面向高速公路环境的VANETs中V2V链路时延的动态预测

考虑到现有移动自组网络（MANETs）和车载自组网络（VANETs）链路时延理论分析方法太复杂,不适合动态预测实际VANETs中两车链路时延,提出了动态预测链路时延（DPLD）的数学模型,该模型考虑了两车相对速度分布、距离变化和交通流密度变化因素对两车之间链路时延的影响,能够预测预期要发生的两车的链路时延。该模型的实现取决于相对速度分布的估计方法、基于指数移动平均（EMA）的数据预先处理以及通过处理速度的变化解决交通密度对链路时延的影响。仿真结果表明此DPLD模型在预测高速公路上两车链路时延上具有很高的准确性。     

汽车自组织网络链路时延预测(LDP)模型的扩展及扩展后的性能分析

为了克服前期提出的汽车自组织网络(VANETs)链路时延预测(LDP)模型只能预测高速公路直行场景的链路时延的局限,扩展了LDP模型的功能,构建了扩展的LDP模型——ELDP模型,并对该模型的链路时延预测过程进行了理论分析,对其预测性能进行了仿真分析。ELDP模型考虑了两车相对速度值的分布、相对速度驶过距离的变化以及在交叉口转弯对两车之间链路时延的影响,可以动态地预测车辆转弯时的两车链路时延,能够估计任意一对汽车预期要发生的链路时延。该模型实现取决于对相对速度值的分布参数估计方法、基于指数移动平均法对相对速度值的异常处理以及对在道路交叉口汽车转弯角度对链路时延的影响的估计。仿真结果表明,ELDP模型能够非常准确地预测高速公路中两车的链路时延。     

应用于Ad Hoc网络的时延敏感自适应路由协议

针对Ad Hoc网络中实时业务对网络平均时延的要求，提出了一种应用于Ad Hoc网络的新型路由协议——时延敏感的自适应路由协议。该协议在保持“最少跳数”的最佳路由条件下，增加了“平均最短时延”的约束条件，从而不仅可以为实时业务(即时延敏感的业务)提供可靠的路由，同时还能根据网络节点当前的业务流量，动态地选择最佳路径，降低网络的平均时延。这是一种新型的有QoS保证的路由协议。仿真结果表明，该协议的确可以有效地改善网络的性能。     

自组网中一种可靠的层次路由协议

针对自组网中基于多层有中心分级结构(MCHS)的分级状态路由(HSR)协议存在结构稳定性差、结构维护开销大、可靠性不高和丢包问题严重等问题,提出一种可靠的层次路由协议(RHRP)。它基于一种新的多层无中心分级结构(MCLHS),该结构采用无中心策略,有利于提高结构稳定性和降低结构维护开销,并能进一步提高可靠性和降低路由开销。RHRP采用"高层虚拟链路以群为构成元素"的策略,使高层虚拟链路更稳定,有利于提高可靠性。更稳定的结构和高层虚拟链路可以减少丢包数目和重路由次数,从而降低传输时延和路由开销。通过分析路由可靠度,从理论上证明了RHRP的可靠性较高。通过仿真评价RHRP和HSR的性能,结果表明,RHRP在投递率、平均端到端时延和路由开销等指标上都优于HSR。     

基于多指标感知的命名数据网络自适应拥塞控制算法

为解决命名数据网络拥塞控制算法普遍存在的瓶颈链路缓存队列积压问题,提出一种基于多指标感知的命名数据网络自适应拥塞控制(MACC)算法。在网内节点,根据实时监测的接收端数据接收速率、数据包排队时延、链路带宽等多个指标估计链路负载程度,并通告终端节点。在终端节点,根据Data包携带的链路负载信息,自适应地调整发送窗口,以实现高吞吐、低时延目标。基于ndnSIM的仿真结果表明,该算法能有效实现终端高吞吐量、瓶颈链路低队列,并在实现流间公平性方面具有显著优势。     

一种改进的FAST TCP协议及其在OPNET下的仿真实现

FASTTCP在地面大带宽时延积网络中具有很好的性能,针对FAST TCP拥塞控制机制在卫星网络中的应用开展研究,卫星网络链路随机丢包严重导致FAST TCP吞吐量下降的问题,采用对网络可用带宽估计的方法区分丢包原因,提出一种改进的FAST TCP协议。通过在OPNET下的实现,对改进FAST TCP协议在大带宽、长延时、链路随机丢包严重的网络中的吞吐量情况进行仿真,验证协议性能。     

一种基于改进蚁群优化算法的WSNs路由协议

面对无线传感网络(wireless sensor network,WSN)路由问题,提出新颖生物激励-自我组织的安全自适应路由协议(biological inspired self-organized secure autonomous routing protocol,BIOSARP)。BIOSARP采用改进蚁群优化算法(improved ant colony optimization,IACO),利用端到端传输时延、剩余电量和链路质量计算信息素,并据此信息决策最优转发节点,从而减小广播次数和数据包负担,降低时延、数据包丢失率和功率消耗。仿真结果表明:提出的BIOSARP在数据包传递率、能量消耗优于安全实时负荷分配协议(secure real-time load distribution,SRTLD),数据包传递率提高24.75%,能量消耗降低31.8%。     

Ad Hoc网中的OLSR路由协议研究

本文主要描述了优化链路状态路由算法(Optimized Link State Routing Protocol：“OLSR”)的特点，并且对OLSR路由算法的性能进行仿真分析。主要评估的参数有：数据分组成功接收率，数据分组投递的平均端到端时延，点到点数据传输平均速率。在此基础上研究了OLSR在传统的链路状态路由算法上引入的优化策略多点中继站(multipoint relay，MPR)：采用选择一部分邻居节点来转发控制信息。     

低时延能耗均衡的水声传感器网络簇间路由算法

针对水声传感器网络的簇间路由选择问题,提出了一种基于前向网关的低时延能耗均衡路由算法,该算法采用最优方向角原则和能耗均衡原则选择中继簇头和中继网关,以减小长延迟和高能耗对水声通信的影响。仿真结果表明该算法在网络平均能耗、端到端时延和网络生命周期等方面具有较好的性能。     

一种适用于WIA-PA网络的安全路由机制

路由是WIA-PA网络通信的前提,路由安全是WIA-PA网络通信安全的基础,本文设计了一种集中式和分布式相结合的信任管理机制,提出了一种适用于WIA-PA网络的安全路由机制,能够在保证时延和能耗平衡的基础上有效的抵制选择性转发等内部攻击的入侵。     

一种新的基于移动预测的MANET路由协议

移动自组网是一种由一系列可以自由移动的节点主机聚集而成的一个临时性动态网络。它没有固定基站，也没有作为控制管理中心的节点主机，由于其拓扑的动态性，其路由协议与其他传统网络有很大的区别。为了能更有效地移动自组网中实现数据的传送，本文提出了一种基于移动预测下的MANET路由协议，该协议综合考虑了传输路径的延时和稳定性，选择在延时限制下平均拥有最稳特性的传输路径，模拟结果表明，这种方法比基于移动预测量稳路径路由协议的传输时延要短，传送成功概率要高，而控制开销却相关不大。     

基于贝叶斯网络的核电站应急电力系统安全评价

在故障树分析法(FTA)基础上提出了一种基于贝叶斯网络(BN)的核电站应急电力系统安全评价方法,比较了FTA和BN在建立安全评价模型和评价能力上的不同.该方法在应对众多影响因素上有很大优势,能进行更多有意义的分析:既能进行前向的预测推理,又能进行后向的诊断推理,可以找出影响故障的组合模式,从而能够找出系统的薄弱环节.同时采用基于Matlab的BNT软件包,大大简化了计算过程.通过对10MW高温气冷堆(HTR-10)应急电力系统的安全评价实例的分析,证明该方法是对传统的基于故障树分析的安全评价方法的有益改进.     

TCP Yolanda:无线和有线混合网络中的TCP改进算法

在TCP Westwood基础上提出了一种适合无线有线混合网络的TCP改进算法——TCP Yolanda,该算法以瓶颈链路缓冲区长度测量值为参数,采用分两个子阶段的方式改进拥塞避免阶段以更有效进行传输控制,使传输过程能更长时间保持在稳定的高速率状态,并能在误码率较高的无线网络环境下快速恢复拥塞窗口大小,另外在传输发生错误时能判断丢包原因并进行区别处理。基于ns2的仿真实验表明,改进后的TCP算法在网络传输吞吐率、传输稳定性等方面的性能有较大提升,并且保持较好的连接公平性和友好性。     

多出口网络链路负载均衡系统的研究

针对当前广泛使用的多链路技术,研究了多链路网络的运行机制,对多链路的流量特性、负载分配策略进行了分析.将企业网日常的Internet流量分为Outbound流量和Inbound流量,并结合FreeBSD下的PF包过滤和动态DNS解析技术,分别给出了Inbound和Outbound流量的负载均衡策略和模型.基于该模型研制的系统,能成功地依照事先定义的负载均衡策略实现Inbound和Outbound流量的负载均衡,多个Internet链路的合理分配利用而使得总访问带宽扩大,能够很好地消除几大ISP间互访的瓶颈,还为内部网上SERVER提供更高的可靠性和性能.     

JOINT CONFIGURATION OF BACKBONE AND LOGICAL NETWORKS ON A RECONFIGURABLE PACKET-SWITCHED NETWORK WITH UNRELIABLE LINKS

Abstract

This paper considers a problem of configuring both backbone and logical networks in a reconfigurable packet-switched network where links are subject to failures. The objective is to design feasible backbone and logical networks at least cost where the network cost includes backbone link capacity expansion cost and average packet delay penalty cost due to link failures. The problem is formulated as a zero-one non-linear mixed integer programming problem, for which an effective solution procedure is developed by using a Lagrangean relaxation technique for finding a lower bound and a heuristic method is exploited for improving the upper bound of an intermediate solution. The solution procedure is tested for its effectiveness with various numerical examples.     

Wireless mesh networks channel reservation: modelling and delay analysis

In order to overcome the negotiation procedure bottleneck of the standard DCF in wireless mesh networks, the authors propose a new channel reservation function (CRF) that reduces the negotiation overhead of the DCF, which as a result reduces the overall transmission delay effectively without of any extra bandwidth consumption. Furthermore, the authors provide an analytical model for the proposed scheme for which the simulation results measure the amount that the new method can reduce the average total delay for both regular and fragmented mesh topologies demonstrating superiority of the new method over the classic 802.11 solution. Additionally, the authors extend the scheme to multichannel CRF upon which the proposed method can be used for multichannel applications.     

Exact algorithm for delay-constrained capacitated minimum spanning tree network

The delay-constrained capacitated minimum spanning tree (DC-CMST) problem of finding several broadcast trees from a source node is discussed. While the traditional CMST problem deals with only the traffic capacity constraint served by a port of the source node, and delay-constrained minimum spanning tree (DCMST) considers only the maximum end-end delay constraint, the DC-CMST problem deals with both the mean network delay and traffic capacity constraints. The DC-CMST problem consists of finding a set of minimum cost spanning trees to link end-nodes to a source node satisfying the traffic requirements at end-nodes and the required mean delay of the network. In the DC-CMST problem, the objective function is to minimise the total link cost. A dynamic programming-based three-phase algorithm that solves the DC-CMST problem is proposed. In the first phase, the algorithm generates feasible solutions to satisfy the traffic capacity constraint. It finds the CMSTs in the second phase, and allocates the optimal link capacities to satisfy the mean delay constraint in the third phase. Performance evaluation shows that the proposed algorithm has good efficiency for any network with less than 30 nodes and light traffic. The proposed algorithm can be applied to any network regardless of its configuration, and used for the topological design of local networks and for efficient routing algorithms capable of constructing least cost broadcast trees.     

供应链时间瓶颈及其价值评价研究

供应链整体的时间优化取决于少数的薄弱环节,即供应链上的"时间瓶颈",时间瓶颈包括能力瓶颈、不增值瓶颈、调度瓶颈和界面瓶颈四种形式,分析了形成这些瓶颈的主要因素;为了在多个瓶颈中确定突破重点,以瓶颈消除后供应链的产出速率和供应链总体流程周期的改善率为依据,建立了时间瓶颈的价值评价模型;总结了供应链上时间压缩和瓶颈消除应遵循的结构化程序.     

Cross-layer queuing analysis on multihop relaying networks with adaptive modulation and coding

Multihop relaying is one of the promising techniques in future generation wireless networks. The adaptive modulation and coding (AMC) mechanisms can be applied in order to increase the spectral efficiency of wireless multihop networks. However, most of these mechanisms concentrate on the physical layer without taking the queuing effects at the data link layer into account, whose performances are overestimated. Therefore the cross-layer analytical framework is presented in analysing the quality-of-service (QoS) performances of the decode-and-forward (DF) relaying wireless networks, where the AMC is employed at the physical layer under the conditions of unsaturated traffic and finite-length queue at the data link layer. Considering the characteristics of DF relaying protocol at the physical layer, the authors first propose modelling a two-hop DF relaying wireless channel with AMC as an equivalent Finite State Markov Chain (FSMC) in queuing analysis. Then, the performances in terms of queuing delay, packet loss rate and average throughput are derived. The numerical results show that the proposed analytical method can be efficiently applied for studying the issues including the relay deployment and the cross-layer design in the multihop relaying networks.     

Exact topology discovery algorithm for the capacity and delay constrained loop network

We have developed an exact model and algorithm for the delay-constrained minimum cost loop problem (DC-MCLP) of finding broadcast loops from a source node. While the traditional minimum cost loop problem (MCLP) deals with only the traffic capacity constraint served by a port of source node, the DC-MCLP deals with the mean network delay and traffic capacity constraints simultaneously. The DC-MCLP consists of finding a set of minimum cost loops to link end-user nodes to a source node satisfying the traffic requirements at end-nodes and the required mean delay of the network. In the DC-MCLP, the objective function is to minimise the total link cost. We have formulated the DC-MCLP and proposed an exact algorithm for its solution. The proposed algorithm is composed of two phases: in the first phase, it generates feasible paths to satisfy the traffic capacity constraint; in the second phase it finds the exact loop topology through matching and allocating optimal link capacity to satisfy the mean delay constraint. In addition, we have derived several properties including the memory and time complexity of the proposed algorithm. Performance evaluation shows that the proposed algorithm has good efficiency for networks with less than thirty nodes and light traffic. Our proposed algorithm can be applied to find the broadcast loops for real-time multimedia traffic