Several countries in the world have their own satellite navigation systems.

Four countries, namely, GPS in the United States, Beidou in China, Galileo in the European Union and GLONASS in Russia.

1, GPS is an omni-directional, all-weather, all-time and high-precision satellite navigation system developed by the U.S. Department of Defense, which can provide low-cost and high-precision three-dimensional navigation information such as position, speed and accurate timing for users all over the world. It is a typical application of satellite communication technology in navigation field, which greatly improves the information level of the earth society and effectively promotes the development of digital economy.

GPS can provide vehicle positioning, anti-theft, anti-robbery, driving route monitoring, call command and other functions. To achieve all the above functions, we must have three elements: GPS terminal, transmission network and monitoring platform.

2. Beidou satellite navigation system (hereinafter referred to as Beidou system) is a satellite navigation system independently built and operated by China with a view to the needs of national security and economic and social development. It is an important national space infrastructure that provides all-weather, all-day, high-precision positioning, navigation and timing services for users around the world.

With the development of Beidou system construction and service capacity, related products have been widely used in transportation, marine fishery, hydrological monitoring, weather forecasting, surveying and mapping geographic information, forest fire prevention, communication timing, power dispatching, emergency rescue and emergency search and rescue. And gradually penetrated into all aspects of human social production and people's lives, injecting new vitality into global economic and social development.

Extended data

Galileo satellite navigation system

1999, the European union announced the Galileo satellite navigation system plan for the first time, with the aim of getting rid of Europe's dependence on the American global positioning system and breaking its monopoly position. The project will launch 32 satellites with a total investment of 3.4 billion euros. Due to differences among member states, the plan was postponed several times.

Council of Europe's report 1999 proposed two constellation selection schemes for Galileo system:

The first is the 2 1+6 scheme, which uses 2 1 medium and high orbit satellites plus 6 geosynchronous orbit satellites. This scheme can basically meet the needs of Europe, but it also needs to combine the GPS system of the United States and the local differential enhancement system.

The second is the 36+9 scheme, which uses 36 medium and high orbit satellites and 9 geosynchronous orbit satellites or only 36 medium and high orbit satellites. This scheme can meet all the needs of Europe without relying on GPS system. The ground part of the system will be composed of a real European monitoring system, an orbit measurement and control system, a time synchronization system and a system management center.

Global navigation satellite system

GLONASS was initiated by the Soviet Union in 1976. GLONASS system will use 24 satellites to realize global positioning service, which can provide high-precision three-dimensional space and speed information, as well as time service.

According to the design, the satellites in GLONASS constellation are composed of 24 medium-orbit satellites, including 2 1 working star and 3 spare stars, which are distributed on three circular orbital planes with orbital heights of 1 9 100km and an inclination of 64.8.

Different from GPS system, GLONASS system adopts frequency division multiple access (FDMA), and each GLONASS satellite broadcasts two signals, L 1 and L2.

Specifically, the frequencies are L1=1602+0.5625 * k (MHz) and L2= 1246+0.4375*k(MHz), where k is 1 ~ 24, which is the frequency of each satellite. Under the condition of 95% probability, the positioning accuracy of GLONASS system is 100 m in the horizontal direction and 150 m in the vertical direction.

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