In the study of complex networks (systems), the scaling phenomenon of flow fluctuations refers to a certain powerlaw between the mean flux (activity) (Fi) of the i-th node and its variance σi as σi α (Fi)α...In the study of complex networks (systems), the scaling phenomenon of flow fluctuations refers to a certain powerlaw between the mean flux (activity) (Fi) of the i-th node and its variance σi as σi α (Fi)α Such scaling laws are found to be prevalent both in natural and man-made network systems, but the understanding of their origins still remains limited. This paper proposes a non-stationary Poisson process model to give an analytical explanation of the non-universal scaling phenomenon: the exponent α varies between 1/2 and 1 depending on the size of sampling time window and the relative strength of the external/internal driven forces of the systems. The crossover behaviour and the relation of fluctuation scaling with pseudo long range dependence are also accounted for by the model. Numerical experiments show that the proposed model can recover the multi-scaiing phenomenon.展开更多
The clutter direction-Doppler curves are not aligned on the near range bins for forward looking airborne radar. As a result, the performance of clutter suppression by Space-Time Adaptive Processing (STAP) degrades gre...The clutter direction-Doppler curves are not aligned on the near range bins for forward looking airborne radar. As a result, the performance of clutter suppression by Space-Time Adaptive Processing (STAP) degrades greatly because of the clutter range dependence. To deal with this problem, a new compensated method is proposed in this paper. The method rebuilds the clutter covariance matrix based on spatial high resolution Minimum Variance Distortionless Response (MVDR) spectrum, and then finds a matrix to transform the covariance matrix of short-range gate to the referred far-range gate. The method can compensate the clutter range dependence well. The simulation results show validity of the method.展开更多
The alpha stable self-similar stochastic process has been proved an effective model for high variable data traffic. A deep insight into some special issues and considerations on use of the process to model aggregated ...The alpha stable self-similar stochastic process has been proved an effective model for high variable data traffic. A deep insight into some special issues and considerations on use of the process to model aggregated VBR video traffic is made. Different methods to estimate stability parameter a and self-similar parameter H are compared. Processes to generate the linear fractional stable noise (LFSN) and the alpha stable random variables are provided. Model construction and the quantitative comparisons with fractional Brown motion (FBM) and real traffic are also examined. Open problems and future directions are also given with thoughtful discussions.展开更多
Variable bit rate(VBR)video will be the predominant application in the future's multimedia communication networks.Understanding the characteristics of VBR video is important for us to utilize network resources ef...Variable bit rate(VBR)video will be the predominant application in the future's multimedia communication networks.Understanding the characteristics of VBR video is important for us to utilize network resources effectively.A brief description of MPEG 1 video sources is given.The essentials of self similarity and long range dependence are also presented.Furthermore,some methods of estimating Hurst parameter are described in details.We analyze an hour long MPEG 1 video trace,and the details of statistical results are discussed.The results highlight that the trace generated by MPEG 1 code has both the short range dependence and long range dependence structures.展开更多
基金Project supported in part by National Basic Research Program of China (973 Project) (Grant No 2006CB705506)Hi-Tech Research and Development Program of China (863 Project) (Grant No 2007AA11Z222)National Natural Science Foundation of China (Grant Nos 60721003 and 60774034)
文摘In the study of complex networks (systems), the scaling phenomenon of flow fluctuations refers to a certain powerlaw between the mean flux (activity) (Fi) of the i-th node and its variance σi as σi α (Fi)α Such scaling laws are found to be prevalent both in natural and man-made network systems, but the understanding of their origins still remains limited. This paper proposes a non-stationary Poisson process model to give an analytical explanation of the non-universal scaling phenomenon: the exponent α varies between 1/2 and 1 depending on the size of sampling time window and the relative strength of the external/internal driven forces of the systems. The crossover behaviour and the relation of fluctuation scaling with pseudo long range dependence are also accounted for by the model. Numerical experiments show that the proposed model can recover the multi-scaiing phenomenon.
基金Supported by Education Department of Hunan Province Project (09C201)Hunan Provincial Natural Science Foundation of China (10jj6091) Planned Science and Technology Project of Hunan Province (2010FJ6015)
文摘The clutter direction-Doppler curves are not aligned on the near range bins for forward looking airborne radar. As a result, the performance of clutter suppression by Space-Time Adaptive Processing (STAP) degrades greatly because of the clutter range dependence. To deal with this problem, a new compensated method is proposed in this paper. The method rebuilds the clutter covariance matrix based on spatial high resolution Minimum Variance Distortionless Response (MVDR) spectrum, and then finds a matrix to transform the covariance matrix of short-range gate to the referred far-range gate. The method can compensate the clutter range dependence well. The simulation results show validity of the method.
文摘The alpha stable self-similar stochastic process has been proved an effective model for high variable data traffic. A deep insight into some special issues and considerations on use of the process to model aggregated VBR video traffic is made. Different methods to estimate stability parameter a and self-similar parameter H are compared. Processes to generate the linear fractional stable noise (LFSN) and the alpha stable random variables are provided. Model construction and the quantitative comparisons with fractional Brown motion (FBM) and real traffic are also examined. Open problems and future directions are also given with thoughtful discussions.
文摘Variable bit rate(VBR)video will be the predominant application in the future's multimedia communication networks.Understanding the characteristics of VBR video is important for us to utilize network resources effectively.A brief description of MPEG 1 video sources is given.The essentials of self similarity and long range dependence are also presented.Furthermore,some methods of estimating Hurst parameter are described in details.We analyze an hour long MPEG 1 video trace,and the details of statistical results are discussed.The results highlight that the trace generated by MPEG 1 code has both the short range dependence and long range dependence structures.