[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!
Regards
Craig
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