GPS principle

　　The basic principle of the GPS navigation system is to measure the distance between the known positions and the user receiver, and then the data of multiple satellites can know the specific location of the receiver. To achieve this, the position of the satellite can be detected in the satellite star calendar according to the time recorded by the Star -shown clock. The distance from the user to the satellite is transmitted to the time of the user through the record satellite signal, and then multiplied at the speed of light (due to the interference of the ionization layer of the atmosphere, this distance is not the true distance between the user and the satellite, but it is, but the satellite, but it, but it, but is not the true distance between the satellite, but it is, but the satellite. Pseudo -distance (PR): When the GPS satellite works normally, it will continue to use the pseudo -random code (referred to as a pseudo -code) composed of 1 and 0 binary code elements. There are two types of pseudo -code used in the GPS system, namely Civilian C/A code and military P (y) code. C/A code frequency is 1.023MHz, one milliseconds of repeated cycle, code spacing of 1 microsecond, equivalent to 300m; P code frequency 10.23MHz, repeated cycle 266.4 days, code code, code code, code code, code code, code code, code code, code code, code code The spacing is 0.1 microsecond, which is equivalent to 30M. The Y code is formed on the basis of the P code, and the confidentiality performance is better. Navigation electricity includes satellite stars, working conditions, clock correction, ionizing layer delay correction, atmospheric refraction correction, etc. Information. It is decoded from the satellite signal, which is emitted on the load frequency with 50B/s. Each main frame of the navigation electrical text contains 5 subframes in the length of 6s. Repeat every thirty seconds and update every hour. The latter two frames have a total of 15,000B. The contents of the navigation electrical text mainly include remote test codes, conversion codes, 1, 2, and 3 data blocks. When the user receives the navigation electrical text, the satellite time is extracted and the comparison with his clock to learn the distance between the satellite and the user. Users such as the location speed of the user in the WGS-84 land coordinate system can be known.

　　GPS receiver

　　The GPS receiver can receive the time information that can be used to be used for time -to -nano -seconds; it is used to predict the forecast star calendar in the future of satellites in the next few months; , The accuracy is several meters to tens of meters (different satellites are different, changing at any time); and GPS system information, such as satellite conditions.

　　The measurement of the GPS receiver's code can get the distance from the satellite to the receiver. Because the error containing the receiver satellite clock and the atmospheric dissemination error, it is called a pseudo -distance. The pseudo -tagging distance from 0A is called UA code pseudo -pseudo -pseudo -pseudo -pseudo -pseudo -pseudo -precision is about 20 meters. The pseudo -pseudo distance measured by the P code is called P code pseudo -pseudo distance, with an accuracy of about 2 meters.

　　The GPS receiving machine decodes or uses other technologies for the receiving satellite signals. After removing the information on the carrier, the carrier can be restored. Strictly speaking, the carrier phase should be called the carrier frequency phase. It is the difference between the signal phase of the satellite signal carrier of the Doppler frequency transfer and the receiving machine. Generally, the number of times of the calendar time determined by the receiver clock and maintaining the tracking of satellite signals can record the change value of the phase, but the initial value of the receiver and the satellite oscillator when you start observation is unknown. The phase integer of the original element is also unknown, that is, the vagueness of the week, and can only be used as a parameter solution in data processing. The accuracy of the phase observation value is as high as millimeter, but the premise is to solve the fuzzyness of the whole week. Therefore, the phase observation value can be used only when the relative positioning and a continuous observation value can be used. Can use phase observation values.

　　The theory of relativity provides the required correction for GPS

　　According to the positioning method, GPS positioning is divided into single -point positioning and relative positioning (differential positioning). The single -point positioning is to determine the position of the receiving machine based on the observation data of a receiver. It can only use a pseudo -distance observation capacity, which can be used for rough navigation positioning of vehicles and boats. Relative positioning (differential positioning) is a method of determining the relative position between the observation points based on the observation data of the receiver of the two units. Use phase observation values for relative positioning.

　　In the GPS observation measurement contains errors such as satellite and receiving machines, delayed atmospheric communication, and multi -path effects. When the positioning is calculated, it is also affected by the satellite radio calendar error. Cancel off or weakening, so the positioning accuracy will be greatly improved. The dual -frequency receiver can offset the main part of the ionization error of the atmosphere in the atmosphere according to the observation of the two frequencies. ), A dual -frequency receiver should be selected.

　　The theory of relativity provides the required correction for GPS

　　The timing signal of the GPS satellite of the global positioning system provides latitude, longitude, and height information. The accurate distance measurement requires a precise clock. Therefore, the accurate GPS receiver must use relativity effects.

　　The GPS receiver with accuracy within 30 meters means that it has used the relativity effect. The physicist at the University of Washington, CLIFFORD M. Will, explained in detail: "If the relativity effect is not considered, the clock on the satellite is not synchronized with the clock of the earth." The theory of relativity believes that the passage of fast moving objects is slower than the static. Will calculates that each GPS satellite across about 14,000 kilometers per hour, which means that its star -load atomic clock is 7 microseconds slower every day than the clock on the earth.

　　Gravity exerts a greater relativity effect on time. At a high altitude of about 20,000 kilometers, the gravitational tension of GPS satellites is equivalent to about a quarter of the ground. The result is that the starcap clock is faster 45 microseconds a day, and the GPS is included in the deviation of a total of 38 microseconds. Ashby explained: "If there is no frequency compensation on the satellite, it will increase an error of 11 kilometers a day." (This effect is more complicated in fact, because the satellite is along a biased orbit, sometimes closer to the earth, sometimes again again Far away.)

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