无人值守放牧监测系统报警准确率的研究

通过ZigBee技术、GPS定位追踪技术和远程无线通信技术的结合,计算了ZigBee节点传输距离,并提出一种双系统的监测牛群数量的策略,通过对系统误报率的分析,设定误报率门限,从而确定双系统的组成方式,提高牛群数量监测的准确性,降低误警概率.在此基础上设计了一套智能牛群检测系统,并通过实验验证了理论计算结果.该系统可以在无人值守的情况下,自动监测草原牧场上牛群数量并记录牛群位置,实现自动上传功能.     

基于流量和IP熵特性的DDoS攻击检测方法

针对现有DDoS(Distributed Deny of Service)攻击检测率低、误报率较高等问题进行了深入研究。根据DDoS攻击发生时网络中的流量特性和IP熵特性,建立了相应的流量隶属函数和IP熵隶属函数,隶属函数的上下限参数通过对真实网络环境仿真得到。提出了基于流量和IP熵特性的DDoS攻击检测算法,先判断流量是否异常,再判断熵是否异常,进而判断是否发生了DDoS攻击,提高了。由仿真结果可以看出：单独依靠流量或IP熵都不能很好地检测出DDoS攻击。该算法将流量和IP熵特性综合考虑,准确地检测出了DDoS攻击,降低了误报率,提高了检测率。     

移动自组网自私行为闭环惩罚模型设计

针对移动自组网MAC层开环模型缺乏自私行为惩罚机制的不足,设计一种包括报文信息统计、统计信息共享和判决惩罚模块的闭环改进协议PDCF。报文信息统计定义转发率、丢弃度等指标衡量节点行为,修改仿真软件内置函数实现节点行为信息的统计。统计信息共享定义行为量化等级,改进DCF预留字段和CSMA/CA机制,实现节点行为信息的全网覆盖。判决惩罚模块对节点行为建立一维马尔科夫链惩罚模型,限制节点自私行为。仿真结果表明,与DCF相比,PDCF时延、丢包率和控制开销基本不变,但稳态时自私节点比例得到有效控制,且吞吐量增加2.7Mbps,网络性能得到改善。     

一种基于虚拟力的分布式Voronoi控制策略

针对无线移动传感器网络在目标区域的覆盖问题,提出了一种基于移动距离的局部分布式算法,利用Voronoi多边形的特征对目标区域进行有效的分割,运用力学的矢量概念,根据Voronoi图的边和顶点确定虚拟力的方向和大小即节点的移动方向和距离,提出了基于移动距离的分布式Voronoi控制算法,以确定节点移动状态。仿真实验表明,所提算法不仅使得节点在目标区域实现了高覆盖率,同时在时间上也较早地达到了收敛,优化了网络的覆盖控制。     

Optimal replacement policy for a two-dissimilar-component cold standby system with different repair actions

In this paper, a cold standby repairable system consisting of two dissimilar components and one repairman is studied. When failures occur, the repair of both component 1 and component 2 are not ‘as good as new’. The consecutive operating times of component 1 after repair constitute a decreasing geometric process, while the repair times of component 1 are independent and identically distributed. For component 2, its failure is rectified by minimal repair, and the repair time is negligible. Component 1 has priority in use when both components are good. The replacement policy N is based on the failure number of component 1. Under policy N, we derive the explicit expression of the long-run average cost rate C(N) as well as the average number of repairs of component 2 before the system replaced. The optimal replacement policy N*, which minimises the long-run average cost rate C(N), is obtained theoretically. If the failure rate r(t) of component 2 is increasing, the existence and uniqueness of the optimal policy N* is also proved. Finally, a numerical example is given to validate the developed theoretical model. Some sensitivity analyses are provided to show the influence of some parameters, such as the costs for replacement and repair, and the parameters of the lifetime and repair time distributions of both components, to the optimal replacement policy N* and corresponding average cost rate C(N*).     

Containment control of multi-agent systems with unbounded communication delays

In this paper, we address the containment control problem for multi-agent systems under heterogeneous unbounded communication delays with emphasis on the convergence rate analysis. Different from most works on multi-agent systems, we resort to a viewpoint from the area of positive delay systems. We first cast the containment control problem into the stability analysis of an associated error system. In order to capture the convergence rate, we introduce a nondecreasing positive function whose reciprocal represents the decay rate of the associated error system. Under the assumption that each follower has access to at least one leader and some mild hypotheses on the communication delays, an explicit condition is given to characterise the decay rate of the associated error system in terms of linear programming. In addition, we provide several special cases when the communication delays are restricted by linear, sublinear and logarithmic growth rates, respectively. Finally, through numerical examples, it is shown that the convergence rate is dominated by the delays being the highest order infinitely large quantity.     

Optimal number of minimal repairs with cumulative repair cost limit for a two-unit system with failure rate interactions

A discrete replacement model is presented that includes a cumulative repair cost limit for a two-unit system with failure rate interactions between the units. We assume a failure in unit 1 causes the failure rate in unit 2 to increase, whereas a failure in unit 2 causes a failure in unit 1, resulting in a total system failure. If unit 1 fails and the cumulative repair cost till to this failure is less than a limit L, then unit 1 is repaired. If there is a failure in unit 1 and the cumulative repair cost exceeds L or the number of failures equals n, the entire system is preventively replaced. The system is also replaced at a total failure, and such replacement cost is higher than the preventive replacement cost. The long-term expected cost per unit time is derived using the expected costs as the optimality criterion. The minimum-cost policy is derived, and existence and uniqueness are proved.     

基于Seam Carving的图像放大算法研究与改进

针对Seam Carving图像放大算法中,能量值前k小的像素带可能出现共用点的情况,提出了一种改进的图像放大自适应算法,通过判断图像中出现共用点的像素带的情况及计算其共用率的值,经过一定的策略确定待新增的像素带位置,该算法使得图像中视觉关注非重要信息区域像素带的增加能得到较均匀的分布;实现了人工干预选择视觉关注重要区域的方法,避免了自适应算法本身因误判视觉关注重要区域而带来关注对象发生变形扭曲的情况.实验证明,改进的算法能得到更好的放大效果.     

Performance Analysis of The Auxiliary‐Model‐Based Multi‐Innovation Stochastic Newton Recursive Algorithm for Dual‐Rate Systems

The stochastic Newton recursive algorithm is studied for dual‐rate system identification. Owing to a lack of intersample measurements, the single‐rate model cannot be identified directly. The auxiliary model technique is adopted to provide the intersample estimations to guarantee the recursion process continues. Intersample estimations have a great influence on the convergence of parameter estimations, and one‐step innovation may lead to a large fluctuation or even divergence during the recursion. In the meantime, the sample covariance matrix may appear singular. The recursive process would cease for these reasons. In order to guarantee the recursion process and to also improve estimation accuracy, multi‐innovation is utilized for correcting the parameter estimations. Combining the auxiliary model and multi‐innovation theory, the auxiliary‐model‐based multi‐innovation stochastic Newton recursive algorithm is proposed for time‐invariant dual‐rate systems. The consistency of this algorithm is analyzed in detail. The final simulations confirm the effectiveness of the proposed algorithm.