The satellite signal or device restrictions

Therefore, the location of the satellite is a function of time, the GPS observation volume issued precision measurements as the basis, corresponding to the satellite position information is coded information sent through the satellite signal to the receiver. GPS positioning, whether it is observation of the code phase or carrier phase observations require the satellite clock and receiver clock to maintain strict synchronization. In fact, the GPS satellites are equipped with high-precision atomic clock (rubidium and cesium clock), but they are between the ideal of GPS, there are still difficult to avoid bias and drift. The total amount of this deviation is less than 1ms.

This deviation of the satellite clock, usually by the master station of the satellite, determined by continuous monitoring of the status of the satellite clock is running, and through the satellite navigation data to the receiver. After clock error correction, synchronization between the satellites is poor, can be maintained at less than 20ns.

In relative positioning, satellite clock difference may be measured through the concept of differencing (or difference) method to eliminate.

Estimated satellite orbit deviation is more difficult, mainly due to the complexity of the various perturbation effects, in the operation of satellite ground stations in order to not be fully reliable determination of this force and to grasp their role The law of the satellite orbit information by the navigation data to get it.

It should be said that the satellite orbit error is one of the main error sources of GPS measurement. The longer the length of the baseline measurement, the greater the impact of this error.

GPS location measurement, processing of satellite orbit errors in the following ways:

Satellite orbit information from the navigation message, this method shall not consider the actual existence of the satellite orbit errors, so for the lower precision real-time point positioning.

This method is in the data processing, the introduction of the correction parameter characterization of the satellite orbit deviation, and assuming that these parameters in a short time constant, will be in conjunction with other knowledge the number of solving.

This approach is the use of two or more observatories with simultaneous observations of the same satellite differencing. To weaken the impact of satellite orbit errors. Measured by the same satellite position error on the synchronization concept of the different observatories, with the nature of the systematic errors, so by the differencing method, can significantly weakened the impact of satellite orbit errors, especially when the baseline is shorter, its effectiveness obvious.

Related to the satellite signal error include atmospheric refraction error and multipath effects

Other electromagnetic signals of the GPS satellite signals through the ionosphere, will be the impact of the dispersion characteristics of this media, then the signal propagation path changes. When the GPS satellite in the zenith direction, the ionospheric refraction with minimal impact on the signal propagation path, and when the satellite close to the horizon, the greatest impact.

Since the ionosphere is a function of signal frequency, so the electromagnetic signals of different frequencies were observed.Main products: car dvd player and car dvd , are with good quality. Will be able to determine their impact on the concept of measurement to be amended. Therefore, with the dual-frequency GPS receiver, has been widely used in precision positioning measurement. However, it should be clearly pointed out that should try to avoid the observation of solar radiation at noon or in the abnormal period of sunspot activity.