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研究生： 董育彰
Yu-chung Tung
論文名稱： IEEE 802.11e 無線區域網路之非均勻後退狀態指配法之研究
A study of non-uniform backoff state assignment scheme in IEEE 802.11e wireless local area networks
指導教授： 鍾順平
Shun-Ping Chung
口試委員: 王乃堅
Nai-Jian Wang
林永松
none
學位類別： 碩士
Master
系所名稱： 電資學院 - 電機工程系
Department of Electrical Engineering
論文出版年： 2007
畢業學年度： 95
語文別： 英文
論文頁數： 86
中文關鍵詞： IEEE 802.11e 、服務品質 、成功送達率 、非均勻後退狀態指配法 、三維馬可夫鏈
外文關鍵詞： IEEE 802.11e, Quality of Service (QoS), throughput, nonuniform backoff state assignment scheme, three dimensional Markov chain
相關次數： 點閱：275  下載：1 
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    • 近年來由於IEEE 802.11無線區域網路的低成本與移動性，使得它獲得普遍的流行。隨著IEEE 802.11 應用的增加，使用者對無線區域網路的功能有著更多的需求。由於多媒體的盛行，服務品質的需求也越來越高。為了保證即時性資料的服務品質，IEEE 802.11e被提出。IEEE 802.11e的MAC層引進多種方式來達到服務品質差異化，其中包括EDCA (Enhanced Distributed Channel Access)。EDCA引進四種進接類別，且每種進接類別使用不同的系統參數來達成服務品質之差異化。EDCA採用均勻後退狀態指配法來避免碰撞。當使用者數目增加時，均勻後退狀態指配法可能會造成系統效能大幅下降。這篇論文中，我們採用一個新的非均勻後退狀態指配法來改善IEEE 802.11e無線區域網路在使用者數目增加時的系統效能。我們使用一個三維的馬可夫鏈來塑模所考慮的系統，並推導相關的解析方法以計算感興趣的系統效能量度，例如成功送達率。我們展示，無論是基本或RTS/CTS進接機制，非均勻後退法對於重載時的系統效能都可提供卓越的改良。最後但非最不重要，我們以C語言自行撰寫相關之模擬程式，以驗證解析結果的準確度與進行更複雜的系統效能分析。

    IEEE 802.11 wireless local area networks have gained a lot of popularity in recent years due to its low cost and mobility. With applications over IEEE 802.11 increasing, users expect more functions from WLANs. Quality of Service (QoS) demands increase rapidly due to the popularity of multimedia. To guarantee QoS of real-time information, IEEE 802.11e is proposed. The MAC layer of IEEE 802.11e has adopted many methods to achieve QoS differentiation, including EDCA (Enhanced Distributed Channel Access). EDCA introduces four access categories (AC), and each AC uses different system parameters to realize QoS differentiation. EDCA adopts uniform backoff state assignment scheme to avoid collisions. When the number of stations increases, uniform backoff state assignment scheme may result in serious degradation of system performance. In this work, we adopt a new nonuniform backoff state assignment scheme to improve system performance of an IEEE 802.11e WLAN when the number of stations increases. We use a three dimensional Markov chain to model the system considered, and an analytical method is derived to calculate the performance measures of interest, e.g., throughput. It is demonstrated that when the number of stations is large, nonuniform backoff state assignment scheme can achieve significant performance improvement for either basic or RTC/CTS access mechanism. Last but not least, computer simulation programs are written in C language to verify the accuracy of analytical results and perform more complicated performance analysis.

    Chapter 1 Introduction 1 Chapter 2 Related Works 3 2.1 The 802.11 Legacy 3 2.1.1 The 802.11 PHY Layer 3 2.1.2 The 802.11 MAC Layer 3 2.1.3 Distributed Coordination Function (DCF) 5 2.1.4 Point Coordination Function (PCF) 6 2.1.5 RTS/CTS Mechanism 8 2.2 The 802.11e Legacy 9 2.2.1 Enhance Distributed Coordination Function (EDCF) 9 2.2.2 Contention Windows (CWs) and AIFS 12 2.2.3 Transmission Opportunity (TXOP) 13 Chapter 3 System Model 14 3.1 Analytical Model 14 3.2 Non-uniform Backoff State Assignment Scheme 16 3.3 State Transition Probabilities 17 3.4 Steady State Probability Distribution 20 3.5 Throughput Analysis 30 Chapter 4 Numerical Results 38 4.1 Uniform Backoff with RTS/CTS 38 4.2 Non-uniform Backoff with RTS/CTS 38 4.2.1 Throughput 40 4.2.2 Mean Access Delay 42 4.3 Uniform Backoff with Basic Access 43 4.4 Non-uniform Backoff with Basic Access 44 4.4.1 Throughput 44 4.4.2 Mean Access Delay 47 4.5 Comparison with RTS/CTS and Basic 47 4.6 Unfairness 48 4.7 Contention Window 48 4.7.1 Throughput 49 4.7.2 Mean Access Delay 50 4.7.3 Unfairness 51 Chapter 5 Conclusions 83 References 84

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