GNSS is the standard generic term for satellite navigation systems that provide autonomous geo-spatial positioning with global coverage. It includes the global GPS of the United States, China’s Beidou, Russia’s Glonass, and the European Union’s Galileo. There are also regional navigation systems, such as Japan’s Quasi-Zenith (QZSS) and India’s IRNSS. Enhanced systems include WAAS (the USA), MSAS (Japan), EGNOS (the EU), Gagan (India), and NIG-Gomsat-1 (Nigeria).

The satellite navigation system consists of three parts: the space constellation part, the ground monitoring part and the user equipment part. The space constellation part is the satellites, with the four navigation system satellites occupying different orbits. The number of satellites, composition, and communication principles vary from systems. The ground monitoring center receives and measures the satellite signal, determines the orbit information of the satellite, and sends it to the satellite. The user’s device is the receiver, which can be a professional multi-frequency multi-system receiver or a GPS module in our mobile phone. The location of the user can be determined through the satellite orbit information calculated by the signal.