臺灣博碩士論文加值系統

為了在無線網路802.11上提供服務品質保證(Quality of Service) ，IEEE 802.11 Group E提出了802.11e，用以確保多媒體服務的品質能夠得到保證。其中提出了混合式協調功能(Hybrid Coordination Function，HCF)，包括了以輪詢為基礎的HCF通道存取機制(HCCA)和以分散競爭為基礎的EDCF通道存取機制(EDCA)，本文主要研究EDCA機制的各種效能。
在IEEE 802.11a規範中明定實體層的八種傳送速率，而訊號雜訊比門檻值（Threshold）的設定往往被作為切換速率的標準。本論文提出以輸出量（Throughput）及封包錯誤率（PER）作為訊號雜訊比門檻值的兩種依據；在輸出量的考量上，本論文又區分為兩種，其一為依據純通道輸出量機制，其二為依據加入EDCA退後機制（Backoff Mechanisms）後的輸出量，來選定訊號雜訊比門檻值。所選定的三組門檻值被用來對EDCA的通道使用率（Channel Utility）、整體輸出量、封包錯誤率及封包延遲（Packet Delay）作觀察。此外，本論文亦找出EDCA所能傳送的飽和容量，並對三組門檻值設定對EDCA飽和容量的影響作研究。本論文在採用IEEE及BRAN-A兩種通道模型所做的模擬結果中發現，以EDCA退後機制下的輸出量為依據所設定的訊號雜訊比門檻值，在三組門檻值的設定中，除了保有較佳的輸出量外，尚能降低封包延遲。

In order to provide Quality of Service in WLAN, the IEEE 802.11 Task Group E has been working on a proposal for QoS Enhancements. IEEE 802.11e issues hybrid coordination function（HCF）, including polling-based hybrid coordination channel access (HCCA) and contention-based enhanced coordination channel access (EDCA). In the thesis, we major focused on the performance effects during EDCA .
IEEE 802.11a supports eight different data rates in physical layer, and the rate selected is commonly decided by a set of SNR（Single to Noise Ratio）thresholds. This thesis proposes two approaches for choosing SNR thresholds, one is by throughput and the other is by packet error rate（PER）.Choosing by throughput can be further classified into two categories: one is according to the pure channel throughput without considering ACK and backoff, the other is according to the channel throughput followed backoff mechanism in EDCA. These three sets of SNR thresholds are used to observe the channel utilization, throughput, PER and packet delay during EDCA. Besides, the thesis also investigates the saturate capacity of EDCA, and studies the influence of different sets of SNR thresholds on it. Simulation results for IEEE and BRAN-A channel models show that the set of SNR thresholds chosen by throughput measured in EDCA not only has better performance of throughput, but also reduces the packet delay in most of cases.

中文摘要----------------------------------------i
英文摘要---------------------------------------ii
誌謝------------------------------------------iii
目錄-------------------------------------------iv
表目錄-----------------------------------------vi
圖目錄----------------------------------------iii
第一章 緒論-------------------------------------1
1.1 研究動機------------------------------------1
1.2 研究目的------------------------------------1
1.3 研究方法與內容------------------------------2
1.4 各章提要------------------------------------2
第二章 IEEE 802.11 MAC層簡介--------------------3
2.1 競爭式服務與免競爭式服務--------------------3
2.2 MAC通訊協定---------------------------------4
2.3 分散式協調功能------------------------------5
2.4 具品質服務保證的802.11e功能----------------10
2.5 EDCA相關參數的定義-------------------------13
2.6 EDCA運作情形-------------------------------15
2.7 Controlled Access Period (CAP)的介紹-------18
第三章 系統模擬及數據分析----------------------19
3.1 前言--------------------------------------19
3.2 系統模型----------------------------------19
3.2.1非即時性資料------------------------------21
3.2.2採用通道模擬軟體--------------------------23
3.2.3訊框時間的計算----------------------------25
3.2.4EDCA參數說明------------------------------26
3.5 計算封包延遲時間--------------------------28
第四章 模擬結果與分析--------------------------29
4.1 模擬結果（一）----------------------------29
4.1.1訊雜比門檻值決定--------------------------29
4.1.2通道輸出量機制選擇訊雜比門檻值------------29
4.1.3EDCA機制輸出量選擇訊雜比門檻值------------33
4.1.4封包錯誤率選擇訊雜比門檻值----------------37
4.2 模擬結果（二）----------------------------39
4.2.1考量通道輸出量機制之飽和容量--------------39
4.2.2考量EDCA機制之工作站飽和容量--------------41
4.2.3考量PER機制之工作站飽和容量---------------43
4.3 模擬結果（三）----------------------------45
4.3.1IEEE通道效能分析--------------------------45
4.3.2BRAN-A通道效能分析------------------------53
第五章 結論與未來研究方向----------------------59
參考文獻 --------------------------------------60
作者簡歷 --------------------------------------62

[1] IEEE Std 802.11e/D13.0 Jan 2005, IEEE Standard for Information technology - Telecommunications and Information exchange between systems – Local and metropolitan area networks - Specific requirements. Part 11: wireless LAN Medium Access Control (MAC) and Physical Layer(PHY).
[2] IEEE Std 802.11-1999 Information Technology-telecommunications And Information exchange Between Systems - Local And Metropolitan Area Networks - specific Requirements - part 11: Wireless Lan Medium Access Control (MAC) And Physical Layer (PHY) Specifications, 1999.
[3] IBM Zurich Research Laboratory, “Performance Evaluation of the QoS Enhanced IEEE 802.11e MAC Layer,” Research Report, Oct. 2002.
[4] S. Mangold, “IEEE 802.11e: Coexistence of Overlapping Basic Service Sets,” In Proceedings of the Mobile Venue''02, pp.131-135, Athens, Greece, May 2002.
[5] S. Mangold, S. Choi, P. May, and G. Hiertz, “IEEE 802.11e - Fair Resource Sharing between Overlapping Basic Service Sets,” in Proc. PIMRC 2002, pp.166-171, Sep, 2002.
[6] A.Grilo, M.Macedo and M. Nunes, “A scheduling algorithm for QoS support in IEEE 802.11e Networks,” Wireless Communitions, vol.10, issue 3,pp.36-43,June 2003.
[7] IEEE Std 802.11a-1999 Supplement to IEEE standard for information technology - telecommunications and information exchange between systems – local and metropolitan area networks – specific c requirements. Part 11：wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) , 1999. Networks-specific Requirements-part 11: Wireless Lan Medium Access Control (MAC) And Physical Layer (PHY) Specifications, 1999.
[8] Antonio Grilo and Mario Nunes, “Performance Evaluation of IEEE 802.11e,” PIMRC, 2002.