| With the continuous development and improvement of satellite navigation systems,the high-precision positioning and other services can be provided for various application fields.The correctness and stability of the broadcast ephemeris are the key factors to ensure the accuracy of positioning.The broadcast ephemeris fault will cause large errors in the satellite position,which affects the accuracy of positioning,and reduces the availability of the system.Therefore,how to effectively improve the sensitivity of broadcast ephemeris fault monitoring is a problem that must be solved in positioning of users related to life safety.The broadcast ephemeris broadcasted by the Bei Dou Navigation Satellite System(BDS)is selected as the research object in this paper.This paper conducts research from three aspects: sensitivity analysis of broadcast ephemeris parameters,broadcast ephemeris type B fault monitoring,and broadcast ephemeris type A fault monitoring.It aims to effectively monitor BDS broadcast ephemeris fault,ensure the integrity of positioning of users related to life safety.The main research contents of the paper are as follows:(1)In order to realize the monitoring of broadcast ephemeris parameters into the monitoring of satellite position error,the sensitivity of broadcast ephemeris parameters is studied.Based on the sensitivity analysis of the broadcast ephemeris parameters,the influence of broadcast ephemeris parameter change on the satellite position error is obtained,and the parameters are classified based on this influence.The prediction method of different orders can be used to predict parameters in different influence levels to obtain higherprecision broadcast ephemeris parameters.Experimental results show that the parameters that have a greater impact on the satellite position error are the mean anomaly,longitude of ascending node of orbit plane,inclination and argument of perigee.The parameters that have little impact on the satellite position error are 6 harmonic correction amplitudes.According to the different degree of influence on satellite position error,15 broadcast ephemeris parameters are classified to provide a basis for broadcast ephemeris prediction classification processing.(2)Aiming at the problems of the traditional Global Positioning System(GPS)Yesterday’s Ephemeris minus Today’s ephemeris(YE-TE)method in broadcast ephemeris type B fault monitoring,such as low monitoring sensitivity and limitation of application to BDS satellites,the Predict Ephemeris minus Today’s Ephemeris(PE-TE)method suitable for BDS satellites is proposed.Based on the high,medium,and low-level classification of broadcast ephemeris parameters,the high and low-order collocation method is used to obtain higher-precision broadcast ephemeris parameter.The test statistics is constructed and compared with the threshold that meets the continuity requirement of Ground-Based Augmentation Systems(GBAS)Category I(CAT I)precision approach.The experimental results show that under the condition that no broadcast ephemeris fault,the numbers of test statistics of GEO,IGSO and MEO satellites greater than the threshold are within the allowable range of false alarms,which meets the continuity requirement of the system.(3)Considering the missed detection during the broadcast ephemeris type B fault monitoring,the PE-TE method is used to conduct missed detection for broadcast ephemeris fault monitoring.The Minimum Detectable Error(MDE)that reflects the satellite position error is constructed and compared with the threshold that meets the integrity risk requirement of GBAS CAT I precision approach to conduct missed detection.The experimental results show that the MDEs of GEO,IGSO and MEO satellites are all less than the detection threshold of 3500 m under the condition that the broadcast ephemeris is fault-free,which meets the integrity risk requirement of the system.In the case of a broadcast ephemeris fault,the missed detection rates of GEO,IGSO and MEO satellites are all less than that to the integrity risk requirement of system.The PE-TE method can effectively monitor the BDS broadcast ephemeris type B fault and improve the sensitivity of fault monitoring.(4)Aiming at the problems of traditional single-type satellite observations in broadcast ephemeris type A fault monitoring,such as large observation noise or complex fixed resolution of ambiguity,a type A fault monitoring method based on improved Receiver Autonomous Integrity Monitoring(RAIM)is proposed.The pseudorange differential and the double-difference carrier phase are used to measure the position error to construct observation equation in this method.Then the MDE is calculated and compared with the detection threshold that meets the integrity risk requirement of GBAS CAT I precision approach.The experimental results show that after the parameters affecting MDE meet the performance requirements specified in the GBAS observing station deployment standard,only a certain parameter is changed,the MDEs are less than the detection threshold of3500 m,which meets the integrity risk requirement of system.In the case of broadcast ephemeris fault,the missed detection rates of GEO,IGSO and MEO satellites are all less than that to the integrity risk requirement of system.This method can effectively monitor BDS broadcast ephemeris type A fault,while improving the observation accuracy of broadcast ephemeris fault,and reducing the complexity of fixed resolution of ambiguity. |
