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EU and US Agree on Galileo
An anonymous reader writes "The EU and USA have reached an agreement over the Galileo satellite positioning system, ending several years of negotiations." We had some good Galileo information in a story last month.
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No they can't "just put up other sats".
- The sats have to be daily checked and correted by people on earth, like giving to each sat the positions of others sats ( this information is transmitted to the GPS receiver, to know how much sats it should be able to "see" ). This need a common agreement and cooperation.
- Signals must not overlaps or corrupt other signals ( not as easy as it seems, the usable frequency window is quite narrow ).
- the EU Gallileo will be free for personal use. You must pay a fixed fee ( payed when you pruchase the receiver ) to use the US GPS
- USA can decide at ANY TIME to reduce the precision of the GPS signal delivered to cityzens in any zone ( by a ratio of 1 to 100 ) making it totally useless.
- GPS sats become older and older, their lifespan is limited and a few should be replaced ( 27 are needed to give a good global coverage, some of the ones in the sky are not fully functionnal anymore ). It would be a good time to change a few ( some don't even got a good ol' cesium atomic clock ).
- Galileo will provide more different levels of precision than GPS with different prices and secured and garanteed precisions for the most expensive ones.
I'm not web-surfing at work, I conduct a very broad technological survey.
It was more than that. The US was concerned that Galileo would interfere with the P-code portion of the GPS signal. It is one thing to claim that the decision was a cave allowing the US to 'jam' Galileo... quite a nother to point out that Galileo was designed to overlap channels with the US system, potentially interfering. How is this different than, say, another slashdot hot topic: the broadband over powerline controversy in that it interferes with HAM radio?
"It takes considerable knowledge just to realize the extent of your own ignorance." - Thomas Sowell
Not quite right.
The "lockout" was known as selective availability which was used to intentionally make the civilian code, called C/A for coarse acquisition, less accurate than it could be.
But there is still P(Y), p for precision, code which is military only. The encryption keys for using this code are classified. P(Y) code is more accurate than C/A code because it is a much, much longer sequence before it repeats.
C/A code repeats every 1 ms. P(Y) code lasts 1 week (it doesn't repeat every week, but the difference is not important here). Therefore, the pseudorandom number sequence that the GPS receiver correlates against is much, much longer allowing for better accuracy.
One part of the article almost gets it right,
Unfortunately, it looks like the EU caved in, so it will not be safe to assume that Galileo will be operational for the safety critical applications which it is designed for, such as air traffic control.
flossie
Write now. Defend liberty
You're partly correct. The P(Y) codes do allow greater precision in position, but not because the PRN codes are longer. The long PRN codes are primarily for security. The reason you get better accuracy with the P(Y) codes is they are dual frequency, unlike the C/A codes which operate on a single frequency. The dual freqency system allows the receiver to make corrections for ionospheric delays, as the two frequencies are delayed by different amounts by the ionosphere. By correcting for these delays, more accurate positioning is possible.
If I can be modded down for being a troll, can I be modded up for being an orc, or a balrog?
Googling for "3D position tracking RF" turns up a number of companies.
You didn't mention inertial tracking; calibrate a start position and then just measure movement.
Differential GPS doesn't use a second location reference signal per se. It places a GPS unit at a known location (say, on top of a USGS survey marker). Then, you can measure the difference between the GPS reported position and actual position. Make the assumption that any nearby GPS receiver will have much the same error, and subtract that error from the position reported on the second receiver.
- the EU Gallileo will be free for personal use. You must pay a fixed fee ( payed when you pruchase the receiver ) to use the US GPS
Really? Someone better tell the government then because they've posted the specs online for free!!.
-1, Disinformative
I can provide a reference for the contradiction: ICD-200, the GPS Interface Control Document. This doc describes in exquisite detail exactly what the satellites are broadcasting, and between that and a little matrix algebra, anyone who wishes to can build a GPS receiver capable of getting the civilian signals.
It also describes the military signals to sufficient precision that you could use them if they were unencoded. From that, all you need is the magic decoder ring and you can use the military signals, too.
My university offers quite a few courses on GPS, including one in which the class builds a GPS receiver from scratch, and another one which I took in which we learned how to process the signals and get a position.
ICD-200 is freely available (one click away from the link above), and anyone in the world is free to implement it. The fixed fee is paid when you pay your taxes, and is only paid by americans. It's not like Big Brother can detect who is using GPS, since they are receivers only. No one can meter or charge for the GPS signals, they fall to the ground, free for the taking by anyone who cares. The EUropeans are trying to charge for some Galileo services, but they do that by selling the magic decoder rings.
If you don't believe me, and don't trust your GarminTM, use ICD-200 to build your own.