说明：  本文首先通过Bianchi模型，对标准DCF算法的性能作出全面定量分析，然后提出提高无线接入点通信能力的DCF改进算法，同时还提出改进算法的二维离散时间Markov模型并作了定量分析。随后设计原协议和改进协议的仿真算法，并使用Matlab仿真工具进行算法的仿真实验，并对它们的仿真结果作对比。理论和仿真结果都证明改进算法可以大幅度提高网络整体性能。 在对标准DCF算法作性能分析的过程中，作者注意到网络的性能随活动无线节点数量的增加衰减较快。主要原因在于网络负载较大时，冲突发生率高，但可以通过加快竞争窗口增加速度来减小冲突发生率，于是设计了基于活动无线节点数量的自适应X进制退避算法。随后作出的理论与仿真结果都证明这种算法可以在活动节点数量较大时一定程度上提高网络性能
(In this thesis, the performance of the original IEEE 802.11 DCF is quantitatively analyzed through Bianchi’s model. Whereafter an approache to alleviate this problem is proposed. Theoretical analysis and related simulations is performed. The results show that our proposed methods can improve DCF perofrmance in WLAN by a large margin (compared with the original standard). In the process of analyzing the performance of the original DCF, another problem was heeded that the DCF performance reduces with increasing number of active stations in the network.The main reason of this problem is the high probability of collision, when the load of the network is high. This problem can be solved by speeding up the process of contention window incressing. A new algorithm is designed in which the active stations can adapt their backoff exponent to the channel conditions dynamically. The theoretical analysis is performed and its accuracy is valuated by related simulations.The effective througuput of t)