基于802.11e的无线Mesh网络中视频传输优化方案

针对无线Mesh网络环境下视频数据传输的延迟、吞吐量、丢包率等问题,改进了一种数据映射方案,将不同重要程度的数据与IEEE 802.11e中的接入类别相对应,优先发送级别高的数据。对压缩视频数据传输进行了仿真实验,并对仿真结果进行了分析,证明了在不同的网络业务负载下,改进的映射方案对网络性能有一定的改善。     

802.11无线网状网中基于时频信道的准动态信道分配算法

该文首次在多天线多信道802.11无线网状网中提出了时频信道的概念。时频信道是通过在时间和频率两个维度划分无线资源取得的。这种划分方法增加了信道数量,使信道划分更加精细,为提高系统的信道利用率做了准备。在时频信道的基础上,提出了准动态信道分配算法。该算法可以和现有的固定信道分配算法结合,实现准动态信道分配,根据链路上负载变化,取得最大的吞吐量。该算法先根据固定信道分配算法为各链路分配相同数量的时频信道,剩余部分当作公共信道。在通信过程中,各链路首先使用分配给自己的信道和空闲的公共信道。如果分配给一个链路的信道不够,且别的链路上的信道有空闲,该链路还可以暂时使用这些空闲信道。理论分析和仿真结果证明该算法可以有效提高系统的吞吐量。     

Provisioning of Parameterized Quality of Service in 802.11e Based Wireless Mesh Networks

There has been a growing interest in the use of wireless mesh networks. Today’s wireless technology enables very high data rate up to hundreds of Megabits per second, which creates the high demand of supporting real-time multimedia applications over wireless mesh networks. Hence it is imperative to support quality of service (QoS) in wireless mesh networks. In this paper, we design a framework to provide parameterized QoS in 802.11e based wireless mesh networks. Our framework consists of admission control algorithms and scheduling algorithms, which aim at supporting constant bit-rate (CBR) traffic flows, as well as variable bit-rate (VBR) traffic flows. We first present deterministic end-to-end delay bounds for CBR traffic. We then prove that the delay of VBR traffic can be bounded if the traffic flow conforms to a leaky-bucket regulator. We further study different admission control algorithms for VBR traffic. Our simulation results show that, by taking advantage of statistical multiplexing, much more traffic flows can be admitted.     

Achieving End-to-end Fairness in 802.11e Based Wireless Multi-Hop Mesh Networks Without Coordination

To mitigate the damaging impacts caused by interference and hidden terminals, it has been proposed to use orthogonal channels in wireless multi-hop mesh networks. We demonstrate however that even if these issues are completely eliminated with perfectly assigned channels, gross unfairness can still exist amongst competing flows which traverse multiple hops. We propose the use of 802.11e’s TXOP mechanism to restore/enforce fairness. The proposed scheme is simple, implementable using off-the-shelf devices and fully decentralised (requires no message passing).     

Adaptive Physical Carrier Sense in Topology-Controlled Wireless Networks

Transmit power and carrier sense threshold are key MAC/PHY parameters in carrier sense multiple access (CSMA) wireless networks. Transmit power control has been extensively studied in the context of topology control. However, the effect of carrier sense threshold on topology control has not been properly investigated in spite of its crucial role. Our key motivation is that the performance of a topology-controlled network may become worse than that of a network without any topology control unless carrier sense threshold is properly chosen. In order to remedy this deficiency of conventional topology control, we present a framework on how to incorporate physical carrier sense into topology control. We identify that joint control of transmit power and carrier sense threshold can be efficiently divided into topology control and carrier sense adaptation. We devise a distributed carrier sense update algorithm (DCUA), by which each node drives its carrier sense threshold toward a desirable operating point in a fully distributed manner. We derive a sufficient condition for the convergence of DCUA. To demonstrate the utility of integrating physical carrier sense into topology control, we equip a localized topology control algorithm, LMST, with the capability of DCUA. Simulation studies show that LMST-DCUA significantly outperforms LMST and the standard CSMA protocol.     

A Distributed End-to-End Reservation Protocol for IEEE 802.11-Based Wireless Mesh Networks

This paper presents an end-to-end reservation protocol for quality-of-service (QoS) support in the medium access control layer of wireless multihop mesh networks. It reserves periodically repeating time slots for QoS-demanding applications, while retaining the distributed coordination function (DCF) for best effort applications. The key features of the new protocol, called "distributed end-to-end allocation of time slots for real-time traffic (DARE), are distributed setup, interference protection, and scheduling of real-time data packets, as well as the repair of broken reservations and the release of unused reservations. A simulation-based performance study compares the delay and throughput of DARE with those of DCF and the priority-based enhanced distributed channel access (EDCA) used in IEEE 802.11e. In contrast to DCF and EDCA, DARE has a low, nonvarying delay and a constant throughput for each reserved flow     

无线Ad hoc网络一种最小化链路干扰的载波监听机制设计

无线Ad hoc网络中,干扰产生于接收节点处的接收信号被其他无用信号叠加,干扰问题严重影响接收端解码信息的能力,导致数据包冲突和重传的增加.如何最小化链路干扰,减少数据包冲突概率,是提高网络性能的关键.MAC协议中,合理的载波监听机制是减小链路干扰的有效方式之一,通过合适的感知门限设计,可以有效地降低链路中的干扰和冲突...     

基于IEEE802.11s的多射频多信道无线mesh网络路由判据的探究

无线mesh网络是下一代无线网络技术中人们研究与关注的热点技术之一。根据最新IEEE 802.11s协议,其路由判据是基于无线感知的空时链路判据(airtime link metric,ALM)。这种路由判据比传统的以跳数作为判据要好,但是当多信道或多射频条件下时,这种判据会引起信道容量的衰减,不足以满足如今的网络需求。因此,有许多新的路由判据被提出。例如,加权累计期望传输时间,干扰及信道切换,归一化的瓶颈链路容量等。本文主要定性的比较这些判据的特点,然后通过NS-2进行网络仿真,根据IEEE 802.11s协议中默认的路由协议,将这些多信道条件下的路由判据进行相互比较。由此,得出结论,明确各种路由判据所适用的不同的场合。     

无线Mesh网络综述

无线Mesh网络是无线局域网和移动自组织网络相结合的产物,是一种全新的网络架构,有着极大的应用前景。简要介绍了无线Mesh网络体系结构、特点和应用领域,总结了无线Mesh网络路由协议的研究状况,探讨了存在的问题和今后发展的方向。     

On a Distributed Cognitive MAC Protocol for IEEE 802.11s Wireless Mesh Networks

A distributed frequency agile medium access control (MAC) extension to the IEEE 802.11s for the next generation wireless mesh networks is proposed. The introduced protocol enhancements are capable of concurrent deployment of existing frequency opportunities in order to coordinate simultaneous data transmissions. The root concept is mainly based on the deployment of well-known ISM frequency bands, where the legacy 802.11-based wireless equipments operate, as the common control channel in order to establish contemporaneous transmissions. We apply the aforementioned key concept to the IEEE 802.11s common channel framework to attain two important goals: To improve the channel utilization using the concept of cognitive radio, and to lower the access delay. Through extensive event-driven simulations, taking into account primary user appearance in non-ISM frequency bands, performance of the proposed MAC enhancement is evaluated showing its higher efficiency compared to the existing solutions, in addition to its better wireless medium management.     

基于无线Mesh网络的交通信息系统

本文提出了一种基于无线Mesh网络的交通信息系统,系统由探测汽车采集实时交通信息,依托无线Mesh网络将采集得到的信息发送到信息处理中心.该系统能够提供准确实时的路况信息,无需大量固定基础设施支持,具有建设成本低、周期短、维护费用低的特点,特别适合我国交通事业发展的现状.     

IEEE 802.11无线网络的两步指数退避算法

IEEE 802.11标准引入二进制指数退避(Binary Exponential Backoff, BEB) 算法以降低节点发送数据包碰撞的概率。然而,BEB存在着不足之处,当数据包碰撞概率较大时,节点的竞争窗口长度会出现振荡,即节点每次发送数据包之前,需要多次加倍扩大竞争窗口长度,而在发送成功之后又把竞争窗口长度缩小到最小值,这个过程反复出现。为了克服竞争窗口振荡问题以增加吞吐量,该文提出两步指数退避(Two-step BEB, TBEB)算法,利用2维马尔可夫链进行建模,导出TBEB算法中节点的退避状态概率分布、平均竞争窗口长度、平均退避次数、每发送一个数据帧所耗时间以及吞吐量等指标,并通过仿真进行验证。通过求解一个简单的优化问题,TBEB可以获得最优竞争窗口长度复位值,使吞吐量达到最优。     

Distributed Contention-Aware Call Admission Control for IEEE 802.11 Multi-Radio Multi-Rate Multi-Channel Wireless Mesh Networks

In this paper, we focus on call admission control (CAC) in IEEE 802.11 multi-radio multi-rate multi-channel (MR²-MC) wireless mesh networks (WMNs). CAC is the key component of QoS routing protocols. The goal of CAC is to protect existing flows from QoS violations and fully utilize available radio resource on channels. We propose a CAC mechanism, called Contention-Aware Multi-channel Call Admission Control (CMC), for MR²-MC WMNs based on IEEE 802.11 DCF. CMC is fully distributed, relies on local information to estimate the residual bandwidth of a path, and can be integrated into existing routing protocols for MR²-MC WMNs to provide QoS. We evaluate the performance of CMC via ns-2 simulations. The results show that CMC can precisely predict the end-to-end residual bandwidths of paths, successfully protects existing flows from QoS violations, and fully utilizes the bandwidths on channels.     

基于ECC的无线Mesh网络身份认证方案

文章对于无线Mesh网络环境,提出了一种基于ECC的双向身份认证方案。方案采用公钥证书、Hash函数等技术,不仅提供了安全的身份认证和密钥协商功能,而且具有运算量小、传输参数少的优点,较容易在无线Mesh网络中实现。     

IEEE 802.11 Wireless Local Area Networks

The draft IEEE 802.11 wireless local area network (WLAN) specification is approaching completion. In this article, the IEEE 802.11 protocol is explained, with particular emphasis on the medium access control sublayer. Performance results are provided for packetized data and a combination of packetized data and voice over the WLAN. Our performance investigation reveals that an IEEE 802.11 network may be able to carry traffic with time-bounded requirements using the point coordination function. However, our findings suggest that packetized voice traffic must be handled in conjunction with an echo canceler     

无线Mesh技术和网络

无线网状网（WMN）是近年被高度重视和快速发展的新型网络技术,支持宽带高速多媒体业务服务。文章就无线Mesh网络技术和应用进行讨论,综述无线Mesh网络的发展由来、基本技术、典型应用和现在的发展。随着未来无线分布技术和无线分布网络的发展,无线Mesh技术和网络将会成为无线移动通信的基本网络技术和网络结构,渗透到各种无线网络中,发挥更大作用。     

新一代无线Mesh网络

无线Mesh网络是下一代无线网络的关键技术之一,近几年得到了人们的广泛关注和快速发展.为了以低成本的代价实现无处不在的高速Intemet,新一代无线Mesh网络的发展势在必行.新一代无线Mesh网络旨在能够提供高性能和高可靠性的服务.本文介绍了传统无线Me8h网络的优缺点,分析了研究现状,并阐诛了新一代无线Mesh网络面临的技术挑战.     

802.11 Mesh network中WBDMR分布式路由协议的研究

提出了一种适用于中等规模的802．11 Mesh network网络的无线分布式路由协议（WBDMR）。该协议借鉴了基于Ad-Hoc 的ADOV协议并进行了改造,实现了不同BSS（基本服务集）间无线客户端通过无线中继相互通信。利用节点间交换链路损耗信息实现了动态负载平衡、有效地抑制了冗余路由信息的传播、消除了路由环路、建立了备份路由。仿真结果表明,WBDMR协议具有较好的路由特性和时延特性。