Whoo hoo!! That's great news!
Now if we can just get the FCC to make sure that it's an outdoor only
band At least for the time being.
Marlon
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- Original Message -
From: Sascha Meinrath [EMAIL PROTECTED]
To: wireless@wispa.org
Sent: Thursday, August 09, 2007 12:56 PM
Subject: [WISPA] Unlicensed Devices in the TV Bands (was: FCC Says
White-Space Spectrum Device Doesn't Work)
Hi all,
If one reads through the actual FCC report findings, you'll see that
unlicensed
devices in the TV bands are not just workable, but that the data the FCC
itself
collected supports the view that they're a viable technology. Keep in
mind that
these devices are 1st generation prototypes. Meanwhile, here's some food
for
thought:
First, let me just say that the Microsoft prototype sucked -- there's no
other
way around that one -- it doesn't perform even close to spec and fails
miserably
on just about every single benchmark that was tested. I find it hard to
believe
that the device was performing as engineered, but then again, Microsoft
has been
known to lay an egg from time to time. That said, as it turns out, the
Phillips
prototype performed exceptionally well.
One _major_ measurement decision directly affecting the results of the
study
needs to get drawn out -- there is no standard for the sensing threshold
for
these devices. The White Spaces Coalition created a standard of -114 dBm
as the
necessary level of measure. However, the 802.22 committee has also been
working
on a standard (which is not yet set) of -116 dBm. The prototypes were
ngineered to the -114 dBm standard; however, the FCC researchers tested
them
based on the IEEE proposal of -116 dBm. In essence, they were tested
outside of
spec to begin with (you can read the FCC's statement to the effect in the
second
paragraph of section 3.1 of the report).
Several figures included in the report include the gradients from -119 dBm
to
-113 dBm -- so one can find out how the Phillips prototype did at the -114
dBm
that it was manufactured to -- and the results are _stunning_:
Figure 3-4. Baseline Detection Threshold Results for Prototype B (page 14
of the
report) -- measures how well the prototype detects a DTV signal on the
same
channel. At -114 dBm this prototype detected a signal 100% of the time
(not a
lot, majority, most, or almost all, but 100%). At -115 dBm is also detects
TV
signal 100% of the time (i.e., the prototype performs even better than it
was
manufactured to do). It's only at the -116 dBm mark (which is out of
spec) that
it only detects things about 97% of the time on two of the channels and
less
than 40% of the time on a third channel. Of course, only the
out-of-spec -116
dBm results were widely disseminating while the in-spec -114 dBm home run
wasn't
mentioned at all.
Figure 3-9. Two-Channel Detection Threshold Test Results for WSD Prototype
B
(page 18 of the report) -- measures how well the prototype detects DTV
signal on
adjacent channels. Once again, at -114 dBm the Phillips prototype detects
adjacent channel signals 100% of the time. It does poorly at the -116 dBm
mark,
but it was never manufactured to measure at that sensitivity.
The Phillips prototype was never used in field tests (at the request of
the
manufacturer). But taken together, it appears that unlicensed devices can
work
_extremely well_ within the TV-Band at the level of sensitivity they are
manufactured to see. The problem is that they were tested completely
out-of-spec (I suspect that the manufacturers did not know that the FCC
would
use a different testing metric than they were using). When tested
in-spec, the
Phillips Prototype scored a whopping 100% on both bench tests -- which is
both
remarkable and quite promising for the technology.
It's rare that I find something so completely different from what has been
reported. But in this case, the news has all been that the idea is a
complete
failure; yet it appears that the Phillips Prototype has demonstrated quite
conclusively that unlicensed devices in unused bands are quite possible.
--Sascha Meinrath
Research Director
Wireless Futures Program
New America Foundation
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