Research On Multi-Constellation Train Positioning Envelope Calculation Method Using Non-Differential Range Measurements

Train localization system is the core element to ensure the safety and improve the efficiency of transportation.With the increasing demand for high-efficiency and intelligence railways,the satellite positioning applications for railways have become research hotspots.The Global Navigation Satellite System(GNSS)can provide real-time navigation services,all-day and all-weather.In particular,with the full completion of China’s Bei Dou navigation satellite System(BDS),the BDS-assisted upgrading of the railway system has become the developing objective for rail industry.In order to satisfy the rising transport demand,improve the application level of the BDS and enrich the positioning capabilities of the train localization system,the GNSS-based optimization and evaluation methods are in urgent need for train positioning techniques.Therefore,considering the basic performance of GNSS,the corresponding optimization methods are proposed based on the performance of GNSS constellation and Signal In Space(SIS).The coverage and availability of GNSS constellation is improved by using multi-constellation strategy,aidding by precision range measurement,the positioning accuracy is optimized,and combined with the Receiver Autonomous Integrity Monitoring(RAIM)algorithm,the GNSS SIS performance is optimized.In order to estimate the GNSS-based train trusted location,the real-time positioning error index is calculated based on the optimized positioning method,and the GNSS-based train positioning envelope is further formed.The main contributions of this research are summarized as follows:(1)The multi-constellation strategy is applied for train positioning solutions,which focus on space-time unification framework of GPS/BDS combination method.The priori factor models are estabilished based on satellite signal differences,considering the constellation discrepancies,a multi-constellation optimization method using priori model combined with posterior variance estimation algorithm is proposed.(2)The GNSS measurement models of pseudo range,carrier phase and Doppler shift are established,and the error correction models of BDS and GPS are built respectively.Based on Kalman filter algorithm,the clock error and clock drift are modeled,and a train positioning method using non-differential measurements is proposed,while an observability analysis based verification method is applied for comparing different measurements combination models.(3)Considering the quantitative estimation method of the positioning solutions,the existing train safety envelope concept is consulted.Based on the basic performance of GNSS,the positioning accuracy estimation method and the RAIM algorithm are considered.A feasible protection level estimation method is applied to conforms with the proposed positioning model.Comprehensively considering horizontal positioning error index and the influence of communication delay,a GNSS-based positioning envelope estimation method is formed.In this paper,the field tests are designed and conducted to verify the optimization method of multi-constellation stochastic model and the non-differential measurements based train positioning methods,respectively,and the proposed GNSS-based train positioning envelope is verified by scenes and levels.The experimental results show that the multi-constellation positioning strategy can optimize the satellite geometry,improve the accuracy of positioning solutions and further reduce the risk of system failure.The proposed non-differential positioning method can output real-time positioning solutions,the horizontal position and velocity estimation errors are less than4 m and 0.5 m/s,respectively,which can improve the accuracy and capacity of GNSS railway applications.Compared with other measurements combination models,the proposed method illustrates the optimal observability degree.Meanwhile,the horizontal positioning errors are contained in the proposed train positioning envelope,which can meet the availability of GNSS receiver and provide an alternative approach for the safety application of train positioning technology.There are 58 pictures,26 tables and 92 references.