在此篇論文中為了要增進IEEE 802.11e無線區域網路的效能，藉由擁塞避免(congestion avoidance)的觀念，我們提出一個簡單的MAC層允許控制機制SCAS(Self-Conscious Congestion Avoidance Scheme)。在競爭存取模式下高頻道負載時，依網路狀態適當地暫時停止某些工作站競爭頻道，藉以降低競爭存取模式中碰撞發生的機率。SCAS建構在競爭存取模式下的頻道擷取方法上，因此不但能夠適用在原本IEEE 802.11e頻道擷取方法(EDCA[2])上也能夠適用在其它頻道擷取方法(AEDCF[12])上。此外SCAS採用分散式的方式由各個工作站獨自的運作，不需透過基地台AP(Access Point)或上層來運作。
最後經由模擬分析來驗證我們所提出的機制(SCAS)在競爭存取模式下不同頻道擷取方法(EDCA與AEDCF)上其效能改善之程度。模擬結果顯示SCAS機制除了能夠有效地降低EDCA與AEDCF碰撞發生的次數外，對於訊框平均的延遲時間(mean delay time)與系統的產能(throughput)也都能夠獲得不錯的效益，特別是當競爭頻道的工作站增加時，其效益更加顯著。

In this paper in order to improve the performance of the IEEE 802.11e WLAN (Wireless Local Area Network), we propose a simple MAC layer access control mechanism SCAS (Self-Conscious Congestion Avoidance Scheme). During the contention period, if the traffic load is high, we adaptively temporary stop some STAs (stations) contending for the channel to reduce the collision rate according to the network conditions. SCAS is on the MAC layer. Hence, it can not only be applied to the IEEE 802.11e medium access method (EDCA [2]) but also be applied to AEDCF [12]. Besides, each STA can operate SCAS by itself not through AP (Access Point) or higher layer.
Finally we evaluate the performance of SCAS on EDCA and AEDCF through simulations. Results show that SCAS can not only reduce collision rate of EDCA and AEDCF efficiently but also improve mean delay time and system throughput especially in high traffic load conditions.

目錄............. I
圖目錄......... III
表目錄......... V
第一章 導論............. 1
1.1 前言............. 1
1.2 研究動機..... 3
1.3 論文架構..... 5
第二章 相關背景與研究.............. 6
2.1 IEEE 802.11 WLAN基礎知識............ 6
2.1.1 IEEE 802.11 WLAN相關名詞介紹.. 6
2.1.2 IEEE 802.11 WLAN基本架構.......... 8
2.2 IEEE 802.11 WLAN MAC................... 10
2.2.1 分散式協調功能(DCF)...................... 11
2.2.2 集中式式協調功能(PCF)................... 16
2.2.3 對QoS支援的改進與研究................. 19
2.3 IEEE 802.11e WLAN基礎知識.......... 24
2.3.1 IEEE 802.11e WLAN相關名詞介紹 ..24
2.4 IEEE 802.11e WLAN MAC................. 28
2.4.1 競爭式存取EDCA.............................. 29
2.4.2 免競爭式/中控式存取HCCA............. 35
2.4.3 對服務品質支援的改進與研究......... 39
第三章 以MAC層允許控制增進IEEE 802.11e競爭存取模式下之效能................................................................. 44
3.1 所需準備與參數設定....................................... 46
3.2 SCAS—優先權較高的資料流(具時效性)...... 52
3.3 SCAS—優先權較低的資料流(不具時效性).. 54
第四章 模擬環境與結果.............. .....................58
4.1 模擬環境與參數................................... 58
4.2 模擬結果..... ...........................................60
第五章 結論............. ...........................................68
參考文獻 69

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