| Intelligent transportation system(ITS)is a very large system full of complexities,of which the dynamic route guidance system(DRGS)is one of the most important components.The techniques of electronic communication,computer networks,satellite navigation and positioning,internet of things,etc,are integrated in DRGS,to provide both the real-time traffic information and the optimal path planning for travelers.As a carrier of DRGS,vehicle navigation terminal provides great conveniences for vehicles in the aspects of avoiding traffic control and congestion,and navigating intelligently,and in the meanwhile the high-precision,efficient and reliable performances collectively construct the foundation of the real-time positioning.Beidou satellite navigation system(BDS)is a global satellite positioning and communication system developed in China.It is the third mature satellite navigation system after U.S.global positioning system(GPS)and the Russian GLONASS system.As the second generation of Beidou navigation system is established successfully in the Asia Pacific region,high precision Beidou vehicle terminal navigation system becomes an important direction and research focus.However,the GPS system has been put into research earlier and has been used for a long time,so its performance is relatively perfect.Presently,most of the vehicle terminal navigation systems are occupied by GPS.In this case,it is considerably important to speed up the deep research and industrialization promotion of high precision Beidou Positioning technology.In this paper,the positioning technology of vehicle terminal and path guidance technology based on Beidou navigation system are studied and developed from the viewpoint of improving the real-time dynamic Beidou positioning accuracy.Finally,a vehicle terminal system based on Beidou Positioning chip is designed and implemented.The main research work of this thesis includes the following aspects:(1)High-precision single point positioning technology of BDSThe static positioning of Beidou navigation system is deeply studied by using least-square estimation method and ionosphere free model.Firstly,the observational equations of the static and precise single point positioning of the compass are introduced in details.Afterwards,to realize the least-square estimation of the observation equation,the nonlinear equation of observation is linearized.Lastly,the weighted least-square estimation approach and implementation steps are characterized.(2)High-precision dynamic relative positioning technologyof BDSThis paper introduces the principle and method of high precision Beidou dynamic relative positioning,focuses on the observation model used in Beidou relative positioning,and analyzes the composition,characteristics and application of the combined observations of the single-difference between stations,double-difference between stations and satellite and the triple-difference between stations,satelliteand epoch.Subsequently,we propose a parameter estimation method and an ambiguity fixing method used for dynamic relative positioning processing,and introduce some technical details on the application of Kalman filtering algorithm in dynamic relative positioning as well as the principle of LAMBDA algorithm for ambiguity fixing.Finally,the dynamic relative positioning verification experiment of Beidou is carried out by using short baseline and middle and long baseline relative positioning data,respectively.(3)High-precision real-time single point positioning of BDS based on AmbiguityAs the differential positioning is limited by the range of reference stations within the area,in this paper,a precise point position-ambiguity resolution(PPP-AR)for precise point positioning technology(PPP)is investigated,which needs to calculate the satellite clock difference and atmospheric correction parameters by using the received real-time precise satellite orbit signals.The integer information of ambiguity is separated by specific means,and the method of non differential positioning is adopted to realize the real-time high precision positioning.Firstly,the function model of non differenced real time precise point positioning is introduced,and then the reason why ambiguity cannot be fixed directly to integer is analyzed comprehensively in non-differential PPP positioning.The hardware delay parameters at the satellite and receiver terminals which affect the ambiguity parameters are distinguished and separated,and the method to estimate the ambiguity of the wide lane and narrow lane and the satellite side unadjusted delay is introduced,through further data ground monitoring network separation of the above parameters.Lastly,the Beidou real-time precise positioning service process is constructed.(4)The shortest path guidance based on two ways search A*algorithmPresently,the optimization problem of many paths is to find the shortest path problem in a specific road network.In navigation system,with the aid of the Beidou Positioning System,the user's starting point is obtained in the road network,and the path is searched between the starting point and the end point which input by the users,thus the path is searched.When the vehicle terminal does not obtain the real-time traffic information,the system will solve the shortest path according to the storage map.Firstly,the paper reviews the classical path planning algorithm;and then improves the traditional A*algorithm.Two ways search is adopted to improve the algorithm evaluation function by introducing an intelligent algorithm to enlighten the function selection factor.The search time of the algorithm is effectively reduced,and the search dynamics is enhanced.Finally,an example is given to illustrate the feasibility of the algorithm.(5)The shortest time path guidance based on improved ant colony algorithmThe application of improved ant colony algorithm in urban road navigation is studied.In this paper,the ant colony algorithm is improved from the aspects of pheromone updating,heuristic function and state transition rules.It is applied to path guidance,so that the algorithm can effectively jump out of the local optimum and find the global optimal path.Through simulation and comprehensive analyses,the improved ant colony search algorithm features the short search time,avoiding congestion and high search success rate,and hence the path navigation effect is better.(6)Suboptimal alternative path guidance based on Q learning algorithmAn efficient Q learning algorithm is proposed to solve the multiple path planning problems in urban center intersection.Different from traditional multipath algorithms,it is easier to obtain suboptimal Q values with iterative methods to select several alternative paths..Besides,logic is used to improve response speed and constraints are imposed on path generation to ensure the reliability of the candidate path set.Finally,the effectiveness and adaptability of the proposed algorithm are illustrated through simulation results.(7)Design and implementation of vehicle terminal guidance system based on high-precision BDS PositioningBased on the theoretical research above,using S3C2440A microprocessor as the core of the system and WindosCE6.0 as the operating system,this paper designs the hardware and software solutions using a high precision Beidou Positioning Vehicle navigation terminal system,and completes the design of hardware circuit and application software development.In the end,the test demonstrates that the designed Beidou Positioning Vehicle navigation system runs stably and reliably,and achieves the desirable positioning and.navigation performances.This dissertation was supported in part by National Natural Science Foundation of China under the grant 60974047,in part by Guangdong outstanding young teachers training program under the grant Yq2013201,and in part by Guangdong science and technology program under the grant 2014A010103002. |
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