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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.