Research On Improved RAIM Algorithm For Train Positioning

With the rapid development of high-speed railway,the demand for train positioning services is also increasing,and the train positioning is gradually shifting from using traditional ground equipment to relying on continuous satellite positioning.Bei Dou Navigation Satellite System(BDS)is a Satellite Navigation System independently developed by China and has been applied in many fields.Train positioning based on BDS will also be widely used.When the train is positioned through BDS,positioning accuracy and reliability requirements need to be considered.Receiver Autonomous Integrity Monitoring algorithm(RAIM)can send alarm information when errors occur,and has the ability of Integrity Monitoring to ensure the safety of positioning.The railway operation environment is complex,and trains have high requirements for positioning accuracy.Therefore,it is significant to improve the positioning accuracy and integrity performance of RAIM algorithm for its application in the field of train positioning.In this thesis,according to the needs of train positioning,on the basis of the research status at domestic and abroad,the RAIM algorithm is further analyzed.RAIM algorithm is improved to enhance the accuracy and reliability of positioning and meet the needs of railway transportation.The main work are as follows:First of all,the existing domestic and foreign train positioning methods and positioning requirements of high-speed railway are analyzed.The BDS related standards,interpretation of satellite related documents,BDS coordinate system and time system conversion principle and determination method of satellite position are described,and then the BDS train positioning principle is analyzed and explained.Secondly,RAIM technical theory and related concepts are described,mainly including the availability and integrity of RAIM algorithm.By judging the situation,the system is divided into four states: normal operation,missed alarm,false alarm and alarm,so as to analyze whether the system fails.The Least Square method and Parity Vector method are analyzed theoretically,and the requirements of precision,availability and completeness in railway positioning are explained.Furthermore,considering the requirements of railway positioning accuracy,an improved RAIM algorithm is proposed.By analyzing the error sources of the algorithm,the weight models are established from the aspects of the distribution structure of the satellite itself and the transmission process of the satellite signal,so as to optimize the algorithm performance and improve the positioning accuracy.In the aspect of satellite structure,the influence of satellite characteristic slope on the algorithm is analyzed.The slope weighting model is proposed and the slope satellite selection algorithm is designed to decrease dilution of precision.In the process of satellite signal transmission,the influence of ionosphere and troposphere on signal transmission is mainly considered to build the weight model.Through simulation experiments,the performance of the improved algorithm of the two weight models is analyzed to prove the availability and effectiveness of the improved algorithm.Finally,due to the complex and changeable environment during train operation,there may be poor distribution of visible satellite structure and abnormal error of observation information,which makes the reliability of RAIM algorithm difficult to be guaranteed and the positioning accuracy susceptible to error.An auxiliary RAIM algorithm of Inertial Navigation System(INS)based on robust estimation is proposed.Assisted by INS information,the pseudorange observation equation is extended and the redundancy of observation equation is increased.With the help of three visible satellites,train positioning and fault detection can be realized.Robust estimation is introduced to improve positioning accuracy and enhance fault detection performance.Experimental results show that the proposed algorithm can solve the problem of large positioning error caused by error interference,improve the fault detection rate of the algorithm,make the system more reliable in the same fault situation,and effectively improve the safety performance of train operation in complex environment.