適用於IEEE 802.11 無線區域網路之碰撞感知式退避機制

An Improved Collision-Aware Backoff Mechanism for IEEE 802.11 WLANs

孫莉婷(Li-Ting Sun)

指導教授 ： 汪順祥

大同大學/電機資訊學院/通訊工程研究所/碩士(2011年)

摘要

近幾年來，無線區域網路漸漸的成為無線通訊和網路存取的重要工具。在目前很多被提出關於管理無線多方存取的協定機制中，其中最被廣泛採用的的是 IEEE 802.11。在IEEE 802.11中，是透過載波感測多重存取碰撞壁面架構(Carrier Sense Multiple Access with Collision Avoidence, CSMA/CA)採用二元指數倒退 (Binary Exponential Backoff, BEB) 演算法來避免碰撞產生，進行分散式協調功能(Distributed Coordination Function, DCF)之機制。在以上的這些論點之下，本文提出了新的存取機制，依據通道的歷史通訊競爭狀況來動態的調整對目前通道狀況之下，最合適的競爭窗口(contention window; CW)的大小。其中通訊競爭狀況是由傳送資料的失敗率為依據所做的評估。模擬結果顯示相較於IEEE 802.11所提出存取機制，本文所提出的存取機制表現較具優勢。特別是在平均延遲和系統傳輸量。

關鍵字

倒退演算法 ； 802.11 分散式協調功能協定

並列摘要

In recent years, wireless local area networks (WLANs) are emerging as important instruments of wireless communications and network access. Several protocols have been proposed to manage multiple access to the shared wireless medium with the IEEE 802.11 being the most implemented protocol. The distributed coordination function (DCF) is the most widely deployed medium access control (MAC) protocol for IEEE 802.11 WLANs. The DCF is based on carrier sense multiple access with collision avoidance (CSMA/CA) scheme which employs the binary exponential backoff (BEB) algorithm. In the thesis, we propose an Improved Collision-Aware Backoff Mechanism (ICABM) which can dynamically select a suitable contention window size according to the contention level of current network and the history of the past trials. A contention level is separately estimated by each station depending on unsuccessful frame transmission ratios. Simulation results show that our scheme outperforms the standard protocol in terms of the average delay and system throughput.

並列關鍵字

Backoff algorithm ； IEEE 802.11 DCF

參考文獻

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