研究指出IEEE 802.11分散式協調機制（Distributed Coordination Function；DCF）所使用之二元指數撤退演算法（Binary Exponential Back-off；BEB）在競爭者較多的無線網路環境下會因碰撞機率增高而導致網路效能不彰。因此，研究人員乃提出許多改良方法，藉由改變或調整傳送成功（失敗）時之競爭視窗（Contention Window；CW）增量（減量），有效改善了IEEE 802.11無線區域網路在高負載傳輸環境下之效能。然而，這些方法在傳輸負載變化較大的網路環境中卻也可能導致較多的媒體存取延遲（access delay）時間。本論文提出一可通用於這些改良方法的補償機制，使其在多變的網路傳輸環境中提供高吞吐量與低延遲的網路效能。

It has been shown that the Binary Exponential Back-off (BEB) algorithm, which is adopted in the IEEE 802.11 Distributed Coordination Function (DCF), can lead to significant performance degradation due to the high collision rate of transmissions among a large number of competing wireless nodes under the heavy traffic condition. To cope with this problem, a number of researchers proposed the mechanisms known as XIXDs to adjust the increment and decrement of Contention Window (CW) for the failure and success of any frame transmission, respectively. While XIXDs can improve aggregated throughput of the IEEE 802.11 network under high traffic conditions, they may also introduce additional network access delay under bursty traffic conditions. In this thesis, a general enhancement of XIXDs is proposed to provide the high through and the low access delay of the IEEE 802.11 network under unexpected traffic conditions. Numeric results show that the proposed enhancement can be applied to any existing XIXD and the reduced access delay can be achieved.
Keywods: IEEE 802.11, Distributed Coordination Function (DCF), Binary Exponential Back-off (BEB), XIXD, Contention Window (CW), access delay

中文摘要
ABSTRACT II
致 謝 III
目 錄 IV
圖目錄 VI
表目錄 VII
第一章 緒論 1
1-1 前言 1
1-2 研究動機與目的 2
1-3 論文架構 3
第二章 背景與相關研究 4
2-1 IEEE 802.11 簡介 4
2-2 效能改進之相關機制 7
2-2-1 BEB 8
2-2-2 EIED 9
2-2-3 LILD 11
2-2-4 ELBA 12
2-2-5 MILD 13
第三章 研究方法 14
3-1 問題描述 14
3-2 解決方案 16
第四章 NS2模組實作 19
4-1 XIXDs 實作 19
4-2 XIXD Timer 機制 24
4-3 XIXD Timer 實作 25
4-3-1 XIXD Timer類別 26
4-3-2 XIXD Timer啟動 28
4-3-3 XIXD Timer處理程序 29
第五章 模擬結果與分析 30
5-1 EIED 32
5-2 LILD 34
5-3 ELBA 35
5-4 MILD 36
5-5 總結 38
第六章 結論 40
參考文獻 41
附 錄 43

參考文獻

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