| GNSS precision point technology can obtain high-precision station coordinates only by using a single receiver,which has the advantages of flexible operation,low cost and free from distance limitation.With the development of GNSS,satellite constellations and available satellite frequency bands are becoming more and more abundant,so that the multi-GNSS PPP has more available satellite observations and stronger satellite geometric structure,effectively shortening the convergence time of multi-PPP and improving the accuracy and reliability of PPP positioning.Compared with single GPS PPP,muilti-GNSS PPP also brings more theoretical and application problems.For example,how to use multi GNSS to realize PPP-ambiguity resolution is an urgent problem to be solved.Satellite clock estimation plays an important role in precise single-point positioning,so how to select global tracking stations effectively to estimate satellite clock error and reasonably evaluate the quality of clock error products is the premise to achieve high precision PPP positioning.At present,PPP commercial software is expensive and less open source software,which brings some difficulties to researchers.The article focuses on "multi-GNSS positioning","fixed ambiguity","clock error estimation",and "software development".The specific research content is as follows:.(1)The basic theory of GNSS precision point positioning is systematically studied,including the conversion of different time-space references,hardware deviations and all kinds of errors,and the influence of phase deviations on the PPP ambiguity.In addition,the mathematical model and random model of multi-mode GNSS PPP,Kalman filter parameter estimation,gross error,cycle slip and receiver clock slip detection and repair methods are studied.(2)The importance of PPP ambiguity research is analyzed.Using the stepwise ambiguity fixation model,the PPP ambiguity fixation is achieved by selecting the FCB product of CNES Analysis Center.Completed the fixed solution of GPS,Galileo and GPS/GAL combined PPP.The results show that the fixed solution reaches 1,23cm,1.71m and 1.98cm in the E,N,and U directions,respectively,which is an increase of 49.33%,2.82%,and 38.55%compared to the floating solution.The epoch fixation rate of a single system can reach more than 80%,and the epoch fixation rate of the GPS/GAL combined system can be increased to more than 90%.The epoch fixing rate and convergence accuracy of the PPP composite system are higher than those of the single system.(3)The performance of the receiver clock and its influence on the estimation of the satellite clock error are studied.On the basis of taking into account the performance of the receiver clock,the spherical Delaunay triangulation network is used to optimize the global tracking station,and then the satellite clock error is estimated.Comparing the self-estimated clock error with the existing analysis center clock error products,the results show that the accuracy of the self-estimated clock error is better than 0.1ns.The PPP experiment further confirmed the correctness of the spherical Delaunay triangulation global point selection algorithm and the satellite clock error estimation algorithm and the accuracy of the estimated clock error.(4)Designed and developed PPP software by transplanting open source software on the market,and introduced the design methods and functions of PPP software in detail.In order to further verify the reliability of the developed software,PPP static experiment,PPP imitation dynamic experiment and PPP dynamic experiment were carried out respectively.Through the experimental test,the positioning accuracy can reach centimeter level in the static experiment,and the accuracy can reach 5cm and 0.5m in the simulated dynamic and dynamic precision respectively. |
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