As we all know, the U.S. GPS and Russian GLONASS satellite is independent of space-based satellite positioning systems, GPS using CDMA (Code Division Multiple Access) mode, according to the difference between the satellite code modulation, all GPS satellites in the same carrier frequency are fL1 = 1575.42 MHz and fL2 = 1227.6 MHz. GLONASS satellites used FDMA (Frequency Division Multiple Access) mode, according to the carrier frequency to make distinctions between different satellites, each satellite broadcast made for the two frequencies were 1 602 +0.562 K (MHz) and 1 246 +0.4375 K (MHz), which K 1 ~ 24 satellites of the frequency number. As a result of these two satellite-based navigation system in the system configuration, navigation and positioning mechanism, the working frequency band, modulation, signal and ephemeris data structure is basically the same as for the use of a user terminal to receive two satellite signals at the same time possible. Satellite navigation receiver is not a simple GPS, GLONASS satellite data receiver to switch between, but the opening 12 parallel tracking GPS satellite tracking of the mouth and 12 parallel port GLONASS satellites, while observing more than 10 navigation satellites, the GPS and GLONASS satellite data after the main time synchronization, to carry out coordinate transformation, real-time optimization algorithm based on a fusion of the two navigation satellite system, select the PDOP (geometric precision of the smallest) value of a group of satellites, the best constellation to provide the most accurate positioning.

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