GPS or Global Positioning System is space-based global navigation satellite system (GNSS). GNSS is used for satellite navigation system with global coverage. GPS provides location and time information in all weather, anywhere on Earh (where there is an obstructed line to four or more GPS satellite). GPS is maintained by United States goverment and available to anyone with GPS receiver.

Other satellite positioning systems available are GLONASS from Rusia, Compass

navigation system from China and European Union’s Galileo positioning system. Compass and Galileo are under development and scheduled to operate by 2020.

GPS which maintained by US consist of a constellation of 24 operational satellite. Each GPS satellite transmits a signal, which has a number of component : 2 sine wave (carrier signal), 2 digital codes, and a navigation message. carriers and codes are used mainly for measuring the distance between gps receiver and the satellite. while, navigation message contains, along with other information, the coordinate of the satellite as a function of time. Transmitted signals are controlled by highly accurate atomic clock on board the satellite.

GPS consists of three segments :
1. Control Segment : Worldwide network tracking stations, with its master control station in Colorado
2. Space Segment : Satellite
3. User Segment : Military and Civil user