Global Positioning System

How Does GPS (Global Positioning System) Work?

GPS is a system of 30+ navigation satellites circling Earth. We know where they are because they constantly send out signals. A GPS receiver in your phone listens for these signals. Once the receiver calculates its distance from four or more GPS satellites, it can figure out where you are.Global Positioning System (GPS) provides improved location accuracy, in the range of operations of each system, from the 15-meter nominal GPS accuracy

1. GPS works by using a method called

   
   

   “Triangulation” or “Trilateration”

   
   
2. It needs to get a message from at least three, preferably four satellites
3. To “triangulate”, a GPS receiver measures the distance between itself and each satellite. It can measure distance because it works out exactly how long it took for each satellite’s message to arrive. (distance = time of arrival * speed of light)
4. To measure travel time, GPS needs very accurate timing which it achieves with Atomic clocks on board each satellite.
5. Along with distance, the device needs to know exactly where the satellites are in space at any given time. This information is held inside the GPS receiver itself.
6. Finally, because it knows exactly where the satellites are at that instant, by using some very clever mathematics, it can work out where it is on the ground.

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Triangulation

is the key idea behind GPS. It makes use of satellites in space as reference points for locations here on earth. By very, very accurately measuring our distance from at least three satellites we can “triangulate” our position anywhere on earth.

With GPS it is more usual to use four line-of-sight satellites as you can see in the image above.

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