| Precise point positioning can achieve high precision static and kinematic positioning results with a single receiver,it has the advantages of data acquisition and data processing more convenient,simple,high efficiency,low cost and so on.However,the PPP based on single satellite system has a long convergence time,and can't obtain high precision positioning results due to the limitation of the number of visible satellites in the complex observation environment such as mountain area or urban proper.Therefore,the application of PPP technology in some fields is limited.In recent years,the satellite navigation system presents a multi-mode multifrequency development pattern,PPP users can obtain more observation values and better satellite space geometry configuration,which makes it possible to improve the timeliness,reliability and accuracy of PPP.However,the Multi-GNSS precise point positioning is not a simple combination of signals,but there are still many key problems to be solved.In view of the problems of the convergence rate,the satellites selection algorithm,the positioning accuracy,and the parameter estimation of the precise point positioning,the key issues of PPP data processing are studied and analyzed.The main work and conclusions of this paper are as follows:(1)In view of BDS,GPS,GLONASS and GALILEO using different coordinates and time frame.This paper discusses the characteristics of the time and space datum of each constellation,and determines the way to coordinate the coordinate system to the WGS-84 coordinate system,and the time system is unified to the world coordinate.(2)The characteristics of the main error sources in PPP and its influence on the calculation precision are analyzed.The magnitude of the different error sources is divided.Then the error handling strategy of multi-GNSS PPP is determined(3)PPP has a high sampling rate,if all the observation epochs are adjusted by the least squares estimation method,the high dimensional parameter matrix and the coefficient matrix will make the solution appear abnormal.On the basis of studying the EKF dynamic model and observation model,the forward and backward smoothing filter algorithm is applied to data processing for multi-GNSS PPP.The experimental results show that the smoothing filter can improve the convergence speed and efficiency(4)Based on the influence of the constellation space configuration on the po sitioning accuracy,the geometric two-dimensional convex hull Graham scanning method is applied to fast satellites selection.This algorithm can realize the fast and effective satellites selection under the premise of meeting the requirement of the user,it improves the spatial configuration and the convergence speed of PPP.(5)This paper analyzes the relationship between wide lane and narrow lane ambiguity,and the model of wide and narrow lane ambiguity test is given.The parameters are solved by backward extended Kalman filter algorithm,the ambiguity are solved by MLAMBDA,the data of the MGEX tracking station is the data source,the fixed accuracy and convergence rate of PPP ambiguity fixed solution and floating point solution are analyzed experimentally.It is proved that the fixed solution of PPP can improve the positioning precision and convergence speed of floating solution.(6)This paper discusses the convergence speed and positioning accuracy of the dual system combination GPS/ BDS,GPS/ GLONASS and four system combination BDS/ GPS/ GLONASS/ GALILEO through the design of experimental programs.The experimental results show that the positioning accuracy and convergence speed of the combined system are significantly improved compared with the single GPS PPP in short time static and dynamic positioning,but the improvement of the zenith direction is not obvious. |
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