多信道多跳无线网络端到端时延最小化路由评价指标的研究

提出一种适用于多接口多信道无线网络的路由评价指标,DSRM.与传统的评价指标单纯注重网络吞吐量相比,DSRM采用整条路径的端到端时延作为评价指标,以适应日益频繁的时延敏感的应用需求.在DSRM中,综合考虑了网络传输过程中的竞争接入时延、基于等效带宽计算的传输时延、节点内的信道队列因素,并分析了整条路径的端到端重传时延.通过Qualnet仿真,证明了DSRM较WCETT、WEED等路由评价指标在平均端到端时延等网络性能参数上有了明显提升.     

基于最低开销模型的传感网络通信优化仿真

当传感网络中某条链路发生变化时,需要重新计算最短路径树,一旦传感网络规模较大,传统的算法采用抑制链路改变的方法提高传感网络通信容量,但这大幅抑制通信节点周期内路径选择灵活性,通信延迟明显.提出一种改进的A-OSPF算法并应用到传感网络通信优化中,该算法在原始的OSPF基础上融人了最低开销节点机制,增强了传感网络中节点构建的概率,考虑了节点移动性,将更加平稳的链路当成节点,按照链路代价原理得到源节点到目标节点的最佳路径,确保数据包可在链路质量最高的路径上进行传递,降低传感网络数据传送的平均端到端延时.仿真结果表明改进算法在传感网络生存周期以及平均端到端延时方法优于原始的OSPF算法,实现了延长传感网络生存周期以及能量均衡的目标.     

一种无线网络路径容量分析模型

旨在为移动计算中多跳网络链路的研究建立一个计算复杂度较低的通用分析模型,奠定一定的数学研究基础.在已有成果的基础上,将研究的粒度从节点扩展到由若干节点组成的路径,并提出了基于流水排队策略的无线多跳路径容量分析模型.这个模型可以有助于在无线多跳网络中规整地探索网络传输的吞吐能力的状况,可以为研究MANET和Sensor network的传输链路的通信能力的工作提供一种比较高效的计算和分析模式.所得到的多跳环境下的网络容量表达式,计算比较简单,可以用于动态调整系统参数的设计中,在设计QoS路由算法时也是很有裨益的.     

基于虚拟时钟的MANET端到端性能分析模型

在MANET中,节点移动对端到端性能产生消极影响。为了量化此影响,结合链路可用度的概念,将分组发送至下一跳的平均时间作为虚拟时钟节拍,提出一种基于虚拟时钟的MANET性能分析模型。通过此模型可以较准确地求出路径吞吐量和分组平均端到端时延等性能指标,并分析出节点速度、传输半径、分布密度等环境配置参数对这2个陛能指标的影响。     

基于队列约束的多层无线网状网络容量研究

在常规和随机多层无线网络中,有研究已经得到了网络可以达到的吞吐量数量级,然而对单个节点吞吐量和端到端时延的研究却很少.为了解决这一问题,对多跳常规多层无线网状网络中的单节点最大吞吐量和端到端时延进行了研究.推导了网络中的分组吸收概率;根据网络的排队模型,在这个分组吸收概率的基础上,使用扩散近似法得到了单节点可达吞吐量和端到端时延.仿真分析了业务模式和网络拓扑对端到端时延和单节点最大吞吐量的影响,通过仿真结果可以发现使网络处理大量节点的最优辅助节点数,这有助于优化网络资源分配,且减少网络的拥塞.     

基于信息熵的IP网端到端行为分析与建模

具有开放、分布式、不协作、异构、无中心控制等特点的Internet复杂巨系统的管理、容量规划、新一代网络体系结构设计与分析和性能预测都离不开对网络行为的充分理解。而端到端行为作为网络行为的一个重要组成部分,具有一定的研究价值。该文利用信息熵原理建立用于分析端到端整体宏观行为的信息熵模型,该模型能很好地反映端到端整体宏观行为与链路上各节点的状态概率之间关系,根据该模型可以分析端到端链路上各节点之间的相互作用关系以及它们是如何引起端到端整体宏观行为的。最后,给出了该模型的有效性和稳定性定量分析的判别式。     

一种基于pathchar算法的改进的网络端到端带宽测量方法

在网络端到端带宽的测量中,Pathchar测量算法是目前网络链路带宽测量算法中最成功的算法之一,但是也存在不能对反方向路径上各段链路带宽进行测量、背景流量和逐跳误差累积影响等问题.本文提出一种改进的基于pathchar的测量方法较好的解决了上述问题,提高了测量的精度和抗干扰性.     

基于虚拟信道多路径融合认知无线网络路由算法

针对认知无线网络中频谱的动态性、时变性、多样性以及节点移动性, 提出了一种基于虚拟信道的多路径融合认知无线网络路由算法. 在路由建立过程中, 为解决源节点与目的节点信道同步问题, 源节点在公共控制信道上广播添加虚拟信道的路由请求, 在当前所处信道为虚拟信道的节点中转发. 目的节点对多条路径通过信道切换进行融合, 以规避主用户的活动区域, 减少路径跳数, 提高链路的稳定性. 在路由维护阶段, 通过卡尔曼滤波对节点移动速度进行预测, 在链路断裂之前启动路由修复. 最后通过NS2中CRCN Simulator仿真结果表明, 该算法在链路通信的稳定性、分组投递率、吞吐量、端到端时延等方面有明显的改善, 提高了网络的整体性能.     

针对大规模无线多跳网络的鱼眼机会路由协议

考虑到无线网络中广播特性、丢包特性、节点移动等对网络性能的影响,提出一种针对大规模无线多跳网络的鱼眼机会路由协议。在机会路由的基础上加入鱼眼技术,减少链路状态更新信息。在鱼眼路由表中加入链路传输概率,得到转发列表,并且简化机会路由协议的报文头结构,从而实现高效的数据传输。NS2仿真结果表明,该协议能降低网络端到端延时,提高网络吞吐量。     

基于双向树的WSNs端到端位置隐私保护

针对多源节点的情况下的无线传感器网络(WSNs)端到端位置隐私保护进行研究,提出了一种基于双向树形拓扑结构的隐私保护方案(BTBLPS).该方案采用最短路径方式进行真实数据包传输,然后在最短路径的交叉点上产生双向的假包传输分支.其中,临近源节点一侧分支上的假包传输方向是从分支末端节点传输到交叉点,而临近基站的一侧恰好相反,以此来达到同时对源节点和基站的位置隐私进行保护的目的.理论分析与仿真结果表明:所提的方案是可行的,并且具有良好的安全性能.     

Evaluating transport protocol performance over a wireless mesh backbone

IEEE 802.11n wireless physical layer technology increases the deployment of high throughput wireless indoor mesh backbones for ubiquitous Internet connectivity at the urban and metropolitan areas. Most of the network traffic flows in today’s Internet use ‘Transmission Control Protocol’ (TCP) as the transport layer protocol. There has been extensive works that deal with TCP issues over wireless mesh networks as well as noisy wireless channels. Further, IEEE 802.11n is well known for its susceptibility to increased channel losses during high data rate communication. This paper investigates the dynamics of an end-to-end transport layer protocol like TCP in the presence of burst and correlated losses during IEEE 802.11n high data rate communication, while maintaining fairness among all the end-to-end flows. For this purpose, we evaluate four TCP variants-Loss Tolerant TCP (LT-TCP), Network Coded TCP (TCP/NC), TCP-Horizon and Wireless Control Protocol (WCP), where the first two protocols are known to perform very well in extreme lossy networks, and the last two are specifically designed for mesh networks. Our evaluation shows that WCP performs better in a IEEE 802.11n supported mesh networks compared to other three variants. However, WCP also results in negative impact at high data rates, where end-to-end goodput drops with the increase in physical data rate. The analysis of the results reveals that explicit loss notifications and flow balancing are not sufficient to improve transport protocol performance in an IEEE 802.11n supported mesh backbone, rather a specific mechanism is required to synchronize the transport queue management with lower layer scheduling that depends on IEEE 802.11n features, like channel bonding and frame aggregation. The findings of this paper give the direction to design a new transport protocol that can utilize the full capacity of IEEE 802.11n mesh backbone.     

存在隐藏终端的IEEE 802.11e多跳无线网络模型分析*

首次将802.11e的接入机制放入多跳环境中进行仿真分析和定量研究。提出一种新的多跳环境下802.11e网络模型,结合M/G/1/K排队模型,定量分析在隐藏终端影响下802.11e网络的MAC层吞吐率、MAC时延和帧丢失率,研究802.11e在多跳环境下性能表现的内在原因。经过仿真实验结果与数值分析结果的对比,验证了分析模型的准确性;通过有（无）隐藏终端影响下MAC层性能的对比分析,指出了802.11e在多跳无线网络中支持QoS的局限性：受隐藏终端的影响,802.11e对不同接入等级的业务提供QoS区分的性能明显降级。因而有必要研究隐藏终端问题的解决方案,提高802.11e在多跳环境下的性能。     

存在隐藏终端的IEEE802.11e多跳无线网络模型分析

首次将802.11e的接入机制放入多跳环境中进行仿真分析和定量研究。提出一种新的多跳环境下802.11e网络模型,结合M/G/1/K排队模型,定量分析在隐藏终端影响下802.11e网络的MAC层吞吐率、MAC时延和帧丢失率,研究802.11e在多跳环境下性能表现的内在原因。经过仿真实验结果与数值分析结果的对比,验证了分析模型的准确性;通过有(无)隐藏终端影响下MAC层性能的对比分析,指出了802.11e在多跳无线网络中支持QoS的局限性:受隐藏终端的影响,802.11e对不同接入等级的业务提供QoS区分的性能明显降级。因而有必要研究隐藏终端问题的解决方案,提高802.11e在多跳环境下的性能。     

Channel measurement-based access point selection in IEEE 802.11 WLANs

With the wide deployment of IEEE 802.11 Wireless Local Area Networks, it has become common for mobile nodes (MNs) to have multiple access points (APs) to associate with. With the Received Signal Strength Indicator (RSSI)-based AP selection algorithm, which is implemented in most commercial IEEE 802.11 clients, the AP with the best signal strength is selected regardless of the candidate AP’s available throughput, resulting in unbalanced distribution of clients among the APs in the network. Several studies have shown performance improvement in not just the new MN (nMN), but also the network as a whole when the selection process considers the current load status of candidate APs. However, the proposed algorithms in these studies assume that there are no hidden terminal problems that severely affect the performance of the network. Hidden terminal problems frequently occur in wireless networks with unlicensed frequencies, like IEEE 802.11 in the 2.4 GHz band. Moreover, none of the previous studies have considered frame aggregation, a major improvement in transmission efficiency introduced and widely deployed with the IEEE 802.11n standard. In this paper, we propose a new AP selection algorithm based on the estimation of available throughput calculated with a model based on the IEEE 802.11 distributed coordination function in consideration of hidden terminal problems and frame aggregation. The proposed algorithm is evaluated through extensive simulation, and the results show that the nMN with the proposed AP selection algorithm can achieve up to 55.84% and 22.31% higher throughput compared to the traditional RSSI-based approach and the selection algorithm solely based on the network load, respectively.     

无线自组织网络中可用带宽估计准则研究

本文对无线Ad Hoc网络中可用带宽估计准则进行了研究,提出应将全局QoS保障作为带宽需求是否能被网络满足的判定条件.建立了基于IEEE 802.11 MAC协议的无线网络的分析模型并得出了时延、丢包率和吞吐量等QoS度量的解析表达式,并给出了该网络环境下的可用带宽判定准则.仿真实验证明了本文提出的分析模型的精确性与...     

Throughput analysis of IEEE 802.11 multirate WLANs with collision aware rate adaptation algorithm

This paper presents a mathematical model that analyzes the throughput of the IEEE 802.11b distributed coordination function (DCF) with the collision aware rate adaptation (CARA) algorithm. IEEE 802.11 WLANs provide multiple transmission rates to improve system throughput by adapting the transmission rate to the current channel conditions. The system throughput is determined by some stations using low transmission rates due to bad channel conditions. CARA algorithm does not disturb the existing IEEE 802.11b formats and it can be easily incorporated into the commercial wireless local area networks (WLAN) devices. Finally, we verify our findings with simulation.     

基于显式阻塞通知的自组织网络MAC协议

IEEE802.11 DCF协议利用RTS/CTS握手机制解决无线网络中重要的隐终端问题.但是该协议并不能解决所有的隐终端问题,如隐接收终端问题.本文提出一种显式阻塞通知（Explicit Blocking Notification,EBN）机制的握手协议来解决无线自组织网络中的隐接收终端问题.通过采用RTS/CTS/BN/DATA/ACK握手序列来提前通知邻居节点隐终端的当前状态,避免邻居节点盲目的分组传输.仿真结果显示,EBN机制可以获得比IEEE802.11 DCF协议更加稳定的流量,同时节约带宽资源,减小分组延迟.     

对IEEE 802.11 MAC层协议公平性改进的研究

Ad Hoc网络中基于IEEE 802.11的MAC层协议采用CSMA/CA机制,通过侦听只能获取一跳范围内节点的信息,存在隐终端问题,影响了网络流调度的公平性.文中对IEEE 802.11提出了一种修改方案,该方案通过邻居结点间的信息交换,使网络中每个节点具有其二跳范围内所有结点的信息,以发现网络中的隐终端,提高网络流调度的公平性.对比仿真实验结果表明,修改后的IEEE 802.11与原协议的网络吞吐量基本相当,但具有更好的公平性.     

Delay-Constrained Optimized Packet Aggregation in High-Speed Wireless Networks

High-speed wireless networks such as IEEE 802.11n have been introduced based on IEEE 802.11 to meet the growing demand for high-throughput and multimedia applications. It is known that the medium access control (MAC) efficiency of IEEE 802.11 decreases with increasing the physical rate. To improve efficiency, few solutions have been proposed such as Aggregation to concatenate a number of packets into a larger frame and send it at once to reduce the protocol overhead. Since transmitting larger frames eventuates to dramatic delay and jitter increase in other nodes, bounding the maximum aggregated frame size is important to satisfy delay requirements of especially multimedia applications. In this paper, we propose a scheme called Optimized Packet Aggregation (OPA) which models the network by constrained convex optimization to obtain the optimal aggregation size of each node regarding to delay constraints of other nodes. OPA attains proportionally fair sharing of the channel while satisfying delay constrains. Furthermore, reaching the optimal point is guaranteed in OPA with low complexity. Simulation results show that OPA can successfully bound delay and meet the requirements of nodes with only an insignificant throughput penalty due to limiting the aggregation size even in dynamic conditions.     

Modeling multiple hop wireless networks with varying transmission power and data rate

Wireless multi-hop networks can vary both the transmission power and modulation of links. Those two parameters provide several design choices, which influence the performance of wireless multi-hop networks, e.g. minimize energy consumption, increase throughput, reduce contention, and maximize link quality. However, only network-wide metrics are considered in previous works. Further, per-flow performance metrics, such as the end-to-end energy consumption and latency, have not been studied. Those parameters directly impact the experience of users, which should be considered in capacity and performance studies. Our model incorporates per-flow metrics while also considering fading, contention, hidden terminals and packet error probabilities. We instantiate the model into an IEEE 802.11 multi-hop scenario, and evaluate common routing decisions such as maximizing link quality, maximizing data rate or minimizing the transmission power.