Research On Signal-in-space Error Anomaly Detection And Performance Assessment Of BDS Satellites

The signal-in-space anomaly of GNSS has a great impact on user's navigation and positioning performance.The detection and performance evaluation of the abnormal signal broadcasted by navigation ephemeris are particularly important for the signal-in-space continuity,availability and integrity.BeiDou Navigation Satellite System(BDS),except for the unmonitored signal-in-space anomalies existed inevitably,which is similar to other navigation system.Meanwhile,due to the peculiar configuration of constellation,the orbit maneuvers of GEO and IGSO are more frequent.During the orbit maneuver,the satellite ephemeris broadcasted by navigation message is not the true orbit of satellite,which also leads to signal-in-space anomalies.In the existing ARAIM research,the satellite failure allocation and failure rate are all conservative estimations,which are inconsistent with the actual performance of BDS,and also leading to a certain risk in application.Therefore,how to accurately detect the signal-in-space anomalies caused by BDS satellite orbit maneuvers,satellite clocks and orbit errors,and to provide users with reliable system availability and continuity assessment indicators are especially urgent.So the systematic researches are carried out in this paper based on the above issues,and the main achievements and innovation points are as follows:(1)The control measures of orbit maneuver and the effect of orbit maneuver on orbit elements were systematically studied.An orbit maneuver detection method based on ROOTA and healthy flag from broadcast ephemeris was proposed.Then the period of orbit maneuver and the recovery time of BDS satellites were obtained through the broadcast ephemeris in 2015.The results show that the control intervals of GEO C04 satellite is about 73 d,the other GEO satellites are about 30 d,and the IGSO satellites are about 180 d.The duration of recovery time of these satellites is about 6-10 hours.(2)The effect of BDS satellite orbit maneuver on service performance wsa studied,especially the influence of GEO satellite orbit maneuver on the RAIM availability in non-precision approach(NPA)of BDS system was studied.The simulation results show that when the orbit maneuvers of GEO satellites occurs in UTC 08 h and 15-16 h,the service availability of BDS in the Aisa-Pacific region would reduce to 97.8% at the maximum extent;moreover,from the analysis of actual orbit maneuver period,the orbit maneuver period of C04 at UTC 14-23 h and C05 at 00-05 h make the RAIM availability of BDS in the Aisa-Pacific region lower than 99.9%,the influenced scope from the two satellites is mainly at the upper and lower corner in the Aisa-Pacific region.(3)Considering the traditional precise ephemeris comparison method used for BDS signal-in-space anomaly detection at present,there has a problem that the threshold are difficult to be determined and susceptible to be polluted by the gross error of the clock,an improved method for detecting the signal-in-space anomalies using precise ephemeris is proposed.Firstly,the median method is used to detect the gross error of clock in the improved method,which avoiding the signal-in-space error to be polluted by the gross error in clock datum.Secondly,a two-step threshold strategy,which is the initial experience threshold combined with the RMS calculated by the trimmed data of SISRE(Signal-in-space Range Error),is used to detect the signal-in-space anomalies.The detection results from 2015 to 2016 show that the improved method could avoid the constellation fault caused by the gross error from the satellite's clock effectively.Except for C13,the average accumulated hours of anomalies for BDS satellites are 9.7h for IGSO,10.4h for GEO and 56 h for MEO;among the detected anomalies,the anomalies caused by the clock error accounted for about 83.04%,the anomalies caused by the orbit accounted for about 12.28%,and the integration of both is about 4.68%.(4)A real-time signal-in-space anomaly detection algorithm based on the real-time observation data from multiple stations is proposed and explored.The new strategies are proposed in the solution of receiver clock and the calculation and statistics of IURE(Instantaneous User Range Error),and the issue that the use of observation data to detect signal-in-space anomalies requires the precise ephemeris is settled.And the signal-in-space anomalies in January 2015 are detected using the above algorithm.The results show that the employed of the improved method in the multi-station data could eliminated the failure caused by receiver effectively,and the starting and ending time of signal-in-space anomaly(including orbit maneuver)could be accurately detected by the new algorithm.(5)Four failure modes of BDS satellite signal-in-space error were firstly analyzed and summarized,which including the long-term failures related to the service life of the satellite,the maintenance failures related to satellite orbit maneuvers,the short-term failures related to the stochastic and repairable anomalies,as well as the equivalent failures composed by the above three failures.Then the mean time between failure(MTBF)and mean time to repair(MTTR)of all kinds of failures are obtained.Thereby the signal-in-space availability and continuity of BDS satellites are assessed in these failures.The statistical results show that the MTBF of IGSO satellite is higher than that of GEO satellite under the maintenance failure,and the MTTR of the GEO and IGSO satellites are the same basically,so the availability of IGSO satellite is higher than that of GEO satellite;the availability of the GEO and IGSO satellites is higher than that of the MEO satellite under the short-term failure,of which the availability of C11 is the lowest,because of the higher failure rate;the single satellite availability of individual GEO satellite under the equivalent failure is lower than the indicator requirement of BDS-OS-PS-1.0,but the continuity could be satisfied with the requirement.