We consider the spectrum handoff delay of a Secondary User(SU)in cognitive radio networks.We propose a spectrum handoff scheme based on Recommended Channel Sensing Sequence(RCSS),which aims to optimise the spectrum ha...We consider the spectrum handoff delay of a Secondary User(SU)in cognitive radio networks.We propose a spectrum handoff scheme based on Recommended Channel Sensing Sequence(RCSS),which aims to optimise the spectrum handoff delay subject to the sensing reliability and link maintenance constraints.There are two cases that should be considered:1)the SU performs spectrum handoff successfully during the current frame,and 2)the SU successfully performs the spectrum handoff using several frames.We develop a dynamic programming algorithm for RCSS to identify the optimal sensing sequence for the first case,and an updating algorithm for RCSS to improve the handoff performance for the second case.The numerical results confirm that the proposed RCSS handoff scheme can achieve better handoff delay performance than others when the received signal-to-noise ratios of the Pus' signals on different channels are non-identical.展开更多
A lot of work has been focused on desig-ning and analyzing various cooperative diversity pro-tocols for wireless relay networks. To provide a uni-fied queuing analytic framework, we fonmlate an em-bedded Markov chain,...A lot of work has been focused on desig-ning and analyzing various cooperative diversity pro-tocols for wireless relay networks. To provide a uni-fied queuing analytic framework, we fonmlate an em-bedded Markov chain, which rams out to be a Quasi-Birth-and-Death （QBD） process. Using the Matrix-Ce-ometric method, we can analyze the average delay in a unified way. Theoretical analysis is validated by simu-lation results. We show that the delay performances of Amplify-and-Forward or Decode-and-Forwaxd （AF/ DF） and incremental AF/DF schemes can be analyzed in the unified way. Thus, we can always choose the best cooperative diversity scheme in different scenari-os for delay minimization.展开更多
The time delay（TD） of femtoseeond pulses is studied for the first time, which generated from the nonlinear optical loop mirror composed of dispersion decreasing fiber（DDF-NOLM）. The results show that the higher-or...The time delay（TD） of femtoseeond pulses is studied for the first time, which generated from the nonlinear optical loop mirror composed of dispersion decreasing fiber（DDF-NOLM）. The results show that the higher-order dispersion and high order nonlinearities such as Raman frequency shift play a key role in producing TD, and that the time delay ean be suppressed by the third-order dispersion（TOD） in DDF-NOLM. The mechanism of the time delay suppression is also discussed in detail.展开更多
Based on the new data from the database of the University of Michigan Radio Astronomy Observatory （UMRAO）, we analyze the spectral index and optical variability of OJ287 and 3C279. The main results show that 1） the...Based on the new data from the database of the University of Michigan Radio Astronomy Observatory （UMRAO）, we analyze the spectral index and optical variability of OJ287 and 3C279. The main results show that 1） the time delay among three radio bands （4.8, 8, and 14.5 GHz） shows： r8-14.5 = 31 d, r4.8-8 = 41 d for OJ287, but no time delay lying in 3C279; 2） strong correlation lies in the polarization and flux density at 8 GHz for OJ287 and at 8, 14.5 GHz for 3C279; 3） the logarithmic brightness temperature log（TB） = 14.l K for OJ287 is 14.1 K, log（TB） = 15.1 K for 3C279.展开更多
基金supported by the National Natural Science Foundation of China under Grant No. 61172067
文摘We consider the spectrum handoff delay of a Secondary User(SU)in cognitive radio networks.We propose a spectrum handoff scheme based on Recommended Channel Sensing Sequence(RCSS),which aims to optimise the spectrum handoff delay subject to the sensing reliability and link maintenance constraints.There are two cases that should be considered:1)the SU performs spectrum handoff successfully during the current frame,and 2)the SU successfully performs the spectrum handoff using several frames.We develop a dynamic programming algorithm for RCSS to identify the optimal sensing sequence for the first case,and an updating algorithm for RCSS to improve the handoff performance for the second case.The numerical results confirm that the proposed RCSS handoff scheme can achieve better handoff delay performance than others when the received signal-to-noise ratios of the Pus' signals on different channels are non-identical.
基金This work was supported by the National Basic Research Program of China under Crant No. 2012CB316001 the National Science Foundation of China under Crants No. （：13832008, No. 03902001.
文摘A lot of work has been focused on desig-ning and analyzing various cooperative diversity pro-tocols for wireless relay networks. To provide a uni-fied queuing analytic framework, we fonmlate an em-bedded Markov chain, which rams out to be a Quasi-Birth-and-Death （QBD） process. Using the Matrix-Ce-ometric method, we can analyze the average delay in a unified way. Theoretical analysis is validated by simu-lation results. We show that the delay performances of Amplify-and-Forward or Decode-and-Forwaxd （AF/ DF） and incremental AF/DF schemes can be analyzed in the unified way. Thus, we can always choose the best cooperative diversity scheme in different scenari-os for delay minimization.
文摘The time delay（TD） of femtoseeond pulses is studied for the first time, which generated from the nonlinear optical loop mirror composed of dispersion decreasing fiber（DDF-NOLM）. The results show that the higher-order dispersion and high order nonlinearities such as Raman frequency shift play a key role in producing TD, and that the time delay ean be suppressed by the third-order dispersion（TOD） in DDF-NOLM. The mechanism of the time delay suppression is also discussed in detail.
基金supported by the National Natural Science Foundation of China (Grant No. 10633010)the National Basic Research Program of China (Grant No. 2007CB815405)+1 种基金the Bureau of Education of Guangzhou Municipality (Grant No. 11 Sui-Jiao-Ke[2009]),and GDUPS (2009)supported by the University of Michigan and the National Science Foundation
文摘Based on the new data from the database of the University of Michigan Radio Astronomy Observatory （UMRAO）, we analyze the spectral index and optical variability of OJ287 and 3C279. The main results show that 1） the time delay among three radio bands （4.8, 8, and 14.5 GHz） shows： r8-14.5 = 31 d, r4.8-8 = 41 d for OJ287, but no time delay lying in 3C279; 2） strong correlation lies in the polarization and flux density at 8 GHz for OJ287 and at 8, 14.5 GHz for 3C279; 3） the logarithmic brightness temperature log（TB） = 14.l K for OJ287 is 14.1 K, log（TB） = 15.1 K for 3C279.
