The Global Positioning System (GPS) is a space-based navigation system that provides location and time information in all weather conditions, anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. In addition to GPS, other systems are in use or under development. The Russian Global Navigation Satellite System (GLONASS) was developed contemporaneously with GPS. The BeiDou Navigation Satellite System (BDS) is a Chinese satellite navigation system. Assisted GPS (A-GPS and less commonly as aGPS) is a system that is often able to significantly improve the startup performance of a GPS satellite-based positioning system. A-GPS is extensively used with GPS-capable smartphones.

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