The navigation information is modulated on the L1 carrier, and its signal frequency is 50Hz, including the orbit parameters of the GPS satellites, the satellite clock correction number and some other system parameters. The user generally needs to use this navigation information to calculate the position of the GPS satellite in the earth orbit at a certain moment, and the navigation information is also called broadcast ephemeris.

　　SPS and PPS are GPS systems that provide two different types of services for different users. One is the Standard Positioning Service (SPSS Standard Positioning Service), and the other is the Precision Positioning Service (PPSPrecision Positioning Service). These two different types of services are provided by two different subsystems, the standard positioning service is provided by the standard positioning subsystem (SPSS Standard Positioning System), and the precision positioning service is provided by the precise positioning subsystem (PPSPrecision Positioning System).

　　SPS is mainly for civilian users all over the world.

　　PPS is mainly for the military departments of the United States and its allies, as well as civilian licensed users.

　　In GPS positioning, one or more of the following observations are often used for data processing to determine the coordinates of the to-be-determined point or the baseline vector between the to-be-determined points:

　　L1 carrier phase observations

　　L2 carrier phase observations (half-wave or full-wave)

　　C/A code pseudorange modulated on L1

　　P-code pseudorange modulated on L1

　　P-code pseudorange modulated on L2

　　Doppler shift on L1

　　Doppler shift on L2

　　In fact, in the GPS positioning, in addition to using a large number of the above observations for data processing, some special observations formed by certain combinations of the above observations are often used, such as wide-lane observations (Wide- Lane), narrow-lane observations (Narrow-Lane), and ionospheric delay-eliminated observations (Ion-Free) for data processing.

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