Research On Multipath Mitigation For BDS Precise Point Positioning

Precise Point Positioning(PPP)is a Precise Positioning method.It uses pseudo-distance observations and carrier phase observations,and It uses high-precision satellite orbits and precision clock products.At the same time,it carefully considered the correction of errors.In the Global Navigation Satellite System(GNSS),PPP has the advantages of low cost,high accuracy and no base station assistance.It is widely used in Marine mapping and weather forecasting.With the global network of China's Bei Dou Navigation Satellite System(BDS),it will gradually become capable of global coverage and provide PPP services to provide high-precision location reference for Marine applications.Compared with the Global Position System(GPS),the Bei Dou satellite constellation configuration and large unmodeled observation errors further increase the convergence time of single Bei Dou PPP and limit its application.Multipath error is the main unmodeled error in pseudo-distance observation,it seriously affects the convergence time of PPP.In PPP data processing,multipath error is usually suppressed by constructing a random model.However,due to the uncertainty of the random model,the suppression effect of this method on multipath error is limited,especially in the first convergence stage of precise single-point positioning,which will seriously affect the convergence time of positioning results.In addition,although the ionospheric first-order delay can be eliminated by adopting ionospheric combination,it will magnify the noise level,further worsen the convergence time of PPP and make it difficult to meet the real-time requirement.In order to better suppress the multipath error,improve the accuracy of pseudo-distance observation,and accelerate the convergence rate of PPP,so as to accelerate the convergence rate of PPP.In view of the above problems,the main research contents of this paper are as follows:(1)The mathematical model of precise single point positioning and its corresponding random model are studied,and the traditional ionospheric combination model is mainly analyzed.Then,the correction methods of a series of major errors such as ionosphere and troposphere in precise single point positioning are studied.Finally,the parameter estimation method of PPP is studied and the program simulation of BDS precise single point positioning algorithm is realized and the simulation results are obtained.The results show that the precision of the mathematical model and the random model selected in this paper is within 10 cm after the convergence,and its convergence time is 1 hour.(2)The generation of multipath is closely related to the environment of the receiver and the operation of the satellite.In this paper,the generating principle and influencing factors of multipath error are studied,and the extraction method of multipath error is studied.For a stationary receiver,when the surrounding environment does not change,because the satellite's movement is repetitive in space,the multipath error sequence is also periodic.In this paper,the periodicity and correlation of the multipath errors of two adjacent days are calculated and analyzed.The results show that for the Geostationary Earth Orbits(GEO)satellites there is a high correlation in multipath.For Inclined Geosynchronous Satellite Orbits(IGSO)Satellite and the Medium Earth Orbit(MEO)satellite,there is a significant correlation in multipath.(3)In the traditional precise single point of ionospheric combination,the random model based on height Angle weighting can suppress multipath error and noise,but because the measurement error will be magnified by the ionospheric combination model,the convergence level of carrier phase ambiguity will be seriously affected in the initial phase of precise single point positioning.On this basis,a method of carrier phase smoothing pseudo-distance is studied to suppress multipath errors.In this paper,a stochastic model based on the combination of height Angle and multipath error is studied to suppress multipath error.In this paper,the suppression method of pseudo-distance multipath by sidereal filtering is studied.The results show that these three methods can suppress the influence of pseudo-distance multipath error.(4)In this paper,based on the traditional precision single-point positioning method and the random model based on the height Angle,the multipath suppression method based on the carrier phase smoothing pseudo-distance is used,the random model suppression method based on the height Angle and the combination of the multipath is used,and the method based on the Sidereal filtering is used to suppress the multipath error.The results show that by suppressing the multipath error before convergence,the three methods can improve the estimation speed of carrier phase ambiguity and accelerate the convergence speed of PPP.The convergence time increased by 75.3%,71.5% and 76.3%,respectively.The positioning accuracy was improved to 62.6%,29.6% and 58.4%,respectively.It is verified that the three PPP location algorithms based on pseudo-distance multipath error suppression are helpful to improve the convergence time of PPP.