基于二元决策图的节点不可靠网络可靠度计算

针对节点不可靠网络可靠度计算效率较低的问题,提出一种基于二元决策图的网络可靠度计算方法.通过因子分解得到节点可靠网络的有序二元决策图(OBDD),根据节点和边的关系对边的变量节点执行边替换操作,生成节点不可靠网络的OBDD,并利用其高效存储结构提高不可靠节点的处理效率.在遍历OBDD计算可靠度时,引入Hash表以避免对同一节点的重复访问,从而减少冗余计算,进一步提高计算效率.在基准网络中的对比实验结果表明,该方法不仅能正确计算网络可靠度,而且能快速分析大型网络.     

网络可靠性分析中自顶向下的二叉决策图构造研究

采用边界分区标识网络的思想,实现基于边界分区的自顶向下K端可靠度二叉决策图(BDD)构建算法。针对BDD构建过程中存在的节点冗余问题,提出无效边冗余消除和K点非连通冗余消除2种处理技术。在规则网络和实际工程中的实验结果表明,利用无效边冗余消除和K点非连通消除技术后的BDD改进算法,在不影响算法时间性能的情况下,可大幅缩减BDD尺度,提升K端网络可靠度分析算法性能,适用于大规模的网络可靠度分析。     

基于网络化简和向量集分解的网络两终端可靠度算法*

可靠度是衡量网络性能最重要的指标之一,不交和算法和因子分解算法是计算网络可靠度最重要的两种方法。不交和算法需要提前枚举网络所有极小路或极小割,因子分解算法虽然不需要枚举极小路或极小割,但每次只能分解一条边的状态。为了克服这两种算法的不足,基于网络化简和向量集分解,提出一个计算网络可靠度的高效、实用算法。该算法具有如下特点：a）算法首先求得网络的不可靠度,进而可得网络的可靠度;b）算法不需要提前枚举网络所有极小路和极小割;c）通过引入网络化简操作和向量集分解方法,算法每次可以分解多条边的状态,从而能更快速、     

计算网络两终端可靠度的新分解算法

网络可靠度是衡量网络性能的一个核心指标,随着网络模型被广泛应用于现实生活,人们对网络可靠度的研究也越来越重视。针对不交和算法和因子分解算法在计算网络可靠度方面存在的不足,给出一个计算网络两终端可靠度的新分解算法。该算法具有如下的优点：不需要提前枚举网络的所有极小路和所有极小割;通过引入网络化简操作和新的分解技术。该算法每次可以分解多条边的状态,从而它能够更快速、更高效地去分解网络的状态向量集,使得网络可靠度的计算更简单,更高效。通过实例以及和其他算法的比较验证了所提出算法的正确性和有效性。     

基于边状态枚举计算多状态网络可靠度动态界

为降低计算多状态网络可靠度的复杂性,综合考虑网络中具有多态性的边处于各中间状态的概率及从某中间状态转换到相邻状态对网络性能的影响,提出了一种基于边状态枚举计算多状态网络可靠度上下界的算法.该算法首先令网络中各边仅取完全工作和完全失效两种状态,将处于中间状态的概率分别叠加到完全工作和完全失效状态的概率上,得到可靠度上下界的初始值;而后按照对可靠度影响递减的顺序迭代枚举边的中间状态,通过集合间的比较,计算可靠度上下界的改变值,同时获得不断减小的可靠度上界和不断增加的可靠度下界,使其最终收敛于可靠度精确值.该算法不需提前求取网络d-最小割(路)集,且枚举较少的网络状态即可得到紧凑的可靠度上下界.相关引理的证明及算例分析验证了该算法的正确性和有效性.     

基于故障树的无线传感器网络可靠度符号计算

以无线传感器网络（WSN ）中应用通信可靠性（ACR）为背景,利用故障树模型中的事件元素与逻辑门元素,建立基于故障树的WSN可靠性结构。为降低WSN可靠度计算的复杂性,给出从WSN可靠性结构转换到二元决策图BDD结构的算法,利用BDD算法优化计算过程。以分层簇型网络中可用路径以及节点冗余下的应用通信可靠性问题为例,给出其可靠性结构,利用CUDD软件包给出用递归方法实现构建基于故障树的WSN可靠性结构的BDD算法,计算以上两种情况下的WSN可靠度。实验结果表明,该方法具有可行性。     

基于多值决策图的动态故障树分析方法

针对具有动态故障模式的复杂系统,动态故障树分析一直是很重要的可靠性分析技术。为了提升可靠性分析效率,已有研究提出了各种模块化方法,但是对于实际动态故障树模型中由于事件关联导致的大型动态子树,这些模块化方法的状态空间爆炸问题仍然很突出。因此介绍了一种基于多值决策图(Multiple-valued Decision Diagrams,MDD)来分析动态故障树的方法,通过多值变量编码动态门,利用单一系统MDD模型刻画各种动态和静态可靠性行为,有效地缓解了状态爆炸问题。通过一个具体的实例说明了多值决策图方法的应用和优势。     

基于Voronoi图的无线传感器网络K覆盖算法

针对无线传感器网络(WSN)在随机高密度部署节点情况下的多重覆盖问题,提出一个基于Voronoi图的K覆盖算法。该算法利用邻居节点信息计算Voronoi覆盖邻居节点集,构建有向Voronoi覆盖关系图,通过调整关系图中的节点状态实现K覆盖。仿真结果表明,该算法能正确判断网络覆盖率,连通K覆盖的近似最小活动节点集数目少于CCP算法。     

融合链接预测相似度矩阵的属性网络嵌入算法

在属性网络中,与节点相关联的属性信息有助于提升网络嵌入各种任务的性能,但网络是一种图状结构,节点不仅包含属性信息还隐含着丰富的结构信息。为了充分融合结构信息,首先通过定义节点的影响力特性、空间关系特征;然后根据链接预测领域基于相似度的定义构建相似度矩阵,将节点二元组中的关联向量映射到相似度矩阵这一关系空间中,从而保留与节点相关的结构向量信息;再基于图的拉普拉斯矩阵融合属性信息和标签特征,将上述三类信息集成到一个最优化框架中;最后,通过二阶导数求局部最大值计算投影矩阵获取节点的特征表示进行网络嵌入。实验结果表明,提出的算法能够充分利用节点二元组的邻接结构信息,相比于其他基准网络嵌入算法,本模型在节点分类任务上取得了更好的结果。     

带路径约束的双端网络可靠性分析磁

针对带路径约束的双端网络可靠性分析问题,即一个数据包从 S 点发送到 T 点,必须经过中间若干个节点,并且经过这些节点的先后顺序具有一定约束,提出了基于 BDD 的可靠性分析算法。该算法基于边扩展图实现路径约束,即在边扩展过程中只保留符合条件的约束路径,然后构建 BDD 以及进行双端网络可靠性分析。实例分析结果验证了算法的可行性和有效性。     

An optimal production and inspection strategy with preventive maintenance error and rework

This study considers the integrated problem of production, preventive maintenance (PM), inspection, and inventory for an imperfect production process where rework and PM error exist. PM is performed when the process is in a controlled state. The correct implementation of PM results in a lower system failure rate, whereas a PM error results in the system shifting to the out-of-control state with a certain probability. The age of the system after PM is correlated with the level of PM performed. When the process in an out-of-control state produces a certain percentage of non-conforming items, we assume that a certain proportion of the non-conforming items can be reworked into conforming items. In a deteriorating production system, we determine the optimal inspection interval, inspection frequency, and production quantity that will yield the maximal unit expected profit. Numerical analyses are used to investigate the effectiveness of imperfect PM and to explore the effect of rework and PM error on profit.     

多用户MIMO系统预编码技术的研究

多天线基站和多用户可以组成一个多用户MIMO系统,为获得更高的系统容量和高效传输性能。预编码是一种应用于发射端以达到抑制多用户间干扰的预均衡方法。基于非理想信道状态信息(CSI)条件,针对多用户MIMO系统的下行信道,研究了线性ZF预编码和非线性THP预编码的性能,给出了接收端信号与干扰和噪声比SINR的近似表达式。对两种THP变体结构,dTHP结构和cTHP结构进行了性能仿真比较。仿真结果表明,cTHP结构的性能要优于dTHP结构。同时,给出了信道估计误差对cTHP结构BER影响的定量仿真结果。对非理想CSI下的预编码技术选择提供了一定的依据,并对限定信道估计误差的偏差程度具有参考意义。     

Realizing the vision for web services: Strategies for dealing with imperfect standards

Organizations considering the adoption of the web services framework for their Information Technology (IT) applications are confronted with a period of technological ferment, as standards for supporting non-trivial business process functionality are not yet in place. Evolving standardization poses challenges in the form of inter-temporal dependencies as organizations’ conformance to the standards that emerge in the future is contingent on their current design choices that need to be made ex-ante without complete information of how standards will evolve. At the same time, there are significant early-mover benefits to be gained by executing an IT strategy using web services as a cornerstone. This paper draws upon coordination theory to develop a conceptual framework outlining three approaches for organizations to deal with changing standardization regimes: (a) The dependencies across components, conforming to different standardization regimes, are continually bridged through intermediary services (e.g., using a protocol adapter that translates to an unanticipated emergent standard), (b) The dependencies across components are minimized through loose coupling so that standardization regime changes for any component have a minimal impact on other components (e.g., encapsulating the functionality susceptible to design change into a module with abstract interfaces), and (c) The impacted components are rapidly reconfigurable as and when standardization regime changes (e.g., by building in “extension” features into applications). The risk for organizations investing in web services can be further managed by mechanisms such as organization’s attention to signals from the periphery, undertaking low-risk experiments to learn in different areas, and bricolage-like improvisations of their legacy components at hand.

Joint replenishment with imperfect items and price discount

A joint replenishment problem is presented to determine the ordering policy for multiple items having a certain percentage of defective units. The purpose of this paper is to study the impact of the percentage of defective units on the ordering policy. Two different scenarios are presented for joint replenishment problem: (1) without price discount and (2) with price discount. For each scenario, the total expected cost per unit time is derived and algorithms are presented to determine the family cycle length and the integer number of intervals that the replenishment quantity of each item will last. Numerical examples are presented and the results are discussed.     

Economic ordering policy for an item with imperfect quality subject to the in-house inspection

This article considers a production/inventory system where each lot of items received or produced contains a random proportion of defective units, items of imperfect quality. The purchaser contacts a 100% inspection in order to identify the perfect (acceptable) quality items. The model examines the following two options for the imperfect quality items: sell them to a secondary market, as a single batch and at a price lower to that of new ones, or rework them at some cost and then use them as new ones to satisfy demand. After inspection, the good quality items are sent to the working inventory warehouse in batches of equal size. For both of these cases, the optimal ordering lot size and the optimal number of batches are obtained. A numerical example illustrates the solution procedure and sensitivity analysis results are reported.     

A two-dimensional warranty servicing strategy based on reduction in product failure intensity

The cost of servicing a warranty depends, amongst other factors, on the type of repair performed under warranty. Although “all minimal repair” and “all replacement” policies are easy to implement and analyze, they are not always feasible and/or practical. Having a combination of different types of repair often leads to lower warranty servicing costs. In this article, to reduce the warranty servicing cost, we study a servicing strategy that involves performing imperfect repairs in place of some of the minimal repairs of an “all minimal repair” strategy; the effect of an imperfect repair is characterized by a drop in the conditional intensity function of the failure process. We consider both fixed and random degrees of repair. For a given type of product, we partition the warranty region so that the expected total warranty servicing cost is minimized. We provide a numerical illustration and a comparison with previously-studied repair-replacement strategies.     

A study on negative binomial inspection for imperfect production systems

Production systems continuously deteriorate with age and usage due to corrosion, fatigue, and cumulative wear in production processes, resulting in an increasing possibility of producing defective products. To prevent selling defective products, inspection is usually carried out to ensure that the performance of a sold product satisfies the customer requirements. Nevertheless, some defective products may still be sold in practice. In such a case, warranties are essential in marketing products and can improve the unfavorable image by applying higher product quality and better customer service. The purpose of this paper is to provide manufacturers with an effective inspection strategy in which the task of quality management is performed under the considerations of related costs for production, sampling, inventory, and warranty. A Weibull power law process is used to describe the imperfection of the production system, and a negative binomial sampling is adopted to learn the operational states of the production process. A free replacement warranty policy is assumed in this paper, and the reworking of defective products before shipment is also discussed. A numerical application is employed to demonstrate the usefulness of the proposed approach, and sensitivity analyses are performed to study the various effects of some influential factors.     

Computing optimal base-stock levels for an inventory system with imperfect supply

We study a single-item, single-site, periodic-review inventory system with negligible fixed ordering costs. The supplier to this system is not entirely reliable, such that each order is a Bernoulli trial, meaning that, with a given probability, the supplier delivers the current order and any accumulated backorders at the end of the current period, resulting in a Geometric distribution for the actual resupply lead time. We develop a recursive expression for the steady-state probability vector of a discrete-time Markov process (DTMP) model of this imperfect-supply inventory system. We use this recursive expression to prove the convexity of the inventory system objective function, and also to prove the optimality of our computational procedure for finding the optimal base-stock level. We present a service-constrained version of the problem and show how the computation of the optimal base-stock level using our DTMP method, incorporating the explicit distribution of demand over the lead time plus review (LTR) period, compares to approaches in the literature that approximate this distribution. We also show that the version of the problem employing an explicit penalty cost can be solved in closed-form for the optimal base-stock level for two specific period demand distributions, and we explore the behavior of the optimal base-stock level and the corresponding optimal service level under various values of the problem parameters.     

认知网中一种基于隐马尔可夫的多信道功率控制机制

在分布式多信道接入认知无线网中,针对用户获取环境信息不对称导致资源分配冲突的问题,根据非授权用户对信道状态判决结果的相关性,提出一种基于隐马尔可夫的多信道功率博弈机制。该机制选取合理的价格函数和有效地抑制非授权用户的自私行为,实现了非授权用户之间的频谱共享,并使其对信道上其他用户是否参与博弈进行推测,以获得较准确的博弈信息,从而选择更优的发射功率。仿真表明,该机制能使系统获得更高的有效容量,同时保证更多的用户达到速率需求。