This paper proposed an optimal algorithm using the sun line-of-sight vector to improve the probe attitude estimation accuracy in deep-space mission.Firstly,the elaborate analysis of the attitude estimation error from ...This paper proposed an optimal algorithm using the sun line-of-sight vector to improve the probe attitude estimation accuracy in deep-space mission.Firstly,the elaborate analysis of the attitude estimation error from vector observations was done to demonstrate that the geometric relation between the reference vectors is an important factor which influences the accuracy of attitude estimation.Then,with introduction of the sun line-of-sight vector,the attitude quaternion obtained from the star-sensor was converted into a pair of mutually perpendicular reference vectors perpendicular to the sun vector.The normalized weights were calculated according to the accuracy of the sensors.Furthermore,the optimal attitude estimation in the least squares sense was achieved with the quaternion estimation method.Finally,the results of simulation demonstrated the validity of the proposed optimal algorithm based on the practical data of the Deep Impact mission.展开更多
Since the Asia Pacific Workshop on Multilateral Cooperation in Space Technology and Applications was held in Beijing in December, 1992, the preparatory committee for Asia-Pacific Space Cooperation Mechanism and the Li...Since the Asia Pacific Workshop on Multilateral Cooperation in Space Technology and Applications was held in Beijing in December, 1992, the preparatory committee for Asia-Pacific Space Cooperation Mechanism and the Liaison Committee for AP-MC-STA have done many fruitful works. Thanks to the First Asia Pacific Conference on Multilateral Cooperation in Space Tech-展开更多
Recently,free space optical(FSO)communication is gaining much attention towards the research community.The reason for this attention is the promises of high data-rate,license-free deployment,and non-interfering links....Recently,free space optical(FSO)communication is gaining much attention towards the research community.The reason for this attention is the promises of high data-rate,license-free deployment,and non-interfering links.It can,however,give rise to major system difficulties concerning alignment and atmospheric turbulence.FSO is the degradation in the signal quality because of atmospheric channel impairments and conditions.The worst effect is due to fog particles.Though,Radio Frequency(RF)links are able to transmit the data in foggy conditions but not in rain.To overcome these issues related to both the FSO and RF links.A free space communication system(FSCS)is proposed,in which the hybrid technology is based on the individual FSO and RF channel.FSCS is a capable solution to overcome the difficulties of the existing systems(FSO and RF)as well as to enhance the overall link reliability and availability.In this paper,FSCS is investigated in terms of performance throughput(i.e.,outage probability and bit-error-rate(BER))by implementing the receive diversity combining techniques.An analysis of the outage probability of the proposed system along with the individual FSO and RF system is developed.Simulation results are presented to support the analysis.It is shown that the proposed system outperforms the individual FSO andRF system and gives a power gain of 3dB over a distinct number of receive antennas.展开更多
为了弥补现有的研究成果对处理障碍环境下空间Skyline查询问题的不足,提出了在障碍环境下基于Voronoi图的空间Skyline查询方法。该方法在实际应用中可以用来解决多目标决策问题。依据查询点集合是否发生变化提出了两种情况下的障碍环境...为了弥补现有的研究成果对处理障碍环境下空间Skyline查询问题的不足,提出了在障碍环境下基于Voronoi图的空间Skyline查询方法。该方法在实际应用中可以用来解决多目标决策问题。依据查询点集合是否发生变化提出了两种情况下的障碍环境中空间Skyline查询(spatial Skyline queries in obstacle space,OSSQ)方法:一种是静态查询点的障碍环境中空间Skyline查询(static query points of Skyline query in obstacle space,STA_OSSQ)方法,该查询方法主要包括约剪数据集和支配检查两个过程,最后得到Skyline集合;另一种是动态查询点状态下的障碍环境中Skyline查询(dynamic query points of Skyline query in obstacle space,DYN_OSSQ)方法,该方法主要处理了查询点动态增加和减少情况下障碍环境中空间Skyline查询问题。理论研究和实验表明所提出的方法具有较高的效率。展开更多
Around the globe, streets and sidewalks in cities are being contested as spaces that should be used for more than transportation. This paper analyzes street spaces as public goods, or their nature as a 'public poo...Around the globe, streets and sidewalks in cities are being contested as spaces that should be used for more than transportation. This paper analyzes street spaces as public goods, or their nature as a 'public pool,' from the perspective of property rights. After conducting a picture for the use of public street spaces in two innovative districts in Beijing via big data description and field investigation, this paper analyzes the use of public spaces from the perspective of property rights, spatial supply and demand, and the distribution and management of public goods. It further proposes three strategies for street design transformation, including refined management, design integrity, and planning priority transformation.展开更多
文摘This paper proposed an optimal algorithm using the sun line-of-sight vector to improve the probe attitude estimation accuracy in deep-space mission.Firstly,the elaborate analysis of the attitude estimation error from vector observations was done to demonstrate that the geometric relation between the reference vectors is an important factor which influences the accuracy of attitude estimation.Then,with introduction of the sun line-of-sight vector,the attitude quaternion obtained from the star-sensor was converted into a pair of mutually perpendicular reference vectors perpendicular to the sun vector.The normalized weights were calculated according to the accuracy of the sensors.Furthermore,the optimal attitude estimation in the least squares sense was achieved with the quaternion estimation method.Finally,the results of simulation demonstrated the validity of the proposed optimal algorithm based on the practical data of the Deep Impact mission.
文摘Since the Asia Pacific Workshop on Multilateral Cooperation in Space Technology and Applications was held in Beijing in December, 1992, the preparatory committee for Asia-Pacific Space Cooperation Mechanism and the Liaison Committee for AP-MC-STA have done many fruitful works. Thanks to the First Asia Pacific Conference on Multilateral Cooperation in Space Tech-
文摘Recently,free space optical(FSO)communication is gaining much attention towards the research community.The reason for this attention is the promises of high data-rate,license-free deployment,and non-interfering links.It can,however,give rise to major system difficulties concerning alignment and atmospheric turbulence.FSO is the degradation in the signal quality because of atmospheric channel impairments and conditions.The worst effect is due to fog particles.Though,Radio Frequency(RF)links are able to transmit the data in foggy conditions but not in rain.To overcome these issues related to both the FSO and RF links.A free space communication system(FSCS)is proposed,in which the hybrid technology is based on the individual FSO and RF channel.FSCS is a capable solution to overcome the difficulties of the existing systems(FSO and RF)as well as to enhance the overall link reliability and availability.In this paper,FSCS is investigated in terms of performance throughput(i.e.,outage probability and bit-error-rate(BER))by implementing the receive diversity combining techniques.An analysis of the outage probability of the proposed system along with the individual FSO and RF system is developed.Simulation results are presented to support the analysis.It is shown that the proposed system outperforms the individual FSO andRF system and gives a power gain of 3dB over a distinct number of receive antennas.
文摘为了弥补现有的研究成果对处理障碍环境下空间Skyline查询问题的不足,提出了在障碍环境下基于Voronoi图的空间Skyline查询方法。该方法在实际应用中可以用来解决多目标决策问题。依据查询点集合是否发生变化提出了两种情况下的障碍环境中空间Skyline查询(spatial Skyline queries in obstacle space,OSSQ)方法:一种是静态查询点的障碍环境中空间Skyline查询(static query points of Skyline query in obstacle space,STA_OSSQ)方法,该查询方法主要包括约剪数据集和支配检查两个过程,最后得到Skyline集合;另一种是动态查询点状态下的障碍环境中Skyline查询(dynamic query points of Skyline query in obstacle space,DYN_OSSQ)方法,该方法主要处理了查询点动态增加和减少情况下障碍环境中空间Skyline查询问题。理论研究和实验表明所提出的方法具有较高的效率。
基金supported by the National Natural Science Foundation of China(51608294,51978359)the Beijing Social Science Funding(17GLC055)
文摘Around the globe, streets and sidewalks in cities are being contested as spaces that should be used for more than transportation. This paper analyzes street spaces as public goods, or their nature as a 'public pool,' from the perspective of property rights. After conducting a picture for the use of public street spaces in two innovative districts in Beijing via big data description and field investigation, this paper analyzes the use of public spaces from the perspective of property rights, spatial supply and demand, and the distribution and management of public goods. It further proposes three strategies for street design transformation, including refined management, design integrity, and planning priority transformation.
