【作者】 赵红敏；

【导师】 陈建二；

【作者基本信息】 中南大学 ， 计算机软件与理论， 2009， 硕士

【摘要】 无线局域网（WLAN）是计算机网络与无线通信技术相结合的一种无线网络。它具有应用灵活、安装速度快、建设周期短、地理适用性强等特点,已经广泛应用在各行各业。在无线局域网中,网络的性能主要取决于MAC子层的接入协议,因此MAC协议的设计是一个核心的问题。研究无线局域网MAC机制,提高无线局域网的吞吐率和公平性保证及低延时,成为当前研究的热点。信道竞争算法是解决无线信道冲突的一种方法,信道竞争算法的研究对提高网络总吞吐率具有重要意义。本文首先通过测试,获得了IEEE 802.11b真实无线局域网中数据帧的长度分布。接下来分别分析了节点间数据帧长和信道发送速率各异给网络总吞吐率带来的影响,并针对这种影响,设计了算法FRA（Frame-cum-Rate Algorithm）。FRA将数据帧长和信道速率结合起来作为调节CW_min的因子,提高了发送长数据帧或者高速节点的信道占用时问。仿真实验表明,FRA算法在速率、帧长各异的无线网络环境下,相比MAC层DCF协议,能够大幅提高网络总吞吐率,并保证其成比例公平性高于DCF。随后,利用Markov模型,分析了在信道上存在一定误帧率情况下MAC层介质访问延时和网络吞吐率,提供了比之前研究更为精确的计算模型。本文最后对所做的研究工作进行了总结,并阐述了进一步的研究方向。更多还原

【Abstract】 Wireless Local Area Network （WLAN） is one kind of wireless networks which combinates between computer network and wireless communication technique. As the extendibility of wired network, WLAN has been widely used in every way of life because it has good features such as the application of flexible, fast installation, shot construction period and good applicability.In WLAN, the performance of network depends primarily on access to the MAC sublayer protocol, so design of MAC protocol is a key problem. Research about MAC protocol in WLAN and improvement of network throughput, fairness and low delay are the critical factors in academic and professional fields now.MAC channel contention algorithm is very important for reducing the collision probability and improving the throughput of the network. Firstly, this paper gets the distribution of frame size by caputuring the frame on the wireless channel. Nextly, this paper analyzes the impact of different frame size and multirate on the network throughput, and designs an algorithm whose name is FRA（Frame-cum-Rate Algorithm）. In FRA, the value of CW_min is adjusted based on frame size and transmission rate. The wireless station with large frame size and high transmission rate can obtain high probability to access wireless channel. Simulation results show that compared with DCF, FRA increases the network throughput drasmaticaly when different frame size and transmission rate coexist.Subsequently, this paper analyzes MAC medium access delay and throughput based on Markov model with certain BER on the wireless channel. It gives a more precise computing model comparision with previous research.The dissertation summarizes our research work in the last chapter and a further research direction has been explored for future work.更多还原