【作者】 商彦磊；

【导师】 程时端；

【作者基本信息】 北京邮电大学 ， 计算机应用技术， 2006， 博士

【摘要】 近年来，无线网络以其方便、快捷的优点，受到产业界和学术界的关注。但是同有线网络相比，它们所提供的服务质量还有很大的差距。所有的无线网络都是共享媒介的，物理层提供了信息的通道，MAC层则定义了信息的传输方式，对网络的性能起非常重要的作用。随着网络上业务种类的日益丰富，物理层数据传输速率越来越高，无线网络MAC层的作用更显突出，对无线网络MAC层协议的性能分析和改善具有非常重要的意义。本文主要做了如下工作： (1)通过分析IEEE 802．11e基于竞争的接入机制——EDCA提供区分服务的本质，提出了一个四维离散Markov链模型。本文的研究基于退避的和基于帧间隔的优先级区分机制，包含了实际冲突与虚冲突。仿真结果表明四维Markov模型可以更精确地表达EDCA的性能。论文研究了初始竞争窗口大小与AIFS在IEEE 802.11eEDCA服务区分机制中的作用。通过对结果进行分析，指出IEEE 802．11e EDCA存在的问题。 (2)针对IEEE 802．11e EDCA存在的问题，为IEEE 802．11e EDCA提出了一个QoS增强机制，包括三个部分：(1)通过QAP的虚拟排队实现不同优先级AC之间的隔离。(2)对具有QoS要求的AC实行接纳控制。(3)对尽力而为的AC[0]，通过调整初始竞争窗口使饱和吞吐量稳定在最大值附近，仗各个业务源具有相同的发送机会，即保证了效率与公平。并通过建模分析以及仿真试验验证了算法的有效性。 (3)在分析影响Ad hoc网络性能因素的基础上，提出了一个Ad hoc的聚簇算法以解决Ad hoc的可扩展问题。算法以达到簇结构的稳定性为聚簇的目标，考虑节点的移动特性以及节点在网络的位置。通过熵来度量节点与周围邻居节点的相对移动性，用节点度衡量节点在网络中的重要程度，利用遗传算法寻找最优的簇首集合，使得所得到的聚簇结构尽可能地稳定。 (4)为IEEE 802．1 6提出了一个新的的上行调度算法，BS中的上行调度器负责收集来自各个连接的带宽请求信息，根据各个连接的QoS特性制定相应的调度决策，将计算得到的各个SS应得的Data Grants分配给SS，具体的调度算法在SS更多还原

【Abstract】 Recent advances in portable computing and wireless technologies are opening up exciting possibilities for the future of wireless networks. There are great differences between wireline network and wireless network. The channel is shared by all nodes in the wireless networks. PHY layer provides the wireless channel and MAC layer manages the transmission of information over the channel. With the richness of traffic types and the increase of bandwidth, MAC will play a more and more important role in the performance of wireless network. More notably, Wireless Local and Metropolitan Area Networks (WLAN and WMAN) technologies are expected to revolutionize the way we live. Given their unprecedented importance, in the dissertation we investigate the performance of MAC layer and suggest some new solutions in the context of WLAN and WMAN, including Ad hoc network. The main contributions are as follows:(1) By the analysis of the Enhanced Distributed Channel Access (EDCA) of IEEE 802.11e wireless LANs, a four-dimension Markov chain model is proposed in this paper. Based on the Markov model, We have studied the priority differentiation based on backoff and based on Inter-Frame Space (IFS). The research takes the real collision and virtual collision into account. The consistency of analysis and simulation validates the Markov chain model. By analyzing the simulation results, we find some performance deficiencies of IEEE 802.11 e EDCA.(2) We introduce an enhanced QoS mechanism for IEEE 802.11e EDCA based on the previous conclusion. There are three parts in this QoS architecture: Firstly, the collision separation among many ACes is implemented through the virtual queuing in QAP. Secondly, to guarantee the previous traffic, it is necessary to control the access of these ACes with the same priority. Finally, the saturated throughput of the ACfO] achieves the stable maximum by adjusting the initial contention window. Because of the equal transmitting opportunity, it is fair among BE traffics. The analysis and simulation validate the efficiency of our algorithm.(3) Based on the analysis of some performance factors of Mobile Ad hoc NETwork (MANET), a clustering algorithm is proposed to improve the scalability of Ad hoc network. By considering the node mobility and node locality in the network, this clustering algorithm is aimed at a more stable clustering structure. We model the relative mobility between a node and its neighbor nodes by the concept of Entropy in information theory. And we estimate the contribution of a node to the whole network by the concept of the Node Degree in graph theory. Based on the Entropy and Node Degree,更多还原