Modeling And Assessment Of BDS/GPS Precise Point Positioning And Research On Ambiguity Resolution

With the continuously strengthening of China's comprehensive national strength,the BeiDou Navigation Satellite System is developing rapidly.It has gradually broken the domination of GPS in China,which has deeply influenced and changed the situation of satellite navigation and positioning.Multi-GNSS and compatible interoperability have become the important trend in the development of GNSS.Therefore,how to use the existing mature GPS system to enhance the performance of Beidou is a very important issue.However,due to the immature of BeiDou,there are many problems that need to be researched.Therefore,this paper focuses on the problem of BDS/GPS combined positioning.The full text focuses on the research of combined precise point positioning(PPP)from float solutions to fixed solutions.The main research content of this article are as follows:(1)The basic principles and methods of PPP.Based on previous studies,this paper summarizes the basic mathematical model of precise point positioning,and derives the relevant formula.The main error corrections,parameter estimation methods,determination of stochastic models,data preprocessing and quality control methods in PPP are introduced.(2)The combined mathematical model of BDS/GPS PPP.The relevant formulas of combined PPP are deduced,and the principle,methods and strategies of combined positioning are described.Through a large number of experimental data,the RMS of the float solution for the BDS PPP was 4.35cm,3.01cm and 6.40cm in the direction of East,North and Up.The RMS of single GPS PPP was 1.21cm,0.48cm and 1.79cm in the direction of East,North and Up.The RMS of the combined system for BDS/GPS PPP is 1.21cm,0.50cm and 1.87cm respectively in the direction of East,North and Up.The positioning accuracy of the float solution for the combined system is basically the same as that of the single GPS system,higher than that of the single BDS system.However,the convergence speed of the combined system is obviously faster than that of the single system.(3)The ambiguity solution of GPS PPP.The reason why the ambiguity of traditional PPP model does not have integer characteristics is deduced through formula derivation.In addition,method of GPS ambiguity solution and the estimation of fractional cycle bias are derived by formula,and the method of how to use the decimal deviation to fix the ambiguity is expounded.The short-term and long-term time-varying characteristics of GPS widelane fractional cycle bias and the narrowlane fractional cycle bias are calculated and analyzed.Then,the interval is determined.The estimated fractional cycle bias are used to fix GPS ambiguity and the accuracy and result of its positioning are analyzed.(4)The ambiguity solution of BDS PPP.The BeiDou satellite-induced code pseudorange variations are discussed in the paper.The correction of the segmented current model proposed by Wanninger and Beer is verified by experiments.The BDS widelane and narrowlane fractional cycle bias are estimated,and the time-varying characteristics of the decimal deviation between widelanelane and narrowlane are analyzed.By using estimated widelanelane and narrowlane fractional cycle bias,the ambiguity of BDS is determined,the fixed solution of BDS is obtained,and the BDS fixed solution is analyzed.(5)The ambiguity solution of BDS/GPS PPP.On the basis of the above studies,the fractional cycle bias of BDS and GPS is comprehensively estimated,and the ambiguity of BDS/GPS combination system is fixed.The results of fixed solution and float solution are compared.The fixed solution for single system and the combined system are analyzed in the direction of East,North and Up.The results show that the precision of fixed solution for the combined system and the GPS fixed solution are basically equal,which are higher than that of the single BDS.