Global Positioning System is a fully functional Global Navigation Satellite System. This system uses an artificial constellation of 24 medium Earth orbit satellites. These satellites transmit microwave signals, thus enabling a GPS receiver to determine its location, speed, direction and time.
It has become a very useful tool for making maps, surveying landscapes, commerce and many scientific uses. It also provides time reference which can be used in many applications which include study of earthquake and telecommunication network synchronization.
A GPS receiver simply calculates the distance between itself and three more GPS satellite. Each satellite has an atomic clock in it continually transmits certain data containing its exact time, location of the transmitting satellite and the almanac.
The Global Positioning System is used in a variety of Military and Civilian Applications. It allows soldiers find their objectives in a dark or completely unfamiliar territory and coordinate troop movement and supplies. GPS receivers which military personnel use are called Commanders and Soldier Digital Assistants. A combination of GPS and communication through radio enables real time vehicle tracking.
It is also used in marking targets as hostile and enables the precision guided munitions to allow them engage these targets with high accuracy. Air to Ground roles of military aircrafts use GPS to find targets. GPS also allows targeting for military weapons like ICBMs, Cruise missiles, precision guided missile.
GPS helps civilians a lot in surveying and navigation. Its ability to calculate local speed and orientation is extremely useful. Time transfer is possible because of its capability to synchronize clock. A widely used example of use of GPS is CDMA digital cell phone. Each base uses a GPS timing receiver to synchronize the codes with different base stations and thus making it easy inter-cellular hand off and thus support emergency phone calls and other many applications.