Research On LEO Satellite And GNSS Precise Point Positioning

With the rapid development of Global Navigation Satellite System(GNSS),its positioning,navigation and timing(PNT)functions have been in deep research and widely used in production and life.In recent years,Precise Point Positioning(PPP)has become a research hotspot in the field of satellite navigation.PPP that is one of the new development technologies of GNSS has global,all-weather high-precision positioning based on pseudo-range observations and carrier phase observations.Nowadays,singlesystem PPP positioning tends to be mature.Multi-GNSS PPP positioning technology makes up for the short board of single system PPP positioning with less visible satellites,and significantly improves the positioning performance.However,the long initialization time limits its wide application in real-time scenarios.Low earth orbit(LEO)satellite brings a rapid geometry change and consequently results in a shorter convergence time of precise positioning.This feature can complement the advantages of the GNSS system,and the research on LEO and GNSS fusion positioning technology is of great significance to achieve rapid and precise positioning.Based on the theory of GNSS positioning,this paper studies the existing multiGNSS PPP positioning technology,performs dynamic PPP positioning calculation and error analysis on the satellite-borne GPS observation data of LEO satellites,and further studies LEO enhanced GNSS(LeGNSS)PPP technology.The main research results are as follows:(1)The multi-GNSS PPP positioning was studied,and the corresponding static and dynamic positioning performance analysis was completed.The static and dynamic calculations under five positioning modes are performed on the observation data of the four actual stations of IGS.The results show that the convergence speed after multiGNSS is significantly improved,the positioning performance of the four-system combination is the best.The RMS average value of GRCE combined PPP static positioning can converge to 2cm within 20 minutes,and the RMS average value of GRCE dynamic PPP positioning can converge to 5cm within 30 minutes.(2)The analysis of the period error of the LEO satellite-borne GPS PPP is carried out,and an effective strategy to reduce the period error is proposed.Based on the 28-day actual satellite-borne observation data of LEO satellites,the PPP dynamic calculation is carried out,and two methods to eliminate the periodic errors are proposed for the periodic errors in the positioning results.The positioning accuracy is increased from 50 cm to 20 cm,and the advantages and disadvantages of the two methods are discussed.(3)The PPP function model of LEO enhanced GNSS is established,and the positioning performance evaluation of SPP and PPP is completed.Based on the simulation data of GNSS and 60 LEO satellites,the positioning solutions of LeGNSS SPP and LeGNSS PPP are carried out.The results show that the positioning accuracy of SPP and PPP is significantly improved after adding LEO observation data,the positioning accuracy of PPP is improved by 20%-40%,the convergence time is improved by 70%-90%,and the PPP can converge to 5cm in 3min after LEO participation.