Research On The Algorithms Of Ionospheric Delay And Ambiguity Resolution In Undifferenced Uncombined Model

The satellite navigation and positioning system has developed from the only GPS system to multi-GNSS system.Meanwhile,multi-frequency and multi-type observations are available at present.Under this background,undifferenced and uncombined data processing model has become a hot research topic.Moreover,the application field of GNSS has extended from navigation and positioning to GNSS aerology,and high precision positioning technologies,such as PPP and PPP-RTK,have developed form traditional RTK technology.Therefore,ionospheric delay processing strategy and undifferenced ambiguity resolution method have become the key point of undifferenced and uncombined data processing model.Based on undifferenced and uncombined data processing model,this contribute carried out a series of work on ionospheric delay processing strategy and undifferenced ambiguity resolution method.The main contents and contributions of this contribute are as follow:1.Established an undifferenced and uncombined ionospheric parameterization model by analyzing the structure and periodic part of ionospheric delay,and constraining the stochastic part by random walk method.The ionospheric parameterization model established can effectively express the structure and periodic characteristic,together with the stochastic characteristic of ionospheric delay.2.Established an undifferenced and uncombined data processing model with ionospheric delay constrained by ionospheric parameterization model.PPP experiments of G/C/R/E have been carried out and the results indicated that,comparing with ionosphere-free model,ionospheric parameterization model can effectively improve the position precision and convergence speed.In single-and dual-frequency PPP,3D RMS can be improved by 37% and 17.8%,respectively.3.Based on the ionospheric parameterization model,an DCB estimation method based on undifferenced and uncombined model has been put forward,and been applied in BDS-3 DCB estimation.With very limited track stations and imperfect clock and orbit products,undifferenced and uncombined DCB estimation method still gave a relatively reliable estimation result.The STDs of B1B2 and B1B3 DCB on satellite side are 0.331 ns and 0.204 ns.While on receiver side,the STDs are 0.56 and 0.42 ns.Benefited from high precision clock and orbit products,undifferenced and uncombined DCB estimation method performed better than the estimation method based on geometry-free method in BDS-2 and GPS DCB estimation.4.In undifferenced and uncombined ambiguity resolution,this contribute confirmed the select criterion of alternative ambiguity vector set,and put forward the analysis strategy of ambiguity invariant in alternative ambiguity vector set.Thus,this contribute established an undifferenced and uncombined partial ambiguity resolution method by ambiguity invariant analysis.Experiments showed that this PAR method can greatly shorten the time to first fix(TTFF)and increased the fix rate,for both wide-lane and narrow-lane ambiguity.Meanwhile,the positioning precision,especial on E direction,can be improved,as well.5.This contribute applied the undifferenced and uncombined partial ambiguity resolution method by ambiguity invariant analysis into PPP-AR,and carried out PPP-AR experiments based on observations of single GPS,single BDS and GPS+BDS dual system.The experiment results indicated that,with ambiguity fixed by PAR method put forward by this contribute,the fix rate of both wide-lane and narrow-lane ambiguity are greatly increased,up to 80%.In experiments of single GPS and GPS+BDS dual system,the fix solution of PAR method can effectively achieve accuracy improvement,compared with float solution.The average RMS of 3D and E direction can improved by 6.7% and 9.1%,respectively.However,in single BDS experiment,the performance of PAR method was unsatisfactory,and accuracy improvement only occurred in E direction,which means this PAR method still needs modification in BDS data processing.