臺灣博碩士論文加值系統

傳統的IEEE 802.11 DCF，是採用隨機退避窗口機制，提供競爭式無線網路通道存取的方法。但近來許多的研究顯示，這些傳統的退避機制，通常只適於低的或是高的活躍節點密度的網路環境。尤其是在隨意式無線網路，活躍節點數會經常的改變，當競爭窗口的收斂慢，會在短期間造成較高的碰撞或延遲(delay)現象，所以傳統的退避機制並不適用於隨意式無線網路。因此，本論文提出了一種新的競爭窗口算法稱為動態自適應退避算法（DABA）。它可以根據現行網路的狀態，動態地調整合適的競爭窗口，以加速競爭窗口的收斂速度和提高網路效能。通過深入的分析吞吐量與競爭窗口的關係後，我們證實DABA方法的效能表現優於現有傳統的退避算法

The traditional IEEE 802.11 DCF incorporates a random backoff scheme to provide a contention-based channel access mechanism in wireless networks. However, according to recent research, legacy schemes are only appropriate in a network environment of low or high active nodes density. In mobile ad hoc networks (MANETs), the number of active nodes changes dynamically. Thus, slow convergence of contention window (CW) could cause high collision and large delay. This makes the legacy backoff scheme not suitable for MANETs. Therefore, this thesis presents a novel backoff algorithm called Dynamic Adaptive Backoff Algorithm (DABA) to speed up CW convergence and increase network throughput by adjusting CW size dynamically according to network states. Through thorough analysis on the relationship between CW size and throughput, we confirmed that DABA performs superior to existing legacy backoff schemes.

ABSTRACT IN CHINESE IV
ABSTRACT IN ENGLISH V
ACKNOWLEDGEMENT VI
TABLE OF CONTENTS VII
LIST OF FIGURES VIII
LIST OF TABLES IX
1. INTRODUCTION 1
1.1. BACKGROUND AND MOTIVATION 1
1.2. PROPOSED APPROACH AND CONTRIBUTION 2
1.3. ORGANIZATION OF THE THESIS 2
2. RELATED WORK 3
2.1. BACKOFF SCHEME APPROACH 3
2.2. NON-MEASUREMENT BASED SCHEME 3
2.3. MEASUREMENT BASED SCHEME 7
2.4. COMPARISON OF RELATED WORKS 8
3. DYNAMIC ADAPTATION BACKOFF ALGORITHM 10
3.1. THROUGHPUT ANALYSIS 10
3.2. DESIGNING PRINCIPLES OF THE BACKOFF ALGORITHM 13
3.3. BEACON PARAMETERS 14
3.4. DESCRIPTION OF THE DABA ALGORITHM 15
4. SIMULATION RESULTS 19
4.1. SIMULATION ENVIRONMENT AND PARAMETERS 19
4.2. COMPARISONS OF SATURATION THROUGHPUT 20
4.3. RETRANSMISSION ATTEMPTS AND MEDIUM ACCESS DELAY 22
4.4. FAIRNESS OF DABA SCHEME 25
5. CONCLUSION AND FUTURE WORKS 26

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