隨著無線技術的進步，越來越多的設備都有無線裝置，諸如：筆記型電腦、PDA 以及手機等；使用無線技術的應用也越來越多，從最早只提供語音的手機，到現在有能上網收信瀏覽網頁的GPRS手機，以及能夠支援視訊的筆記型電腦等，越來越多的應用，使得傳統無線技術面臨一些問題，例如頻寬不足以及無法保證服務品質等，本篇論文提出一個在無線區域網路上利用虛擬允入控制來提供服務品質的方法。 我們首先研究了目前被提出來的一些提供服務品質的方法，例如：改變訊框間距長度(inter-frame space)、改變遞後存取期間 (backoff window)，以及基於自制機制的虛擬MAC (virtual MAC)，還有目前仍是草稿 (draft)階段的802.11e等；我們結合了上述方法的優點，提出了一個應用於無線區域網路上的虛擬允入控制方法，可以在無線媒介情況良好時，讓新的應用加進來，而不會使無線媒介惡化。在論文中，我們定義了一些參數以及建立了一個模擬環境，來檢驗所提出的方法的效能。 With the promotion of wireless technologies, more and more devices are built-in wireless capabilities such as notebook, PDA and cell phones. There are much more wireless applications from the cell phone, GRPS (General Packet Radio Service) mobile phone capable of browsing the Internet, to the notebook that supports video conference. The traditional wireless technology confronted with some shortcomings in practical use, such as insufficiency for bandwidth, and lack of guaranteed the QoS (Quality of Services). In this thesis, we propose an algorithm, called VAC (Virtual Admission Control), to regulate the call request for the provisioning of QoS in wireless LAN. First, we study some methods that have been proposed to support QoS in wireless LAN. These methods include changing the IFSs, changing backoff window in MAC, VS/VMAC and currently 802.11e draft. We combine the advantages of the above methods and propose the VAC algorithm applied for the wireless LAN. VAC can admit some requested demands without deteriorating the wireless medium too much. Finally, we define some notations and construct a simulation environment to verity the performance of the proposed algorithm.
