According to the fact that the secondary users＇ delay requirements for data transmission are not unitary in cognitive radio networks, the secondary users are divided into two classes, denoted by SU1 and SU2, respecti...According to the fact that the secondary users＇ delay requirements for data transmission are not unitary in cognitive radio networks, the secondary users are divided into two classes, denoted by SU1 and SU2, respectively. It is assumed that SU1 has a higher priority to occupy the primary users＇ unutilized channels than SU2. A preemptive resume priority M/G/1 queuing network is used to model the multiple spectrum handoffs processing. By using a state transition probability matrix and a cost matrix, the average cumulative delays of SU1 and SU2 are calculated, respectively. Numerical results show that the more the primary user＇s traffic load, the more rapidly the SU2＇s cumulative handoff delay grows. Compared with the networks where secondary users are unitary, the lower the SUI＇s arrival rate, the more obviously both SUI＇s and SU2＇s handoff delays decrease. The admission access regions limited by the maximum tolerable delay can also facilitate the design of admission control rules for graded secondary users.展开更多
Ground-and space-based optical observation is an efficient way to catalog objects in the cislunar space.Initial orbit determination based on optical data is still an open problem for cislunar objects.The motion of the...Ground-and space-based optical observation is an efficient way to catalog objects in the cislunar space.Initial orbit determination based on optical data is still an open problem for cislunar objects.The motion of these objects usually follows the law of three bodies instead of the two-body one,so current algorithms based on the two-body relation should be revised.Moreover,due to the long duration of most cislunar objects,optical observations of even hours can cover only a small fraction of one orbit,making the initial orbit determination of these objects a typical too-short-arc problem,which is difficult.A way to address this problem is to use the admissible region.In this study,an efficient algorithm constrained by the admissible region is proposed.It is easy to implement because it uses only simple iterations.Its efficiency is proven by comparing it with that of one traditional initial orbit determination algorithm.展开更多
基金The National Natural Science Foundation of China(No.60972026,61271207)the National Science and Technology Major Project(No.2010ZX03006-002-01)+1 种基金the Specialized Research Fund for the Doctoral Program of Higher Education(No.20090092110009)the Specialized Development Foundation for the Achievement Transformation of Jiangsu Province(No.BA2010023)
文摘According to the fact that the secondary users＇ delay requirements for data transmission are not unitary in cognitive radio networks, the secondary users are divided into two classes, denoted by SU1 and SU2, respectively. It is assumed that SU1 has a higher priority to occupy the primary users＇ unutilized channels than SU2. A preemptive resume priority M/G/1 queuing network is used to model the multiple spectrum handoffs processing. By using a state transition probability matrix and a cost matrix, the average cumulative delays of SU1 and SU2 are calculated, respectively. Numerical results show that the more the primary user＇s traffic load, the more rapidly the SU2＇s cumulative handoff delay grows. Compared with the networks where secondary users are unitary, the lower the SUI＇s arrival rate, the more obviously both SUI＇s and SU2＇s handoff delays decrease. The admission access regions limited by the maximum tolerable delay can also facilitate the design of admission control rules for graded secondary users.
基金supported by the National Natural Science Foundation of China(No.12233003)The author Xiyun Hou also wishes to thank support from the Space Debris and Near-Earth Asteroid Defense Research Project of China(No.KJSP2020020205)support from the Laboratory of Pinghu,Pinghu,China.
文摘Ground-and space-based optical observation is an efficient way to catalog objects in the cislunar space.Initial orbit determination based on optical data is still an open problem for cislunar objects.The motion of these objects usually follows the law of three bodies instead of the two-body one,so current algorithms based on the two-body relation should be revised.Moreover,due to the long duration of most cislunar objects,optical observations of even hours can cover only a small fraction of one orbit,making the initial orbit determination of these objects a typical too-short-arc problem,which is difficult.A way to address this problem is to use the admissible region.In this study,an efficient algorithm constrained by the admissible region is proposed.It is easy to implement because it uses only simple iterations.Its efficiency is proven by comparing it with that of one traditional initial orbit determination algorithm.
