How Does Gps Work?

The Global Positioning System (GPS) is a network of about 30 satellites orbiting the Earth at an altitude of 20,000 km. The system was originally developed by the US government for militarynavigation but now anyone with a GPS device, be it a SatNav, mobile phone or handheld GPS unit, can receive the radio signals that the satellites broadcast.

Wherever you are on the planet, at least four GPSsatellites are ‘visible’ at any time. Each one transmits information about its position and the current time at regular intervals. These signals, traveling at the speed of light, are intercepted byyour GPS receiver, which calculates how far away each satellite is based on how long it took for the messages to arrive.

Once it has information on how far away at least three satellites are, yourGPS receiver can pinpoint your location using a process called trilateration.Trilateration is the process of determining absolute or relative locations of points by measurement of distances.

GPSalso is related with Relativity. GPS satellites have atomic clocks on board to keep accurate time. General and Special Relativity however predict that differences will appear between these clocks and anidentical clock on Earth. General Relativity predicts that time will appear to run slower under stronger gravitational pull, the clocks on board the satellites will therefore seem to run faster than aclock on Earth. Special Relativity predicts that because the satellites’ clocks are moving relative to a clock on Earth, they will appear to run slower.

The GPS satellites transmit signals to aGPS receiver. These receivers, receive satellite signals; they do not transmit, so they can only be used effectively outdoors. Early receivers did not perform well within forested areas or near tallbuildings but later receiver designs, have overcome this and improved performance and sensitivity markedly. GPS operations depend on a very accurate time reference, which is provided by atomic clocks...