Research Of BDS Positioning Method Based On Nonlinear Filtering

BeiDou navigation satellite system(BDS)is a global satellite navigation system developed and operated independently by our country,which can provide all-day navigation service for Asian-Pacific region.By the end of 2016,there have been 20 satellites working on orbit.According to the results of the detection,positioning accuracy of BDS has reached 10 meters in horizontal,15 meters in elevation,0.2 m/s in speed.BDS plays an important role in civil and military affairs,related products have been used in power systems,transportation and many other fields,bringing great benefits.Because of the vital function of BDS,how to further enhance the advantages of BDS and improve the positioning accuracy of BDS has become the research hotspot.There are many errors in BDS positioning and the important one is random measurement error,which need to be taken away by the corresponding filtering algorithms.In view of the nonlinearity of the measurement equation,EKF(Extended Kalman Filter)and UKF(Unscented Kalman Filter)are often used to navigation in the current study.But EKF and UKF have their own shortcomings.This paper applies SRUKF algorithm to BDS localization model and the covariance matrix is replaced by the square root form of the state covariance matrix in the process of filter iteration.So the covariance matrix is positive all the time and the round-off error is reduced effectively.SRUKF can solve the divergence problem of traditional Kalman filters and has more advantages than traditional filters.The noise covariance of BDS localization model should be assumed beforehand when applying SRUKF and if the assumption does' s match the real model,it will reduce the reliability of estimation.So,Particle Swarm Optimization(PSO)is introduced to this paper to calculate noise covariance more accurately.PSO_SRUKF based on PSO and SRUKF is proposed,which further improves the filtering performance of SRUKF.Experimental results show that SRUKF can improve the positioning precision and stability of BDS effectively and the positioning accuracy increases with the increase of the number of particles and the number of iterations.With the release of ?Beidou System Open Service Performance Specification(1st edition)?and ?Beidou System Space Signal Interface Control File(version?)?,users can receive the signals of B1 band and B2 band to perform localization.So BDS has been into the era of multiple frequency application,which means BDS has become the first system that has two civil codes on dual bands and has provided service.Based on PSO_SRUKF,this paper selects the appropriate method to positioning using dual-band.Due to the instability of receiving dual-band signals of the Beidou satellites,a strategy to select satellites is developed.According to the experimental results,this method can get the positioning results of higher precision.This research can provide a theoretical basis for BDS navigation positioning,and provide technical reference to apply well to future multi-band combined positioning.