According to the geometrical positioning principle of navigation parameters, satellite navigation can be divided into angular measurement, time ranging, doppler velocity measurement and combinatorial method, among which the angular measurement method and combinatorial method have no practical application due to low accuracy and other reasons.
(1) Doppler velocity location: “meridian” satellite navigation system to take this method.The user positioning equipment measures the doppler frequency shift curve based on the doppler frequency shift between the signal frequency received from the navigation satellite and the signal frequency sent by the satellite. The user’s position can be calculated based on this curve and satellite orbit parameters
(2) time ranging navigation and positioning: “navigation star” global positioning system adopts this system.Users receive accurate measurement equipment consists of four satellites system is not in the same plane (in order to ensure the result only, 4 satellites in the same plane) from the signal propagation time, and then completed a set of four mathematical equations of the model, can calculate the user’s position and 3 d coordinate and user clock error of the system time.
The difference between the user’s own geographical position coordinates measured by the navigation satellite and the real geographical position coordinates is called positioning error, which is the most important performance index of the satellite navigation system.Positioning accuracy mainly depends on orbit prediction accuracy navigation parameter measurement accuracy geometric amplification coefficient and user dynamic characteristic measurement accuracy.The accuracy of orbit prediction is mainly affected by the earth’s gravitational field model and other orbit perturbation forces.The measurement accuracy of navigation parameters is mainly affected by satellite and user equipment performance, signal errors in the ionosphere, tropospheric refraction and multi-path, etc., and its geometric amplification coefficient is determined by the geometric relationship between satellite and user position during positioning.The measurement accuracy of the user’s dynamic characteristics refers to the user’s course, speed and antenna height measurement accuracy during the positioning period.