分散式協調功能(DCF)是傳統IEEE 802.11無線區域網路媒介存取控制(MAC)協定所採用的基本擷取方法，也就是利用載波感測多重擷取及碰撞避免(CSMA/CA)的技術，以及隨機延遲時間機制(binary slotted exponential backoff scheme)來達成工作站傳送與接收資料。然而，這種方法並不適合用來傳遞即時性資料，因為隨機延遲時間機制會產生很大的訊框延遲(delay)以及延遲的變動(jitter)。因此，我們提出一個改良的分散式協調功能(MDCF)。MDCF利用提前時間延遲機制(forward backoff scheme)讓即時性資料擁有較高的優先權，降低了即時性資料的訊框延遲和延遲變動。同時，我們利用連線允入控制(CAC)來處理網路過載現象，避免因網路過於擁塞所造成的碰撞。我們的協定可以對即時性服務提供網路輸出率、訊框延遲及訊框延遲變動等服務品質保證(QOS)。實驗結果顯示，MDCF比其他DCF的方法有更低的訊框延遲和延遲變動，更適合用來傳送即時性資料。

The Distributed Coordination Function (DCF) which uses Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) and binary slotted exponential backoff scheme is the basis of the IEEE 802.11 Medium Access Control (MAC) protocol. However, the DCF is not suitable for real-time traffic control since the backoff scheme may cause huge frame delay and jitter. We propose a modified DCF which uses a forward backoff scheme to remedy this disadvantage. In addition, a call admission control (CAC) is also proposed. Our protocol can guarantee service qualities such as the network throughput, frame delay, and jitter for real-time traffics. Besides, the modified DCF is still compliant with the IEEE 802.11 standard. Simulation results have shown that our method performs better than other DCF disciplines.

摘要 i
Abstract ii
第一章 簡介 1
第二章 IEEE 802.11 無線區域網路 4
2.1 IEEE 802.11 無線區域網路的硬體架構 4
2.2 IEEE 802.11 媒介存取控制層的通訊協定 7
2.2.1 分散式協調功能(DCF) 10
2.2.2 集中式協調功能(PCF) 14
2.3 IEEE 802.11 的同步處理 15
第三章 文獻探討 16
第四章 改良的分散式協調功能 21
4.1 相關前置工作 21
4.1.1 訊框定義 21
4.1.2 即時表格的建立與維護 22
4.2 提前時間延遲機制 25
4.2.1 提前時間延遲機制的操作 25
4.2.2 實例 27
4.3 連線允入控制 29
4.3.1 相關專有名詞的定義 30
4.3.2 連線允入控制的操作 31
第五章 數學分析 35
5.1 Markov Chain Model 35
5.2 Throughput Analysis 38
第六章 模擬結果與分析 40
6.1 模擬環境 40
6.2 實驗一 42
6.3 實驗二 49
6.4 實驗三 53
第七章 結論 57
參考文獻 58

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