Train Precise Point Positioning Method With Limited Satellite Signal

The train control system based on GNSS technology requires to obtain train location and speed information accurately and reliably,which could not only reduce the number of track circuit and balise,but alse meet the requirements of train positioning accuracy with the support of differential GNSS technology.Precise point positioning(PPP)can provide decimeter-to-centimeter-level accuracy with using a single receiver and not be dependent on differential correction,could be widely used in the railways of China's western regions which have the characteristics of long mileage and low traffic volume.PPP results not only further improve the train positioning accuracy without the limitation of the operation range,but lower set-up and maintenance cost at the same time.At present,the research on the application of PPP in the field of train dynamic location is limited,and there are not enough analysis results for the train kinematic positioning accuracy computed by the different IGS products.Moreover,GNSS signals would inevitably be restricted by limited satellite signal areas such as tunnels,bridges and valleys during the train operation process.It is necessary to select suitable on-board sensors to establish the satellite augmentation system in GNSS difficult areas,so as to obtain more accurate and reliable train location results.Therefore,aiming at the typical scene in railway environment,this thesis focuses on the method of train precision point positioning with limited satellite signal.The main research contents include:(1)This thesis constructs a train kinematic location model based on PPP.The appropriate error models and estimation algorithms are adopted to correct PPP main errors,then establishes PPP mathematic model and construct PPP train positioning algorithm based on ambiguity-float PPP solution.According to the result of the train kinematic positioning results,the realization of the train PPP algorithm is analyzed.(2)This thesis studies a method of train integrated positioning based on PPP.According to the environment of low density railway,choose Inertial Navigation System,Odometer and other on-board sensors to build the satellite augmentation system,completes the INS initial alignment method of train positioning system under the static state,establishes the accurate GNSS/INS and INS/ODO mathematical models and error equations,then constructs the GNSS/INS/ODO integrated positioning method.Besides,with the map-matching algorithm applied,the train location could be further determined precisely to meet the continuous positioning requirements in the different environment.(3)This thesis validates the method of train integrated positioning based on PPP under the condition of limited satellite signal.In order to evaluate the proposed system,a real experiment is conducted in the western regions of China to verify and analyze the positioning performance of the GNSS/INS/ODO/MM train integrated positioning system under the continuous satellite signal difficult areas with the laboratory simulation data and the actual collection data,then studies the PPP-GNSS/INS/ODO kinematic positioning accuracy computed by different types of IGS products and final products from different IGS analysis centers and the positioning performance in the tunnel environment.The experimental results indicate that the proposed train integrated navigation system could provide continuous and usable positioning results for the train control system in both open-sky and GNSS signal-obstructed environments.Compared with the measurements of DGNSS,the horizontal DRMS value of PPP-GNSS/INS/ODO integrated navigation positioning results computed by IGS final products is 0.5477m,while the horizontal DRMS value of integrated positioning results computed by IGS Ultra-rapid products released one hour ahead of the test time is 1.0278 m,which means the proposed train integrated navigation system is satisfied the requirement of train positioning precision of China's western region.