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Author: 李志民
Chih-Mim Li
Thesis Title: IEEE 802.16d網狀網路下有效迷你時槽配置機制
An Efficient Minislot Allocation Scheme for IEEE 802.16d Mesh Networks
Advisor: 黎碧煌
Bih-Hwang Lee
Committee: 吳傳嘉
Chwan-Chia Wu
Yuan-Cheng Lai
Ray-Guang Cheng
Huei-Wen Ferng
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: 55
Keywords (in Chinese): IEEE 802.16正交分頻多工網狀網路分散式排程
Keywords (in other languages): IEEE 802.16, OFDM, Mesh Netwok, Distributed Scheduling
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IEEE 802.16標準是一種都會型無線網路的協定,並支援點對多點(point to multi-point)和網狀(mesh)兩種模式。而在IEEE 802.16標準網狀模式中,網路資源的分配可以用集中式(centralized)及分散式(distributed)兩種排程模式來做處理。在分散式排程模式中,每一節點利用EBTT(election-based transmission timing)的競爭機制與其二跳躍內的節點共同競爭控制子訊框傳輸排程資訊的機會。而資料子訊框內迷你時槽(minislot)的配置係採用三向交握(three-way handshaking)的機制,與相鄰節點間交換Request、Grant及Confirm等排程資訊,而迷你時槽的利用率對於媒體存取控制層的排程效能是相當重要的一項議題。
由於資源的不足及節點無法得知距離為二跳躍(2-hop)的節點之排程資訊,使得三向交握過程發生要求失效的問題,如主要衝突(primary conflict)及次要衝突(secondary conflict)等問題,而導致三向交握於Grant階段或Confirm階段發生失效,此三向交握失效問題將會導致傳輸產能的降低。
在本論文中,我們提出了二個強化分散式排程的方法,稱為部份回應機制(partial grant scheme;PGS)及預先配置機制(pre-allocation scheme;PAS)以降低三向交握的失效率,藉以改善網路資源的利用率。經由模擬結果顯示,部份回應機制可有效降低Grant階段所發生的失效率,而預先配置機制則可有效降低Confirm階段所發生的失效率。當同時採用部份回應及預先配置機制時,不論輕載或重載時,三向交握失效率均可獲得降低,進而提昇系統產能。

The IEEE 802.16 standard is a protocol for wireless metropolitan networks. IEEE 802.16 MAC protocol supports both of point-to-multipoint(PMP) and mesh mode. In the 802.16 mesh mode, network resource allocation can be handled in the centralized and distributed scheduling modes. In the distributed scheduling mode, every node competes for channel access using election-based transmission timing mechanism based on the MSH-DSCH Scheduling IE of the two hop neighbors. The minislots in data subframe are allocated based on a three-way handshaking mechanism by exchanging the Request , the Grant, and the Confirm information among the nodes. The minislot utilization is essential to achieving good performances of MAC-layer scheduling.
Because resource limited and local nodes do not know the exact scheduling information of 2-hop neighbors, the grant messages sent back by the receiver have the chance to conflict with other’s decision, known as primary and secondary conflict and cause three-way handshaking invalid in Grant step or Confirm step, and thus decreases throughput.
We propose two novel distributed scheduling schemes, known as partial grant scheme(PGS) and pre-allocation scheme(PAS) to decrease three-way handshaking invalid and improve network utilization. Our simulation results show that the PGS scheme can decrease Grant step fail and the PAS scheme can decrease Confirm step fail efficiency. The PGS+PAS scheme is better in throughput and three-way handshaking invalid ratio than others in light and heavy loading.

中文摘要 iv 英文摘要 v 誌謝 vi 圖目次 ix 表目次 xii 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 802.16分散式排程機制 4 2.1 IEEE 802.16標準網狀網路 4 2.2 控制子訊框排程機制 6 2.3 資料子訊框排程機制 10 2.4 迷你時槽狀態表及三向交握失效 16 2.4.1 迷你時槽狀態表 16 2.4.2 三向交握失效 17 第三章 迷你時槽配置機制介紹 20 3.1基本選擇機制介紹 20 3.2部份回應機制介紹 21 3.3預先配置機制介紹 22 第四章 系統模擬與結果 31 4.1 網路拓樸 31 4.2 系統參數 32 4.3 效能評估項目 33 4.3.1 Grant階段失效率(Grant step fail ratio) 33 4.3.2 Confirm階段失效率(Confirm step fail ratio) 33 4.3.3三向交握失效率(handshaking fail ratio) 34 4.3.4節點傳輸產能(node throughput) 34 4.4 模擬結果分析與比較 35 4.4.1 鏈狀網路拓樸之分析與比較 35 4.4.2 一般網路拓樸之分析與比較 44 第五章 結論及未來研究 51 參考文獻 53

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