[IP] more on FCC votes to let low-power devices use empty TV channels after digital switchover
Begin forwarded message:
From: Brett Glass <brett@xxxxxxxxxx>
Date: October 13, 2006 5:57:28 PM EDT
To: dave@xxxxxxxxxx, ip@xxxxxxxxxxxxxx
Subject: Re: [IP] FCC votes to let low-power devices use empty TV
channels after digital switchover
fyi re fcc and unlicensed spectrum re digital broadcasting etc- big
news! comments?
<http://www.openspectrum.info/news-oct06-014.html>
Dave:
For IP, if you'd like.
The FCC's press releases and statements on this decision can be found at
http://www.fcc.gov/
Unfortunately, some of the Commissioners are leaning toward a Part 15-
like regime for these frequencies -- the same one used for Wi-Fi and
the massively congested 900 MHz band. Alas, such a regime would
vastly decrease the usefulness of the spectrum.
Here's why. Firstly, Because these lower frequencies propagate
readily through the external walls of buildings, the signal from
every bit of consumer gear that used these frequencies -- be it a
cordless phone, a baby monitor, a remote control, or what have you --
would propagate far outside the area where it was needed, raising
noise levels on the band. This would create a cacophony similar to
what is already being experienced on the 900 MHz band, which is now
dubbed the "band of last resort" for wireless broadband. (See http://
www.brettglass.com/Laramie900.jpg for a spectrum measurement showing
the noise on the 900 MHz band in our small town of 27,000 souls.)
Secondly, there isn't all that much spectrum there. Even if we
include TV channels 2 through 20 -- the largest swatch that might be
allocated in some areas -- we're talking one to two hundred
megahertz, in several discontiguous chunks. Devices which operated on
these bands would not be faster than the latest Wi-Fi gear, simply
because there is less spectrum and more noise than in the existing
unlicensed bands.
Thirdly, as the frequency of a signal gets lower, it becomes less and
less practical to build good directional antennas for it. For
example, a highly focused 21 dBi panel antenna for 5.8 GHz takes up
less than a square foot. (Note to non-engineers: A "21 dBi" antenna
is one which focuses its signal in one direction about 128 times more
intensely than an "isotropic radiator," which sends it in every
direction, would.) But an equally focused antenna for the 900 MHz
band would have to be a dish or panel several feet in diameter; the
larger wavelength simply precludes it from being smaller. So, on the
relevant TV frequencies, which are much lower than 900 MHz (most are
in the 4th row of the chart at http://www.ntia.doc.gov/osmhome/
allochrt.pdf), trying to "aim at" a particular transmitter and away
from others which interfere will be difficult.
Finally, there has been no claim -- before the FCC or anywhere else
-- that the amount of spectrum currently available for indoor
consumer devices is inadequate. The big spectrum crunch -- the one
which is producing the comments to which the Commissioners alluded in
their comments -- is in spectrum for outdoor wireless broadband
networks, which need to reach across long distances and penetrate
thick vegetation to provide service to end users.
For these reasons, the best and most productive use of unused TV
spectrum would be under a regime similar to the "lightly licensed"
one proposed for the 3.65 GHz band. Under this regime, the band is
reserved for point-to-point outdoor wireless broadband applications,
and users are required to cooperate so as not to interfere with one
another's signals or waste the spectrum. Licenses should not be
difficult or expensive to obtain, but should be required to allow
enforcement of the requirement to cooperate and to allow users who
violate that requirement to be identified.
If new spectrum is needed for indoor uses (though there is currently
no indication of such a need; the current 2.4 and 5.8 GHz bands seem
more than adequate), it would be best if it were at higher
frequencies, most of which are less likely to penetrate to the
outside. This would permit spectrum reuse within adjacent buildings.
For example, reclamation of the 23 GHz LMDS "B" band, which has
proven impractical for outdoor applications because the signals are
so badly attenuated by rain and obstacles, might well be better used
indoors. It could provide very high speed communications within a
room or building with antennas small enough to fit completely within
the devices.
In short, as new spectrum becomes available, the FCC policy that
would best serve the public would be this: Allocate frequencies below
1 GHz, which are sorely needed to provide a "wireless first mile," to
point-to-multipoint outdoor uses such as the provision of wireless
broadband, specifically because they penetrate foliage and can
penetrate some distance into buildings. Require coordination among
users of these lower frequencies, so that this valuable spectrum does
not fall prey to tragedies of the commons and is not wasted or abused.
On the other hand, when new frequencies above 5 GHz become available,
allocate them to unlicensed indoor uses (which will allow maximum
reuse because the signals will not be able to escape into the
outdoors as easily) and to "point-to-point" outdoor uses (where the
shorter wavelength makes it practical to create very well focused
antennas that allow outdoor reuse). Require that parties who use
these frequencies for outdoor point-to-point links use very well
focused, high gain antennas with a minimum gain of 30 dBi -- 1000
times more focused than an antenna which spewed signals in every
direction would be. At these frequencies, such a well focused antenna
would take the form of a dish less than two feet in diameter or a
panel less than 18 inches on a side, and so would be easy to deploy.
We have here a situation in which the laws of physics can guide
public policy so as to make the most productive possible use of
spectrum. Let's not make the mistake of assuming that what worked on
one band will necessarily work well on another with very different
properties. If the unused TV spectrum is allocated and regulated
properly, we have a real opportunity to maximize its utility to the
public -- specifically in the deployment of wireless broadband --
rather than repeating the disaster we've already seen on nearby
frequencies, where consumer electronics ultimately destroyed the
utility of the band.
--Brett Glass, LARIAT.NET
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