GPS system

GPS:
A typical GPS receiver calculates its position using the signals from four or more GPS satellites.Four satellites are needed since the process needs a very accurate local time.In other words, the receiver uses four measurements to solve for four variables: x, y, z, and t. These values are then turned into more user-friendly forms, such as latitude/longitude or location on a map, then displayed to the user.

Each GPS satellite has an atomic clock, and continually transmits messages containing the current time at the start of the message, parameters to calculate the location of the satellite.The receiver uses the arrival time to compute the distance to each satellite, from which it determines the position of the receiver using geometry and trigonometry.

Technical description
The current GPS consists of three major segments. These are the
1. space segment (SS): GPS satellites
2. control segment (CS): US Air Force monitoring stations
3. user segment (US): user's GPS receiver