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scross

join:2002-09-13
Cordova, TN
reply to jseymour

Re: Any competent RF engineer could have told them

said by jseymour:

What Dave wrote above is dead on the money and bears repeating often.

That this entire fiasco has gone on this long, and promises to continue, says a lot about U.S. business practices and politics, and none of it good.

So, um, IF (as I understand the situation) GPS is actually operating outside of the spectrum which was allocated for it (meaning that from a technical perspective, at least, LightSquared is not at fault here), AND the GPS industry is unwilling or unable to mitigate this error (making them spectrum squatters), THEN shouldn't they be held accountable for this in some way - maybe by reallocating the problem spectrum to GPS and letting them reimburse someone (LS, the govt) for it? This seems a far more reasonable course of action than trying to pin all of the blame on LS and making them into some sort of pariah - which strikes me as something akin to shooting the messenger.

That said, I'm not at all surprised to find a "we must protect GPS at all costs" mentality, given how dependent we've become on it. But it seems that LS has offered several potential technical solutions thus far, including an offer to use only a portion of their spectrum (at least to start off with), while the GPS industry has yet to even own up to the fact that this whole situation is largely their fault.

Austinloop

join:2001-08-19
Austin, TX
kudos:1

No, GPS is transmitting in their allocated block. Do some reading on red and blue shift, then reconsider your post.

Yes, it should be protected, since it is a U.S. military program, which should trump a doofus company getting a conditional license to use a frequency allocation as an earth based transmitter system, rather than the satellite to earth usage originally intended.

LightSquared had a flawed plan and now are in the whine mode.



a333
A hot cup of integrals please

join:2007-06-12
Rego Park, NY
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reply to scross

Nope... GPS is perfectly within their spectrum... it's more the fact that you simply cannot have a situation where a signal transmitted from a satellite hundreds of miles out in orbit is competing with one on an adjacent (interfering due to red/blue-shift) band that is transmitting from the GROUND. The fact of the matter is that the satellite-based GPS signal is thousands (possibly hundreds of thousands) of times weaker than a terrestrial signal, by the time it gets to a GPS receiver near the Earth's surface (just think of the fact that the satellite is transmitting its signal over a simply ENORMOUS area of the Earth's surface, from a transmitter of limited power).
Technical limitations aside, the argument stands that Lightsquared originally purchased a band of frequencies intended by the FCC to be used for earth-space comms. They instead opted to take a gamble that not listening to RF engineers and bribing some politicians would work in their favor. Guess what... they lost, and now they are whining like children denied of their favorite candy.

-a333
--
Physics: Will you break the laws of physics, or will the laws of physics break you?
If physicists stand on each other's shoulders, computer scientists stand on each other's toes, and computer programmers dig each other's graves.


scross

join:2002-09-13
Cordova, TN
reply to Austinloop

Actually, I never said anything about transmissions; it's my understanding that it's the receivers which are at fault here, for not filtering out frequencies from outside the GPS band. And I understand red and blue shift and guard bands and such, but again - if GPS can't operate without red/blue shift pushing things outside their allotted spectrum, then by definition this excess spectrum should be (or should have been) allocated to GPS, with the GPS industry compensating the government or whomever for it.

LightSquared's argument (as I understand it) is that GPS can work perfectly fine within its allotted band, but unfortunately GPS manufacturers went cheap on their receiver filters because up until now they could get away with this. But now that LS has called them out on it, GPS manufacturers are refusing to acknowledge their own blame here, and refusing to cooperate in trying to mitigate the situation. If I were LS I would be angry, too.

In any case, I totally agree that LS was stupid to make promises, sign contracts, collect money, and so on without first having all of their technical ducks in a row. If it's true that they've blown "billions" of investor dollars on this (just a few million, more likely), then they no doubt deserve what they've got coming. But from a spectrum perspective I don't necessarily agree that they are the primary ones to blame. Even if LS up and disappears tomorrow, the FCC should still hold the GPS industry accountable for the current situation.


Austinloop

join:2001-08-19
Austin, TX
kudos:1

You are failing to acknowledge that LSq wanted to change the spectrum allocation from satellite based transmission to the ground to ground based transmitters.

Further, if the filters are tightened too much, functionality will be lost and GPS probably won't work. Again, fortunately, more intelligent minds took control and LSq should be relegated to the dust bin of history.

Yes, they have right to be angry, but at themselves, for their boneheaded plan.

And as for someone compensating the government for additional spectrum for GPS, you are aware that GPS belongs to the military, and they don't usually pay for spectrum.