在802.11 無線區域網路環境中，在媒體存取控制層中Binary Exponential Backoff (BEB)碰撞解決機制是負責用來解決在同一AP下，許多無線點的相互競爭問題，但不幸的，BEB在許多無線點的環境下，容易造成資料訊框相互碰撞而使得無線網路的效能下降。不只效能下降，BEB還會引起短暫不公平的嚴重問題。所以本篇論文提出一個利用動態的調整競爭視窗大小的碰撞解決機制Random and Random (RR)來解決BEB所發生的問題。

　　本論文利用Markov chain為分析模型去分析、驗證、計算RR的效能並與BEB做比較。不止如此，本論文利用NS2網路模擬軟體去模擬並驗證是否與理論分析結果相同，最後在依據RR的機制去模擬出不同方面的效能，並與BEB做比較，我們可以發現RR在網路流量、公平性與利用率方面擁有比較好的效能。

　　除了之前所提到的問題，RR因為只是修改原本機制的一小部分，所以它是非常容易去設置在現有的AP上。

　In IEEE 802.11 wireless local area networks, the binary exponential backoff (BEB) algorithm is used in the medium access control (MAC) protocol to resolve contention problems of mobile stations. Unfortunately, BEB has been shown to be highly easy to collide in the case of large number of mobile stations and causes poor utilization of the channel. In addition to the problem of collision, the problem of unfairness is a severe shortage of BEB.

　Hence, this thesis proposes an improved window control mechanism named Random and Random (RR) to improve the performance of the wireless channel by dynamically modifying the contention window size. In this thesis, we use Markov chain model to analyze, prove, and compute the performance parameters and we make a comparison of the analytical performance between BEB and RR. Not only that, we show the performance comparisons of different aspects between the proposed and standard algorithms by using the network simulator NS2. Eventually, we can realize that RR can get a better performance of throughput, fairness, and degree of utilizing wireless channel from the conclusion of this thesis.

　In addition to the resolution of problem mention before, it is very easy to implement the new contention window control mechanism and just a few changes in control message structure and access procedures in DCF.

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