A new prediction method based on the nonlinear autoregressive model is proposed to improve the accuracy of medium-term and long-term predictions of Satellite Clock Bias(SCB).Forecast experiments for three time periods...A new prediction method based on the nonlinear autoregressive model is proposed to improve the accuracy of medium-term and long-term predictions of Satellite Clock Bias(SCB).Forecast experiments for three time periods were implemented based on the precision SCB published on the International GNSS Server(IGS)server.The results show that the medium-term and long-term prediction accuracy of the proposed approach is significantly better compared to other traditional models,with the training time being much shorter than the wavelet neural network model.展开更多
Real-time satellite orbit and clock corrections obtained from the broadcast ephemerides can be improved using IGS real-time service (RTS) products. Recent research showed that applying such corrections for broadcast e...Real-time satellite orbit and clock corrections obtained from the broadcast ephemerides can be improved using IGS real-time service (RTS) products. Recent research showed that applying such corrections for broadcast ephemerides can significantly improve the RMS of the estimated coordinates. However, unintentional streaming interruption may happen for many reasons such as software or hardware failure. Streaming interruption, if happened, will cause sudden degradation of the obtained solution if only the broadcast ephemerides are used. A better solution can be obtained in real-time if the predicted part of the ultra-rapid products is used. In this paper, Harmonic analysis technique is used to predict the IGS RTS corrections using historical broadcasted data. It is shown that using the predicted clock corrections improves the RMS of the estimated coordinates by about 72%, 58%, and 72% in latitude, longitude, and height directions, respectively and reduces the 2D and 3D errors by about 80% compared with the predicted part of the IGS ultra-rapid clock corrections.展开更多
Due to the disadvantages such as complex calculation, low accuracy of estimation, and being non real time in present methods, a new real-time algorithm is developed for on-orbit mag- netometer bias determination of mi...Due to the disadvantages such as complex calculation, low accuracy of estimation, and being non real time in present methods, a new real-time algorithm is developed for on-orbit mag- netometer bias determination of micro-satellites without attitude knowledge in this paper. This method uses the differential value approach. It avoids the impact of quartic nature and uses the iterative method to satisfy real-time applications. Simulation results indicate that the new real-time algorithm is more accurate compared with other methods, which are also tested by an experiment system using real noise data. With the new real-time algorithm, a magnetometer calibration can be taken on-orbit and will reduce the demand for computing power effectively.展开更多
Real-time satellite orbit and clock estimations are the prerequisite for Global Navigation Satellite System(GNSS)real-time precise positioning services.To meet the high-rate update requirement of satellite clock corre...Real-time satellite orbit and clock estimations are the prerequisite for Global Navigation Satellite System(GNSS)real-time precise positioning services.To meet the high-rate update requirement of satellite clock corrections,the computational efficiency is a key factor and a challenge due to the rapid development of multi-GNSS constellations.The Square Root Information Filter(SRIF)is widely used in real-time GNSS data processing thanks to its high numerical stability and computational efficiency.In real-time clock estimation,the outlier detection and elimination are critical to guarantee the precision and stability of the product but could be time-consuming.In this study,we developed a new quality control procedure including the three standard steps:i.e.,detection,identification,and adaption,for real-time data processing of huge GNSS networks.Effort is made to improve the computational efficiency by optimizing the algorithm to provide only the essential information required in the processing,so that it can be applied in real-time and high-rate estimation of satellite clocks.The processing procedure is implemented in the PANDA(Positioning and Navigation Data Analyst)software package and evaluated in the operational generation of real-time GNSS orbit and clock products.We demonstrated that the new algorithm can efficiently eliminate outliers,and a clock precision of 0.06 ns,0.24 ns,0.06 ns,and 0.11 ns can be achieved for the GPS,GLONASS,Galileo,and BDS-2 IGSO/MEO satellites,respectively.The computation time per epoch is about 2 to 3 s depending on the number of existing outliers.Overall,the algorithm can satisfy the IGS real-time clock estimation in terms of both the computational efficiency and product quality.展开更多
【目的】基于精密单点定位(Precise Point Positioning,PPP)的时间传递技术因其高精度、广覆盖而成为GNSS时间传递中的优势性方法。然而,实践过程中发现接收机码偏差天内短时变化是影响接收机钟差估值精准度的主要偏差之一。【方法】因...【目的】基于精密单点定位(Precise Point Positioning,PPP)的时间传递技术因其高精度、广覆盖而成为GNSS时间传递中的优势性方法。然而,实践过程中发现接收机码偏差天内短时变化是影响接收机钟差估值精准度的主要偏差之一。【方法】因此,本文提出了一种改进的非组合精密单点定位(Modified Precise Point Positioning,MPPP)模型,将接收机码偏差作为时变参数估计,并基于模拟与实测数据进行了方法验证。【结果】结果表明:同等条件下,MPPP授时精度可达0.1~1ns,相较于PPP精度提升30%以上,【结论】可有效克服接收机码偏差变化对实时授时的影响。展开更多
In order to facilitate high-precision and real-time Precise Point Positioning(PPP),the International GNSS(Global Navigation Satellite System)Service(IGS),BDS-3(BeiDou-3 Navigation Satellite System),and Galileo navigat...In order to facilitate high-precision and real-time Precise Point Positioning(PPP),the International GNSS(Global Navigation Satellite System)Service(IGS),BDS-3(BeiDou-3 Navigation Satellite System),and Galileo navigation satellite system(Galileo)have provided real-time satellite clock correction,which is updated at a high-frequency.However,the frequent updates pose the challenges of increasing the computational burden and compromising the timeliness of these correction parameters.To address this issue,an improved Real-Time Service(RTS)method is developed using an extrapolation algorithm and a linear model.The results indicate that a 1 h arc length of the satellite clock correction series is optimal for fitting a linear model of the RTS.With this approach,the 1 h extrapolation results for BDS-3 and Galileo are superior to 0.09 ns.Moreover,when these model coefficients are transmitted and updated at the intervals of 1,2,5,and 10 min,the corresponding PPP can converge at the centimeter-level.It is evident that these improved RTS methods outperform the current approach with high-frequency interval transmission,as they effectively mitigate the challenges associated with maintaining the timeliness of correction parameters.展开更多
The Fractional Cycle Bias(FCB)product is crucial for the Ambiguity Resolution(AR)in Precise Point Positioning(PPP).Different from the traditional method using the ionospheric-free ambiguity which is formed by the Wide...The Fractional Cycle Bias(FCB)product is crucial for the Ambiguity Resolution(AR)in Precise Point Positioning(PPP).Different from the traditional method using the ionospheric-free ambiguity which is formed by the Wide Lane(WL)and Narrow Lane(NL)combinations,the uncombined PPP model is flexible and effective to generate the FCB prod-ucts.This study presents the FCB estimation method based on the multi-Global Navigation Satellite System(GNSS)precise satellite orbit and clock corrections from the international GNSS Monitoring and Assessment System(iGMAS)observations using the uncombined PPP model.The dual-frequency raw ambiguities are combined by the integer coefficients(4,−3)and(1,−1)to directly estimate the FCBs.The details of FCB estimation are described with the Global Positioning System(GPS),BeiDou-2 Navigation Satellite System(BDS-2)and Galileo Navigation Satellite System(Galileo).For the estimated FCBs,the Root Mean Squares(RMSs)of the posterior residuals are smaller than 0.1 cycles,which indicates a high consistency for the float ambiguities.The stability of the WL FCBs series is better than 0.02 cycles for the three GNSS systems,while the STandard Deviation(STD)of the NL FCBs for BDS-2 is larger than 0.139 cycles.The combined FCBs have better stability than the raw series.With the multi-GNSS FCB products,the PPP AR for GPS/BDS-2/Galileo is demonstrated using the raw observations.For hourly static positioning results,the performance of the PPP AR with the three-system observations is improved by 42.6%,but only 13.1%for kinematic positioning results.The results indicate that precise and reliable positioning can be achieved with the PPP AR of GPS/BDS-2/Galileo,supported by multi-GNSS satellite orbit,clock,and FCB products based on iGMAS.展开更多
The Real-Time Global Navigation Satellite System(GNSS)Precise Positioning Service(RTPPS)is recognized as the most promising system by providing precise satellite orbit and clock correc-tions for users to achieve centi...The Real-Time Global Navigation Satellite System(GNSS)Precise Positioning Service(RTPPS)is recognized as the most promising system by providing precise satellite orbit and clock correc-tions for users to achieve centimeter-level positioning with a stand-alone receiver in real-time.Although the products are available with high accuracy almost all the time,they may occasionally suffer from unexpected significant biases,which consequently degrades the positioning perfor-mance.Therefore,quality monitoring at the system-level has become more and more crucial for providing a reliable GNSS service.In this paper,we propose a method for the monitoring of realtime satellite orbit and clock products using a monitoring station network based on the Quality Control(QC)theory.The satellites with possible biases are first detected based on the outliers identified by Precise Point Positioning(PPP)in the monitoring station network.Then,the corresponding orbit and clock parameters with temporal constraints are introduced and esti-mated through the sequential Least Square(LS)estimator and the corresponding Instantaneous User Range Errors(IUREs)can be determined.A quality indicator is calculated based on the IUREs in the monitoring network and compared with a pre-defined threshold.The quality monitoring method is experimentally evaluated by monitoring the real-time orbit and clock products generated by GeoForschungsZentrum(GFZ),Potsdam.The results confirm that the problematic satellites can be detected accurately and effectively with missed detection rate 4×10^(-6) and false alarm rate 1:2×10^(-5).Considering the quality alarms,the PPP results in terms of RMS of positioning differences with respect to the International GNSS Service(IGS)weekly solution in the north,east and up directions can be improved by 12%,10%and 27%,respectively.展开更多
Aiming at the problem that the traditional inter-system double-difference model is not suitable for non-overlapping signal frequencies,we propose a new inter-system double-difference model with single difference ambig...Aiming at the problem that the traditional inter-system double-difference model is not suitable for non-overlapping signal frequencies,we propose a new inter-system double-difference model with single difference ambiguity estimation,which can be applied for both overlapping and non-overlapping signal frequencies.The single difference ambiguities of all satellites and Differential Inter-System Biases(DISB)are first estimated,and the intra-system double difference ambiguities,which have integer characteristics,are then fixed.After the ambiguities are successfully fixed,high-precision coordinates and DISB can be obtained with a constructed transformation matrix.The model effectively avoids the DISB parameter filtering discontinuity caused by the reference satellite transformation and the low precision of the reference satellite single difference ambiguity calculated with the code.A zero-baseline using multiple types of receivers is selected to verify the stability of the estimated DISB.Three baselines with different lengths are selected to assess the positioning performance of the model.The ionospheric-fixed and ionospheric-float models are used for short and medium-long baselines,respectively.The results show that the Differential Inter-System Code Biases(DISCB)and Differential Inter-System Phase Biases(DISPB)have good stability regardless of the receivers type and the signal frequency used and can be calibrated to enhance the strength of the positioning model.The positioning results with three baselines of different lengths show that the proposed inter-system double-difference model can improve the positioning accuracy by 6–22%compared with the intra-system double-difference model which selects the reference satellite independently for each system.The Time to First Fix(TTFF)of the two medium-long baselines is reduced by 30%and 29%,respectively.展开更多
Global navigation satellite system(GNSS)carrier phase observations are two orders of higher accuracy than pseudo-range observations,and they are less affected by multipath besides.As a result,the time transfer accurac...Global navigation satellite system(GNSS)carrier phase observations are two orders of higher accuracy than pseudo-range observations,and they are less affected by multipath besides.As a result,the time transfer accuracy can reach 0.1 ns,and the frequency transfer stability can reach 1×10^-15 with carrier phase(CP)method,therefore CP method is considered the most accurate and promising time transfer technology.The focus of this paper is to present a comprehensive summary of CP method,with specific attention directed toward day-boundary clock jump,ambiguity resolution(AR),multi-system time transfer and real-time time transfer.Day-boundary clock jump is essentially caused by pseudo-range noise.Several approaches were proposed to solve the problem,such as continuously processing strategy,sliding batch and bidirectional filtering methods which were compared in this study.Additionally,researches on AR in CP method were introduced.Many scholars attempted to fix the single-difference ambiguities to improve the time transfer result,however,owing to the uncalibrated phase delay(UPD)was not considered,the current studies on AR in CP method were still immature.Moreover,because four GNSS systems could be used for time-transfer currently,which was helpful to increase the accuracy and reliability,the researches on multi-system time transfer were reviewed.What’s more,real-time time transfer attracted more attention nowadays,the preliminary research results were presented.展开更多
Over the past years the International Global Navigation Satellite System(GNSS)Monitoring and Assessment System(iGMAS)Wuhan Innovation Application Center(IAC)dedicated to exploring the potential of multi-GNSS signals a...Over the past years the International Global Navigation Satellite System(GNSS)Monitoring and Assessment System(iGMAS)Wuhan Innovation Application Center(IAC)dedicated to exploring the potential of multi-GNSS signals and providing a set of products and services.This contribution summarizes the strategies,achievements,and innovations of multi-GNSS orbit/clock/bias determination in iGMAS Wuhan IAC.Both the precise products and Real-Time Services(RTS)are evaluated and discussed.The precise orbit and clock products have comparable accuracy with the precise products of the International GNSS Service(IGS)and iGMAS.The multi-frequency code and phase bias products for Global Positioning System(GPS),BeiDou Navigation Satellite System(BDS),Galileo navigation satellite system(Galileo),and GLObal NAvigation Satellite System(GLONASS)are provided to support multi-GNSS and multi-frequency Precise Point Positioning(PPP)Ambiguity Resolution(AR).Compared with dual-frequency PPP AR,the time to first fix of triple-frequency solution is improved by 30%.For RTS,the proposed orbit prediction strategy improves the three dimensional accuracy of predicted orbit by 1 cm.The multi-thread strategy and high-performance matrix library are employed to accelerate the real-time orbit and clock determination.The results with respect to the IGS precise products show the high accuracy of RTS orbits and clocks,4–9 cm and 0.1–0.2 ns,respectively.Using real-time satellite corrections,real-time PPP solutions achieve satisfactory performance with horizontal and vertical positioning errors within 2 and 4 cm,respectively,and convergence time of 16.97 min.展开更多
The Spatio-Temporal Consistency Language(STeC)is a high-level modeling language that deals natively with spatio-temporal behaviour,i.e.,behaviour relating to certain locations and time.Such restriction by both locatio...The Spatio-Temporal Consistency Language(STeC)is a high-level modeling language that deals natively with spatio-temporal behaviour,i.e.,behaviour relating to certain locations and time.Such restriction by both locations and time is of first importance for some types of real-time systems.CCSL is a formal specification language based on logical clocks.It is used to describe some crucial safety properties for real-time systems,due to its powerful expressiveness of logical and chronometric time constraints.We consider a novel verification framework combining STeC and CCSL,with the advantages of addressing spatio-temporal consistency of system behaviour and easily expressing some crucial time constraints.We propose a theory combining these two languages and a method verifying CCSL properties in STeC models.We adopt UPPAAL as the model checking tool and give a simple example to illustrate how to carry out verification in our framework.展开更多
The BeiDou global navigation satellite system(BDS-3)constellation deployment has been completed on June 23,2020,with a full constellation comprising 30 satellites.In this study,we present the performance assessment of...The BeiDou global navigation satellite system(BDS-3)constellation deployment has been completed on June 23,2020,with a full constellation comprising 30 satellites.In this study,we present the performance assessment of single-epoch Real-Time Kinematic(RTK)positioning with tightly combined BeiDou regional navigation satellite system(BDS-2)and BDS-3.We first investigate whether code and phase Differential Inter-System Biases(DISBs)exist between the legacy B1I/B3I signals of BDS-3/BDS-2.It is discovered that the DISBs are in fact about zero for the baselines with the same or different receiver types at their endpoints.These results imply that BDS-3 and BDS-2 are fully interoperable and can be regarded as one constellation without additional DISBs when the legacy B1I/B3I signals are used for precise relative positioning.Then we preliminarily evaluate the single-epoch short baseline RTK performance of tightly combined BDS-2 and the newly completed BDS-3.The performance is evaluated through ambiguity resolution success rate,ambiguity dilution of precision,as well as positioning accuracy in kinematic and static modes using the datasets collected in Wuhan.Experimental results demonstrate that the current BDS-3 only solutions can deliver comparable ambiguity resolution performance and much better positioning accuracy with respect to BDS-2 only solutions.Moreover,the RTK performance is much improved with tightly combined BDS-3/BDS-2,particularly in challenging or harsh conditions.The single-frequency single-epoch tightly combined BDS-3/BDS-2 solution could deliver an ambiguity resolution success rate of 96.9%even with an elevation cut-off angle of 40°,indicating that the tightly combined BDS-3/BDS-2 could achieve superior RTK positioning performance in the Asia-Pacific region.Meanwhile,the three-dimensional(East/North/Up)positioning accuracy of BDS-3 only solution(0.52 cm/0.39 cm/2.14 cm)in the kinematic test is significantly better than that of the BDS-2 only solution(0.85 cm/1.02 cm/3.01 cm)due to the better geometry of the current BDS-3 constellation.The tightly combined BDS-3/BDS-2 solution can provide the positioning accuracy of 0.52 cm,0.22 cm,and 1.80 cm,respectively.展开更多
基金2022 Basic Scientific Research Project supported by Liaoning Provincial Education Department(No.LJKMZ20221686)。
文摘A new prediction method based on the nonlinear autoregressive model is proposed to improve the accuracy of medium-term and long-term predictions of Satellite Clock Bias(SCB).Forecast experiments for three time periods were implemented based on the precision SCB published on the International GNSS Server(IGS)server.The results show that the medium-term and long-term prediction accuracy of the proposed approach is significantly better compared to other traditional models,with the training time being much shorter than the wavelet neural network model.
文摘Real-time satellite orbit and clock corrections obtained from the broadcast ephemerides can be improved using IGS real-time service (RTS) products. Recent research showed that applying such corrections for broadcast ephemerides can significantly improve the RMS of the estimated coordinates. However, unintentional streaming interruption may happen for many reasons such as software or hardware failure. Streaming interruption, if happened, will cause sudden degradation of the obtained solution if only the broadcast ephemerides are used. A better solution can be obtained in real-time if the predicted part of the ultra-rapid products is used. In this paper, Harmonic analysis technique is used to predict the IGS RTS corrections using historical broadcasted data. It is shown that using the predicted clock corrections improves the RMS of the estimated coordinates by about 72%, 58%, and 72% in latitude, longitude, and height directions, respectively and reduces the 2D and 3D errors by about 80% compared with the predicted part of the IGS ultra-rapid clock corrections.
文摘Due to the disadvantages such as complex calculation, low accuracy of estimation, and being non real time in present methods, a new real-time algorithm is developed for on-orbit mag- netometer bias determination of micro-satellites without attitude knowledge in this paper. This method uses the differential value approach. It avoids the impact of quartic nature and uses the iterative method to satisfy real-time applications. Simulation results indicate that the new real-time algorithm is more accurate compared with other methods, which are also tested by an experiment system using real noise data. With the new real-time algorithm, a magnetometer calibration can be taken on-orbit and will reduce the demand for computing power effectively.
基金the project“Early-Warning and Rapid Impact Assessment with real-time GNSS in the Mediterranean(EWRICA)”Funded by the Federal Ministry of Education and Research,Germany.
文摘Real-time satellite orbit and clock estimations are the prerequisite for Global Navigation Satellite System(GNSS)real-time precise positioning services.To meet the high-rate update requirement of satellite clock corrections,the computational efficiency is a key factor and a challenge due to the rapid development of multi-GNSS constellations.The Square Root Information Filter(SRIF)is widely used in real-time GNSS data processing thanks to its high numerical stability and computational efficiency.In real-time clock estimation,the outlier detection and elimination are critical to guarantee the precision and stability of the product but could be time-consuming.In this study,we developed a new quality control procedure including the three standard steps:i.e.,detection,identification,and adaption,for real-time data processing of huge GNSS networks.Effort is made to improve the computational efficiency by optimizing the algorithm to provide only the essential information required in the processing,so that it can be applied in real-time and high-rate estimation of satellite clocks.The processing procedure is implemented in the PANDA(Positioning and Navigation Data Analyst)software package and evaluated in the operational generation of real-time GNSS orbit and clock products.We demonstrated that the new algorithm can efficiently eliminate outliers,and a clock precision of 0.06 ns,0.24 ns,0.06 ns,and 0.11 ns can be achieved for the GPS,GLONASS,Galileo,and BDS-2 IGSO/MEO satellites,respectively.The computation time per epoch is about 2 to 3 s depending on the number of existing outliers.Overall,the algorithm can satisfy the IGS real-time clock estimation in terms of both the computational efficiency and product quality.
文摘【目的】基于精密单点定位(Precise Point Positioning,PPP)的时间传递技术因其高精度、广覆盖而成为GNSS时间传递中的优势性方法。然而,实践过程中发现接收机码偏差天内短时变化是影响接收机钟差估值精准度的主要偏差之一。【方法】因此,本文提出了一种改进的非组合精密单点定位(Modified Precise Point Positioning,MPPP)模型,将接收机码偏差作为时变参数估计,并基于模拟与实测数据进行了方法验证。【结果】结果表明:同等条件下,MPPP授时精度可达0.1~1ns,相较于PPP精度提升30%以上,【结论】可有效克服接收机码偏差变化对实时授时的影响。
基金This research is supported by the National Natural Science Foundation of China(NSFC)(Nos.42174019 and 41974025)the Fundamental Research Funds for the Central Universities.
文摘In order to facilitate high-precision and real-time Precise Point Positioning(PPP),the International GNSS(Global Navigation Satellite System)Service(IGS),BDS-3(BeiDou-3 Navigation Satellite System),and Galileo navigation satellite system(Galileo)have provided real-time satellite clock correction,which is updated at a high-frequency.However,the frequent updates pose the challenges of increasing the computational burden and compromising the timeliness of these correction parameters.To address this issue,an improved Real-Time Service(RTS)method is developed using an extrapolation algorithm and a linear model.The results indicate that a 1 h arc length of the satellite clock correction series is optimal for fitting a linear model of the RTS.With this approach,the 1 h extrapolation results for BDS-3 and Galileo are superior to 0.09 ns.Moreover,when these model coefficients are transmitted and updated at the intervals of 1,2,5,and 10 min,the corresponding PPP can converge at the centimeter-level.It is evident that these improved RTS methods outperform the current approach with high-frequency interval transmission,as they effectively mitigate the challenges associated with maintaining the timeliness of correction parameters.
基金The National Key Research and Development Program of China(2018YFC1505102)the Programs of the National Natural Science Foundation of China(41774025,41731066)+2 种基金the Special Fund for Technological Innovation Guidance of Shaanxi Province(2018XNCGG05)the Special Fund for Basic Scientific Research of Central Colleges(CHD300102269305,CHD300102268305)the Grand Projects of the BDS-2 System(GFZX0301040308)supported this study.
文摘The Fractional Cycle Bias(FCB)product is crucial for the Ambiguity Resolution(AR)in Precise Point Positioning(PPP).Different from the traditional method using the ionospheric-free ambiguity which is formed by the Wide Lane(WL)and Narrow Lane(NL)combinations,the uncombined PPP model is flexible and effective to generate the FCB prod-ucts.This study presents the FCB estimation method based on the multi-Global Navigation Satellite System(GNSS)precise satellite orbit and clock corrections from the international GNSS Monitoring and Assessment System(iGMAS)observations using the uncombined PPP model.The dual-frequency raw ambiguities are combined by the integer coefficients(4,−3)and(1,−1)to directly estimate the FCBs.The details of FCB estimation are described with the Global Positioning System(GPS),BeiDou-2 Navigation Satellite System(BDS-2)and Galileo Navigation Satellite System(Galileo).For the estimated FCBs,the Root Mean Squares(RMSs)of the posterior residuals are smaller than 0.1 cycles,which indicates a high consistency for the float ambiguities.The stability of the WL FCBs series is better than 0.02 cycles for the three GNSS systems,while the STandard Deviation(STD)of the NL FCBs for BDS-2 is larger than 0.139 cycles.The combined FCBs have better stability than the raw series.With the multi-GNSS FCB products,the PPP AR for GPS/BDS-2/Galileo is demonstrated using the raw observations.For hourly static positioning results,the performance of the PPP AR with the three-system observations is improved by 42.6%,but only 13.1%for kinematic positioning results.The results indicate that precise and reliable positioning can be achieved with the PPP AR of GPS/BDS-2/Galileo,supported by multi-GNSS satellite orbit,clock,and FCB products based on iGMAS.
基金funded by the National Natural Science Foundation of China(42030109).
文摘The Real-Time Global Navigation Satellite System(GNSS)Precise Positioning Service(RTPPS)is recognized as the most promising system by providing precise satellite orbit and clock correc-tions for users to achieve centimeter-level positioning with a stand-alone receiver in real-time.Although the products are available with high accuracy almost all the time,they may occasionally suffer from unexpected significant biases,which consequently degrades the positioning perfor-mance.Therefore,quality monitoring at the system-level has become more and more crucial for providing a reliable GNSS service.In this paper,we propose a method for the monitoring of realtime satellite orbit and clock products using a monitoring station network based on the Quality Control(QC)theory.The satellites with possible biases are first detected based on the outliers identified by Precise Point Positioning(PPP)in the monitoring station network.Then,the corresponding orbit and clock parameters with temporal constraints are introduced and esti-mated through the sequential Least Square(LS)estimator and the corresponding Instantaneous User Range Errors(IUREs)can be determined.A quality indicator is calculated based on the IUREs in the monitoring network and compared with a pre-defined threshold.The quality monitoring method is experimentally evaluated by monitoring the real-time orbit and clock products generated by GeoForschungsZentrum(GFZ),Potsdam.The results confirm that the problematic satellites can be detected accurately and effectively with missed detection rate 4×10^(-6) and false alarm rate 1:2×10^(-5).Considering the quality alarms,the PPP results in terms of RMS of positioning differences with respect to the International GNSS Service(IGS)weekly solution in the north,east and up directions can be improved by 12%,10%and 27%,respectively.
基金This work was jointly supported by the National Key Research Program of China Collaborative Precision Positioning Project(No.2016YFB0501900)the National Natural Science Foundation of China(Grant No.41774017).
文摘Aiming at the problem that the traditional inter-system double-difference model is not suitable for non-overlapping signal frequencies,we propose a new inter-system double-difference model with single difference ambiguity estimation,which can be applied for both overlapping and non-overlapping signal frequencies.The single difference ambiguities of all satellites and Differential Inter-System Biases(DISB)are first estimated,and the intra-system double difference ambiguities,which have integer characteristics,are then fixed.After the ambiguities are successfully fixed,high-precision coordinates and DISB can be obtained with a constructed transformation matrix.The model effectively avoids the DISB parameter filtering discontinuity caused by the reference satellite transformation and the low precision of the reference satellite single difference ambiguity calculated with the code.A zero-baseline using multiple types of receivers is selected to verify the stability of the estimated DISB.Three baselines with different lengths are selected to assess the positioning performance of the model.The ionospheric-fixed and ionospheric-float models are used for short and medium-long baselines,respectively.The results show that the Differential Inter-System Code Biases(DISCB)and Differential Inter-System Phase Biases(DISPB)have good stability regardless of the receivers type and the signal frequency used and can be calibrated to enhance the strength of the positioning model.The positioning results with three baselines of different lengths show that the proposed inter-system double-difference model can improve the positioning accuracy by 6–22%compared with the intra-system double-difference model which selects the reference satellite independently for each system.The Time to First Fix(TTFF)of the two medium-long baselines is reduced by 30%and 29%,respectively.
文摘设计了一种嵌入于FPGA芯片的锁相环,实现了四相位时钟、倍频、半整数可编程分频、可调节相位输出功能,满足对于FPGA芯片时钟管理的要求.锁相环采用了自偏置结构,拓展了锁相环的工作范围,缩短了锁定时间,其阻尼系数以及环路带宽和工作频率的比值都仅由电容的比值决定,有效地减小了工艺、电压、温度等对电路的影响.锁相环采用0.18μm CMOS数字工艺,嵌入复旦大学自主研发的FPGA芯片FDP-Ⅱ,经过流片验证,实现了工作频率范围10~600 MHz,整体电路功耗仅为29 mW,锁定时间小于4μs,峰峰值抖动小于±145 ps.
基金supported in part by the National Key Research and Development Program of China(Grant No.2016YFB0800401)in part by the National Natural Science Foundation of China(Grants Nos.61621003,61532020&11472290)。
文摘Global navigation satellite system(GNSS)carrier phase observations are two orders of higher accuracy than pseudo-range observations,and they are less affected by multipath besides.As a result,the time transfer accuracy can reach 0.1 ns,and the frequency transfer stability can reach 1×10^-15 with carrier phase(CP)method,therefore CP method is considered the most accurate and promising time transfer technology.The focus of this paper is to present a comprehensive summary of CP method,with specific attention directed toward day-boundary clock jump,ambiguity resolution(AR),multi-system time transfer and real-time time transfer.Day-boundary clock jump is essentially caused by pseudo-range noise.Several approaches were proposed to solve the problem,such as continuously processing strategy,sliding batch and bidirectional filtering methods which were compared in this study.Additionally,researches on AR in CP method were introduced.Many scholars attempted to fix the single-difference ambiguities to improve the time transfer result,however,owing to the uncalibrated phase delay(UPD)was not considered,the current studies on AR in CP method were still immature.Moreover,because four GNSS systems could be used for time-transfer currently,which was helpful to increase the accuracy and reliability,the researches on multi-system time transfer were reviewed.What’s more,real-time time transfer attracted more attention nowadays,the preliminary research results were presented.
基金National Natural Science Foundation of China(No.41974027)National Key Research and Development Program of China(2021YFB2501102)Sino-German mobility programme(Grant No.M-0054).
文摘Over the past years the International Global Navigation Satellite System(GNSS)Monitoring and Assessment System(iGMAS)Wuhan Innovation Application Center(IAC)dedicated to exploring the potential of multi-GNSS signals and providing a set of products and services.This contribution summarizes the strategies,achievements,and innovations of multi-GNSS orbit/clock/bias determination in iGMAS Wuhan IAC.Both the precise products and Real-Time Services(RTS)are evaluated and discussed.The precise orbit and clock products have comparable accuracy with the precise products of the International GNSS Service(IGS)and iGMAS.The multi-frequency code and phase bias products for Global Positioning System(GPS),BeiDou Navigation Satellite System(BDS),Galileo navigation satellite system(Galileo),and GLObal NAvigation Satellite System(GLONASS)are provided to support multi-GNSS and multi-frequency Precise Point Positioning(PPP)Ambiguity Resolution(AR).Compared with dual-frequency PPP AR,the time to first fix of triple-frequency solution is improved by 30%.For RTS,the proposed orbit prediction strategy improves the three dimensional accuracy of predicted orbit by 1 cm.The multi-thread strategy and high-performance matrix library are employed to accelerate the real-time orbit and clock determination.The results with respect to the IGS precise products show the high accuracy of RTS orbits and clocks,4–9 cm and 0.1–0.2 ns,respectively.Using real-time satellite corrections,real-time PPP solutions achieve satisfactory performance with horizontal and vertical positioning errors within 2 and 4 cm,respectively,and convergence time of 16.97 min.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.61370100,61321064)Shanghai Knowledge Service Platform Project(ZF1213)+1 种基金Shanghai Municipal Science and Technology Commission Project(14511100400)Defense Industrial Technology Development Program JCKY(2016212B004-2).
文摘The Spatio-Temporal Consistency Language(STeC)is a high-level modeling language that deals natively with spatio-temporal behaviour,i.e.,behaviour relating to certain locations and time.Such restriction by both locations and time is of first importance for some types of real-time systems.CCSL is a formal specification language based on logical clocks.It is used to describe some crucial safety properties for real-time systems,due to its powerful expressiveness of logical and chronometric time constraints.We consider a novel verification framework combining STeC and CCSL,with the advantages of addressing spatio-temporal consistency of system behaviour and easily expressing some crucial time constraints.We propose a theory combining these two languages and a method verifying CCSL properties in STeC models.We adopt UPPAAL as the model checking tool and give a simple example to illustrate how to carry out verification in our framework.
基金the National Natural Science Foundation of China(Nos.41774031,41904035,91638203)Hubei Provincial Natural Science Foundation of China(No.2019CFB261)+1 种基金the National Science Fund for Distinguished Young Scholars(No.41825009)Key Laboratory of Geospace Environment and Geodesy,Ministry of Education,Wuhan University(No.19-01-06).
文摘The BeiDou global navigation satellite system(BDS-3)constellation deployment has been completed on June 23,2020,with a full constellation comprising 30 satellites.In this study,we present the performance assessment of single-epoch Real-Time Kinematic(RTK)positioning with tightly combined BeiDou regional navigation satellite system(BDS-2)and BDS-3.We first investigate whether code and phase Differential Inter-System Biases(DISBs)exist between the legacy B1I/B3I signals of BDS-3/BDS-2.It is discovered that the DISBs are in fact about zero for the baselines with the same or different receiver types at their endpoints.These results imply that BDS-3 and BDS-2 are fully interoperable and can be regarded as one constellation without additional DISBs when the legacy B1I/B3I signals are used for precise relative positioning.Then we preliminarily evaluate the single-epoch short baseline RTK performance of tightly combined BDS-2 and the newly completed BDS-3.The performance is evaluated through ambiguity resolution success rate,ambiguity dilution of precision,as well as positioning accuracy in kinematic and static modes using the datasets collected in Wuhan.Experimental results demonstrate that the current BDS-3 only solutions can deliver comparable ambiguity resolution performance and much better positioning accuracy with respect to BDS-2 only solutions.Moreover,the RTK performance is much improved with tightly combined BDS-3/BDS-2,particularly in challenging or harsh conditions.The single-frequency single-epoch tightly combined BDS-3/BDS-2 solution could deliver an ambiguity resolution success rate of 96.9%even with an elevation cut-off angle of 40°,indicating that the tightly combined BDS-3/BDS-2 could achieve superior RTK positioning performance in the Asia-Pacific region.Meanwhile,the three-dimensional(East/North/Up)positioning accuracy of BDS-3 only solution(0.52 cm/0.39 cm/2.14 cm)in the kinematic test is significantly better than that of the BDS-2 only solution(0.85 cm/1.02 cm/3.01 cm)due to the better geometry of the current BDS-3 constellation.The tightly combined BDS-3/BDS-2 solution can provide the positioning accuracy of 0.52 cm,0.22 cm,and 1.80 cm,respectively.