In the equatorial region,deep amplitude fading in global positioning system(GPS)signals frequently occurs during the strong ionospheric scintillation,it can lead to the loss of lock in GPS carrier tracking loops,and r...In the equatorial region,deep amplitude fading in global positioning system(GPS)signals frequently occurs during the strong ionospheric scintillation,it can lead to the loss of lock in GPS carrier tracking loops,and result in increased positioning error and even navigation interruption.The relationships between amplitude scintillation indices and detrended carrier frequency are investigated,based on GPS L1 C/A signals during the last peak of the solar cycle at the low latitude site of São Josédos Campos,Brazil(23.2S,45.9W)from 2013 to 2015.Corresponding mathematic model of the probability distribution function is built for the first time to provide statistical analysis on the above relationships.The results show that the standard carrier frequencies reveal an almost linear relation with the amplitude scintillation indices.Moreover,the frequency widths of detrended frequency are proportional to levels of amplitude scintillation when the value of the peak probability is lower than the corresponding boundary.A conclusion can be drawn that different levels of amplitude scintillation will influence the fluctuation of the carrier frequency.The analysis will provide useful guidance to set the receiver’s bandwidth with respect to the different scintillation levels and design the advanced tracking algorithms to improve the robustness and precision of the GPS receiver.展开更多
To realize the automatic detection of solar radio burst(SRB)intensity,detection based on a modified multifactor support vector machine(SVM)algorithm is proposed.First,the influence of SRB on global navigation satellit...To realize the automatic detection of solar radio burst(SRB)intensity,detection based on a modified multifactor support vector machine(SVM)algorithm is proposed.First,the influence of SRB on global navigation satellite system(GNSS)signals is analyzed.Feature vectors,which can reflect the SRB intensity of stations,are also extracted.SRB intensity is classified according to the solar radio flux,and different class labels correspond to different SRB intensity types.The training samples are composed of feature vectors and their corresponding class labels.Second,training samples are input into SVM classifiers to one-against-one training to obtain the optimal classification models.Finally,the optimal classification model is synthesized into a modified multifactor SVM classifier,which is used to automatically detect the SRB intensity of new data.Experimental results indicate that for historical SRB events,the average accuracy of SRB intensity detection is greater than 90%when the solar incident angle is higher than 20°.Compared with other methods,the proposed method considers many factors with higher accuracy and does not rely on radio telescopes,thereby saving cost.展开更多
To detect the occurrence of ionospheric scintillation in the equatorial region,a coherent/non-coherent integration method is adopted on the accumulation of intermediate frequency(IF)signal and local code,in the proces...To detect the occurrence of ionospheric scintillation in the equatorial region,a coherent/non-coherent integration method is adopted on the accumulation of intermediate frequency(IF)signal and local code,in the process of signal acquisition based on software receiver.The processes of polynomial fitting and sixth-order Butterworth filtering are introduced to detrend the tracking results.Combining with ionospheric scintillation detection algorithm and preset thresholds,signal acquisition and tracking,scintillation detection,positioning solution are realized under the influence of strong ionospheric scintillation.Under the condition that the preset threshold of amplitude and carrier phase scintillation indices are set to 0.5 and 0.15,and the percentage of scin-tillation occurrence is 50%,respectively,PRN 12 and 31 affected by strong amplitude scintillation are detected effectively.Results show that the positioning errors in the horizontal direction are below 5m approximately.The software receiver holds performances of accurate acquisition,tracking and positioning on the strong ionospheric scintillation conditions,which can provide important basis and helpful guidance for relevant research on ionospheric scintillation,space weather and receiver design with high performance.展开更多
With the deepening of neural network research,object detection has been developed rapidly in recent years,and video object detection methods have gradually attracted the attention of scholars,especially frameworks inc...With the deepening of neural network research,object detection has been developed rapidly in recent years,and video object detection methods have gradually attracted the attention of scholars,especially frameworks including multiple object tracking and detection.Most current works prefer to build the paradigm for multiple object tracking and detection by multi-task learning.Different with others,a multi-level temporal feature fusion structure is proposed in this paper to improve the performance of framework by utilizing the constraint of video temporal consistency.For training the temporal network end-to-end,a feature exchange training strategy is put forward for training the temporal feature fusion structure efficiently.The proposed method is tested on several acknowledged benchmarks,and encouraging results are obtained compared with the famous joint detection and tracking framework.The ablation experiment answers the problem of a good position for temporal feature fusion.展开更多
Accurate estimationand real-time compensation for phase offset and Doppler shift are essential for coherent multi-input multi-output(MIMO)systems.Here,a spatial multiplexing MIMO scheme with non-coherent frequency-shi...Accurate estimationand real-time compensation for phase offset and Doppler shift are essential for coherent multi-input multi-output(MIMO)systems.Here,a spatial multiplexing MIMO scheme with non-coherent frequency-shift keying(FSK)detection is proposed.It is immune to random phase interference and Doppler shift while increasing capacity.It is valuable that the proposed spatial multiplexing MIMO based on energy detection(ED)is equivalent to a linear system,and there is no mutual interference caused by the product of simultaneous signals in square-law processing.The equivalent MIMO channel model is derived as a real matrix,which remains maximal multiplexing capacity and reduces the channel estimation complexity.Simulation results show that the proposed scheme has outstanding performance over Rician flat fading channel,and experimental system obtains four times the capacity through 4 antennas on both transmitter and receiver.展开更多
基金This work was supported by the National Key Research and Development Plan of China(2018YFB0505103)the National Natural Science Foundation of China(61873064)the Science and Technology Project of State Grid Corporation of China(SGSHJX00KXJS1901531).
文摘In the equatorial region,deep amplitude fading in global positioning system(GPS)signals frequently occurs during the strong ionospheric scintillation,it can lead to the loss of lock in GPS carrier tracking loops,and result in increased positioning error and even navigation interruption.The relationships between amplitude scintillation indices and detrended carrier frequency are investigated,based on GPS L1 C/A signals during the last peak of the solar cycle at the low latitude site of São Josédos Campos,Brazil(23.2S,45.9W)from 2013 to 2015.Corresponding mathematic model of the probability distribution function is built for the first time to provide statistical analysis on the above relationships.The results show that the standard carrier frequencies reveal an almost linear relation with the amplitude scintillation indices.Moreover,the frequency widths of detrended frequency are proportional to levels of amplitude scintillation when the value of the peak probability is lower than the corresponding boundary.A conclusion can be drawn that different levels of amplitude scintillation will influence the fluctuation of the carrier frequency.The analysis will provide useful guidance to set the receiver’s bandwidth with respect to the different scintillation levels and design the advanced tracking algorithms to improve the robustness and precision of the GPS receiver.
基金The National Key Research and Development Plan of China(No.2018YFB0505103)the National Natural Science Foundation of China(No.61873064)。
文摘To realize the automatic detection of solar radio burst(SRB)intensity,detection based on a modified multifactor support vector machine(SVM)algorithm is proposed.First,the influence of SRB on global navigation satellite system(GNSS)signals is analyzed.Feature vectors,which can reflect the SRB intensity of stations,are also extracted.SRB intensity is classified according to the solar radio flux,and different class labels correspond to different SRB intensity types.The training samples are composed of feature vectors and their corresponding class labels.Second,training samples are input into SVM classifiers to one-against-one training to obtain the optimal classification models.Finally,the optimal classification model is synthesized into a modified multifactor SVM classifier,which is used to automatically detect the SRB intensity of new data.Experimental results indicate that for historical SRB events,the average accuracy of SRB intensity detection is greater than 90%when the solar incident angle is higher than 20°.Compared with other methods,the proposed method considers many factors with higher accuracy and does not rely on radio telescopes,thereby saving cost.
文摘To detect the occurrence of ionospheric scintillation in the equatorial region,a coherent/non-coherent integration method is adopted on the accumulation of intermediate frequency(IF)signal and local code,in the process of signal acquisition based on software receiver.The processes of polynomial fitting and sixth-order Butterworth filtering are introduced to detrend the tracking results.Combining with ionospheric scintillation detection algorithm and preset thresholds,signal acquisition and tracking,scintillation detection,positioning solution are realized under the influence of strong ionospheric scintillation.Under the condition that the preset threshold of amplitude and carrier phase scintillation indices are set to 0.5 and 0.15,and the percentage of scin-tillation occurrence is 50%,respectively,PRN 12 and 31 affected by strong amplitude scintillation are detected effectively.Results show that the positioning errors in the horizontal direction are below 5m approximately.The software receiver holds performances of accurate acquisition,tracking and positioning on the strong ionospheric scintillation conditions,which can provide important basis and helpful guidance for relevant research on ionospheric scintillation,space weather and receiver design with high performance.
基金supported by the Zhejiang Provincial Natural Science Foundation of China(No.LQ24F020016)the General Scientific Research Fund of Zhejiang Provincial Education Department(No.Y202248776)+1 种基金the Wenzhou Science and Technology Plan Project(No.G20220035)the Wenzhou Key Laboratory Construction Project(No.2022HZSY0048)。
文摘With the deepening of neural network research,object detection has been developed rapidly in recent years,and video object detection methods have gradually attracted the attention of scholars,especially frameworks including multiple object tracking and detection.Most current works prefer to build the paradigm for multiple object tracking and detection by multi-task learning.Different with others,a multi-level temporal feature fusion structure is proposed in this paper to improve the performance of framework by utilizing the constraint of video temporal consistency.For training the temporal network end-to-end,a feature exchange training strategy is put forward for training the temporal feature fusion structure efficiently.The proposed method is tested on several acknowledged benchmarks,and encouraging results are obtained compared with the famous joint detection and tracking framework.The ablation experiment answers the problem of a good position for temporal feature fusion.
基金the National Natural Science Foundation of China(61571149,61761014)the Guangxi Key Research and Development Plan(Guike AB18126030)。
文摘Accurate estimationand real-time compensation for phase offset and Doppler shift are essential for coherent multi-input multi-output(MIMO)systems.Here,a spatial multiplexing MIMO scheme with non-coherent frequency-shift keying(FSK)detection is proposed.It is immune to random phase interference and Doppler shift while increasing capacity.It is valuable that the proposed spatial multiplexing MIMO based on energy detection(ED)is equivalent to a linear system,and there is no mutual interference caused by the product of simultaneous signals in square-law processing.The equivalent MIMO channel model is derived as a real matrix,which remains maximal multiplexing capacity and reduces the channel estimation complexity.Simulation results show that the proposed scheme has outstanding performance over Rician flat fading channel,and experimental system obtains four times the capacity through 4 antennas on both transmitter and receiver.
