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Author: 陳鴻鈞
Hung-chun Chen
Thesis Title: IEEE 802.11s MDA在多通道無線網狀區域網路下的預約機制之研究
Study on IEEE 802.11s MDA Reservation Mechanism for Multi-channel Wireless Mesh Network
Advisor: 黎碧煌
Bih-Hwang Lee
Committee: 陳俊良
Jiann-Liang Chen
Yuan-cheng Lai
Hann-trong Chen
Der-feng Tseng
Degree: 碩士
Department: 電資學院 - 電機工程系
Department of Electrical Engineering
Thesis Publication Year: 2010
Graduation Academic Year: 98
Language: 中文
Pages: 40
Keywords (in Chinese): 802.11sMDA多通道無線網狀區域網路
Keywords (in other languages): 802.11s, MDA, multi-channel, wireless LAN mesh
Reference times: Clicks: 201Downloads: 2
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無線網狀區域網路是由一些支援網狀服務(mesh service)的節點所組成的通訊網路。由於具有隨意網路(ad hoc network)的特性,因此能夠讓傳輸範圍內的節點在不透過存取點(access point, AP)的情況下互相通訊,藉由此特性,我們能用較低的成本來建置較大覆蓋範圍的網路。由於目前IEEE 802.11 a/b/g皆採用碰撞避免式載波偵測多重存取(carrier sense multiple access with collision avoidance, CSMA/CA)機制,在網狀網路架構下將會大幅增加碰撞機率,因此IEEE802.11s草案中,除了導入網狀網路架構外,亦加入以預約為基礎的存取機制,稱為MDA(mesh deterministic access)。MDA能讓節點以較少的競爭與碰撞來進行媒體存取,但只能工作於單通道環境,造成網路流量無法提升。

為了解決上述問題,本論文在網狀網路架構下,將MDA機制加以改善,提出一個多通道存取機制。我們將DTIM(delivery traffic indication map)區間切割為競爭區間與傳輸區間,配合四向交握(four-way handshake)機制及本論文所提出的NMST(neighbor MP status table),能夠使節點更有效地利用通道空間,並避免資訊錯誤可能產生的碰撞情形。從模擬結果可知,與以競爭為基礎的EDCA(enhanced distributed channel access)相比,本論文提出的機制可有效提升整體網路效能。

A wireless mesh LAN is a communications network made up of radio nodes that support mesh service. It combines the feature of ad hoc network, so nodes can communicate with other nodes directly without access point (AP). According to this feature, we can deploy network with larger coverage and lower cost. Because all based on carrier sense multiple access with collision avoidance (CSMA/CA) base to IEEE 802.11 a/b/g wireless system at present, the collision probability will be much higher if we use the scheme in wireless mesh LAN. In IEEE 802.11s draft, not only the mesh network topology be introduced, but also a new reservation based MAC access scheme, MDA, be introduced. Nodes that support MDA can access wireless medium with lower collision probability, but it can just work in single channel, so the capacity of network is limited.

In order to solve the above-mentioned problem, we proposed a new multi-channel access scheme that improved from MDA. We divide the mesh DTIM (delivery traffic indication map) interval into two fields, contention field and transmission field. To operate in coordination with four-way handshake and proposed NMST (neighbor MP status table), nodes can access channels more efficiently, and to avoid collisions with wrong information from other nodes. The simulation results show that the proposed scheme improves the network throughput over collision based scheme, i.e., EDCA.

中文摘要 iv 英文摘要 v 目次 vi 圖表索引 viii 第一章 緒論 1 1.1簡介 1 1.2研究動機與目的 2 1.3章節概要 3 第二章 IEEE 802.11s標準概述 4 2.1 IEEE 802.11s標準簡介 4 2.1.1網路拓樸 4 2.1.2 MAC訊框結構 7 2.2 MDA預約機制概述 8 2.2.1 MDA運作機制 9 2.2.2 MDAOP建立流程 9 2.2.3預約訊框格式 11 2.3相關研究 13 第三章 多通道預約機制介紹 15 3.1問題描述 15 3.2系統運作流程 16 3.2.1系統運作流程簡介 16 3.2.2 NMST 18 3.2.3四向交握機制 21 3.2.4 MDAOP選擇策略 22 3.2.5範例說明 23 第四章 系統模擬與結果 25 4.1模擬環境與參數 25 4.2效能評估項目 27 4.2.1平均節點產能(throughput) 27 4.2.2封包丟棄率(drop ratio) 27 4.2.3平均等待時間(average waiting time) 28 4.3結果分析與比較 29 4.3.1飽和模式下的平均節點產能分析與比較 29 4.3.2非飽和模式下平均節點產能分析與比較 31 4.3.3非飽和模式下平均等待時間分析與比較 33 4.3.4非飽和模式下系統封包丟棄率分析與比較 35 第五章 結論及未來研究 37 5.1結論 37 5.2未來研究 38 參考文獻 39

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