GPS

Global Positioning System (GPS) is a satellite-based radionavigation system that provides geolocation and time information to a receiver on or near the Earth when at least four satellites are visible.

It is owned by the United States government and operated by the U.S. Space Force. The system relies on a constellation of satellites in medium Earth orbit, ground control stations, and user receivers. Each satellite broadcasts a precise timing signal and orbital information, which a receiver uses to calculate its position by trilateration.

Development began in the 1970s for military purposes, with first satellites launched in 1978 and the system becoming fully operational in 1995. Civilian access has been unrestricted since the 1990s, and in 2000 the government turned off selective availability that degraded accuracy.

Modern GPS uses multiple signals, including the L1 C/A civil signal and newer L2C and L5 signals, with ongoing modernization to improve accuracy and robustness. The basic civil accuracy is typically several meters, and accuracy can be improved with augmentation systems such as WAAS or RTK to sub-meter or centimeter levels in specialized applications.

GPS is widely used for navigation in vehicles and smartphones, aviation, maritime transport, surveying, mapping, and offline timing. It is one of the core components of global navigation satellite systems (GNSS), alongside Galileo, GLONASS, and BeiDou.

Limitations include signal obstruction in urban canyons or indoors, multipath effects, atmospheric delays, and potential jamming or spoofing; receivers usually incorporate error correction and integrity monitoring.