臺灣博碩士論文加值系統

IEEE 802.11e在MAC層使用了多種方式來達到服務品質保證的目標，主要的方法包括HCCA（HCF Controlled Channel Access）及EDCA（Enhanced Distributed Channel Access）兩種存取機制。一般而言，對於即時性資料會以HCCA存取機制的輪詢方式進行傳送；而非即時性資料則以EDCA存取機制的競爭方式去爭取通道使用權。由於競爭方式是以延後（Backoff）機制去避免工作站間產生碰撞問題，而延後機制必須犧牲時間以換取減少碰撞機會，這對於強調時效性的即時性資料傳送是不合適的，因此採用輪詢式的HCCA存取機制，在妥善的規劃每個工作站使用通道的時間下，更能符合即時性資料的傳送需求。
本論文主要在進行IEEE 802.11e/a的混合式協調功能之控制通道存取效能研究。我們結合了屬於MAC層IEEE 802.11e HCCA的存取機制，與屬於PHY層的IEEE 802.11a，來進行系統模擬，並在系統中加入重送機制，於兩種不同的通道環境下，觀察於HCCA存取機制中所能容納的站台數目，以及於HCCA中無法順利傳送成功而必須流至EDCA傳送的封包數量。此外，本論文亦針對HCCA的輪詢方式，提出了一種簡易的允入控制（Call Admission Control；CAC）策略。本論文的模擬系統是以Matlab程式語言撰寫完成，其中PHY層是以CommAccess Technologies公司所製作的WLAN Toolbox （mWLAN）進行模擬，並採行mWLAN所提供之 IEEE與BRAN A兩種通道模式作為模擬通道的使用。

IEEE 802.11e MAC uses many ways to reach the goal of quality of service assurance, including HCCA (HCF Controlled Channel Access) and EDCA (Enhanced Distributed Channel Access). Generally, HCCA uses polling mechanism to deliver real-time data, while for non real-time data EDCA uses contention mechanism for granting channel access right for users. In EDCA, the contention mechanism uses time backoff to avoid collision problems between stations, which is time consuming and is not suitable for real-time data delivery. Under proper arranging the channel access time for each station with streaming data, the polling mechanism adopted in HCCA is more suitable for real-time data delivery.
This thesis focuses on the performance study of IEEE 802.11e/a during HCF controlled channel access (HCCA). We combined IEEE 802.11e MAC layer and IEEE 802.11a PHY layer for system simulation under two different channel models with retransmission mechanism included, and examine the number of stations that can be polled in HCCA and the amount of unsuccessfully delivered packets in HCCA. These packets may be retransmitted in EDCA under certain QoS control. Besides, this thesis proposes a simple CAC (Call Admission Control) strategy that can be used in HCCA. The simulation program is written in Matlab and combined with mWLAN (CommAccess Technologies’ WLAN Toolbox), of which two PHY channel models, IEEE and BRAN A, are adopted in our simulation.

中文摘要 ------------------------------------------------------ i
英文摘要 ------------------------------------------------------ ii
誌謝 ------------------------------------------------------ iii
目錄 ------------------------------------------------------ iv
表目錄 ------------------------------------------------------ vi
圖目錄 ------------------------------------------------------ viii
第一章 緒論-------------------------------------------------- 1
1.1 前言-------------------------------------------------- 1
1.2 無線網路簡介------------------------------------------ 1
1.3 研究目的---------------------------------------------- 3
1.4 研究方法與內容---------------------------------------- 4
1.5 各章提要---------------------------------------------- 4
第二章 IEEE 802.11e HCCA存取機制簡介------------------------- 6
2.1 前言-------------------------------------------------- 6
2.2 基本名詞---------------------------------------------- 7
2.3 PCF免競爭服務----------------------------------------- 11
2.3.1 PCF之運作--------------------------------------------- 11
2.3.2 PCF之傳輸--------------------------------------------- 12
2.3.3 電源管理---------------------------------------------- 13
2.4 HCCA存取機制------------------------------------------ 14
2.4.1 Traffic Specification （TSPEC） element -------------- 14
2.4.2 HCCA的運作情形---------------------------------------- 18
第三章 系統模擬---------------------------------------------- 20
3.1 前言-------------------------------------------------- 20
3.2 IEEE 802.11e存取機制設定------------------------------ 20
3.3 系統模型---------------------------------------------- 21
3.3.1 即時性資料-------------------------------------------- 22
3.3.2 實體層傳輸-------------------------------------------- 24
3.3.3 不同通道模型------------------------------------------ 25
3.3.4 準確的訊框傳輸時間------------------------------------ 26
3.3.5 Polled TXOP的估測------------------------------------- 28
3.3.6 行動工作站模型---------------------------------------- 30
3.4 距離與訊雜比間的對映---------------------------------- 33
3.5 各通道環境的雜訊比門檻值------------------------------ 33
3.5.1 IEEE Channel Model的訊雜比門檻值---------------------- 34
3.5.2 BRAN Channel Model - Channel A的訊雜比門檻值---------- 35
3.5.3 具有杜普勒效應的訊雜比門檻值-------------------------- 36
3.6 各通道環境下的各傳輸速率之工作站分布比例-------------- 36
3.6.1 在IEEE Channel Model下的各速率工作站分布比例---------- 37
3.6.2 在BRAN – Channel A下的各速率工作站分布比例----------- 38
第四章 模擬結果與數據分析------------------------------------ 40
4.1 前言-------------------------------------------------- 40
4.2 IEEE Channel Model靜止工作站-------------------------- 40
4.2.1 IEEE模擬結果 – 重送機制下的各速率分布比例------------ 41
4.2.2 IEEE模擬結果 – 重送機制下的各項使用時間-------------- 43
4.2.3 IEEE模擬結果 – 重送機制下的各項錯誤封包數量統計------ 45
4.2.4 IEEE Channel Model靜止工作站數據分析------------------ 46
4.3 BRAN Channel Model – Channel A靜止工作站（1）-------- 50
4.3.1 Channel A（1）– 重送機制下的各速率分布比例----------- 50
4.3.2 Channel A（1）– 重送機制下的各項使用時間------------- 52
4.3.3 Channel A（1）– 重送機制下的各項錯誤封包數量統計----- 53
4.3.4 Channel A靜止工作站（1）數據分析---------------------- 54
4.4 BRAN Channel Model – Channel A靜止工作站（2）-------- 58
4.4.1 Channel A（2）– 重送機制下的各速率分布比例----------- 58
4.4.2 Channel A（2）– 重送機制下的各項使用時間------------- 60
4.4.3 Channel A（2）– 重送機制下的各項錯誤封包數量統計----- 62
4.4.4 Channel A靜止工作站（2）數據分析---------------------- 62
4.5 行動工作站之CAC策略----------------------------------- 64
4.5.1 行動工作站對HCCA的影響-------------------------------- 64
4.5.2 資源配置---------------------------------------------- 66
4.5.3 簡易的CAC策略----------------------------------------- 69
第五章 結論與未來研究方向------------------------------------ 72
7.1 結論-------------------------------------------------- 72
7.2 未來研究方向------------------------------------------ 73
參考文獻 ------------------------------------------------------ 74
附錄一 IEEE Channel Model ----------------------------------- 76
附錄二 BRAN Channel Model – Channel A ---------------------- 77
附錄三 IEEE Channel Model – Doppler Effect ----------------- 78
作者簡歷 ------------------------------------------------------ 79

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