Research On Train Positioning Method Assisted By Pseudolite Under Constrained GNSS Environment In Railway Stations

Real-time and precise measurement of train speed and position is of great significance in train operation control.In recent years,the application of Global Navigation Satellite System(GNSS)such as BDS(Bei Dou Navigation Satellite System)and GPS(Global Positioning System)in railway train positioning has become an important development trend.The performance of satellite positioning is directly affected by the signal observation conditions.When the train enters or passes through a station with shelters such as a canopy,the visibility of the satellite signal will be greatly limited,and the observing quality would not fulfil the performance requirements of positioning including accuracy,continuity and availability.Recently,the ground-based Pseudolite(PL)technology has gained increasing attention,which can assist the GNSS to establish a space-ground cooperative signal system and provide an enhanced positioning service under a GNSS-constrained or even a GNSS-denied environment.The pseudolite-aided GNSS is capable of achieving seamless train positioning in railway station areas,which is of great significance to ensure the safety and efficiency of train operation.Therefore,a train positioning method enhanced by pseudolites under constrained GNSS environment in railway stations is proposed in this thesis.A novel Firefly Algorithm(FA)based on the clustering is designed.According to the constraint characteristics of the GNSS observation conditions at specific stations,an optimization scheme for designing the pseudolite constellation is established based on the improved firefly algorithm iterative optimization approach.A GNSS/PL integrated train positioning solution that is adaptive to different GNSS satellite observation conditions is proposed with a combined observation frame of GNSS satellites and PLs.The main results of this thesis are summarized as follows.(1)By summarizing the error sources of GNSS and PL,a GNSS/PL combined positioning model is designed.Based on that,a GNSS/PL integrated train positioning system architecture is presented with the PL constellation design scheme.(2)By utilizing the adaptive step size,the neighborhood topology structure and the generalized central particle guidance strategy based on the clustering algorithm,an improved firefly algorithm is proposed and the conventional firefly algorithm is effectively improved.(3)A pseudolite constellation optimization method dedicated to the railway station implementation is proposed,which fully considers the temporal and spatial constraint characteristics of the GNSS observation in the station area with shelters and the train operation process.The Performance Indication Factor(PIF)is introduced into the improved firefly optimization algorithm to determine an optimized pseudolite layout solution,which provides a significant foundation to GNSS/PL integrated positioning.In this thesis,a specific verification platform is constructed using field experiment data from a real station and specific simulation systems.The experimental verification is carried out to validate the performance of pseudolite constellation optimization,characteristics of optimized pseudolite layout solution and the performance of GNSS/PL integrated positioning.The comparison test with 10 benchmark test functions and 4 similar firefly optimization algorithms verifies the superiority of the improved firefly algorithm based on clustering proposed in this thesis.Considering the characteristics of pseudolite constellation,the optimal pseudolite constellation is compared with several referencing constellation strategies under the same station environment to demonstrate the effectiveness of the proposed pseudolite constellation optimization method.Effectiveness of the GNSS/PL integrated positioning is illustrated through the comparison with the practical satellite receiver output,where the derived optimized pseudolite constellation is adopted.The performance optimization capability of the PL-assisted GNSS positioning in the constrained station area is analyzed.Compared with the stand-alone GNSS mode,the advanced capability of the proposed solutions in this thesis owing to the optimized pseudolite constellation and integrated positioning has been verified.Results of this thesis provides an effective approach for seamless and enhanced train positioning in railway stations and other constrained environments.Figure 66,table 24,reference 67.