, I was listening to a program on NPR that talked about the national parks. Same sort of argument applies there.

Imagine how many billions of dollars could be made if we allowed development on these national parks. Condos on top of the Grand Canyon, for instance. Time shares in Yosemite.

A totally absurd analogy. If money was the most important consideration we should have recovered the spectrum from TV broadcasters several decades ago. We are not talking about changing the national policy with regards to broadcasting, we are talking about modernizing the broadcast infrastructure to provide:

1. IMPROVED reception of broadcast signals, especially by a new generation of mobile receivers;

2. Significantly increase spectral capacity for new services both for broadcasters and white space devices [and who is to say that broadcasters cannot use these white spaces to create two-way services?

That's a little bit what it sounds like, when self-serving industries try to grab spectrum assigned to other purposes.

Perhaps to you.

Sounds more like thew buggy whip industry arguing that we canno t have cars and trucks because they scare the horses!


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