Research On Multi-Gnss Positioning Based On Satellite Selection And Nonlinear Filtering

As the third generation of Beidou navigation satellite system(BDS)in China is about to be completely built,BDS will provide comprehensive services to the world.As an important global navigation satellite system(GNSS),BDS signals are compatible and interoperable with the signals of other satellite constellations,such as global navigation satellite system(GLONASS)from Russia and global positioning system(GPS)from US.This flexibility promotes the development of GNSS.Many works are in the direction of harnessing the abundance of satellites constellations provided by multiple systems to achieve higher precision and higher reliability.Therefore,multi-GNSS positioning has become a hot topic in the field of satellite navigation.Signals from multiple constellations are received by GNSS receivers,it can improve the accuracy and stability of navigation solution.In addition,enable services when a single satellite system fails.However,there are some problems with multiple constellations,such as discordance of time and space,heavy load for using too much satellites,and low positioning precision for changing satellites.About the work of this thesis,we propose and develop new solutions to problems encountered in multi-system positioning.In addition,it provides a reference for accelerating the practical application of multi-GNSS positioning.The thesis includes the following five sections:1.The unification of the space coordinate and time system of BDS,GLONASS and GPS are realized.The parameters of the spatial coordinate systems are compared and unified into GPS coordinate called WGS-84.2.Based on the comparison of existing satellite selection,we propose a novel fast method.This method exploits the approximate balanced pattern algorithm and regular triangle fast satellite selection algorithm.Introducing the concept of geometric accuracy factor,we analyze its influence on positioning accuracy.Additionally,a comparison to existing algorithms is carried.3.Aiming at the problems existing in the general positioning model,a multi-system positioning model based on pseudo-range and Doppler shipt is established.Achieved by more state quantities in the state transition equations then combine Doppler measurement information to the measurement equations to improve the accuracy of multi-system positioning.4.A non-linear filter algorithm is chosen by comparison of multiple variants of the Kalman filter.After comparing with the extended Kalman filter and the unscented Kalman filter,square root cubature Kalman filter(SCKF),filter with the best comprehensive effect is selected.5.Experiments are designed in different environments to verify the performance of the multi-system positioning algorithm proposed in this thesis based on satellite selection method and nonlinear filtering algorithm.The effect of the algorithm is analyzed to verify its excellent accuracy and environmental adaptability.