Precise Point Positioning(PPP) requires precise products, including high-accuracy satellite orbit and clock parameters. It is impossible to obtain an orbit solution that is sufficiently accurate for PPP services with ...Precise Point Positioning(PPP) requires precise products, including high-accuracy satellite orbit and clock parameters. It is impossible to obtain an orbit solution that is sufficiently accurate for PPP services with a regional tracking network;therefore, satellite orbits are usually estimated by a global tracking network with a large number of ground stations. However, it is expensive to build globally distributed stations. Fortunately, BeiDou-3 satellites carry an InterSatellite Link(ISL) payload, which can track the whole arc of the BeiDou-3 satellites and enhance the orbit determination accuracy with regional ground stations. In this contribution, a novel orbit determination strategy for BeiDou-3 PPP is proposed, in which the BeiDou-3 satellite orbits are enhanced by the ISL. First, the generation of precise satellite products is demonstrated in detail.In addition, the products are assessed by Satellite Laser Ranging(SLR) residuals and overlap comparisons. Moreover, the products are used for receivers in China's Mainland to carry out the static and kinematic modes to research the PPP performance of Bei Dou-3’s 3IGSO/24MEO constellation.The SLR validations of the satellite orbits demonstrate an accuracy better than 0.1 m in the radial component, and the orbit overlap comparisons show accuracies of 0.016 m in the radial component,0.088 m in the along-track component and 0.087 m in the cross-track component. The Standard Deviation(STD) in the differences in overlapping arcs for the estimated satellite clocks is approximately 0.10 ns. The static PPP results demonstrate that the error in both the horizontal and vertical components is smaller than 10 cm after 30 minutes of convergence. After 24 hours of convergence,the errors are 0.70 cm, 0.63 cm and 1.99 cm for the north, east and up components, respectively.The kinematic PPP experiment illustrates that the Root Mean Square(RMS) position errors in the north, east and up components are approximately 3.23 cm, 5.27 cm and 8.64 cm, respectively,after convergence. The obtainable positioning and convergence performances are comparable to those using products generated by global tracking networks.展开更多
A two-way satellite time and frequency transfer(TWSTFT) device equipped in the BeiDou navigation satellite system(BDS)can calculate clock error between satellite and ground master clock. TWSTFT is a real-time method w...A two-way satellite time and frequency transfer(TWSTFT) device equipped in the BeiDou navigation satellite system(BDS)can calculate clock error between satellite and ground master clock. TWSTFT is a real-time method with high accuracy because most system errors such as orbital error, station position error, and tropospheric and ionospheric delay error can be eliminated by calculating the two-way pseudorange difference. Another method, the multi-satellite precision orbit determination(MPOD)method, can be applied to estimate satellite clock errors. By comparison with MPOD clock estimations, this paper discusses the applications of the BDS TWSTFT clock observations in satellite clock measurement, satellite clock prediction, navigation system time monitor, and satellite clock performance assessment in orbit. The results show that with TWSTFT clock observations, the accuracy of satellite clock prediction is higher than MPOD. Five continuous weeks of comparisons with three international GNSS Service(IGS) analysis centers(ACs) show that the reference time difference between BeiDou time(BDT) and golbal positoning system(GPS) time(GPST) realized IGS ACs is in the tens of nanoseconds. Applying the TWSTFT clock error observations may obtain more accurate satellite clock performance evaluation in the 104 s interval because the accuracy of the MPOD clock estimation is not sufficiently high. By comparing the BDS and GPS satellite clock performance, we found that the BDS clock stability at the 103 s interval is approximately 10.12, which is similar to the GPS IIR.展开更多
On December 27,2018,the basic system of the third-generation BeiDou navigation satellite system(BDS-3)completed the deployment of its constellation of 18 MEO networking satellites as well as the construction of the op...On December 27,2018,the basic system of the third-generation BeiDou navigation satellite system(BDS-3)completed the deployment of its constellation of 18 MEO networking satellites as well as the construction of the operation control system(OCS)and began to provide basic navigation services to users worldwide.Compared with BDS-2,BDS-3 aims to offer users better navigation signals and higher precision with a series of new technologies.For example,the spaceborne atomic clock of BDS-3 is upgraded for higher performance,the Ka-band inter-satellite link is adopted for inter-satellite ranging and communication,and new B1C and B2a signals are broadcast in addition to B1I and B3I signals(compatible with BDS-2).In addition,a 9-parameter model based on a spherical harmonic function is employed for ionospheric delay corrections.Using the observation data from 18 satellites of the basic system,this paper conducts a comprehensive evaluation of the pseudorange measurement characteristics,signal-in-space(SIS)accuracy of navigation messages and global service capability of BDS-3.The results indicate that the pseudorange measurement multipath effect and observation noise of BDS-3 satellites are better than those of BDS-2;additionally,with the support of inter-satellite links,the user range error(URE)of the BDS-3 satellite broadcast ephemeris is better than 10 cm,the precision of the broadcast clock parameter is better than 1.5 ns,and the SIS accuracy is better than 0.6 m overall.Different from the traditional Klobuchar model,the BeiDou global broadcast ionospheric delay correction model(BDGIM)can provide ionospheric delay corrections better than 70%for worldwide single-frequency users.The service capability evaluation of the basic system consists mainly of the accuracy improvement of the B1I and B3I signals according to BDS-2 as well as the global positioning accuracy of the new signals.These results prove that the BDS-3 basic system has achieved the design goal;that is,both the horizontal and the vertical global positioning accuracies are better than 10 m(95%).In the future,6 MEO satellites as well as 3 GEO satellites and 3 IGSO satellites for regional enhancement purposes will be deployed for full operation;consequently,BDS-3 will definitely provide a higher SIS accuracy and better service capability.展开更多
With the rapid development of technologies such as autonomous driving and robotic navigation,the demand for accurate and reliable positioning results with BDS has increased.The current status and future development of...With the rapid development of technologies such as autonomous driving and robotic navigation,the demand for accurate and reliable positioning results with BDS has increased.The current status and future development of BDS high precision services are reviewed.The operational PPP-B2b of BDS-3 achieves positioning accuracy at decimeter-level within 14 min and has the drawbacks in regional coverage and long convergence time compared with the international counterparts,such as CLAS of QZSS and HAS of Galileo.A development frame for multi-layer BDS high-precision services is proposed by considering its construction cost,compatibility of user terminal,operating maintenance burden,and service level.The global high-precision service with the improved orbit and clock accuracy enhanced with the inter-satellite link is taken as the most fundamental layer.By incorporating inter-satellite link observations,the orbit errors URE and clock errors are significantly reduced to approximately 0.05 m and 0.16 ns,respectively,which will expand PPP service to global.Based on this,the regional PPP-AR and PPP-RTK services with improved convergence performance are taken as the second layer.With PPP-AR,the convergence time drops to 10 min.With PPP-RTK,the convergence time would be further shortened to less than 3 min.The LEO enhanced PPP service is taken as the third layer which overcomes both drawbacks of the long convergence time of the inter-satellite link enhanced service(the first layer)and the regional coverage of the PPP-AR/PPP-RTK services(the second layer).The simulation results show that by introducing a LEO constellation of 288 satellites,the LEO enhanced PPP can achieve positioning accuracy better than 5 cm within approximately 1 min.In addition,the integration of LEO constellation and PPP-RTK is further proposed to enable instantaneous convergence.The implementation challenges are also presented.展开更多
High-precision Global Navigation Satellite System(GNSS)orbit and clock products are crucial for precise applications.An evenly distributed global network enables continuous tracking for GNSS satellites,while a regiona...High-precision Global Navigation Satellite System(GNSS)orbit and clock products are crucial for precise applications.An evenly distributed global network enables continuous tracking for GNSS satellites,while a regional network may result in tracking gaps in the areas where monitoring stations are not deployed.This also means that the orbit determination accuracy based on a regional network is not comparable to that with a global network.Integrating the measurements from regional ground stations and Low Earth Orbit(LEO)satellites onboard receivers is a potential approach for generating GNSS orbit and clock products with centimeter-level accuracy,which is particularly important for BDS and the local commercial providers relying on a regional network.In the integrated Precise Orbit Determination(POD),LEO satellites are used to compensate for the drawback of regional ground stations in the precise orbit and clock determination of GNSS satellites.To validate the role of LEO satellites in the orbit determination with a regional network,6 International GNSS Service stations around China and 13 LEO satellites from January 20 to 26,2019,including GRACE-C/D,SWARM-A/B/C,Jason-3,Sentinel-3A/B,and SAT-A/B/C/D/E are selected in this study to perform the integrated POD.The orbit and clock accuracies of GPS and LEO satellites are evaluated by comparison with precise products.The average Root Mean Square(RMS)of GPS orbit errors in the radial(R),along-track(T)and cross-track(N)directions are 2.27 cm,3.45 cm,and 3.08 cm,respectively,and the clock accuracy is better than 0.15 ns based on a comparison with the final products provided by Center for Orbit Determination in Europe(CODE).The LEO orbit accuracy is better than 2 cm in the R direction,and the position errors are mostly within 4 cm.The results indicate that the integrated POD can generate high-precision orbit and clock products for GPS and LEO satellites based on regional network stations.Finally,the integrated POD products are assessed for Precise Point Positioning(PPP).Simulated kinematic PPP has a comparable performance in terms of the convergence time and positioning accuracy.With more LEO satellites available,the orbit and clock determination accuracy and PPP positioning accuracy can be improved.展开更多
基金supported by the National Natural Science Foundation of China(No.41804030)。
文摘Precise Point Positioning(PPP) requires precise products, including high-accuracy satellite orbit and clock parameters. It is impossible to obtain an orbit solution that is sufficiently accurate for PPP services with a regional tracking network;therefore, satellite orbits are usually estimated by a global tracking network with a large number of ground stations. However, it is expensive to build globally distributed stations. Fortunately, BeiDou-3 satellites carry an InterSatellite Link(ISL) payload, which can track the whole arc of the BeiDou-3 satellites and enhance the orbit determination accuracy with regional ground stations. In this contribution, a novel orbit determination strategy for BeiDou-3 PPP is proposed, in which the BeiDou-3 satellite orbits are enhanced by the ISL. First, the generation of precise satellite products is demonstrated in detail.In addition, the products are assessed by Satellite Laser Ranging(SLR) residuals and overlap comparisons. Moreover, the products are used for receivers in China's Mainland to carry out the static and kinematic modes to research the PPP performance of Bei Dou-3’s 3IGSO/24MEO constellation.The SLR validations of the satellite orbits demonstrate an accuracy better than 0.1 m in the radial component, and the orbit overlap comparisons show accuracies of 0.016 m in the radial component,0.088 m in the along-track component and 0.087 m in the cross-track component. The Standard Deviation(STD) in the differences in overlapping arcs for the estimated satellite clocks is approximately 0.10 ns. The static PPP results demonstrate that the error in both the horizontal and vertical components is smaller than 10 cm after 30 minutes of convergence. After 24 hours of convergence,the errors are 0.70 cm, 0.63 cm and 1.99 cm for the north, east and up components, respectively.The kinematic PPP experiment illustrates that the Root Mean Square(RMS) position errors in the north, east and up components are approximately 3.23 cm, 5.27 cm and 8.64 cm, respectively,after convergence. The obtainable positioning and convergence performances are comparable to those using products generated by global tracking networks.
基金supported by the National Natural Sciences Foundation of China(Grant No.41574029)Youth Innovation Promotion Association CAS(Grant No.2016242)
文摘A two-way satellite time and frequency transfer(TWSTFT) device equipped in the BeiDou navigation satellite system(BDS)can calculate clock error between satellite and ground master clock. TWSTFT is a real-time method with high accuracy because most system errors such as orbital error, station position error, and tropospheric and ionospheric delay error can be eliminated by calculating the two-way pseudorange difference. Another method, the multi-satellite precision orbit determination(MPOD)method, can be applied to estimate satellite clock errors. By comparison with MPOD clock estimations, this paper discusses the applications of the BDS TWSTFT clock observations in satellite clock measurement, satellite clock prediction, navigation system time monitor, and satellite clock performance assessment in orbit. The results show that with TWSTFT clock observations, the accuracy of satellite clock prediction is higher than MPOD. Five continuous weeks of comparisons with three international GNSS Service(IGS) analysis centers(ACs) show that the reference time difference between BeiDou time(BDT) and golbal positoning system(GPS) time(GPST) realized IGS ACs is in the tens of nanoseconds. Applying the TWSTFT clock error observations may obtain more accurate satellite clock performance evaluation in the 104 s interval because the accuracy of the MPOD clock estimation is not sufficiently high. By comparing the BDS and GPS satellite clock performance, we found that the BDS clock stability at the 103 s interval is approximately 10.12, which is similar to the GPS IIR.
基金supported by the National Natural Science Foundation of China(Grant Nos.41574029,and 11573035)the Youth Innovation Promotion Association CAS(Grant No.2016242)。
文摘On December 27,2018,the basic system of the third-generation BeiDou navigation satellite system(BDS-3)completed the deployment of its constellation of 18 MEO networking satellites as well as the construction of the operation control system(OCS)and began to provide basic navigation services to users worldwide.Compared with BDS-2,BDS-3 aims to offer users better navigation signals and higher precision with a series of new technologies.For example,the spaceborne atomic clock of BDS-3 is upgraded for higher performance,the Ka-band inter-satellite link is adopted for inter-satellite ranging and communication,and new B1C and B2a signals are broadcast in addition to B1I and B3I signals(compatible with BDS-2).In addition,a 9-parameter model based on a spherical harmonic function is employed for ionospheric delay corrections.Using the observation data from 18 satellites of the basic system,this paper conducts a comprehensive evaluation of the pseudorange measurement characteristics,signal-in-space(SIS)accuracy of navigation messages and global service capability of BDS-3.The results indicate that the pseudorange measurement multipath effect and observation noise of BDS-3 satellites are better than those of BDS-2;additionally,with the support of inter-satellite links,the user range error(URE)of the BDS-3 satellite broadcast ephemeris is better than 10 cm,the precision of the broadcast clock parameter is better than 1.5 ns,and the SIS accuracy is better than 0.6 m overall.Different from the traditional Klobuchar model,the BeiDou global broadcast ionospheric delay correction model(BDGIM)can provide ionospheric delay corrections better than 70%for worldwide single-frequency users.The service capability evaluation of the basic system consists mainly of the accuracy improvement of the B1I and B3I signals according to BDS-2 as well as the global positioning accuracy of the new signals.These results prove that the BDS-3 basic system has achieved the design goal;that is,both the horizontal and the vertical global positioning accuracies are better than 10 m(95%).In the future,6 MEO satellites as well as 3 GEO satellites and 3 IGSO satellites for regional enhancement purposes will be deployed for full operation;consequently,BDS-3 will definitely provide a higher SIS accuracy and better service capability.
基金sponsored by the National Natural Science Foundation of China (Grant Nos.41974041,42374044).
文摘With the rapid development of technologies such as autonomous driving and robotic navigation,the demand for accurate and reliable positioning results with BDS has increased.The current status and future development of BDS high precision services are reviewed.The operational PPP-B2b of BDS-3 achieves positioning accuracy at decimeter-level within 14 min and has the drawbacks in regional coverage and long convergence time compared with the international counterparts,such as CLAS of QZSS and HAS of Galileo.A development frame for multi-layer BDS high-precision services is proposed by considering its construction cost,compatibility of user terminal,operating maintenance burden,and service level.The global high-precision service with the improved orbit and clock accuracy enhanced with the inter-satellite link is taken as the most fundamental layer.By incorporating inter-satellite link observations,the orbit errors URE and clock errors are significantly reduced to approximately 0.05 m and 0.16 ns,respectively,which will expand PPP service to global.Based on this,the regional PPP-AR and PPP-RTK services with improved convergence performance are taken as the second layer.With PPP-AR,the convergence time drops to 10 min.With PPP-RTK,the convergence time would be further shortened to less than 3 min.The LEO enhanced PPP service is taken as the third layer which overcomes both drawbacks of the long convergence time of the inter-satellite link enhanced service(the first layer)and the regional coverage of the PPP-AR/PPP-RTK services(the second layer).The simulation results show that by introducing a LEO constellation of 288 satellites,the LEO enhanced PPP can achieve positioning accuracy better than 5 cm within approximately 1 min.In addition,the integration of LEO constellation and PPP-RTK is further proposed to enable instantaneous convergence.The implementation challenges are also presented.
基金This research is sponsored by the National Natural Science Foundation of China (Grant No.12103077Grant No.12173072).
文摘High-precision Global Navigation Satellite System(GNSS)orbit and clock products are crucial for precise applications.An evenly distributed global network enables continuous tracking for GNSS satellites,while a regional network may result in tracking gaps in the areas where monitoring stations are not deployed.This also means that the orbit determination accuracy based on a regional network is not comparable to that with a global network.Integrating the measurements from regional ground stations and Low Earth Orbit(LEO)satellites onboard receivers is a potential approach for generating GNSS orbit and clock products with centimeter-level accuracy,which is particularly important for BDS and the local commercial providers relying on a regional network.In the integrated Precise Orbit Determination(POD),LEO satellites are used to compensate for the drawback of regional ground stations in the precise orbit and clock determination of GNSS satellites.To validate the role of LEO satellites in the orbit determination with a regional network,6 International GNSS Service stations around China and 13 LEO satellites from January 20 to 26,2019,including GRACE-C/D,SWARM-A/B/C,Jason-3,Sentinel-3A/B,and SAT-A/B/C/D/E are selected in this study to perform the integrated POD.The orbit and clock accuracies of GPS and LEO satellites are evaluated by comparison with precise products.The average Root Mean Square(RMS)of GPS orbit errors in the radial(R),along-track(T)and cross-track(N)directions are 2.27 cm,3.45 cm,and 3.08 cm,respectively,and the clock accuracy is better than 0.15 ns based on a comparison with the final products provided by Center for Orbit Determination in Europe(CODE).The LEO orbit accuracy is better than 2 cm in the R direction,and the position errors are mostly within 4 cm.The results indicate that the integrated POD can generate high-precision orbit and clock products for GPS and LEO satellites based on regional network stations.Finally,the integrated POD products are assessed for Precise Point Positioning(PPP).Simulated kinematic PPP has a comparable performance in terms of the convergence time and positioning accuracy.With more LEO satellites available,the orbit and clock determination accuracy and PPP positioning accuracy can be improved.
