【作者】 吴玮；

【导师】 张中兆；

【作者基本信息】 哈尔滨工业大学 ， 信息与通信工程， 2011， 博士

【摘要】 随着无线通信技术的发展和便携设备的不断普及,人们对于低成本、易用的无线网络需求日益增长。而Ad Hoc网络以其优越的自组织特性被认为是最理想的未来移动网络候选构架之一。Ad Hoc网络是一种由若干无线数据传输设备临时组成的、不需要固定通信设施支持的无中心网络。网络节点既是通信终端,又可作为路由器,为其它节点转发数据。Ad Hoc网络节点可以自行组织成网,实现分布式管理。Ad Hoc网络在野外作战、抢险救灾、临时会议、无线家庭网络等军用和民用通信领域都得到广泛的应用。Ad Hoc网络的研究热点主要包括:路由协议、MAC协议、拥塞控制、跨层设计、安全性、QoS保证技术、功率控制与管理、传输层协议等。拥塞问题是制约Ad Hoc网络性能的一个重要因素。Ad Hoc网络节点既有收发任务,还要为其他节点转发数据。有些节点会成为多个数据流的交汇点,因此有很多数据包需要此点排队处理。但如果这种情况持续发生,当缓存耗尽节点就会丢弃数据包,在这些节点上极可能产生拥塞的情况。拥塞会导致整个网络性能的恶化,造成网络的吞吐量降低、丢包率增大、时延增大和开销增加等等。本文针对Ad Hoc网络的拥塞问题,在充分分析和论证各种用于解决拥塞问题的方法基础上,对以下几个方面进行了深入研究:第一,Ad Hoc网络节点的拥塞检测方法。针对Ad Hoc网络拥塞的特点,本文提出了一种基于拥塞趋势度的Ad Hoc网络拥塞检测方法。拥塞趋势度将缓存队列长度和MAC层输入、输出速率相结合,表示了节点缓存到达满载的速率。该方法不仅可以测量节点拥塞程度,还可以反映节点拥塞的变化趋势。为进一步采取适当的拥塞缓解措施,解决网络拥塞问题提供了准确可靠的信息。第二,Ad Hoc网络拥塞缓解路由协议。针对传统Ad Hoc网络路由协议通常以跳数最少作为路由查找的标准,往往忽略了网络拥塞对Ad Hoc网络性能的影响,本文提出了一种基于节点传输势能的Ad Hoc网络拥塞缓解路由协议AH-RBP(Ad Hoc Routing Based on Potential)。AH-RBP协议是一种多路径的Ad Hoc网络协议,通过对节点拥塞情况的检测,给网络中节点赋予适当的传输势能,根据节点的传输势能使数据包沿着拥塞程度较低且路径较短的路由来传输,这样可以使路由绕过拥塞节点,缓解拥塞对网络性能的影响,提高Ad Hoc网络吞吐量、降低丢包率。第三,Ad Hoc网络速率自适应MAC协议。速率自适应MAC协议可以提高信道利用率。但当拥塞发生时,在信道质量较好的链路上以较高速率发送大量数据,会使拥塞进一步恶化。因此,本文提出一种基于拥塞检测的Ad Hoc网络速率自适应MAC协议ARCD(Auto Rate based on Congestion Detection)。ARCD协议根据信道质量选择适当的传输速率,并根据节点的拥塞情况和信道质量来选择一次接入信道后连续发包的数量。ARCD协议可以在信道质量好,节点拥塞程度较低的时候以较高速率连续传输较多的数据包;在信道质量不好,节点拥塞程度较高时,以较低速率发送较少的数据包。ARCD协议可以提高信道资源的利用率,降低由于信道竞争所带来的控制开销,缓解节点拥塞程度,从而提高网络性能。更多还原

【Abstract】 With the development of wireless communication technology and the prevalence of portable devices, the demands of wireless networks with low cost and easy deployment characters keep increasing. Ad Hoc network is thought to be one of the most competitive candidates for the next generation mobile networks, because of its the characteristic of self-organization. Ad Hoc network is a network formed without any central administration which consists of mobile nodes that use a wireless interface to send packet data. The nodes in Ad Hoc networks can serve as routers and hosts, and forward packets for the other nodes. Nodes in Ad Hoc networks can self-organize and realize distributed management. They are widely used in military and civil communication fields such as urgent search, temporary conference and wireless home network.The research hotpots of Ad Hoc networks include: routing protocol, MAC protocol, congestion control, cross layer design, security of network, QoS guarantee, power control and management, transport layer protocol, and so on.Congestion is one of the most important restrictions of Ad Hoc networks. Nodes transmit and receive packets for theirselves and forward packets for others, some of them may become the junctions of several flows, and these nodes are very likely to be congested. Many packets may be accumulated at congested nodes and discarded finally. Congestion may lead to long delay, high overhead and low throughput in wireless Ad Hoc networks. According to analyses of congestion control methods, this paper researches on several aspects about congestion problem in Ad Hoc networks as follows.Firstly, congestion detection method for Ad Hoc networks. According to the characteristics of congestion in Ad Hoc networks, a congestion detection method for Ad Hoc networks, based on Congestion Trend Degree, is proposed. This method combines queue occupancy with input rate and output rate in MAC layer, and it indicates the rate at which the queue goes to full. This method can measure congestion level accurately and timely, and what’s more it can predict the congestion tendency, it can provide accurate information for congestion control methods.Secondely, routing protocol for mitigating congestion in Ad Hoc networks. Routing protocols designed for Ad Hoc networks usually take the shortest path as the routing metric, and always neglect the influence caused by congestion in Ad Hoc networks. A routing protocol for mitigating congestion in Ad Hoc networks is presented in this thesis, called AH-RBP(Ad Hoc Routing Based on Potential). AH-RBP is a multipath routing protocol. The nodes are assigned transmission potential values by congestion detection, and packets route along the shorter path with lower congestion level based on the transmission potential. AH-RBP can mitigate the congestion influence, improve the throughput and packet delivery ratio.Thirdly, Auto rate MAC protocol. Auto rate MAC protocols can improve the channel utilization. However, When congestion occurs, if nodes transmit too much packets at a high rate in a good channel, congestion levels will badly increase. an auto rate MAC protocol for Ad Hoc networks based on congestion detection, called ARCD(Auto Rate based on Congestion Detection) is proposed. ARCD protocol selects transmission rate according to the channel condition, and determines the number of back-to-back packet according to the channel condition and congestion detection. Nodes transmit more back-to-back packets at higher rate when the channel is good and congestion level is low, and transmit less back-to-back packets at lower rate when the channel is bad and congestion level is high. ARCD protocol can improve the channel utilization, decrease the control overhead for channel contention, and mitigate congestion level.更多还原