Satellite navigation is divided into systems such as angle measurement, time ranging, Doppler velocity measurement and combination method according to the geometric positioning principle of measurement navigation parameters. The angle measurement method and combination method have no practical application due to low precision.
1 Doppler speed positioning: "Mid Meridian" satellite navigation system adopts this method. The user positioning device measures the Doppler shift curve based on the Doppler shift between the frequency of the signal received from the navigation satellite and the frequency of the signal transmitted on the satellite, and the position of the user can be calculated from the curve and the satellite orbit parameter.
2 time ranging navigation positioning: "Navigation Star" global positioning system uses this system. The user receiving device accurately measures the propagation time of the signals sent by the four satellites in the system that are not in the same plane (to ensure the unique result, the four satellites cannot be in the same plane), and then complete a set of mathematical operations including four equations. The three-dimensional coordinates of the user's position and the error between the user's clock and the system time can be calculated.
The difference between the geographic location coordinates measured by the navigation satellite and its true geographical location coordinates is called the positioning error. It is the most important performance indicator of the satellite navigation system. The positioning accuracy is mainly determined by the accuracy of the orbit prediction, the measurement accuracy of the navigation parameters, the geometric amplification factor and the measurement accuracy of the user dynamic characteristics. The accuracy of orbit prediction is mainly affected by the gravitational field model of the Earth and other orbital perturbations. The accuracy of navigation parameters is mainly affected by satellite and user equipment performance, signal error factors such as ionosphere, tropospheric refraction and multipath. Its geometric amplification factor is determined by The geometric relationship between the satellite and the user's position during the positioning is graphically determined; the user's dynamic characteristic measurement accuracy refers to the accuracy of the heading, speed and antenna height measurement of the user during positioning.