GNSS is the general term for all navigation and positioning satellites, that is, the Global Navigation Satellite System (Global Navigation Satellite System). BDS, GLONASS in Russia, GALILEO in Europe, etcetera. We can also simply understand it as a positioning system based on artificial earth satellites, which can provide accurate geographic location, speed and time anywhere in the world and in near-Earth space information.
The principle of GNSS positioning is NB Module based on the constant propagation speed of radio waves and the linear nature of the propagation path, by measuring the propagation time of the radio waves in the space to determine the distance difference between the satellite and the user receiver antenna. The distance difference, distance and measurement value, and then use these distance differences as the radius to meet the three spheres, and solve the user position according to the simultaneous equations;
First of all, any location on the earth's surface has its three-dimensional coordinates, that is, longitude, latitude and elevation. The GNSS satellite above its head also has its own three-dimensional coordinates. We can regard the entire space as a coordinate system, and we can draw a cube. The two opposite corners of the cube are the user and the satellite;
Secondly, based on the knowledge of solid geometry, we can know the distance △L between the satellite and the user (this distance is also called "pseudorange"); the equation is as follows:
The coordinates of the satellite are (x', y', z'), which are known, and the coordinates of the user are (x, y, z), which are unknown. At the same time, the satellite can send a signal to the user terminal, and the transmission speed of the signal is basically equal to the speed of light c, and the satellite has a highly accurate atomic clock, so it knows its own time is t.