| With the Precise point Positioning (PPP) being applied more and more widely for the past few years, the data processing method of PPP and multi system combined PPP have become research hotspots. In order to obtain shorter convergence time and higher accuracy,multiple integrated satellite navigation system, such as BDS with GPS and better positioning method are two feasible options. As the traditional Least Squares (LS) has the problem of isolating the relationship between epoch measurements and the Extended Kalman Filter (EKF)has a problem of inaccuracy prior information, this paper proposes a method of using Adaptive extended Kalman Filter (AKF) to adjust the process noise in order to achieve the optimal estimation of system state. The main research contents of this paper are as follows:(1)This paper introduces and studies the PPP float ambiguity resolution and the fixed integer ambiguity resolution method firstly. Focus on the traditional Ionosphere-Free (IF) and has a comparative analysis. As we all know, the IF model can eliminate the first order term of the ionosphere error which can reach 99.9% of the total ionosphere influence, so it is obvious that the IF model can weaken the ionosphere effect mostly.(2)That PPP needs to deal with more error sources is the difference between PPP and differential positioning, single point positioning. The extent of the error correction will directly determine the user positioning accuracy level and index requirements. The error characteristics and error causes of PPP are analyzed in this paper. For different types of error,the paper uses model correction method or parameter estimation method to deal with for a lowest influence on the positioning results, thereby the performance of PPP navigation can be improved better.(3)The data preprocessing method in PPP is related to the accuracy and reliability of the user's position, as well as affect the convergence speed of the filter. The cycle slip detecting and repairing is one of the key issues. In this paper, the problem of cycle slip detecting and repairing of PPP un-differential model is studied. In the case of the detection blind spot of a single method, the combination of the ionosphere residual method and M-W is proposed for the detection. The cycle slip of the two frequency is detected and separated through a combination of observations, and then the cycle slip is repaired. Finally, the experimental data are tested to verify the validity, feasibility and applicability of the method. As a conclusion,the combination of the two methods can fully use the advantages and improve the efficiency of cycle slip detecting and repairing.(4)This paper researches on the processing method of the combined system and analyzes the difference between BDS/GPS combined PPP with. single BDS PPP, single GPS PPP, and then presents the solution model of combined system. The state parameters are estimated by using AKF and the simulation test of MATLAB are realized. Finally, the algorithm is tested and verified through the actual collected experimental data. The results of the AKF algorithm using experimental data show that: compared with the traditional EKF, through the AKF, the convergence time of PPP can improve by 9 minutes, and the positioning accuracy can improve by 33.7%. The combined system has a significant improvement in the positioning accuracy and convergence speed compared with single system. What's more, the combined system has more available satellites, which can guarantee the reliability, availability and continuity of the system. Multi system combined positioning is an important method to improve the positioning accuracy,this paper provides a reference for the GNSS precise point positioning. |
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