【作者】 李瑞芳；

【导师】 李仁发；

【作者基本信息】 湖南大学 ， 通信与信息系统， 2006， 硕士

【摘要】 Ad Hoc网络是由一系列带有无线收发装置的移动主机结点组成的多跳、无固定基站和中心结点的临时性自治网络系统。它具有组网快捷、灵活,且不受有线网络约束的特点,可广泛应用于军事行动、紧急搜索、灾难救助等多种场合,具有广阔的应用前景。Ad Hoc网络中,在单信道条件下,所有移动结点共享一个无线信道,信道资源是非常有限的,因而需要一个有效的MAC(Medium Access Control)协议来协调各结点对信道的访问。同时,由于Ad Hoc网络的应用环境以及多媒体业务流在网络中传输需求Ad Hoc网络支持QoS,且MAC协议是上层各种协议和机制所提供的QoS能否得到保障的一个关键因素,所以设计一个简单有效并能提供服务区分的MAC协议显得至关重要,而退避算法又是制约MAC层公平性以及提供服务区分的关键之所在。该文首先对Ad Hoc网络的概念、特性及研究难点等相关问题进行了介绍,然后对Ad Hoc网络信道接入退避算法的研究成果及其所面临的问题进行了探讨。着重分析了在Ad Hoc网络下,如何改善信道接入的公平性和提供服务区分等问题,进而提出了一种公平服务区分动态退避算法(FSDDB,Fair Service Differentiation Dynamic Backoff),目标是实现一种合理有效的适用于Ad Hoc网络中支持QoS的信道接入退避算法,达到公平退避,同时实现服务区分,以提供对传输包括实时多媒体业务在内的综合业务的支持,并且提高Ad Hoc网络信道接入的公平性。通过在Linux系统下利用Network Simulator(NS2)仿真工具对算法进行计算机仿真分析,结果表明,与IEEE 802.11标准采用的二进制指数退避(BEB)算法相比,该文所提算法更简单、高效,它能在很大程度上提高Ad Hoc网络信道接入的公平性,并能动态地提供服务区分,保障对多媒体等多种实时业务的传输需求,同时,算法可以根据网络当前具体的竞争激烈情况,动态调整退避时间值,从而提高信道的利用率。更多还原

【Abstract】 Ad hoc Network is a network formed by a series of mobile hosts with wireless transceivers. It is a multi-hop and instant self-organizing network without the aid of any established infrastructure or centralized administration. Ad hoc Network can be built up rapidly and flexibly, and it is free from the restriction of wired network, therefore, it can be widely applied to such situations as: military action, emergency search, disaster rescue. In Ad hoc Network, the channel resource is limited due to all of the mobile nodes sharing the same wireless channel under the condition of single channel. Therefore, an effective MAC protocol is required to coordinate the access of the nodes to the channel. At the same time, the application environments and potential applications in commerce require that wireless ad hoc networks should support Quality-of-Service (QoS). A QoS-aware MAC protocol is a key factor for QoS supporting components at upper layers. The simple effective and providing service differentiation MAC protocols are therefore very important, and the backoff algorithm is the key of restricting MAC fairness and providing service differentiation.At first, the characteristics of Ad hoc Network and its related techniques are reviewed in this thesis. Afterwards, the relevant research results and the problems of Ad hoc Network’s MAC protocols are studied deeply. Great attentions are paid to fair scheduling issues and service differentiation. Then proposes a Fair Service Differentiation Dynamic Backoff (FSDDB) algorithm, which can provide service differentiation of the traffic flows dynamically while achieving fair access to all mobile nodes. Simulation is operated with NS2 under Linux, and the simulation results show that, the presented algorithm is simpler and more practical, while it can improve the fairness index of Ad hoc Network to a large extent compared with the IEEE802.11 Binary Exponential Backoff (BEB) algorithm. It can make better use of the wireless channel by dynamically adjusting its backoff timer according to the network’s contest situation. In addition, service differentiation can be achieved among flows with different QoS requirements and thus the QoS for Medium Access Control in Ad hoc network is improved.更多还原