| As an important spatial information infrastructure,Global Navigation Satellite System(GNSS)plays a highly significant role in the field of national economic construction and national defense security.Precise Point Positioning(PPP)technology,as another technological revolution after RTK / network RTK technology,has been widely concerned by scholars at home and abroad in theoretical research and practical applications.In view of the fact that the ambiguity resolution of PPP can effectively shorten the convergence time of PPP and improve the positioning performance,and the multi-GNSS observation can improve satellites geometry and increase the robustness of the observation equation.Meanwhile,Bei Dou Navigation Satellite System Ⅲ(BDS-3)is about to be completed.This paper probes into Fractional Cycle Bias(FCB)products necessary for Multi-GNSS PPP ambiguity.From the estimation method of multi-system FCB products,the performance evaluation index of FCB,PPP positioning performance of BDS-3 has been systematically studied.The main work of this paper is as follows:1.This paper summarizes the development process,current situation and operation of the four major global satellite navigation systems and regional augmentation systems,and briefly analyzes the performance of each system in terms of the ground track,the average number of visible satellites in all parts of the world.The results demonstrate that more than 100 satellites in all satellite navigation systems are currently in an observable state,and apart from the regional enhancement system,each satellite navigation system can achieve global coverage,while each analysis center is also committed to releasing multi-system precision products,which provides a precondition for this paper to estimate multi-system FCB products.2.This paper estimates and evaluates GPS + Galileo + BDS-2 + QZSS FCB products.Starting from the GNSS observation equations,this paper deduces the multi-system FCB observation equations in detail,introduces the method of solving the FCB through the entire network,and explains the file format of FCB products.The FCB products are evaluated in terms of time stability,ambiguity data utilization rate,ambiguity residual,and comparison with CNES products.The results reveal that the wide-lane FCB of the above four systems is relatively stable in one month,and that the narrow-lane FCB is relatively stable in one day time.The standard deviations of the wide-lane FCB of the four systems are 0.019,0.005,0.015,and 0.008 cycles,while that of the narrow-lane FCB are 0.021,0.021,0.057,and 0.010 cycles,respectively.The analyses of the FCB product generated by this paper and the FCB product released by CNES shows that the difference between 93.0% GPS wide-lane FCB and 91.3% Galileo wide-lane FCB is within 0.05 cycles,and that 97.6% GPS narrow-lane FCB and 92.8% Galileo narrow-lane FCB is within 0.05 cycles.The accuracy and reliability of the FCB products generated and released in this paper are at a high level.3.This paper introduces the PPP ambiguity resolution method and combines it with practical calculation examples for positioning evaluation.In this paper,the multi-system PPP ambiguity resolution has been briefly introduced from the aspects of ambiguity resolution method,LAMBDA method and the ambiguity checking index.The data of 31 MGEX stations are employed for the calculation of static and kinematic PPP floating solution and resolution.The results indicate that the ambiguity resolution of the four systems can significantly shorten the convergence time and time to first fixed of PPP.Compared with the GPS ambiguity resolution,the convergence time and the first fixed time are shortened by 27.3% and 29.4% respectively in static PPP,and in kinematic PPP,they are respectively shortened by 42.6% and 51.9%.4.This article estimates and evaluates the BDS-3 FCB products,and makes a preliminary evaluation of the positioning performance of the BDS-3 PPP floating solution and resolution.The results suggest that the standard deviations of wide-lane and narrow-lane FCB of BDS-2 are 0.022 and 0.111 cycles respectively,and those of BDS-3 are 0.040 and 0.067 cycles respectively.The ambiguity residuals and data usage rate of BDS-2 are slightly higher than those of BDS-3.The reason may be that the observations of BDS-3 are relatively less,which makes the results susceptible to individual outliers.In static PPP,the accuracy of the BDS-2+3 ambiguity resolution is improved by 28.57%,33.34%,and 20% relative to the floating solution in the E,N,and U directions respectively;BDS-3 converges faster than BDS-2,and BDS-2+3converges the fastest,which is 52.43% shorter than BDS-2.In contrast,in kinematic PPP,the accuracy of the BDS-2+3 kinematic PPP ambiguity resolution is improved by38.18%,30.56%,and 23.33% relative to the floating solution in the E,N,and U directions respectively,and is improved by 42.37%,50.98% and 33.01% in each direction compared with BDS-2.When BDS-3 is added to the observation data,it can effectively shorten the first fixed time by 36.73%. |
