CRSN中基于随机网络演算的拥塞控制协议QoS边界分析

为了保证认知无线电传感器网络(CRSN)的服务质量(QoS),需精确求解所采用协议的性能边界,为此提出了一种基于随机网络演算(SNC)的QoS性能边界分析方法.以CRSN中的和式增加积式减少(AIMD)拥塞控制机制为评估对象,以通信时延和数据积压为QoS性能指标.根据CR资源传感器的发送速率分布,利用基于矩量母函数(MGF)的随机网络演算推导出AIMD机制的时延和积压边界模型.实验结果表明,不同CRSN场景中的模型计算值都在理论边界范围之内,证明了该边界分析模型具有良好的性能.     

基于随机网络编码的无线广播重传方案及性能分析

针对自动重复重传(ARQ)机制在无线广播系统中吞吐量性能不佳的缺陷,提出一种基于随机网络编码的广播重传方案RNC-ARQ.对于广播节点,采用随机线性码对所有丢失包进行编码组合重传.对于接收节点,当接收的编码包累积到一定数量后可通过解码操作恢复出原始数据.该方案可有效减少重传次数,改善无线广播的吞吐量性能.基于Gilbert-Elliott模型描述的突发错误信道,建立了信道状态和节点接收处理流程合并的多状态马尔可夫模型,并以此为基础推导了RNC-ARQ方案的吞吐量闭合解.最后,使用NS-2模拟器评估RNC-ARQ方案的性能,结果表明在突发差错信道下,基于随机网络编码重传方案的吞吐量优于传统的选择承传ARQ方案和基于异或编码的重传方案.     

基于LFSN业务流量模型的网络拥塞控制算法

网络业务流的多分形本质可以用LFSN（线性分形稳定噪声）准确建模，文中提出了基于LFSN模型预测的网络拥塞控制算法并进行了仿真分析，结果表明该算法提高了网络链路吞吐量，减小了丢包率。     

优先级网络性能的网络演算分析

基于网络演算理论,对考虑信道差错过程影响的优先级网络系统性能进行了综合分析;基于网络演算推导出信道差错过程的随机到达曲线,在此基础上,获得不同优先级用户的随机服务曲线,进而分析相应的网络服务保证,即时延边界和存储空间边界。基于不同的业务到达模型,研究了不同系统配置下的时延边界,并对相应数值结果加以深入分析。     

基于随机几何理论的毫米波蜂窝系统覆盖研究

随着移动多媒体业务的日益发展,蜂窝通信的频带日趋紧张,开辟新的频带资源是解决问题的关键技术之一.毫米波频段丰富的频率资源已经成为关注的焦点,它将是下一代蜂窝网络发展的希望所在.提出一种基于随机几何理论的毫米波蜂窝网络基站建模方法,用线段模型对城市中的建筑物进行建模,根据概率理论推导了毫米波蜂窝网络中建筑物的阻挡数量;分析了建筑物阻挡对覆盖产生的影响,研究了毫米波蜂窝网络的覆盖概率与信干比(Signal To Interference Ratio,SIR)之间的关系,最后通过系统仿真对前面的理论进行了验证,仿真结果与毫米波的传输理论一致.     

基于马尔可夫-蒙特卡洛采样的电源网络分析

电源网络分析是深亚微米集成电路设计的关键因素之一.针对高性能芯片采用IBM C4封装和网状结构片上网络的特点,首先通过随机游走模型推导出电源网络的三个性质,接着基于这些性质给出了深亚微米电源网络的分析框架,最后提出了基于马尔可夫-蒙特卡洛采样的电源网络求解算法.仿真实验表明,与随机采样求解电源网络方程相比,马尔可夫-蒙特卡洛采样在不降低计算精度的前提下,运算速度提高了近两个数量级.     

基于统计网络演算的无线mesh网络流量模型

基于无线mesh网络的基本特征,利用统计网络演算理论,构造了新型的无线mesh网络单节点和多节点的流量模型,该模型充分体现了无线mesh网的随机特性.该流量模型的特征是其求和函数及其输入输出函数的边界函数均受限于一个最小加卷积函数.理论分析证明构造的流量模型能正确描述无线mesh网络的实际情况.     

基于随机演化博弈的WSNs节点协作演化模型

为解决无线传感器网络节点协作策略的选择影响协作效果的问题,考虑到节点数量有限及个体随机性,基于模仿突变Wright-Fisher过程的随机演化博弈,提出了WSNs节点协作随机演化模型,并加入了与节点协作程度相关的惩罚机制.该模型弥补了复制子动态不适用于节点数量有限的WSNs节点协作演化建模问题.经过随机动力学分析,推导并证明了达到演化稳定状态的定理.最后通过实验验证定理并分析了选择强度和惩罚力度对WSNs节点协作演化稳定状态的影响.     

LFSN自相似网络流量模型的相关结构研究

在基于一般线性分形稳定噪声(LFSN)的网络流量模型中,需要对模型与实际流量样本的相关结构进行检验,以验证模型有效性.LFSN作为一种非高斯过程,一般不存在二阶矩,使基于二阶矩的方法不再适用,给检验带来一定的困难.本文考察了样本标准自相关函数(NACF)、共变(Covariation)和共差(Codifference)这三种度量,对相关结构进行实际验证,验证后二者的有效性,提出将一般化共差作为非高斯情况下相关性度量的一种统计手段.     

基于随机几何理论的中继OFDM系统容量分析

该文将随机几何理论应用于特定的基于译码转发(DF)中继的OFDM系统中,通过推导分析建立基于随机几何理论的中继OFDM系统容量模型。文中假设用户在环域范围内服从随机均匀分布,同时假设接入域用户之间存在频率复用,通过在考虑接入中继链路对接入基站链路的共道干扰时,以干扰积分上限值替代实际干扰值等理论分析,在中继和基站节点功率受限的情况下,得到完整的系统闭合容量表达式模型。并通过仿真对基于容量模型的系统传输速率值与理论值进行了比较,仿真结果证实了该文所建立的容量模型的合理性。     

Shape estimation of a circular antenna from observations on the boundary

A smoothing algorithm for estimating the shape of a circular antenna from boundary observations is described. We consider a homogenized static antenna model, consisting of a single partial differential equation with mixed boundary conditions. An exact expression is derived for the smoother, and a suitable approximation is calculated. An FFT based implementation is found to be computationally efficient. Simulation results for 8, 16, 32 and 64 sensors are given, indicating a point of diminishing returns in adding more sensors.     

一种随机Petri网性能等价化简与分析方法

随机Petri网模型是系统性能评价的有力工具,但其状态空间随模型规模的增长而指数性增长的问题限制了其对复杂和大规模系统模型的性能数量分析能力.因此,在对模型进行分析之前,先对其进行适当的性能等价化简,是一种更为可行的分析方法.本文首先讨论了一类随机Petri网-基本随机Petri网(ESPN)的性能等价分析方法,这类随机Petri网由顺序、并行、选择和循环等四种基本结构及其组合构成.作者推导出这四种基本结构的性能等价公式,并运用自底向上逐步综合替代的分层分析方法,给出这类随机Petri网模型的性能等价化简分析方法,该方法的复杂性随模型增长而线性增长,有效解决了其性能数量分析问题.然后,讨论了两种非基本结构到基本结构的转换规则,使得复杂的随机Petri网模型也可能转换为ESPN模型,从而使性能等价算法可应用于一般随机Petri网.     

基于公平性的自相似业务接纳控制研究

文中研究了基于分形稳定运动有效带宽的计算方法,利用迭代过程推导出了聚合流有效带宽的计算公式,提出了一种基于有效带宽的公平性的自相似业务接纳控制算法,在接纳判断过程中引入了公平性机制,保证了业务接纳的公平性,通过MATLAB和OPNET相结合的仿真方法证明了该算法的有效性.结果证明了文中提出的算法保障了网络的服务质量,保证了各业务接纳的公平性,同时保持了网络高的利用率.     

强激光设施能源系统电路的容差设计与分析

系统可靠性设计使用电路容差分析技术来保证电路特性获得稳定而可靠的输出，对于稳定性和可靠性要求高的系统进行容差分析尤其必要。能源系统作为惯性约束聚变(ICF)激光装置的重要组成部分，其可靠性直接关系到激光装置的稳定运行。能源系统电路的容差设计与分析，是激光装置可靠性设计分析必不可少的工作项目之一，对提高能源系统的可靠性进而保证整个激光装置的稳定运行具有重要意义。给出了能源系统电路设计图及其规定功能，然后在对容差设计模型进行一般性描述的基础上，利用随机优化设计方法，建立了能源系统电路容差设计随机优化模型，并对模型的设计变量、随机参数、设计准则、约束条件等进行了详细说明，最后给出了计算机仿真方法求解模型的流程及模型的可行解集。     

A segmentation model using compound Markov random fields based on a boundary model.

Markov random field (MRF) theory has been widely applied to the challenging problem of image segmentation. In this paper, we propose a new nontexture segmentation model using compound MRFs, in which the original label MRF is coupled with a new boundary MRF to help improve the segmentation performance. The boundary model is relatively general and does not need prior training on boundary patterns. Unlike some existing related work, the proposed method offers a more compact interaction between label and boundary MRFs. Furthermore, our boundary model systematically takes into account all the possible scenarios of a single edge existing in a 3 x 3 neighborhood and, thus, incorporates sophisticated prior information about the relation between label and boundary. It is experimentally shown that the proposed model can segment objects with complex boundaries and at the same time is able to work under noise corruption. The new method has been applied to medical image segmentation. Experiments on synthetic images and real clinical datasets show that the proposed model is able to produce more accurate segmentation results and satisfactorily keep the delicate boundary. It is also less sensitive to noise in both high and low signal-to-noise ratio regions than some of the existing models in common use.     

An adaptive distance-based location update algorithm fornext-generation PCS networks

In this paper, we propose a stochastic model to compute the optimal update boundary for the distance-based location update algorithm. The proposed model is flexible and captures some of the real characteristics in the wireless cellular environment. The model can adapt to arbitrary cell topologies in which the number of neighboring base stations at different locations may vary. The cell residence time can follow general distributions which captures the fact that the mobile user may spend more time at certain locations than others. The model also incorporates the concept of a trip in which the mobile user may follow a particular path to a destination. For implementation, the decision of location update can be made by a simple table lookup. Numerical results indicate that the proposed model provides a more accurate update boundary in real environment than that derived from a hexagonal cell configuration with a random walk movement pattern. The proposed model allows the network to maintain a better balance between the processing incurred due to location update and the radio bandwidth utilized for paging between call arrivals     

Absorbing boundary conditions applied to model wave propagation inmicrowave integrated-circuits

A general expression of an absorbing boundary condition is presented in this paper to model wave propagation in passive microwave integrated-circuits by the finite-difference time-domain method. Unlike previously developed absorbing boundary conditions which can only absorb propagating waves, this boundary condition can also absorb evanescent waves effectively. The microstrip line is used as an example to demonstrate how to impose this absorbing boundary condition on different outer boundaries of a computation-domain. It is also demonstrated that the numerical stability of this absorbing boundary condition, when it is applied in its high order form, can be maintained by properly selecting its parameters     

Variational Solution of Integral Equations

A variational solution of the Fredholm integral equation of the first kind resulting from Laplace's equation with Dirichlet boundary conditions is discussed. Positive-definiteness of the integral operator is used to guarantee convergence. The square parallel plate capacitor is given as an example with several different types of trial functions. Special singular functions to handle known field behavior are shown to result in improved accuracy with reduced computing cost. The air-dielectric interface condition is related to a general Neumann-mixed boundary condition for which a variational method with a positive-definite integral operator is presented. Multiple boundary conditions are handled by mutually constraining separate variational expressions for each boundary condition. A T-shaped conductor on a dielectric slab, representative of quasi-static solutions of microstrip discontinuities, is presented as a three-dimensional example with multiple boundary conditions. Generally, it is shown how the finite-element method for the solution of partial differential equations may be extended to handle integral equation formulations.     

Integrating local distribution information with level set for boundary extraction

This paper presents a general object boundary extraction model for piecewise smooth images, which incorporates local intensity distribution information into an edge-based implicit active contour. Unlike traditional edge-based active contours that use gradient to detect edges, our model derives the neighborhood distribution and edge information with two different region-based operators: a Gaussian mixture model (GMM)-based intensity distribution estimator and the Hueckel operator. We propose the local distribution fitting model for more accurate segmentation, which incorporates the operator outcomes into the recent local binary fitting (LBF) model. The GMM and the Hueckel model parameters are estimated before contour evolution, which enables the use of the proposed model without the need for initial contour selection, i.e., the level set function is initialized with a random constant instead of a distance map. Thus our model essentially alleviates the initialization sensitivity problem of most active contours. Experiments on synthetic and real images show the improved performance of our approach over the LBF model.