The Evaluation Of IGS Real-time Product And Research On Positioning Method Of Real-time PPP

Precise point positioning(PPP)technology has been widely used in many engineering projects.The PPP with high real-time requirements used IGU ultra fast ephemeris in the early stage.However,with the improvement of the performance requirements for PPP,the International GNSS Service organization began to broadcast the real-time data stream consisting of correction values relative to the broadcast ephemeris to meet the actual needs.Although the real-time precise point positioning(RT-PPP)using real-time data stream is still facing many problems to be solved after more than ten years of development,in recent years,the accuracy of real-time data stream is constantly improving,and the application of real-time data stream is more and more well regarded.Therefore,this paper conducts an overall evaluation of the real-time data stream of IGS and studies the positioning method of RT-PPP.The key contents of the research are as follows:1.The algorithm of real-time synthesis of precise orbit and clock error using state space representation(SSR)information in real-time data stream is studied.The generation of real-time precise orbit and clock error files of four navigation systems has been realized by programming,and the completeness and accuracy of the real-time data stream products are evaluated.The system data integrity rates of GPS,GLONASS,Galileo and BDS are 94.30%,92.50%,83.16% and 83.06% respectively.The real-time orbit accuracy of GPS is consistent with that of IGU products,followed by Galileo and GLONASS,and the orbit accuracy of BDS II is relatively poor.The clock error accuracy of GPS,GLONASS,Galileo and BDS II are 0.09 ns,0.24 ns,0.18 ns and 0.36 ns respectively.The accuracy of the real-time clock error between different systems is quite different,and so does the accuracy of the satellite clock error within the system.2.This paper discusses the problems of real-time data stream in practical application,explores the influence of delay and issue of data on RT-PPP,compares different prediction methods of clock error short-term interruption,and studies the impact of data interruption on RT-PPP after using the clock error prediction methods,which is concluded that the GPS/GLONASS/Galileo/BDS combination has the best anti short-term interruption ability.3.This paper evaluates the real positioning performance of real-time data stream through static and dynamic rt-ppp experiments.The results show that the performance of GPS /GLONASS has the best performance in 3-hour static PPP.The convergence time of GPS /GLONASS dual system is the shortest,and the gap with using the final product is also the smallest.After adding Galileo and BDS,the convergence time becomes longer.Compared with the real-time GPS system,the real-time GPS / GLONASS positioning results are improved by9.2% and 9.7% in 2D and 3D,respectively.However,the improvement is not as big as that of the final product(23.5% and 13.0%).The positioning accuracy is not improved after adding Galileo and BDS.When using the same combination of GPS,GPS / GLONASS and GPS /GLONASS / Galileo,the RMS of difference between the dynamic rt-ppp positioning results and the final product positioning results is less than 10 cm in the horizontal direction and less than 30 cm in the three-dimensional direction.The positioning mutual difference is enlarged after the data of BDS II is added.Finally,according to the conclusion that the accuracy of the real-time clock error between different systems is quite different,this paper proposes a new weighting strategy that takes into account the accuracy of each satellite in the SSR information,and tests the effectiveness of the weighting strategy through experiments.