How does gps work?

Answer 1

GPS receivers integrate a radio and a navigation computer and can receive the faint, twenty-watt signals coming from the satellites. The computer uses these signals to calculate the distance between the satellites and the receiver. With this information, the computer can further calculate the position and velocity of the receiver.

The number of satellites visible to a receiver constantly varies between four and eleven according to time and location. Each satellite broadcasts a number of unique spread-spectrum codes, but only one, the Coarse Acquisition (C/A) code, is easily accessible for civilian use.

On the ground all GPS receivers have an almanac programmed into their computers that tells them where in the sky each satellite is, moment by moment.

Answer 2

The GPS "constellation" is a bunch of satellites in low earth orbit. Each one carries a super-accurate clock, so for every two satellites you can receive radio from, your receiver can tell the difference in the time it took for the two signals to reach you. That difference in radio time tells the difference in distance from you to each of the satellites. Each satellite also moves in an orbit that is super-precisely controlled, so for every one satellite you can receive, your receiver knows exactly where the satellite is located in its orbit at every instant. How does this information help to locate you ? For every one point that you know your distance from, you know you're somewhere on a sphere that's centered on the point. For every two points that you know your distance from, you know two spheres that you're somewhere on. Since two spheres intersect in a circle, you're somewhere on the circle. For every three points that you know your distance from, you know three spheres that you're somewhere on. Since the three spheres intersect in two points, you know you're either at one of the points or else you're at the other one. If you know your distance from a fourthpoint, then you know which of the two points you're at. The points are the GPS satellites. The atomic clocks in them give you all the distance information, which is combined with prior knowledge of their orbits, and all the math is handled by the receiver in your hand, to give you your location. You need information from a minimum of four satellites to calculate your position on the surface AND your elevation above sea level. But the more satellites you can receive, the more accurate the answer is.

Answer 3

It works by measuring the precise distance between the satellite and the receiver, which is calculated from the signal transit time.