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GPS positioning system for navigation GPS navigation system's basic principle is to measure the known location of the satellite to the user the distance between the receiver and then integrated multi-satellite data can know the exact location of the receiver. To achieve this purpose, the satellite's position can be based on-board clock time recorded in the satellite ephemeris identified. The user to the satellite's distance from the satellite signal transmitted through the record to the user the experience of time, and then multiplied by the speed of light received (due to the interference of the atmosphere ionosphere, this distance is not the user and the real distance between the satellites, but pseudorange (PR): When the GPS satellites normal working hours, will continue to use the binary 1 and 0 symbol consisting of pseudo-random code (PN for short) launched the navigation data. garmin gps using pseudo-code, a total of two, namely civilian C / A code and the military of the P (Y) code. C / A code frequency of 1.023MHz, repeat the cycle of a millisecond, the code distance between a microsecond, the equivalent of 300m; P code frequency of 10.23MHz, repeat the cycle of 266.4 days, Code spacing of 0.1 microseconds, equivalent to 30m. The P code Y code is formed on the basis of confidentiality better performance. gps navigator message including the satellite ephemeris, work status, clock corrections, ionospheric delay correction, atmospheric refraction amendments and other information. It is the solution from the satellite signal modulation out to 50b / s modulation at the carrier frequency on the launch. gps navigation message included in each of the main frame 5 sub frames for each frame size 6s. the first three frames of 10 characters each code; repeat every 30 seconds, updated hourly. After the two were 15000b. navigation data telemetry in the contents of the main code, the conversion code, the first 1,2,3 block, most important of which was ephemeris data. When the user receives the navigation data, the extraction of the satellite time and do it with their own clock compared satellite and the user will be aware of the distance, and then use the navigation data in the satellite ephemeris data, calculate the time of satellite launch message Office location, the user WGS-84 geodetic coordinate system of the position, velocity and other information can be informed. see gps system satellite component of the role is to continue to launch navigation message. However, the user receiver using the onboard clock with the clock not always synchronized, so in addition to the user's three-dimensional coordinates x, y, z, but also introduce a Δt is the time between the satellite and receiver differential as unknowns, and then four equations out of these four unknown solution. So If you want to know the receiver position, at least four satellites can receive the signal. Visit TradeTang.com.