Research On The Application Of RAIM Technology Of BeiDou Navigation System In Train Positioning

With the continuous development of high-speed railway and BeiDou Satellite Navigation system,the positioning method based on BDS has attracted more and more attention.It can provide positioning services for trains all-time and all-weather.When BDS is used as the main positioning mode of the train,in addition to providing positioning service in time,it also needs to have good monitoring performance to send an alarm to the nearby train in case of failure of the satellite.The technology of RAIM(receiver autonomous integrity monitoring)does not need external equipment.It is a widely used method to detect and alarm the faulty satellite at present.The train requires high positioning accuracy,while the train operation environment is complex and changeable,and there are many uncertain factors.Therefore,further research on RAIM technology is of great significance to improve the stability,safety and efficiency of train operation.Based on the research of satellite navigation and positioning at home and abroad,this paper introduces RAIM technology into BDS train positioning,aiming at improving the accuracy of train positioning,and makes an in-depth study of RAIM technology.First of all,this thesis introduces the research results of RAIM technology in different fields at home and abroad and the research results of using satellite positioning technology in train positioning,and deeply understands the pseudo range positioning principle of Beidou satellite navigation and positioning system and the parameters affecting the integrity.Secondly,according to BDS detection principle,the observation model is linearized to get the receiver pseudo range observation equation,considering the particularity of train running along the track,combining with the definition of protection level along the track,the least squares residual observation model is constructed.The improved least squares residual RAIM algorithm is used to detect and identify the faulty satellite.According to the requirements of high-precision users,for the small slowly varying pseudo range deviation of the system,the test statistics are constructed based on the characteristics of the noise uncorrelation and pseudo range deviation correlation of the adjacent pixels.The traditional the parity space vector RAIM algorithm is improved by the accumulation of the number of visible satellites to realize the fault satellite Fast detection and recognition of stars.Finally,the difference model is used to verify the availability of the traditional least squares residual RAIM algorithm.According to the actual data of the same Qinghai-Tibet railway,the simulation of the protection level of the improved least squares residual RAIM algorithm before and after the improvement is compared.It is found that the PL and DOP of the improved algorithm are lower,so the detection of the obstacle is more accurate.Based on the accumulated parity space vector RAIM algorithm,different amounts of health can beaccumulated See the number of satellites for simulation and verification.Simulate the small continuous fault,small oblique fault and small fast change fault of the system under the same conditions.Compare with the simulation of the fault satellite of the traditional parity space vector RAIM algorithm,the results show that the improved algorithm has fast detection speed,rapid identification after the fault occurs,and high efficiency of fault calibration.