Methods Study Of GPS/BDS Real-time Satellite Clock Estimation

Precise point positioning plays an important role in promoting the development of GNSS in both civil and commercial applications,and the application of real-time precise point positioning has also become one of the hot topics in the field of GNSS navigation and positioning research.At present,the application of real-time PPP is difficult to popularize,the main reason is that the accuracy of real-time satellite clock is not high,and satellite atomic clocks are subject to variability due to external and their own factors,so it is difficult to predict accurately and must be estimated by real-time observation data.This paper systematically studies the real-time clock filtering algorithm of GPS/BDS.The main research contents are as follows:(1)This paper expounds the characteristics of various error sources before estimating the real-time clock,introduces the corresponding correction method and mathematic model at the same time.The paper introduces the mothods of the parameter estimation,including the principles of classical linear Kalman filter and square root information filte.The redundant ambiguity parameters can be eliminated in the estimating process,which can improve the efficiency of the estimation.(2)When the ionospheric delay rapidly changes,most of the detection effect of the cycle-slip detection methods reduces significantly.This paper proposes an improved ionospheric delay cycle-slip detection method for double-frequency carrier phase observation cycle-slip,which can accurately detect the 1-2 weeks cycle-slip at low elevation and low sampling rate.What's more,two pseudo-range phase combinations and one non-geometric phase combination are used to detect the triple-frequency carrier phase observation cycle-slip.The results show that this method can effectively detect the cycle-slip of triple-frequency carrier phase observation.(3)This paper uses the improved ionospheric delay cycle-slip detection method and the TurboEdit method to estimate the real-time clock respectively,then analyses the accuracy of the clock estimation.Experiments show that the accuracy of the former real-time clock is nearly the same as that of the latter.(4)Based on the CUM 6 h ultra-rapid forecasting orbit and square root information,the data of 81 IGS/MGEX stations are used to calculate the real-time clock.The accuracy of the real-time clock is compared by using the second-order difference method: the accuracy of the GPS clock is 0.27 ns,the accuracy of the GEO clock of BDS is 1.37 ns,the IGSO is 0.47 ns,and the MEO is 0.39 ns.(5)This paper introduces the real time data transmission of GNSS based on TCP/IP and Ntrip protocol,briefly describes the data structure of RTCM format and the data analysis flow,which can be used to receive the real-time data flow of the station required for positioning.Using GBM's post precision products and the real-time precision products solved in this article respectively perform precise point positioning in GPS and GPS+BDS modes,and analyze the accuracy of the results.In the use of the post-product positioning,convergence speed and positioning accuracy are significantly better than the real-time products,but the timeliness of real-time products makes it have more influences and development prospects than post-product.