Ad hoc网络中QoS关键技术的研究

【作者】 朱颖；

【导师】 武穆清；

【作者基本信息】 北京邮电大学 ， 通信与信息系统， 2008， 博士

【摘要】 Ad hoc网络(MANETs,Mobile Ad hoc Networks)是一种由无线移动节点组成的具有任意和临时性网络拓扑的动态自组织网络系统。组成网络的节点既具有通信终端的功能,又具有路由器的功能,并可自由移动。其业务数据以无线多跳的方式传送,而无需基础设施的支持。由于Ad hoc网络具有较高的灵活性、移动性、自组织性以及随时随地接入等特点,已广泛用于野战通信、自然灾害、紧急救助、临时会议、智能交通、环境监测和旅游探险等各种军用、民用和商用领域,具有广阔的应用前景,是目前国内外的一个研究热点。而应用领域的不断扩展要求无线Ad hoc网络能够为不同业务提供不同的服务质量QoS(Quality of Service)。特别是目前日益增多的音频、视频和高实时性的数据业务都对网络传输平均延迟、延迟抖动、优先级划分、带宽分配等提出了更高的要求。然而,无线Ad hoc网络的多跳性和分布式特性,除带来了组网简单和灵活的特点以外,同时也为其提供服务质量保障带来了巨大的挑战。由于Adhoc网络中媒体接入控制层的分布式自由竞争模式、单跳传输范围的有限性、全网时钟的不同步性、节点对全网信息掌握的不完全性和节点移动导致频繁的网络拓扑改变,都使得无论是固网还是其它有中心结构的无线移动网络所采用的服务质量保障技术很难直接用于Ad hoc网络,因此服务质量保障问题是目前无线Adhoc网络研究的一个难点。另外,Ad hoc网络的特殊性使得各协议层面之间的性能关联很大,这使得其服务质量保障问题并非可以在某一个层次中完全加以解决,所以需要每一个层面都支持服务质量保障技术。正因如此,本论文在完成国家自然基金项目(基于MPLS的Ad hoc无线移动网络关键技术的研究,项目编号60372101和具有感知能力的自适应可重配置Ad hoc网络,项目编号60772109)的过程中,针对Ad hoc网络的特点,分别对其网络层、媒体接入控制层MAC(Medium Access Control)和传输层做了比较深入和系统的研究,并取得了一些创新性的研究成果,主要内容包括:1.简要地介绍了Ad hoc网络的发展史,分析Ad hoc网络的特点、应用前景、研究热点及发展趋势,阐述本论文的立项依据、创新点及研究成果。2.介绍了Ad hoc网络的协议体系结构,综述了目前Ad hoc网络中网络层和媒体接入控制层的协议研究,描述了目前Ad hoc网络中已有的几种服务质量保障框架。3.首先为增强Ad hoc网络的路由健壮性和改善拥塞情况,提出了一种多径路由协议TRND-AODV,在一次路由的过程中同时建立多条节点完全独立的路径。在此基础上,通过将基于Ad hoc路由协议的网络层技术与MPLS的交换技术相结合,提出一种节点独立多径标签交换路由协议AODLS和基于MPLS的Ad hoc无线移动网络模型,使Ad hoc网络不仅能够支持传统的、无连接的IP服务,还能应用于移动MPLS网络。4.借鉴TCP拥塞控制中的慢启动窗口机制提出了一种乘性递增-慢启动递减的MAC层信道接入算法MISSD,在兼顾节点公平性的同时提高网络的带宽利用率。而为进一步在不同网络规模和网络负载情况下都能较好地改善网络的拥塞状况并达到或逼近最佳的网络性能,提出了一种基于最优化参数逼近的MAC层自适应退避算法SAOP,可较好地适用于单跳的无线局域网。5.总结了无线局域网中低优先级业务增多而影响高优先级业务的原因,在用RTS多预约策略进行优先级区分的同时,通过监控网络状态并动态调整算法参数,提出了两种自适应参数调整的多优先级MAC接入算法SAQMR和MRDCW,可以对无线局域网中高优先级业务的服务质量提供更好的保护。6.为解决多跳的Ad hoc网络中转发节点拥塞和低优先级业务增多而影响高优先级业务带宽的问题,在仔细分析无线多跳环境中节点之间的相互影响情况的基础上,提出了一种多跳网络服务质量保证框架WMHQ和自适应合作式MAC层信道接入算法QAC-EDCA。通过实现三层优先级机制、多跳协调机制和接收避免策略较好地保护了多跳Ad hoc网络中高优先级业务的服务质量。7.分析了传输控制协议TCP在Ad hoc网络中存在的问题,提出了一种跨层解决方案,通过提出的CFCA信道接入机制改善TCP-ACK包在MAC层信道接入能力的方法提高Ad hoc网络中TCP协议的性能。通过以上研究,为Ad hoc网络从MAC层到传输层提供了一套比较完整的服务质量保障机制。更多还原

【Abstract】 The Mobile Ad hoc network (MANET) is a dynamic and self-organized network system with temporary network topology, which is composed of mobile stations with wireless transceivers and receivers. Each mobile station can serve not only as a communication terminal but also as a router node. And the data packet is relayed hop-by-hop between two adjacent nodes, without any supports of infrastructure. The distinguish features of the network, such as convenience, flexibility, mobility, self-organization and connecting at any time or any location etc, make Ad hoc network deployed broadly in many military area, civil area and commercial area such as battle communication, disaster relief, emergency rescue, temporary meeting, intelligent transport, exploration and so on. Nowadays, Ad hoc network is a hot research area in home and abroad and has broad prospect.With the increasingly application of the Ad hoc network, the demanding for supporting different quality of service (QoS) in the network arises. Especially the audio, video and real time data communication applications require strict QoS guarantee such as delay, delay jitter, priority differentiation and Bandwidth Allocation. Although the multi-hop and distribution feature makes the Ad hoc network’s constructing more convenient and flexible, it also makes QoS supporting a huge challenge. Because of the distributed free contention access mode in Medium Access Control (MAC) layer, the limited transmission range, asynchronous station clock, not understanding fully about network status and frequent changing of network topology by node moving in Ad hoc network, many QoS technology used in fixed network and some mobile wireless network with point center facility can not be transplanted to Ad hoc network directly. So QoS guarantee is a difficulty for Ad hoc researchers. In Ad hoc network, solving QoS problem in a certain layer is impossible because there are too much influence among protocol layers. So, every protocol layer must offer QoS support technology. As a result, this dissertation conducts in-depth and systematical research in network layer, MAC layer and transport layer of the Ad hoc network, when participating in National Natural Science Fund Project 60372101 and 60772109, and makes some innovative research results:1. Briefly introduces the history of Ad hoc, analyze the characteristic, the main hot spots, application future, development trend of Ad hoc networks, and then present the research background, contents and innovations of this dissertation. 2. Mainly discusses the protocol stack structure of Ad hoc networks, concludes the present research on transport layer, network layer and MAC layer, and describes the QoS guarantee model in Ad hoc network.3. Firstly proposes a multi-path routing protocol TRND-AODV to enhance the routing stability and avoid congestion in Ad hoc, which can realize node disjoint multi-path routing in one routing process. Based on this routing algorithm, a network model and a node disjoint multi-path routing protocol AODLS are proposed, through combining the routing techniques in Ad hoc with the label fast-forwarding techniques in MPLS. It makes the Ad hoc can adapt to the mobile MPLS network.4. Using the slow start window principle in TCP congestion control scheme, a MAC backoff algorithm called MISSD for IEEE 802.11 DCF is proposed, to enhance the node fairness and the network bandwidth utilization. And then in order to improve the network congestion status and achieve or approach the optimum performance in different network scale, a self-adaptive backoff algorithm SAOP based on Optimum Parameter approaching is proposed, which can be applied to WLAN well.5. Summarizes the reason that increasing of low priority data stream influence high priority throughput in WLAN, then two self-adaptive multiple priority algorithm named SAQMR and MRDCW are proposed to protect high priority quality of service better by using RTS multiple reservation priority differentiating and inspecting network status to adjust algorithm parameter dynamically.6. To avoid the relay congestion and guarantee high priority QoS in Ad hoc, a multi-hop network QoS model named WMHQ and adaptive cooperation channel access algorithm named QAC-EDCA with three layer priority mechanism, multi-hop coordination mechanism and reception avoiding Strategy are proposed through analyzing the influence on each other of multi-hop nodes in Ad hoc surrounding.7. Analyzes the problem of transport layer protocol TCP existing in Ad hoc network, a cross-layer solution is proposed, which transfer the TCP-ACK. packet through the CFCA algorithm.Through the research above, the aim of this dissertation is to provide a complete QoS solution mechanism from the MAC layer to transport layer for Ad hoc networks.更多还原