Research On Precise Point Positioning Of Non-difference And Ionospheric

Since entering the 21 st century,services based on location information have developed rapidly,and the Global Navigation Satellite System(GNSS)positioning methods mainly include standard point positioning,standard differential positioning,Precision Point Positioning(PPP)and Real-time kinematic(RTK).Among them,PPP has been widely used in scenarios such as maritime navigation and unmanned land surveying and mapping because it does not require a reference station.First of all,PPP is a single-site positioning technology that cannot eliminate Satellite Clock Bias(SCB)through differential.Secondly,PPP is a precision positioning technology.It needs to measure carrier phase and solve the Ambiguity Resolution(AR),which will cause Cycle Slips detection and repair problems.Therefore,this dissertation has done the following two aspects of the most common non-difference ionospheric-free model in PPP:1.SCB prediction based on Prophet model.In PPP,SCB cannot be eliminated by differential,so positioning error will increase.The prediction accuracy of SCB has become one of the key factors restricting the positioning accuracy.Although the International GNSS Service(IGS)provided a fast ephemeris prediction part(IGU-P),its quality and real-time performance could not meet practical applications.In order to improve the PPP,this dissertation proposes to use the Prophet model to predict SCB.Specifically,SCB is read from the observation part of the fast ephemeris(IGU-O)issued by IGS.Next,SCB between adjacent epochs are subtracted to obtain the SCB single-difference sequence.Then use the Prophet model to predict the single-difference sequence of the SCB.Finally,the prediction result is substituted into the PPP observation equation to obtain the positioning result.The final ephemeris(IGF)published by IGS is used as a benchmark,and the experimental results are compared with the IGU-P.The experimental results show that,the prediction accuracy of SCB of this model is higher.2.Cycle slip detection and repair method based on improved TurboEdit algorithm.In precision positioning,carrier phase observation and the ambiguity of the whole circle is bound to be involved.Therefore,the detection and repair of cycle slip is the key to complete PPP.The traditional TurboEdit algorithm used the MW(Melborne-Wubbena)combination and GF(Geometry-Free)combination of multi-frequency observations.Aiming at the shortcomings of the algorithm,this dissertation proposes an improved TurboEdit method that comprehensively considers the MW combined satellite altitude and the GF combined differential pattern.For the MW combination part of the algorithm,a dynamic smoothing window model is designed,in which the epoch interval for calculating the ambiguity average value can vary with the satellite altitude angle.For the GF combination part of the algorithm,the adjacent epochs are used to perform the second difference to remove the noisy ionospheric errors.The experimental results show that the TurboEdit method,which comprehensively considers the MW combined satellite altitude angle and the GF combined differential pattern,can effectively detect small cycle slips and lays the foundation for the continued calculation of the ambiguity and subsequent precision positioning solutions.