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Research On The Method And Theory Of BDS-3 PNT Service SIS Accuracy Improvement Using Inter-satellite Link

Posted on:2020-08-30Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y F YangFull Text:PDF
GTID:1368330620453217Subject:Surveying the science and technology
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According to the three-step strategy of “first regional,then global”,China will complete the construction of the third-generation BeiDou satellite navigation system(BDS-3)around 2020 and provide positioning,navigation and timing(PNT)services to users worldwide.The signal-in-space(SIS)accuracy is an important factor of satellite navigation systems,which also is the indicator of satellite navigation system construction level.Since BDS ground monitor stations can only be deployed in mainland China,the effective tracking coverage for a medium Earth orbit(MEO)satellite is less than 40%.When MEO satellites depart from the domestic monitor network,the tracking,observation and communication are interrupted.It leads to the accuracy decrease of satellite orbit and clock out of the range of the regional stations,as well as SIS,which is difficult to meet the requirement of the BDS-3 PNT services.The inter-satellite measurement and communication was achieved by Ka-band inter-satellite link(ISL)payload equipped on Beidou-3 satellite,which can provide strong support for the improvement of the Beidou-3 SIS accuracy.In addition,more and more low Earth orbit(LEO)satellites are equipped with GNSS receivers,which establish high-low-orbit ISLs between GNSS and LEO satellites and are expected to serve as “space-based dynamic monitoring stations” to make up the shortcoming of the regional ground monitoring stations and improve the SIS accuracy of the BDS-3 PNT services.This paper focuses on the method and theory of BDS-3 PNT service SIS accuracy improvement based on ground monitoring station observation,ISL observation and LEO on-board GNSS observation.The main work and innovations of the paper are as follows:1.The observation data of BDS-3 ISL was analyzed and result shows that a hybrid range measurement and communication network between high-middle orbit satellites,middle-middle orbit satellites and satellite-ground is build based on ISLs.The full-arc tracking of the BeiDou MEO satellite was realized only relying on domestic monitoring stations.The synchronous update of navigation data for the whole constellation was achieved through domestic injection and in-orbit distribution,which is called “one satellite for the whole constellation”.2.The influence of the monitoring station abnormal data and the processing strategy are studied.A gross error elimination method based on median value is proposed for orbit determination(OD)real-time preprocessing,so as to solve the problem that OD failure caused by abnormal data of the monitoring station.The experiment results show that in the case where observation data from multiple satellites and multiple stations are abnormal,the gross error can still be successfully eliminated,and the OD software operation is unaffected,which greatly improves the robustness of the OD.After fully test,this method has been applied to online operations.3.The theory and method of enhanced orbit determination for BDS-3 satellite using both ground monitoring station data and inter-satellite link ranging data are studied.When the ISL measurements are added,the 3D position RMS of overlapping orbit difference(OOD)is decreased to 0.16 m from 0.61 m,improved by 73.8%.The accuracy of the 24-hour orbit prediction can also be improved from 1.52 m to 0.23 m,improved by 84.9%,and the OD RMS of SLR validation is about 10 cm.The orbit determination and prediction accuracy of the 8 regional monitoring stations and ISL are better than that of 21 global monitoring stations.4.The influence of ground station distribution on the ISL enhanced OD accuracy is studied.With ISL,the OD accuracy based on only 3 ground stations with a distance of several hundred kilometers is equivalent to that based on eight ground stations.The number and distribution requirements of the ground station for OD was greatly lowered by ISL.Only a few ground stations is needed to constrain the positional relationship between the constellation and the earth and avoid the rotation of the constellation,and pretty high orbit accuracy is obtained.5.Hardware delay calibration error can cause clock differences amoung ISL calculated clock from different nod satellite and Two-Way Satellite Time and Frequency Transfer(TWSTFT)clock,which affect the accuracy of the broadcast clock.In this paper,a method is proposed which use ISL relative clock for overall adjustment,establish the quasi-stable satellite time(QST)and using a few satellite-ground links to compare deviation between QST and BDT.The clock deviation can be eliminated,the time synchronization device is greatly simplified,and the dependence on the ground device is reduced,while the broadcast clock accuracy is improved through this method.The RMS of QST estimation residuals is better than 0.2 ns and the RMS of 2-hour prediction error is better than 0.3 ns.The RMS of 2-hour prediction error according with BDT is 0.8 ns and 0.7 ns using TWSTFT station or an anchor station for time traceability,respectively.The max error of 12-day prediction error according with BDT is 20 ns based on a priori information.6.The improvement of BDS-3 satellite URE and URA by ISL are analyzed,the method of establishing BDS-3 coordinate system(BDCS)based on regional station are discussed and the accuracy of SPP and PPP are analyzed.By adding the ISL,the URE of BDS-3 satellite is deceased to 0.22 m,of which the orbit-only URE is decreased by 85%,the clock-only URE is decreased by 27.6%,and the URA is improved to 1.38 m,which is equivalent to that of the GPS satellite.The accuracy of SPP is about 6 m(95%,PDOP<10).BeiDou Satellite's contribution to GPS/BDS dual system positioning is about 25%.The difference between GPS PPP results and BPS PPP results based on regional coordinate system is better than 1.5cm.7.The method of enhanced orbit determination of GNSS satellites using GNSS-LEO satellite link is studied.The results show that the effective tracking coverage for navigation satellite is improved effectively,geometry of navigation satellite orbit determination is enhanced,and the OD accuracy based on regional stations is improved greatly by LEO satellite.By adding one LEO satellite,the OD accuracy of BDS-2 GEO,IGSO and MEO satellite based on regional stations can be improved by 74.8%,70.3% and 66% respectively.
Keywords/Search Tags:BDS-3, inter-satellite link, enhanced orbit determination, clock estimation, PNT, SIS, URE, URA, SPP, PPP, LEO
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