US GPS

　　Features: mature

　　GPS (Global Positioning System) is a global satellite positioning system established by the United States after 20 years and costing more than 30 billion US dollars. There are currently 30 and 4 types of navigation satellites.

　　The satellite orbit height of the system is 20,000 kilometers, which enables users anywhere on the earth to see at least four satellites at any time. It is an all-weather, real-time navigation and positioning system. Mature navigation and positioning system.

　　European Galileo

　　Features: Precise

　　Galileo positioning system is a satellite positioning system under construction in the European Union, known as the "European version of GPS". The Galileo positioning system is expected to launch a total of 30 satellites, of which 27 are working satellites and 3 are backup satellites. The satellite orbit height is about 24,000 kilometers, and its accuracy will be more accurate than GPS.

　　The satellite signals provided by the US GPS to other countries can only detect objects about 10 meters long on the ground, while Galileo's satellites can detect objects 1 meter long. Figuratively speaking, the GPS system can only find the street, and Galileo can find the door.

　　There are already four official Galileo satellites in space. The EU plans to have the Galileo system initially operational in 2014.

　　GLONASS, RUSSIA

　　Features: strong anti-interference ability

　　GLONASS consists of 24 satellites. Although its positioning accuracy is slightly lower than that of GPS and Galileo, its anti-interference ability is the strongest. The GLONASS project was a project launched by the former Soviet Union in 1976 and was initially military in nature. After the disintegration of the Soviet Union, GLONASS's plans continued to be delayed due to lack of adequate funding.

　　In November 2011, with the successful launch of a "GLONASS-M" satellite, all 24 satellites of the system have been rated to work in orbit, and another 4 are in orbit for backup, thus achieving global coverage.

　　China Beidou

　　Features: Combination of SMS and Navigation

　　Beidou satellite navigation system is a global satellite navigation system independently developed and operated by China. The Beidou satellite navigation system consists of three parts: the space segment, the ground segment and the user segment, and is expected to consist of more than 30 satellites.

　　Compared with the American GPS system, the Russian GLONASS system, and the European Galileo system, the combination of SMS and navigation is a unique invention of China's Beidou satellite navigation system. Generally speaking, other global satellite navigation systems in the world just tell the user what time and where they are, while the Beidou system can also send out the user's location information, so that other people the user wants to inform know the user's situation

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