| The precise point positioning(PPP)technology for the Beidou Regional Satellite Navigation System(BDS-2)has been relatively developed.With the completion of the Beidou Global Satellite Navigation System(BDS-3)and the availability of global services,it is vital to study the mechanism of related data processing models and parameters between BDS-2 and BDS-3,and the way to enhance the positioning performance for BDS-2 or other systems with BDS-3,which will improve the performance of global service and international competitiveness for BDS.Therefore,this article mainly focuses on the related technologies of the current BDS-2 and BDS-3 combined PPP.The main work and conclusions are as follows:1.Considering the insufficiency of the epoch-difference method for repairing cycle slips,an improved cycle slip correction method is proposed in this paper and applied to processing BDS dual-frequency observations.The improved method takes three steps to repair cycle slips.The cycle slip float solution and its variance-covariance can be firstly obtained with the leastsquares adjustment.Then,the LAMBDA method is employed to fix the cycle slip float solution to an integer.Finally,the success rate based on ADOP and the ratio test are jointly applied to determine whether to accept the integer solution.The results show that the improved method can improve the successful rate of cycle slip correction by 0.4%-7.5%,and its positioning accuracy is better than that without repairing cycle slips or using the epoch-difference method to repair cycle slips.Besides,it can also speed up or even eliminate the reconvergence caused by cycle slips.2.In view of the rare systematic analysis on the inter-system bias(ISB)between the BDS-2/BDS-3,this paper analyzes the relevant characteristics of the ISB between BDS-2 and BDS-3 with three ISB estimation models,which are the time-constant model,random walk and white noise process,and the precise products from the European Space Agency/Operation Center,Geo Forschungs Zentrum(GFZ)and Wuhan University analysis centers.The results show that when the precise products from the same analysis center are used,the ISB solutions for a singleday obtained by the three estimation models are consistent.However,the ISB solutions for a single-day obtained with the precise products from different analysis centers are obviously different,but their stability is consistent.The ISB solutions obtained with the precise products from different analysis centers and different ISB estimation models are different,and their longterm stability is different.In addition,the change of the ISB solutions have nothing to do with the receiver type and software version number,but is related to the antenna type.The stability of the ISB solutions is related to the relative change of the number of satellites between BDS-2 and BDS-3.3.The PPP positioning performance of BDS-2 and BDS-3 combination in the Asia Pacific region and BDS-3 in the world is analyzed and evaluated in this paper.The results show that:(1)The positioning accuracy of BDS-2 and BDS-3 combined PPP in the Asia Pacific region is equivalent to that of GPS,but the convergence performance of BDS-2 and BDS-3 combined PPP in vertical direction still lags behind that of GPS.(2)At present,the precise products from the GFZ analysis center contain more BDS-3 satellites among three analysis centers,and the PDOP value is the best.In addition,the positioning accuracy obtained using the GFZ products are the best.Therefore,the precise products from the GFZ analysis center are recommended to obtain high precise positioning solutions for BDS-3 global users.(3)The positioning accuracy of BDS-3 PPP in plane and vertical directions is equivalent to that of GPS,but its convergence performance still lags behind that of GPS. |
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