Research On Local Integrity Monitoring Method Of Satellite-based Train Positioning

Real-time,accurate and reliable train positioning is one of the important factors to ensure the safety and efficiency of train operation.The satellite navigation system,which has been developed rapidly in recent years,has become an important approach for autonomous train positioning in new generation train control system in the future.Based on the critical requirement of safety for train control systems,the determination of train position,speed and other related state information using satellite positioning has to meet the accuracy specifications and the requirement of the autonomous integrity monitoring capability.The autonomous integrity monitoring indicates the ability of the satellite navigation system to provide timely warning when there are probable faults or failures the system and the observation,which is of great significance to ensure the safety of train positioning.At present,the research on Receiver Autonomous Integrity Monitoring(RAIM)has been mainly focused in the aviation and maritime fields.Due to the complexity and particularity of the train operation environment,the conventional RAIM methods are confronted with obvious opportunity and challenges.According to the specific demand for train positioning in train control systems,a joint modeling solution of the satellite positioning observation quality covering both the time and space domains of train operation is proposed,which combines the spatial and temporal characterizations of train operation.An improved integrity monitoring method based on the local observation quality models is presented,and the implementation scheme of the local integrity monitoring method is established in this paper.The main research of this paper can be summarized as follows:(1)Based on the principle of train satellite positioning and the performance requirement,the main problems in conventional receiver integrity monitoring methods in train positioning are analyzed.(2)According to the characteristics of spatial/temporal constraints in the train operation process,the concept of local integrity is introduced.The spatial-temporal integrated modeling of satellite observation quality is achieved by historical observation data sets,and a model-assisted RAIM framework based on the local observation quality models is constructed.(3)An improved RAIM method of satellite-based train positioning is designed.The key solutions of this method,including the spatial-temporal grids establishment,horizontal protection level estimation,and the model-assisted integrity monitoring,are analyzed in detail.The implementation scheme for the presented method is summarized.(4)In order to validate the capabilities of the presented method in this paper,the static observation data and the field measurements from Qinghai-Tibet Railway are used in calculation and analysis.The results illustrate the feasibility of the spatial-temporal modeling of satellite observation quality using observation data from multiple receivers.The capability of the proposed monitoring method for detecting the risks of potential faults or failures is effectively demonstrated.The results of this paper illustrate that the presented integrity monitoring method in this paper is capable of making full use of train operating characteristics,establishing the satellite observation quality models using observation information from the trains according to operation plans,optimizing the estimation of horizontal protection levels,and detecting potential faults or failures effectively,which outperforms the conventional integrity monitoring methods.It is validated that the proposed solution could effectively solve the problems of conventional RAIM methods in railway operation environments,and ensure the safe and trustworthy train positioning with satellite navigation systems,which is with great potential in the next generation railway train control systems and other related applications in the future.