Research On Train Precise Point Positioning Method For Train Control System

In the west of China,there are a lot of single track,double track lines,the running speed is less than 160 km per hour,some of which have not be electrified.As with the regional economic development,there is a need to update the train control system.Train positioning is one of two key technologies in train control system,compared with differential GNSS-based train positioning,without base station the Precise Point Positioning(PPP)is able to perform well.This dissertation is focused on Precise Point Positioning technology research in train localization application,its research objectives are to improve positioning performance,availability and safety in safety-critical application in railways on the premise of being compatible with current train control systems.This dissertation is dedicated to proposing a PPP-based scheme in train localization application,so that the positioning accuracy,safety and availability in the application can be improved.In order to fulfill the objectives above,the following critical technical issues have to be solved:(1)Combined with train positioning requirements in low density lines,this dissertation analyzed localization requirements of GNSS-based train control system,a PPP-based train control system scheme applying to low density lines is proposed.In order to solve safety assessment problem of localization unit,PDS method is adapted to model the localization unit,its hardware integrity level was estimated quantitatively taking into account structural constraints and diagnostic coverage.(2)In order to solve the problem of accuracy and safety in train localization application,a maximum pseudo-range-residual-based PPP signal in space(SIS)observation error detection and repair methods is proposed.It degrades the weight of satellite's observation,which holds the maximum pseudo-range at current epoch.The proposed mixture weighting scheme improves the accuracy when there is bias existing in observations.The experimental results indicate that the proposed mixture weighting model improves positioning accuracy by 9.6%under normal circumstances.At least 14.8%improvement in accuracy is obtained under the circumstances of existing biased satellites.(3)In order to solve the problem of accuracy and availability in PPP-based train localization application,this dissertation investigates PPP/INS integrated positioning methods,a digital track map(DTM)aided positioning method is proposed.Based on which,a DTM-aided PPP/INS EKF algorithm is proposed.In addition,by adopting EKF-aided particle filter(EPF),a DTM-aided EPF algorithm is proposed and implemented as well.The experimental results illustrate that due to the proposed EPF algorithm takes advantage of DTM information,compared with filtering algorithms adopting empirical GNSS measurement noise standard deviation,the proposed algorithm reduces 58.6%,11.5%and 47.6%positioning error in SPP,PPP and DGPS positioning respectively.(4)In order to proof the validity of proposed PPP-based train localization algorithms in this dissertation,a PPP-based comprehensive verification system is designed and implemented.The PPP software and related development and debugging environments are also introduced.Based on simulated equipment in the laboratory,the IMU and GNSS data is simulated and implemented.In order to further verify the proposed algorithms,some on-site experiments are conducted in railway operating ernvironments.The experiments conducted in Beijing Academy of Railway Sciences Ring Test Line proves that the proposed pseudo-range-based mixture weighting algorithm is able to detect existing bias in satellite observation,thus performs better than the current algorithms.Some experiments are also conducted in Beijing Academy of Railway Sciences Ring Test Line.The experimental results indicate that proposed DTM-aided GNSS/INS integrated filtering algorithms can adaptively estimate and update GNSS measurement noise standard deviation,so that the positioning accuracy can be improved.(5)In order to improve the creditability of availability analysis of navigation satellite signal in space for safety-related application in railways,this dissertation investigates image-sensor-based navigation satellite SIS availability analysis techniques,a taboo-search-based navigation satellite SIS availability analysis method is proposed.The proposed algorithm is able to improve the creditability of detected open sky by scarifying partial open sky.The experimental results show that the proposed algorithm has a 6.9%misclassification rate,in the meanwhile,the misrecognition rate is less than 2.1%,in addition,the misrecognition risk can be potentially lower.The research on PPP-based train localization application techniques can potentially reduce trackside equipment of train control system.It will support the development of next-generation train control system and provide theoretical support and technological reserve for domestication and capacity expansion of Qinghai-Tibet line.It is of immediate significance.