In an experiment on the round-trip fiber transfer of joint frequency and time signals based on wavelengthdivision multiplexing technology, a specific bidirectional erbium-doped fiber amplifier(Bi-EDFA) with low noise ...In an experiment on the round-trip fiber transfer of joint frequency and time signals based on wavelengthdivision multiplexing technology, a specific bidirectional erbium-doped fiber amplifier(Bi-EDFA) with low noise and high symmetry simultaneously is designed and applied to compensate for the loss of the link. The Allan deviation(ADEV) deterioration of the 1 GHz frequency signal induced by the Bi-EDFA is only 8 × 10-15 at 1 s and 9 × 10-18 at 104s in the forward direction, and is 1.7 × 10-14 at 1 s and 1.2 × 10-17 at 104s in the backward direction. The degraded time deviation(TDEV) caused by the asymmetry of the Bi-EDFA is only 0.8 ps at an average time of 103 s. With the proposed Bi-EDFA, in the field experiment on the 110 km fiber transfer of joint frequency and time signals, the ADEV of the 1 GHz frequency signal is 7.3 × 10-14at1 s and 2.5 × 10-17 at 104s. The TDEV of the 1 pulse per second time signal is 6.8 ps with an average time of 103 s.展开更多
Avionics full duplex switched ethernet（AFDX） is a switched interconnection technology developed to provide reliable data exchange with strong data transmission time guarantees in internal communication of the spacec...Avionics full duplex switched ethernet（AFDX） is a switched interconnection technology developed to provide reliable data exchange with strong data transmission time guarantees in internal communication of the spacecraft or aircraft.Virtual link（VL） is an important concept of AFDX to meet quality of service（QoS） requirements in terms of end-to-end message deadlines.A VL admission control algorithm in AFDX network under hard real-time（HRT） constraints is studied.Based on the scheduling prin-ciple of AFDX protocol,a packet scheduling scheme under HRT constraints is proposed,and after that an efficient VL admission control algorithm is presented.Analytical proof that the algorithm can effectively determine whether VL should be admitted is given.Finally simulative examples are presented to promote the conclusion.展开更多
As an important application research topic of the intelligent aviation multi-station, collaborative detecting must overcome the problem of scouting measurement with status of 'fragmentation', and the NP-hardne...As an important application research topic of the intelligent aviation multi-station, collaborative detecting must overcome the problem of scouting measurement with status of 'fragmentation', and the NP-hardness problem of matching association between target and measurement in the process of scouting to data-link, which has complicated technical architecture of network construction. In this paper, taking advantage of cooperation mechanism on signal level in the aviation multi-station sympathetic network, a method of obtaining target time difference of arrival (TDOA) measurement using multi-station collaborative detecting based on time-frequency association is proposed. The method can not only achieve matching between target and its measurement, but also obtain TDOA measurement by further evolutionary transaction through refreshing sequential pulse time of arrival (TOA) measurement matrix for matching and correlating. Simulation results show that the accuracy of TDOA measurement has significant superiority over TOA, and detection probability of false TDOA measurement introduced by noise and fake measurement can be reduced effectively.展开更多
Purpose-The purpose of this paper is to develop sliding mode control with linear and nonlinear manifolds in discrete-time domain for robot manipulators.Design/methodology/approach–First,a discrete linear sliding mode...Purpose-The purpose of this paper is to develop sliding mode control with linear and nonlinear manifolds in discrete-time domain for robot manipulators.Design/methodology/approach–First,a discrete linear sliding mode controller is designed to an n-link robot based on Gao’s reaching law.In the second step,a discrete terminal sliding mode controller is developed to design a finite time and high precision controller.The stability analysis of both controllers is presented in the presence of model uncertainties and external disturbances.Finally,sampling time effects on the continuous-time system outputs and sliding surfaces are discussed.Findings–Computer simulations on a three-link SCARA robot show that the proposed controllers are robust against model uncertainties and external disturbance.It was also shown that the sampling time has important effects on the closed loop system stability and convergence.Practical implications-The proposed controllers are low cost and easily implemented in practice in comparison with continuous-time ones.Originality/value-The novelty associated with this paper is the development of an approach to finite time and robust control of n-link robot manipulators in discrete-time domain.Also,obtaining an upper bound for the sampling time is another contribution of this work.展开更多
为减小卫星双向时间比对(Two-Way Satellite Time and Frequency Transfer,TWSTFT)中的周日效应,利用北斗共视链路没有周日效应的特点,通过Vondrak-Cepek组合滤波方法对中国科学院国家授时中心(National Time Service Center,NTSC)、德...为减小卫星双向时间比对(Two-Way Satellite Time and Frequency Transfer,TWSTFT)中的周日效应,利用北斗共视链路没有周日效应的特点,通过Vondrak-Cepek组合滤波方法对中国科学院国家授时中心(National Time Service Center,NTSC)、德国物理技术研究院(Physikalisch-Technische Bundesanstalt,PTB)以及中国计量科学研究院(National Institute of Metrology,NIM)间的北斗共视时间比对结果分别与硬件卫星时间和距离测量设备(SAtellite Time and Ranging Equipment,SATRE)TWSTFT和软件接收机(Software-Defined Radio,SDR)TWSTFT结果进行了融合处理。采用时间偏差和幅值频谱两个指标以及GPS精密单点定位(Precise Point Positioning,PPP)时间比对分别对融合结果进行内外符合评估。结果表明,经过Vondrak-Cepek滤波的融合结果中周日效应基本消失,其与GPS PPP链路差值结果的绝对值保持在链路校准的不确定度范围内。对于长基线NTSC-PTB链路,融合结果1 d的时间偏差稳定度对SATRE和SDR TWSTFT的增益因子分别为1.85和1.81;对于短基线NTSC-NIM链路,融合结果对SATRE和SDR TWSTFT的增益因子分别为1.69和1.59。融合结果的短期稳定度显著提高。展开更多
基金supported in part by the National Natural Science Foundation of China under Grant No.61405227
文摘In an experiment on the round-trip fiber transfer of joint frequency and time signals based on wavelengthdivision multiplexing technology, a specific bidirectional erbium-doped fiber amplifier(Bi-EDFA) with low noise and high symmetry simultaneously is designed and applied to compensate for the loss of the link. The Allan deviation(ADEV) deterioration of the 1 GHz frequency signal induced by the Bi-EDFA is only 8 × 10-15 at 1 s and 9 × 10-18 at 104s in the forward direction, and is 1.7 × 10-14 at 1 s and 1.2 × 10-17 at 104s in the backward direction. The degraded time deviation(TDEV) caused by the asymmetry of the Bi-EDFA is only 0.8 ps at an average time of 103 s. With the proposed Bi-EDFA, in the field experiment on the 110 km fiber transfer of joint frequency and time signals, the ADEV of the 1 GHz frequency signal is 7.3 × 10-14at1 s and 2.5 × 10-17 at 104s. The TDEV of the 1 pulse per second time signal is 6.8 ps with an average time of 103 s.
基金National Natural Science Foundation of China (60879024)
文摘Avionics full duplex switched ethernet（AFDX） is a switched interconnection technology developed to provide reliable data exchange with strong data transmission time guarantees in internal communication of the spacecraft or aircraft.Virtual link（VL） is an important concept of AFDX to meet quality of service（QoS） requirements in terms of end-to-end message deadlines.A VL admission control algorithm in AFDX network under hard real-time（HRT） constraints is studied.Based on the scheduling prin-ciple of AFDX protocol,a packet scheduling scheme under HRT constraints is proposed,and after that an efficient VL admission control algorithm is presented.Analytical proof that the algorithm can effectively determine whether VL should be admitted is given.Finally simulative examples are presented to promote the conclusion.
基金supported by the National Natural Science Foundation of China(61472443)the Basic Research Priorities Program of Shaanxi Province Natural Science Foundation of China(2013JQ8042)
文摘As an important application research topic of the intelligent aviation multi-station, collaborative detecting must overcome the problem of scouting measurement with status of 'fragmentation', and the NP-hardness problem of matching association between target and measurement in the process of scouting to data-link, which has complicated technical architecture of network construction. In this paper, taking advantage of cooperation mechanism on signal level in the aviation multi-station sympathetic network, a method of obtaining target time difference of arrival (TDOA) measurement using multi-station collaborative detecting based on time-frequency association is proposed. The method can not only achieve matching between target and its measurement, but also obtain TDOA measurement by further evolutionary transaction through refreshing sequential pulse time of arrival (TOA) measurement matrix for matching and correlating. Simulation results show that the accuracy of TDOA measurement has significant superiority over TOA, and detection probability of false TDOA measurement introduced by noise and fake measurement can be reduced effectively.
文摘Purpose-The purpose of this paper is to develop sliding mode control with linear and nonlinear manifolds in discrete-time domain for robot manipulators.Design/methodology/approach–First,a discrete linear sliding mode controller is designed to an n-link robot based on Gao’s reaching law.In the second step,a discrete terminal sliding mode controller is developed to design a finite time and high precision controller.The stability analysis of both controllers is presented in the presence of model uncertainties and external disturbances.Finally,sampling time effects on the continuous-time system outputs and sliding surfaces are discussed.Findings–Computer simulations on a three-link SCARA robot show that the proposed controllers are robust against model uncertainties and external disturbance.It was also shown that the sampling time has important effects on the closed loop system stability and convergence.Practical implications-The proposed controllers are low cost and easily implemented in practice in comparison with continuous-time ones.Originality/value-The novelty associated with this paper is the development of an approach to finite time and robust control of n-link robot manipulators in discrete-time domain.Also,obtaining an upper bound for the sampling time is another contribution of this work.
文摘为减小卫星双向时间比对(Two-Way Satellite Time and Frequency Transfer,TWSTFT)中的周日效应,利用北斗共视链路没有周日效应的特点,通过Vondrak-Cepek组合滤波方法对中国科学院国家授时中心(National Time Service Center,NTSC)、德国物理技术研究院(Physikalisch-Technische Bundesanstalt,PTB)以及中国计量科学研究院(National Institute of Metrology,NIM)间的北斗共视时间比对结果分别与硬件卫星时间和距离测量设备(SAtellite Time and Ranging Equipment,SATRE)TWSTFT和软件接收机(Software-Defined Radio,SDR)TWSTFT结果进行了融合处理。采用时间偏差和幅值频谱两个指标以及GPS精密单点定位(Precise Point Positioning,PPP)时间比对分别对融合结果进行内外符合评估。结果表明,经过Vondrak-Cepek滤波的融合结果中周日效应基本消失,其与GPS PPP链路差值结果的绝对值保持在链路校准的不确定度范围内。对于长基线NTSC-PTB链路,融合结果1 d的时间偏差稳定度对SATRE和SDR TWSTFT的增益因子分别为1.85和1.81;对于短基线NTSC-NIM链路,融合结果对SATRE和SDR TWSTFT的增益因子分别为1.69和1.59。融合结果的短期稳定度显著提高。
