OOps, sorry I forgot to CC you on this one Lauren.
Thanks Dave, point by point Ill reply:
David P. Reed wrote:
The GPS allocation defines whatever protection the service needs. Does
the 50 MILLION watt transmitter of a typical UHF TV station mess up the
GPS service?
a) due to the distance away in frequency, DTV or Analog megawatt xmtrs
for that matter (its still in use worldwide) do not interfere. Thats
entirely expectable. Move one immediately adjacent to the GPS
allocation, and that most certainly will change.
Why does GPS's allocation now have to be enlarged? Did the GPS
designers (who were the best engineers the US DoD could pay) define an
inadequate band allocation when they designed their system?
b) Enlarged? Not necessarily, but being an incumbent licensed service,
they have protection. This has ALWAYS been the case historically at
FCC, I believe this will prevail as well. If anyone is to move, or
surrender a guard band, it will be the interloper, the new guy. IF we
can argue for sufficient protection, we might make this irresponsible
project un-attractive and have it abandoned at best, or moved as second
choice, or drastic power decreases imposed. Protection of GPS is issue
#1, and I personally dont care how its done.
I would suggest that this has nothing to do with the Gaussian noise
floor issue. We function quite well with 50 Million Watt
transmitters' signals coupling to all antennas.
c) It has everything to do with it, but ignoring it is convenient to
bolster an argument to allow this irresponsible plan to proceed. That
will not be allowed to be ignored.
Regarding your assertion about bribes, etc. I have no interest in
pursuing that concern - there may indeed be bribes being taken.
However, the technical issue is separable.
d) The ends justify the means here. So if we can get the facts out, we
will have another tool to show the incompetence of this plan. There
will be public service announcements, and I think APCO will be on board
with us, decrying the degradation of E911 service and public safety.
No, this is a looser out of the gate.
You know this is irresponsible, and your grasping at straws here. I
talk to some of the most eminent GPS scientists out there, and they're
dead set against it as well in its present configuration. It does not
mean there can be no accommodation but GPS WILL be protected, if it
takes 10-20 years of expensive international litigation. The world
hasn't invested Billion$ in PNT to allow it to be wiped out by a
terrible plan like this one. The US consumer market alone will run the
case into the ground.
Always glad to chat Dave,
Marc Blitz
On 04/07/2011 06:17 PM, ssc wrote:
Sir, Ive been an engineer IN this field for 40+ years
now. I'm talking real-world, not pie-in-the sky.
I am not equating the modulation scheme to interference probability,
merely the low signal levels, Vs. the entirely overpowering ones
immediately adjacent to their band to the degradation of the service.
As you might know, even at best filtering and state of the art design,
the Gaussian noise floor rises in the presence of a huge signal like
the 1500 watt one being described here. That and that alone is enough
to degrade the performance of the GPS signal, and ANY receiver designed
for it. If you insist on degrading the entire worldwide GPS system,
then we will see you in International court, and the US bribe-takers
can frog-march themselves to there to defend their inappropriate, based
on bribes assignment of a license that they KNOW will destroy the GPS
service.
Like I said, this wont pass the muster of a real scientific inspection.
The GPS allocation is a worldwide allocation of PNT services, and as
such there will be a vigorous defense of this resource. No one should
be forced to buy a $10,000 receiver for GPS to accommodate another
piss-ant wireless service.
David P. Reed wrote:
It's
not a bogus argument at all. You're being a bit insulting.
Spread spectrum receivers should work *fine* in this case, because they
are *spread spectrum*.
That means that you have to design them to deal with "co channel"
emissions.
And that is quite within the state of the art of receiver design.
Somehow you seem to conflate spread spectrum design with narrowband
receiver design here.
I'd suggest you research the field.
On 04/07/2011 05:42 PM, ssc wrote:
I find that argument absolutely bogus, when we're talking about a
spread-spectrum signal trying to be detected at a -127dbm, with a 1500
watt transmitter next to it.
What you're asking for in receiver design is absolutely ludicrous!
If nothing else, there should be a guard band imposed, protecting the
GPS constellation.
If its not forthcoming, then the next administration will certainly hire
some real scientists, instead of bribe-takers.
David P. Reed wrote:
During the deep and thoughtful discussions that were carried out in the
Spectrum Policy Task Force at the FCC, and in the FCC Technological
Advisory Committee when I was a part of it, many of us engineers
recognized that the current structure of FCC regulations that regulate
only transmission are the source of many problems.
The problem between LightSquared's licensed band and the GPS receivers
is one example. The FCC doesn't regulate that receivers should not be
designed so that they fail due to transmissions in other bands. This is
because the FCC does not currently regulate receivers at all, unlike the
UK radio spectrum regulators.
The problem, if there is one, is that perfectly legal transmissions that
are in the LightSquared band (and which would have been legal to other
users of that band) are potentially going to make low-quality GPS
receivers malfunction.
Now one of the complainers is Trimble. Trimble does not make GPS
transmitters that I know of. They just make products that gain value
from the GPS transmitters in the sky. Unfortunately, the "quality of
experience" of Trimble's users will degrade, to the extent that their
receivers are poorly designed in terms of dealing with radios operating
in adjacent channels. Why were they poorly designed for this? One
might well ask. Who is responsible to the customers? Well, ultimately
Trimble.
However Trimble and others have a practical problem - their product is
hard to recall.
So instead, they want LightSquared to pay for their design weakness. I
wonder if that is "right"? Rather than recall the products, they could
seek a different remedy - they could pay the FCC for the unusability of
adjacent channel services. Surely Trimble has the money from its
product liability insurers to make such a payment.
Money need not be spent on the "impractical" recall, but can be spent
where the cost of the fix is more practical - paying the US Government
(and the taxpayers who will not get the benefit of the services in the
adjacent channel due to Trimble's mistakes) what their mistake has cost
the public.
This of course would match the value of "auctioning" the spectrum that
would otherwise accrue to the Federal Budget. Probably a few 10's of
Billions of US $ would cover the loss caused by careless design.
[ This seems like an approach certainly worthy of consideration --
though I would expect technically-oriented legal battles over
liability in such cases to be fierce. But from my standpoint, it
is most important that consumer GPS units in the field not be
rendered unusable by LightSquared transmissions. Even if
manufacturers agreed to try replace every unit in the field for
free, many consumers would never be located and more would
routinely ignore all such contacts. Since failure of GPS when
you expect it to work can have very serious consequences,
protection of consumers should be the main priority.
-- Lauren Weinstein
NNSquad Moderator ]
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