Research On BDS PPP/INS Integration Kinematic Continuous Positioning Method

BeiDou navigation satellite System(BDS)is a global satellite navigation and positioning system which is built and operated independently in China,focusing on the needs of national defense,economy,science and technology,etc.Precise Point Positioning(PPP)technology has been widely used in navigation,geodesy,monitoring and other fields for its advantages of low cost,flexible operation and high positioning accuracy.Satellite signal is easy to be blocked or lost in urban canyon,viaduct,tunnel and other environments,which makes the positioning results appear larger error or failure.Inertial Navigation System(INS)provides the position,velocity and attitude information of the carrier according to its own gyroscope and accelerometer group price.It has the advantages of high short-term positioning accuracy,no external radiation energy,fast data update and strong anti-interference ability.However,with the increase of navigation time,the positioning error will increase rapidly.With the continuous improvement of the accuracy and reliability of the carrier position,velocity and attitude information,a single navigation system has been unable to meet the needs of users.There are natural complementary advantages between satellite navigation and inertial navigation.The combination of the two can give full play to their advantages.At present,scholars at home and abroad still have the problem of location discontinuity in the research results of GNSS/INS integrated navigation.This paper focuses on the BDS PPP/INS integrated navigation,aiming to provide users with continuous and high-precision positioning results.The main work and innovations of this paper are summarized as follows:(1)Three kinds of PPP models,including ionospheric-free combination model,UofC model and un-combined model,are analyzed in detail from the aspects of observation equation,parameter estimation,fuzziness,degree of freedom and noise.The raw observation data quality of GNSS and the error terms that affect the positioning accuracy and convergence speed are analyzed.The average convergence time of static experiment is 40.5min,and that of airborne experiment is 44.5min.The results of static and dynamic experiments show that the positioning accuracy of converged BDS PPP can reach centimeter level.(2)This paper analyzes the advantages and disadvantages of four satellite velocity estimation methods:position difference method,raw Doppler method,derived Doppler method and TDCP method in different motion states of the carrier.A dynamic Doppler velocity estimation method based on BDS PPP is proposed,and the method is compared with the traditional method by vehicle,ship and airborne experiments.The results of three dynamic experiments show that the accuracy of the dynamic Doppler velocity measurement method based on BDS PPP is 17%? 38%higher than that of the traditional method,and the accuracy is cm/s.(3)INS mechanical arrangement,INS error model,Allan variance and initial alignment are analyzed.The BDS PPP/INS loosely coopled model and tightly combination model of extended Doppler velocity estimation are derived,and the BDS PPP/INS tightly coupled model of extended Doppler velocity estimation is realized.The vehicle experiment results in complex urban environment show that the BDS PPP/INS tightly coupled positioning accuracy is in Decimeter level,and the velocity measurement accuracy is cm/s level.(4)In view of the complete lack of satellite signals such as viaduct and tunnel,BDS PPP/INS tightly coupled continuous positioning solution with Non-Holonomic Constraint(NHC)and Zero Velocity Update Technology(ZUPT)is proposed with the driving characteristics of land vehicles.The results of vehicle experiments and simulation experiments show that this method can effectively suppress INS error accumulation and maintain the continuity of positioning when the satellite is completely unlocked.(5)Aiming at the problem of large positioning error caused by poor satellite distribution structure such as urban canyon and forest shelter,an adaptive BDS PPP/INS tight coupled continuous positioning method considering PDOP is proposed.PDOP is used as the independent variable to establish the self-adaptive factor,which can achieve high-precision positioning by adjusting the contribution of dynamic model prediction information and observation information to the filtering results.The results of vehicle experiments show that this method can effectively improve the positioning accuracy of BDS PPP/INS Integrated Navigation System in complex environment.