Research On The Theoretical Method Of PPP Ambiguity Fixation In Multi-GNSS

Precise Point Positioning(PPP)is a hot topic in the development of GNSS Positioning technology.It has been developed gradually since the 1990s and has many advantages,such as strong applicability,high flexibility and simple operating conditions.Precise Point Positioning does not need base stations and observation networks.And it can be completed by a single receiver,which has a wide range of applications.However,the ambiguity fixation of PPP has always been a difficult problem in industry research.A large number of scholars have focused on the research for ambiguity fixation in PPP.With the development of GNSS in various countries,multi-GNSS fusion has attracted more and more attention from scholars.Using the more abundant observations provided by multi-GNSS fusion can greatly improve the redundancy of adjustment,which has a positive significance for accelerating the convergence of PPP positioning and improving the fixed rate and fixed speed of ambiguity.In this paper,the following research work is carried out for the fixed ambiguity of PPP:(1)The phase error correction theory and uncalibrated phase delay correction algorithm are introduced,including error structure,uncalibrated phase delay estimation theory and algorithm.Moreover,the stability and availability of the correction generated in this paper are analyzed and evaluated.The experimental results show that,except for some GEO satellites of BDS-2,the wide lane uncalibrated phase delay of each GNSS satellite is relatively stable,and the change of narrow lane uncalibrated phase delay with time is also relatively stable,in the 15-day scale.(2)The basic theory and algorithm of fuzzy degree fixed are sorted out,and the fuzzy degree reliability test and incomplete fuzzy degree algorithm are discussed.Based on the corresponding algorithm model,the PPP fuzzy degree fixed solution is realized in the open source software package.In addition,the fixed speed,the convergence of fixed solution,the epoch of fixed rate and precision are evaluated.The experimental results show that using uncalibrated phase delay product phase deviation correction and use fixed algorithm after incomplete fuzzy degree,GPS ambiguity epoch of fixed rate can reach more than 80%,the convergence speed is comprehensively up to 26.07%and the ultimate position precision is comprehensively increased 19.15%.(3)According to the particularity of BDS-2 constellation,the corresponding error processing strategy is put forward.And the key problems of multi-GNSS fusion--inter-system deviation and ambiguity fusion strategy are studied.Basing on the random walk model and the single difference within the system,the multi-GNSS PPP fixed solution processing strategy is established.The results show that the positioning performance of multi-GNSS is better than that of single GNSS.The average fixation time is shortened to 28.42min,the average duration fixation rate is 88.42%,and the average 3D positioning accuracy is up to 1.087cm.