How do GPS Receivers Work?

The GPS system is a compact satellite navigation system designed and funded by the United States Department of Defense. It contains 24 satellites that can continuously send geographic altitude and time signals. These satellites are evenly distributed in six orbits. Generally speaking, a GPS receiver on the ground can receive 5 to 12 satellite signals. In order to obtain positioning coordinates on the ground, at least 4 satellite signals are required. Three are used to determine the latitude, longitude, and altitude of the GPS receiver. Altitude, and the fourth provides synchronized correction time.