Global navigation satellite system positioning uses pseudo-range, ephemeris, satellite launch time and other observations of a group of satellites, and also must know the user clock difference. The global navigation satellite system is a space-based radio navigation positioning system that can provide users with all-weather 3D coordinates and speed and time information at any location on the surface of the earth or in near-Earth space. Therefore, to put it bluntly, if you want to know the altitude in addition to the latitude and longitude, then you must accurately locate 4 satellites.
Satellite navigation and positioning technology has basically replaced ground-based radio navigation, traditional geodetic and astronomical navigation and positioning technologies, and has promoted new developments in the field of geodetic and navigation positioning. Today, the GNSS system is not only a national security and economic infrastructure, but also an important symbol of the status of a modern power and national comprehensive national strength. Because of its political, economic, and military significance, major military powers and economies in the world are racing to develop independent satellite navigation systems. On April 14, 2007, China successfully launched the first Beidou satellite, marking that the world’s fourth GNSS system has entered a substantial operational stage. It is estimated that by 2020 US GPS, Russian GLONASS, EU GALILEO and Chinese Beidou satellites Four major GNSS systems, such as the navigation system, will be completed or modernized. In addition to the above four global systems, it also includes regional systems and enhanced systems. Among them, regional systems include QZSS in Japan and IRNSS in India. Enhanced systems include WAAS in the United States, MSAS in Japan, EGNOS in the European Union, GAGAN in India, and Niger Asian NIG-GOMSAT-1 and so on. In the next few years, the satellite navigation system will enter a completely new stage. Users will face the situation of nearly 100 navigation satellites coexisting and compatible with each other in the four global systems. Rich navigation information can improve the usability, accuracy, completeness, and reliability of satellite navigation users, but at the same time, it must also face competition in frequency resources, competition in the satellite navigation market, competition in time and frequency dominance, and compatibility and interoperability debates. Many problems.
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