| Multi-system combination has become the main trend in GNSS data processing.GNSS multi-system combination can make full use of each system satellite to improve the reliability and availability of global positioning,while improving the problems of poor satellite spatial geometry structure and insufficient number of visible satellites caused by single-system positioning.As a result,the research in this work focuses on multi-system ambiguity fixing and real-time ambiguity fixing of combined BDS-2 and BDS-3,as well as real-time precision single-point service performance of BDS-3 PPP-B2 b.The following are the thesis’ s main work and results:(1)A multi-system combination PPP positioning model is constructed.The multipath error on BDS-2 satellite and the inter-system deviation when BDS-2 and BDS-3 are combined are considered.The multi-system partial ambiguity fixing algorithm is realized.The results show that both the single-system and multi-system fixed solutions can improve the positioning accuracy and convergence time of the floating-point solution,and the effect is better in the dynamic mode.After the addition of BDS-2/3,the positioning accuracy,fixation rate and first fixation time of GPS,Galileo and GPS+Galileo systems have been improved to a certain extent,and the improvement of Galileo system is the most obvious,but it is limited by precision product accuracy and ambiguity fixation Product accuracy,the improvement of the convergence time of the GPS system and the GPS+Galileo combined system is not obvious,and the improvement of all positioning performances is more significant in the dynamic mode.(2)The principle of IGS real-time orbit and clock difference recovery is introduced,and the real-time orbit and clock difference accuracies of CNES products GPS,BDS-2 and BDS-3are evaluated.The real-time PPP floating-point solution performance of five system modes,including BDS-3,GPS,BDS-3+BDS-2,BDS-3+GPS,and BDS-3+BDS-2+GPS,and the realtime PPP fixed solution performance of three system modes,including GPS,BDS-3+GPS,and BDS-3+BDS-2+GPS,based on CNES products are analyzed.The results show that the CNES real-time orbit and clock difference accuracy of each system are: GPS>BDS-3>BDS-2.In terms of PPP floating point solution,the BDS-3 system has a certain gap with the GPS system in terms of positioning accuracy and convergence time,and the BDS-2 addition has very limited gain on the positioning performance of BDS-3 and BDS-3+GPS systems.The addition of BDS-3 has improved the positioning accuracy and convergence time of GPS systems.BDS-3 and BDS-2 satellites were included in the ambiguity fixation,and the results showed that the three system mode fixation solutions improved the positioning accuracy and convergence time of the floating point solution,but the first fixation time and fixation rate decreased when both BDS-3and GPS satellites were included in the fixation compared to the GPS satellites.The addition of BDS-2 to BDS-3+GPS does not improve the first fixation time and fixation rate.(3)The principle of PPP-B2 b orbit and clock error recovery is introduced,the PPP-B2 b orbit and clock error evaluation model and the PPP positioning model are constructed,and compared with the corresponding broadcast ephemeris,the results show that the PPP-B2 b realtime correction number can be very good Corrected the segmental discontinuity of the orbit and clock difference caused by the update of the broadcast ephemeris,the BDS-3 MEO and IGSO satellite orbit radial errors were 9.1cm and 25.4cm,and the GPS MEO satellite orbit radial error was 6.9cm;BDS-3 and GPS real-time clock difference error STD are 0.07 ns and 0.15 ns respectively.The PPP-B2 b correction number has a better effect on the LNAV ephemeris orbit and clock error correction,because the CNAV1 broadcast ephemeris orbit and clock error have higher accuracy.The positioning accuracy of BDS-3 PPP-B2 b is better than that of GPS,limited by the number of effective satellites,and some stations of GPS single system do not meet the accuracy design requirements,but the optimal level of BDS-3+GPS combined system can reach1.7cm in level and 2.9 in elevation cm positioning accuracy.In addition,the convergence time of the single system is longer,and the convergence time of the dual system is significantly improved compared with the single system. |
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