| China’s third-generation Beidou navigation satellite system has been announced for completion and operation on July 31,2020,enabling high-precision navigation and positioning services across the globe.PPP as a revolutionary technology after RTK/ network RTK,it has the advantages of accurate estimation of station coordinates,receiver clock difference and zenith troposphere delay parameters,etc.It has important application value in precise positioning and orbit determination,atmospheric science and geodynamics.BDS-3satellite provides users with up to five open service signals,two of which are compatible with other GNSS systems.These provide new opportunities for the development of multi-frequency multi-system navigation and positioning.Therefore,according to the signal characteristics of multi-frequency and multi-channel BDS-3,the main error correction models in precise single point positioning and their effects on positioning performance are analyzed.At the same time,the world has a number of institutions to publicly provide products that can be used to achieve BDS-3 PPP fixed solution,which provides great convenience for the research and application of BDS-3 PPP fixed solution technology.The realization of BDS-3 PPP fixed solution will further improve the positioning accuracy and shorten the convergence time.According to the above requirements,this paper mainly studied the BDS-3 in different frequency difference code bias(DCB)and the antenna phase center correction and its effect on the positioning performance of the PPP floating point solutions,introduces in detail the PPP theory and method of ambiguity resolution and its quality control strategy,and put forward the optimizing selection of reference stars which improved the ambiguity fixed rate.The main work of this paper is summarized as follows:1.The DCB correction model of each signal of BDS-3 satellite is derived,and the stability of published BDS-3 DCB products is compared and analyzed.The correlation between DCB and the parameters to be estimated in the observation model and the influence of DCB on the positioning performance of dual-frequency PPP of BDS-3 are analyzed.The results show that DCB correction can significantly shorten the convergence time for different BDS-3 PPP,and the influence on the positioning accuracy can be ignored when the parameters are fully converged.In addition,the phase center correction models and strategies of satellite and receiver antennas at each frequency point of BDS-3 are studied and analyzed,and the influence of different antenna correction schemes on the positioning accuracy of BDS-3 PPP is analyzed.The results show that the PPP positioning accuracy is the highest when the satellite terminal adopts igs14.atx model.If the phase center correction parameter of BDS-3 antenna at the receiver is missing,it can be replaced by the antenna correction parameter of GPS.2.The global availability of BDS-3 constellation,the geometric distribution of satellites and the basic information of system signals for BDS-3 are analyzed in detail.The results show that BDS-3 has a large number of visible satellites and a good spatial geometry distribution,which has the basic condition for achieving high precise point positioning in the global scope.In addition,the PPP calculation of B1I/B3 I and B1C/B2 a combinations of BDS-3 was carried out using the precision products of five IGS analysis centers,and the calculation results were analyzed.The PPP positioning accuracy of B1C/B2 a combination is obviously better than that of B1I/B3 I combination in the elevation direction,and the positioning accuracy of the two combinations is the same in the horizontal direction.The positioning accuracy of WHU,IAC,GFZ and COD has little difference,and the positioning accuracy of SHA is relatively poor.In addition,WHU product has the shortest convergence time,while other analysis centers have relatively long convergence time.3.The PPP ambiguity resolution theory and quality control strategy based on FCB were analyzed,this paper proposes a optimization single differential reference star selection scheme,and is verified through experimental analysis,the results show that the optimized selection of reference star scheme can effectively improve the ambiguity fixed rate,so as to improve the positioning performance of fixed solution.The quality of BDS-3 FCB product is analyzed,PPP ambiguity fixed solution is realized by using BDS-3 FCB product,and its performance is analyzed.And the results show that compared with the floating-solutions,the BDS-3 fixed solution can effectively improve the positioning accuracy and shorten the convergence time. |
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