【作者】 符琦；

【导师】 陈志刚；

【作者基本信息】 中南大学 ， 计算机科学与技术， 2014， 博士

【摘要】 摘要：随着无线设备制造成本的下降以及各种无线通信技术的成熟应用,作为下一代宽带接入的重要技术之一的无线Mesh网络已被广泛应用于无线宽带城市、无线校园(企业)和抗灾抢险等领域。与此同时,基于无线Mesh网络的各种音频、视频和高实时性数据业务(如VOIP、视频会议等)在商业应用上的迅速发展,使得人们对无线Mesh网络数据传输的各项QoS指标(如平均延迟、延迟抖动、带宽分配等)提出了更高的要求。然而,无线Mesh网络MAC层的分布式自由竞争模式、节点对全网信息掌握的不完全性等固有特性,都使得现有无线(有线)网络所采用的QoS保障技术很难直接应用于无线Mesh网络及其上的多媒体业务传输,因此,QoS保障问题是仍然是目前无线Mesh网络研究的热点和难点问题。本文从无线Mesh网络的MAC层、网络层和跨层设计的不同角度,对QoS保障策略进行了相关的分析研究,并提出了相应的解决方案。主要的研究工作包括以下几个部分：(1)针对802.11e的EDCA机制和单路径路由协议在QoS保障方面的不足,从跨层优化的角度,提出了一种优先级自适应的QoS路由策略。该策略通过在网络上层设定各类数据流传输的QoS阈值,并在网络层对MAC层AC队列的状态信息进行实时监控,来动态调整不同业务数据包的优先级别,同时在MAC对不同业务数据包的传输时延进行估算,以获取数据成功发送后不同AC队列的平均时延,并对队列的平均冲突概率进行统计,以自适应地调整各队列的信道竞争参数,从而更好地平衡不同类型业务流占用信道机会,以保证不同业务流之间的传输公平性,提升网络的整体传输效率。(2)针对多路径相邻链路之间的干扰对数据传输质量带来的相关问题,在现有802.11e标准EDCA机制和多路径路由相关问题分析的基础上,利用跨层优化的设计思想,定义了适应于多业务多路径传输的联合路由判据,使网络层的路由选择策略能够根据多媒体数据的业务类型和联合路由判据估算出的当前可用路径的状态与质量信息,合理地选择能满足不同业务类型QoS要求的数据传输路径,同时对EDCA静态的信道竞争参数分配方案进行了自适应改进,使其能适应于无线多跳的数据传输环境,减少了网络中数据包传输的冲突,有效地提高和满足了各类媒体业务数据的传输质量,以及网络传输的公平性。(3)针对802.11e的EDCA机制在业务区分时未能提供良好的QoS保证的问题,提出了一种基于剩余时延界限的CFB数据包转发机制,该机制在现有802.11e EDCA机制的基础上,针对由于具有较大时延界限的数据流长期占用传输信道,而导致具有较低时延界限数据流出现大量丢包、重传,从而影响整个网络的吞吐量及多数据流传输的公平性问题,通过估算数据包的剩余时延,以及动态调整TXOP的时长及CFB突发数据块的大小,来自适应网络中多优先级业务流量的变化,有效地提高了网络中各类业务数据流的吞吐量。更多还原

【Abstract】 Abstract With the cost decline of wireless equipment manufacturing and the mature application of wireless communication technology, wireless mesh networks(WMNs), as one important next generation of broadband wireless access technologies, has been widely applied in wireless broadband city, wireless campus (enterprise) and disaster rescue, etc. Meanwhile, various business applications of audio, video and high real-time data services (e.g. VoIP, video conference, etc.) based on WMNs are developing rapidly so that they give higher requests to the QoS indicators (e.g. average delay, delay jitter and bandwidth allocation, etc.) of WMNs. However, some inherent features, such as model of distributed free competition at MAC layer, incompleteness entire networks information, will make QoS over WMNs very difficult compared to existed wireless(wired) networks QoS technology for multimedia transmission. So how to guarantee the QoS of multimedia transmission service is still a hotspot and difficult problem in WMNs open research.Aimed at the network architecture, characteristics and QoS problem in multimedia application of WMNs, this paper analyse some QoS schemes designed from different perspectives of MAC layer, route layer and cross-layer. Then some solutions and analyses are discussed. The main research work in this paper includes:(1) On the issues of performance lacking of quality of service (QoS) in EDCA mechanism and single-path routing protocol, an adaptive priority-based QoS routing scheme is proposed from the perspective of closs-layer design. This scheme configures some threshold values of the QoS parameters for each multimedia flow in the upper layer, then monitors the real-time information of the AC queues at MAC layer to dynamicly adjust the priority of each multimedia data suited to different AC queues. At the same time, it estimates the transmission delay of the different multimedia data to get the average transmission delay of each AC queues when the data is successfully transferred. With these information above, the scheme can balance the chances of channel occupation between different multimedia flows and make sure that they can be fairly transmitted to promote the whole performance of the networks.(2) To address the related QoS problem caused by the links’ interference in multi-path data transmission,this paper analyses the EDCA mechanism in the IEEE802.11e standard and mulit-path routing technology, then defines some jointed routing metrics based on cross-layer design.By these jointed routing metrics, routing selection scheme can choose the effective forward routing to meet the different multimedia flows’ QoS requirements. The scheme also adopts an improved adaptive parameter assignment method used to channel competition in EDCA and make it can fit the environment of multi-hop transmission.This method can effectively reduce the confliction of data transmission and promote the quality and fairness service of different multimedia transmission.(3) For the lack of QoS supporting in differentiated service of EDCA mechanism in802.11e, a margin delay-bounded based CFB data forwarding scheme is proposed. Aimed at the throughput and fairness problem of the long time occupation of data flow with a longer delay bound, which causes a lot of packet loss and retransmission of data flow with a shorter delay bound value, this scheme estimates the magrin delay bound of data packets and dynamicly adjust the TXOP values and the CFB block values to meet the changes of different multimedia flows and effectivley promote the throughput performance of these flows.更多还原