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標題: 802.11無線網路適應性公平增強分散式協調機制之後退機制研究
The Study of Backoff Functions in IEEE 802.11 Adaptive Fair Enhanced Distributed Coordination Function
作者: 鍾儒光
Chung, Ju-Kuang
關鍵字: 802.11 WLAN
Enhanced Distributed Channel Access
Quality of Service
Exponential Function
出版社: 電機工程學系所
引用: [1] 蔣大偉, “802.11無線網路技術通論第二版”, 歐萊禮, 2006. . [2] 柯志亨, “計算機網路實驗:以NS2模擬工具實作”, 學貫行銷, 2007. [3] Burak Simsek, Katinka Wolter, “Improving the Performance of IEEE 802.11e with an Advanced Scheduling Heuristic”, Springer Berlin / Heidelberg, 2006. [4] Larry L. Peterson, Bruce S. Davie, “Computer Networks: A Systems Approach”, Morgan Kaufmann Publishers, 2003. [5] Mattbew S. Gast ,“ 802.11 Wireless Networks”, O’Reilly , 2006. [6] Kevin Fall and Kannan Varadhan, “The ns Manual”, 2006. [7] Lamia Romdhani, Qiang Ni, and Thierry Turletti, “Adaptive EDCF: Enhanced Service Differentiation for IEEE 802.11 Wireless Ad-Hoc Network”, IEEE Wireless Communication and Networking, vol. 2, pp. 1373-1378, 2003. [8] Younggoo Kwon, Yuguang Fang and Haniph Latchman, “A Novel MAC Protocol with Fast Collision Resolution for Wireless LANs”, IEEE INFOCOM, IEEE Conference on Computer Communications, vol. 2, pp. 853-862, 2003. [9] Younggoo Kwon, Yuguang Fang and Haniph Latchman, “Fast Collision Resolution (FCR) MAC Algorithm for Wireless Local Area Networks”, IEEE GLOBECOM, IEEE Global Telecommunications Conference, vol. 3, pp. 2250-2254, 2002. [10] Mohammad Malli, Qiang Ni, Thierry Turletti, Chadi Barakat, “Adaptive Fair Channel Allocation for QoS Enhancement in IEEE 802.11 Wireless LANs”, IEEE International Conference on Communications, vol. 6, pp. 3470-3475, 2004. [11] “ IEEE 802.11 WG, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specification”, Standard, IEEE, 1999. [12] “AWK Tutorial Guide, version 2.2”,, 中央研究院計算中心. [13] “Tutorial for the Network Simulator ns”, [14] “The ns Manual”, [15] “NS by Example”,
摘要: 隨著無線網路的發展與進步,人類的生活多了許多便利。為了配合使 用上之需求,因而制定了不同的無線網路機制。在802.11 無線區域網路 中,分散式協調機制是主要的媒體存取控制機制,它採用了載波偵測多重 存取的技術來傳輸資料,但由於 DCF 無法提供服務品質的保證,對於即 時性多媒體的日漸使用頻繁,DCF已無法提供良好效能之服務。因此802.11 工作小組制定了一個可以支援服務品質的標準,名為802.11e,其中包含 了一個新的媒介存取機制稱作 EDCA。 雖然EDCA 達到了高優先權資料可以獲得較好之服務品質的效果,但 經由模擬發現,當工作站數目增加到一定的數目後,傳送封包之碰撞率提 高,加上每個佇列在進入競爭週期時,產生之後退時間造成時間槽空閒之 浪費。因此有學者提出AFEDCF 機制,目的在於工作站數目增加時,降低 碰撞率。此方法主要是利用適應性快速後退機制來改善整體的資料流量, 因應當下之通道環境,算出快速後退之臨界值。 我們研究並修改AFEDCF中的快速後退機制,改以指數函數選擇後退 機制的臨界值,再以ns-2模擬不同之網路情形去比較AFEDCF與我們修改 的機制之差別,以分析快速後退機制臨界值的選取對效能的影響。
The development and progress of 802.11 wireless local area networks make our life much more convenient. In order to fulfill different service demands, different standards of wireless network are established. In IEEE 802.11 wireless LANs, the distributed coordination function is the primary medium access control scheme. DCF scheme employs the Carrier Sense Multiple Access with Collision Avoidance method to control access to the media. However, DCF does not provide real-time traffic service, so it does not provide Quality of Service (QoS). Thus, the IEEE 802.11 working group defined a new standard called IEEE 802.11e to support QoS. In 802.11e, a new medium access mechanism called EDCA is defined. Although EDCA provides QoS for high priority flows, it performs poorly when the medium is highly loaded. To reduce the waste of idle time slots, researchers proposed a new mechanism called AFEDCF. AFEDCF uses an adaptive fast backoff mechanism to improve the throughput. In this thesis, we studied and modified the backoff threshold function in AFEDCF. We used an exponential decay backoff threshold function instead of a linear function to determine the backoff threshold value. We implemented our scheme in ns-2 and compared the result to study the effect of different backoff threshold value on the system performance.
其他識別: U0005-2207200912145900
Appears in Collections:電機工程學系所



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