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Today I used the GPS on my Android for the first time, and I was wondering how it actually works.

I know that Android phones have a GPS chip in them, but does the phone establish a direct connection to the GPS server or is there something else going on? If there is a direct server connection, does that mean that every Android user can make a direct server connection?

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3 Answers 3

up vote 13 down vote accepted

GPS itself does not need a network connection to any server to work. It just needs a signal from a least 4 GPS satellites to calculate a good position fix.

There is also the GPS Almanac, which basically provides future data on where the satellites are expected to be in a given time in the future, usually up to 7 days. This can be used to speed up the position calculation. The Almanac is broadcasted by the GPS satellites and it takes up to 15 minutes to download the full Almanac via the GPS system. That's why there are also Servers on the Internet that provide the Almanac data in an more convenient, faster way. Maybe that's what you meant by "GPS Server". Android makes use of that too.

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So, anyone free to use these GPS satellites? That's what I wanted to know... –  c0da Nov 8 '11 at 12:29
    
Did you really expect your mobile phone to send signals to a satellite? ^^ –  neurino Nov 8 '11 at 12:51
1  
@c0da Well, that depends. You are "free" to use GPS system if you have a GPS receiver. The manufacturer of this device is the one that pays to use the GPS system and includes this cost on the cost of the GPS device. This way you don’t have to pay a monthly or annual fee in order to use you GPS. –  Doliveras Nov 8 '11 at 17:08
    
@neurino I wasn't aware of all this... I am new to this GPS thing... –  c0da Nov 8 '11 at 17:28
    
@Doliveras Thanks for adding such a clear explanation... –  c0da Nov 8 '11 at 17:29
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GPS - all GPS systems get signals from the satellites. They never send data to the GPS satellites. Your phone would need a much larger antenna to send a signal to them.

Systems like OnStar do send your position back to their servers. Google servers do get your position information so they can calculate directions and pull in the tiles for the map.

The US government does not charge for the use of GPS. It is global.

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GPS is a passive system. There is a constellation of satellites in orbit, with atomic clocks on board, that essentially just shout out their identifications and the time, for anybody who will listen. A GPS receiver listens for the signals and uses the differences in times that it's hearing from the different satellites -- due to speed-of-light delays and relativistic effects (!) -- and knowledge of the orbits of the satellites (also broadcast by the satellites), to triangulate its position on the earth.

The signals from the satellites are just radio. There is no "network", phone connection, or any two-way communication necessary.

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