【作者】 夏卓群；

【导师】 陈志刚； 赵明；

【作者基本信息】 中南大学 ， 计算机科学与技术， 2012， 博士

【摘要】 无线Mesh网络是一种具有广泛应用前景的无线接入系统,而目前无线Mesh网络中存在一些挑战需要解决,如网络吞吐量受限、服务质量得不到保障等。网络编码允许网络节点对接收的数据包进行加工处理,为解决无线Mesh网络问题提供了一条新途径。本文研究基于网络编码的无线Mesh网络传输关键技术,主要从传输结构和传输特性两个方面展开。针对无线Mesh网络具有多路径传输结构,本文提出基于多路径的分段网络编码算法,并研究了与多路径分段网络编码适应的传输控制协议MPTCP,研究了多路径网络编码中节点的博弈；针对无线Mesh网络的传输特性,本文提出了基于机会路由的确定性网络编码和低时延网络编码算法,提出了自相似流量中基于同步的网络编码算法。本文对基于网络编码的无线Mesh网络传输关键技术进行了深入研究,主要工作如下：(1)针对无线网络多路径传输中数据包部分出错而丢弃的问题,提出了一种基于多路径的分段网络编码算法,并且设计了适应多路径分段网络编码的,PTCP。提出的基于多路径的分段网络编码算法是多路径中的传输节点将数据包以段为单位进行编码,然后把编码后的多份数据沿多条路径进行传输,有效地降低数据包因出错而重传,减少通信量。此外提出了一种适应分段网络编码的MPTCP。在提出的方案中,网络编码层被加入到现有的网络系统,根据目的节点解码数据块的解码自由度,源节点调整发送编码的数据块,实现降低多路径传输中编码数据包超时的影响,提高网络的吞吐量。仿真结果表明所提的算法有效。(2)针对多路径传输路径中存在自私节点使网络性能下降的问题,本文研究了基于博弈理论的多路径流间网络编码,并提出一种对多路径网络编码中自私节点的激励方案。本文研究了多路径流间网络编码中节点的博弈,证明其存在纳什均衡；得到有关多路径网络编码节点博弈的特性。然后,本文提出了一种适合多路径网络编码节点博弈的激励方案。在多路径传输中,使用看门狗检测自私节点的存在。在检测到自私节点后,对于多路径中的自私节点,采用不合作的方法惩罚。证明了如果按照激励方案,各节点可以达到纳什均衡。仿真验证了理论分析。(3)针对目前无线Mesh网络无法满足流媒体的服务质量问题,本文研究了机会路由转发侯选集中编码节点选择的问题,提出一种基于机会路由的确定性网络编码。采用机会路由下无线Mesh网络的链路吞吐量模型,利用确定性网络演算理论,得到无线Mesh网络节点数据积压的上界以及端到端数据流延迟和抖动的上界；然后设计满足流媒体服务质量的确定性网络编码(DNC),提出ETC作为确定机会路由中编码节点的指标；提出ETP作为机会路由中选择候选节点的指标。仿真表明吞吐量在增加的同时,端到端的延时和抖动值得到下降。(4)针对现有基于机会路由的网络编码解码延迟较高,无法满足流媒体无线Mesh网络要求的问题,提出一种低时延的网络编码。该低时延网络编码包括可变长度网络编码和候选节点反馈。提出和详细分析了基于机会路由的可变长度网络编码(VLNC)的编码和解码延迟,可靠性；然后提出了候选结点反馈(CNF)编码数据包的方法。给出了低时延网络编码的算法,在候选结点采用计数器来保证中间节点输出相同秩,在目的节点不能构成满秩解码矩阵时,向候选节点反馈查找所需要的解码向量,实现缩短解码时间。通过仿真,结果表明所提出的低时延网络编码能够降低时延,可以满足无线Mesh网络中流媒体应用。(5)针对自相似流会造成网络中队列长度增加、数据包丢失增加的问题,本文提出自相似流中基于同步的网络编码算法。在网络中发生突发性自相似流量后,采用基于同步的网络编码算法来提高无线Mesh网络性能。该算法是基于数据包的目的地址和长度进行分类后实现的,适合在突发性自相似流中使用,通过仿真验证了算法的有效性,降低了队列的长度和数据包延时。更多还原

【Abstract】 Wireless mesh network (WMN) is becoming a major paradigm for constructing user access networks that provide community or city-wide Internet connectivity. However, there are some challenges in wireless mesh networks.For example,a major barrier for the adoption of wireless mesh networks is severe limits on throughput;and the quality of service (QoS) can not be guaranteed.The network coding, as a new technique which relay nodes in the network not only forward but also process the incoming information flows, will have a good application in wireless mesh network.In our work,there are two routes in the research process of the key technologies for transmission based on the network coding in the wireless mesh network. The first route is transmission construction, and the other route is transmission character of WMN.To the first one, we propose a segment network coding (SNC) based on multipath to improve throughput.Furthermore, a mechanism of multipath transmission control protocol (MPTCP) that naturally adds network coding layer to current network systems is designed; and the game thory is investigated in the selfish nodes of multipath. In the second route of our research, we put emphasis on the network coding based on opportunistic routing; and the network coding based on synchronization is used to improve the performance of self-similar traffic. Through the two researching routes, the key technologies for transimission based on network coding in the wireless mesh networks are studied deeply in this thesis. The main work and contributions are presented in the following aspects:(1)There are some partial error data packets which are dropped in wireless multipath routing. An improved segment network coding algorithm based on multipath routing is proposed. In addition, we propose a MPTCP that naturally adds the segment network coding based on multipath to current network systems.In the segment network coding, we encode a group of segment data into independent new packets and transmit them along multiple paths to reduce the data packets retransmit and communications in relay nodes. In addition,a new MPTCP is investigated.In our scheme, according to the degree of freedom of decoding block from the destination feedback, the source node modify the coded data block to reduce restransmit of timeouts. As a result, the network is achieved higher throughput compared to TCP in the presence of lossy wireless links. Comprehensive simulations and results verify the theoretical results in the paper.(2) There are some selfish nodes which depress the peformance in wireless mesh network multiple paths. In this paper, a game theoretic method is used to investigate multipath inter-session network coding. There are some selfish nodes in wireless mesh network multiple paths. We apply game theory among in the multipath inter-session network coding selfish nodes. Firstly the Nash equilibrium in the proposed multipath transmission game model is derived. Secondly, some characteristic of multipath inter-session network coding game is proved.Lastly we propose a stimulus scheme which is suit for multi-path selfish nodes game. In the multipath transmission, we use the watch dog to check the existence of selfish nodes. For multipath selfish nodes, we adopt non-cooperation method to punish it. It is proved that Nash equilibrium is acquired for all players to obey the incentive scheme honestly. Experiments verify the theoretical analysis.(3)Now, the quality of service of streaming media wireless mesh network can not be guaranteed.A deterministic network coding based on opportunistic routing is proposed. Using of a deterministic network calculus tool, we derive the wireless mesh network nodes’backlog upper bound, the end-to-end upper delay bound and the end-to-end upper delay jitter bound based on the existing link throughput model of opportunistic routing; and then a deterministic network coding (DNC) which meets the QoS of streaming media is designed. An ETC considering the node’s backlog upper bound is proposed to a guide line which determines the encoding nodes. In order to improve the performance, we use network coding before the node’s backlog upper bound is exceeded.The represented ETP considering the jitter and the end-to-end upper delay jitter bound is a guide line which determines the received candidate nodes. The data packets are encoded among the candidate nodes according to the ETC. Comprehensive simulations and results show that the throughput is improved; the delay time and the jitter of end to end are degraded.(4) We present a low delay time network coding against the high decode time based on opportunistic routing in streaming media wireless mesh network this paper. There are two parts of variable length network coding (VLNC) and candidate node feedback (CNF) in the implement of low delay time network coding. Firstly, the decode delay time and reliability of variable length network coding are analyzed. Then, a new algorithm is proposed that the candidate node feedback the encoded data packet. The algorithm of low delay time network coding is implemented in this paper. And the same bank is output by counters in the candidate nodes. When it lack of the decode data packets in the destination node, the candidate node is the first node to find the encoded data packets. As a result, the decode time is reduced. Simulations and results show that the delay time is degraded and the performance is improved.(5) The length of queue and the ratio of data packet drop are increased in the intermidle nodes when self-similar traffic is occurred. An algorithm of network coding to reduce based on the synchronization is presented to reduce the queue length and the delay time when self-similar traffic is occurred. The algorithm is implemented based on synchronization after data packets are classified by destination address and lengths.The algorithm is suit to use in the bursty self-similar traffic. Comprehensive simulations and results show that the delay time is reduced and queue length is shortened.更多还原