Research Of GLONASS/GPS/BDS Multi-mode Combined Positioning Method Based On Nonlinear Filtering

Today GNSS(Global Navigation Satellite System)is developing rapidly,and there are three major advanced and widely used satellite navigation systems.Global Positioning System(GPS)is the most advanced and complete satellite navigation system who can continuously and globally provide real-time and high accuracy 3 dimensional position and velocity as well as time.In recent years,GLONASS,Russian satellite navigation system,are developing so quickly because of effective policy like recovering the capacity of Russia's whole GLONASS constellation,developing the new GLONASS-K/KM/NG satellite.And then,Chinese satellite navigation system BDS now can provide all-day navigation service for Asian-Pacific region and still works on making improvement to realise global navigation.The development of multi-system,on the one hand,can promote international cooperation to make common progress.On the other hand,it provides users with more available satellites,which will help to improve the positioning accuracy and stability.According to statistic information,there are about or more than 140 satellites throughout the world,including the satellites existing,being built or planning.How to use and take advantages of the satellites which belongs to different navigation systems now is a brand-new and challenging research topic.There are several important aspects in this paper:1)The research background and development of GNSS were reviewed,and a detailed introduction was brought to GPS?GLONASS and BDS system components,source of positioning errors and traditional single system positioning model.2)The ways to unify GPS,GLONASS and BDS coordinate system was introduced after analyzing the similarities and differences of the time systems and coordinate systems of the three systems.And then the new model for GPS?GLONASS and BDS three systems combined positioning based on the unified coordinate system was brought up.3)For the shortcomings of traditional Least Square method positioning model,the GPS/GLONASS/BDS three systems combined positioning model based on nonlinear filer was proposed.And as for the jumping of the satellite number which affects significantly on the positioning accuracy,a satellite selection strategy based on pseudorange analysis was designed.4)GPS/GLONASS/BDS three system combined positioning experiment will be conducted to prove that the satellite selection strategy and three system combined positioning model based on nonlinear filter is correct and feasible.And the bad conditions test where single satellites are not enough to position,such as mountains,canyons and urban canyons,also will be done to show the advantages of three system combined positioning.This research can provide a theoretical basis for multimode satellite navigation positioning,and provide technical reference to apply well to future multi-system positioning.