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Author: 謝妙瑜
Miao-Yu Hsieh
Thesis Title: OFDMA無線網狀網路之排程機制研究
A Study of Scheduling Mechanism on Wireless OFDMA Mesh Network
Advisor: 黎碧煌
Bih-Hwang Lee
Committee: 陳添智
Tien-Chi Chen
鍾添曜
Tein-Yaw Chung
吳傳嘉
Chwan-Chia Wu
馮輝文
Huei-Wen Ferng
Degree: 碩士
Master
Department: 電資學院 - 電機工程系
Department of Electrical Engineering
Thesis Publication Year: 2008
Graduation Academic Year: 96
Language: 中文
Pages: 44
Keywords (in Chinese): 公平性網狀網路正交分頻多重接取
Keywords (in other languages): fairness, mesh network, OFDMA
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  • 在無線網路中,網狀模式(mesh mode)的網路具有低網路建置成本、結構擴充容易、非視距傳輸(non-line-of-sight;NLOS)、多重路徑傳輸、網路傳輸可靠度佳、系統容量及網路效能高等優點,可預期無線網狀網路將更能滿足下一代高速寬頻無線網路的需求。然而當行動裝置用戶的人數增多時,每台行動裝置用戶分配到的可使用頻寬(bandwidth)相對降低,傳輸品質與效能便會受到影響。
    由於封包排程機制的優劣、傳送封包的路由方式及頻寬使用率等因素,都將影響無線網路的效率,對於改善服務品質(quality of service; QoS)與避免擁塞亦扮演著很重要的角色,因此在本論文中,我們將就網狀模式下之無線網路排程機制進行研究,提出以正交分頻多重接取(orthogonal frequency division multiple access; OFDMA)技術,設計一個二階段演算法作為頻寬管理機制,為每個節點設定一個權重(weight),稱為權重優先傳送順序演算法(weighted transmission order algorithm; WTO),以排列節點權重之傳送順序,來滿足各節點傳送封包的需求,並維持各節點的公平性。
    最後,我們將所提出的方法與最常見的先進先出(first in first out; FIFO)競爭機制相比較。另外亦將WTO的頻寬配置方式改為OFDM配置並相互比較,從模擬結果顯示,在網狀網路環境下,本論文所提出的方法在網路負載增加時,系統容量及傳輸效能皆較其他兩種方式好,且仍保有各節點傳送資料之公平性。


    In high speed wireless network, mesh model is deemed as a topology with characteristics of multi-path transmission, and thus benefits of high availability, high capacity and efficiency. However, the bandwidth allocated for each mobile device drops down as more devices attached to mesh network.
    The scheduling mechanism, routing method and bandwidth utilization are all key factors for network efficiency, quality of service (QoS) improvement and congestion prevention. In this paper, we study the scheduling mechanism for mesh topology and propose a two-stage algorithm, named weighted transmission order (WTO) algorithm, for bandwidth management of OFDMA. WTO sets a weight for each node according to the topology and the transmission order is then determined respectively. In this way the equality of nodes is maintained.
    We compared the weighted algorithm proposed with the most common first-in-first-out competition mechanism and WTO algorithm with bandwidth management of OFDM. The simulation result shows that in the mesh network environment, WTO retains the transmission throughput and balance of each node regardless of the network loading.

    中文摘要 IV 英文摘要 V 圖目次 VII 表目次 VIII 第一章 緒論 1 1.1無線網路概述 1 1.2研究動機 5 1.3各章節內容摘要 6 第二章 正交分頻多工(OFDM)及正交分頻多重接取(OFDMA)技術介紹 7 2.1正交分頻多工技術起源及標準化 8 2.2正交分頻多工技術簡述 10 2.3正交分頻多工技術原理 13 2.4符號間干擾和保護區間 15 2.5正交分頻多重接取技術 17 2.6相關研究 18 第三章 系統模型 19 3.1網路基本系統架構 19 3.2訊框架構 19 3.3產生路由樹及傳送路徑 21 3.4演算法說明 25 3.4.1節點傳送順序之詳述(Phase I) 26 3.4.2 鏈路頻寬配置之詳述(Phase II) 28 第四章 系統模擬與結果 32 4.1效能量測 32 4.1.1傳輸效能(throughput) 32 4.1.2平均等待時間(average waiting time) 33 4.1.3公平性(fairness) 33 4.2模擬環境 34 4.3系統參數 36 4.4系統模擬結果 37 第五章 結論 42 參考文獻 43

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