Research On Gnss Real-time Satellite Clock Estimation And Ultra-short-term Prediction Implementation

With the growing demand of real-time high-precision positioning for public users,the traditional pseudo-range single point positioning accuracy could not meet the user's requirements.Wide area differential services provide users with worldwide positioning services in the precision range from decimeter level to centimeter.Real-time satellite clock and orbits are important basic products for wide area differential services.Real-time orbits can be predicted through ultra-fast orbit.However,satellite clock are difficult to predict accurately,because of the satellite-borne atomic clocks are susceptible to external and external factors,must be estimated in real time.At the same time,the joint estimation of the GNSS four systems forms a large number of process parameters,which seriously affect the timeliness of the clock.Therefore,the way how to improve the efficiency and accuracy of GNSS satellite clock real-time estimation,and meet the needs of wide area differential in centimeter level location service,have became the difficult problem of industry application and technology development.Based on the results of previous studies,this paper proposes a hybrid estimation method for GNSS satellite clocks that takes into account the inter system bias,improves the computational efficiency,and analysis the effects of orbital errors on real clock,and proposes randomization that consider orbital errors.The model improves the real-time accuracy of the satellite clock.On this basis,the ultra-short-term forecasting model is used to solve the problem of time delay in real-time estimation.The main research contents are as follows:(1)This paper researched and analyzed the current status of GNSS satellite clock real-time estimation and super-short-term forecasts,then defined the purpose and direction of this research.On the basic theory of satellite clock real-time estimation,including timing reference,coordinate datum,function model,and stochastic model,this paper designed the real-time satellite clock estimation process.(2)Combined the high-precision advantage of non-differential method and fast estimation advantage of difference-between-epoch method,this paper put forward a new mathematical model of the satellite clock estimation with the consider of GNSS inter system bias.The results show that the new estimation method realizes the calculation speed of 3.6s one epoch,and achieves the single day real-time accuracy of the GPS system 0.212ns,BDS system 0.230ns,GLONASS system 0.297ns,Galileo system 0.243ns.(3)Analyzed the influence of satellites orbit error on satellites clock,this paper based on the idea that the residue from the second order term of the linear function,a weight function design strategy is proposed.The results show that this new weight function model could improve the real-time accuracy,and reach 8.29%for GPS system,8.67%for BDS system,7.59%for GLONASS system,and 5.33%for Galileo system.(4)In order to solve the problem of time delay caused by data transmission,synchronization,data processing,and data encoding broadcast during the real-time estimation of satellite clock,an ultra-short-term prediction of real clock is implemented.The results show that the gray model has obvious advantages in terms of less initial data and higher forecast accuracy,and has obvious advantages in ultra-short-term forecasting,reaching the forecast accuracy of GPS system satellites 0.006ns,BDS satellites 0.021ns,GLONASS satellites 0.143ns,Galileo satellites 0.004ns.