Research And Implemention On Multi-GNSS RTK With Integrity Monitoring-based Ambiguity Validation

Ambiguity resolution is a key method in real time kinematic positioning.Centimeter positioning accuracy can be obtained by correctly calculating the integer ambiguities.But if the integer ambiguities are not solved correctly,the positioning error of meter level will be caused.Therefore,in order to meet the rigorous requirement of high precision and high reliability in safe of live applications,it is necessary to establish a complete method to validate the integer ambiguities.With the modernization of GNSS,making full use of multi-system and multi-frequency observations can effectively improve the intensity of the model and improve the accuracy of ambiguity resolution.Meanwhile,in order to overcome the shortcomings of the traditional ambiguity validation method which can not change their threshold,a validation method based on integrity monitoring is proposed.The main research of this subject is as follows:(1)The theory of multi-GNSS differential positioning method is studied,and the combined model of GPS and BDS is constructed.Compared with the traditional single system differencing positioning method,the model strength of the system and the success rate of ambiguity resolution are improved.The experimental test shows that the ambiguity fixing rate is improved by 1.2% compared with single BDS system by using GPS/BDS dual system.(2)Aiming at the disadvantage of traditional fixed threshold validation method which is difficult to adapt to navigation environment,this paper uses integrity monitoring idea for reference,takes integrity risk level as a target to achieve,constructs an ambiguity validation method based on intergrity monitoring,and focuses on the implementation of effective constraints on the missing detection of ambiguity resolution,so as to ensure the reliability of ambiguity resolution.Monte Carlo simulation shows that compared with the traditional fixed threshold method,the proposed method can constrain the failure rate of ambiguity resolution more effectively according to the integrity risk index required by users.(3)In order to verify the feasibility and actual performance of the proposed method,considering the requirements of miniaturization and low power consumption,a test system based on DSP+PC platform is designed.The DSP core is responsible for the implementation of navigation theory and algorithm,and the PC is responsible for the displaying the positioning results.The system can support GPS/BDS multi-system and multi-frequency positioning,and the update rate of positioning can reach more than 10 Hz.The designedsystem can meet the requirements of real-time,high precision and high dynamic navigation and positioning applications.(4)Experiments under static and dynamic conditions are tested respectively using the designed platform.The performances of the proposed validation method and traditional RT method under the condition of single BDS system and GPS/BDS dual system are compared and analyzed.Experiments show that the method of multi-system combination can effectively improve the success rate of ambiguity fixing,and the proposed method can adjust the threshold adaptively according to the dynamic environment,and achieve the optimal balance between missed detection rate and false alarm rate.Under good navigation environment,the false alarm rate of the proposed method is the same as that of RT method,but the false alarm rate is only 19.05% of that of RT method.In strict navigation environment,although the false alarm rate of the proposed method is 0.46% higher than that of RT method,the false alarm rate of the proposed method is only 50% of that of RT method.