使用增進式 HCF 模式提供整合語音與數據服務無線區域網路之分析

Abstract

隨著對無線行動通訊的需求日益提升，無論身在何處，每個人都可以用更高的傳輸速度及更經濟的方式連上網際網路。最近，無線區域網路(WLAN)被視為第三代無線通訊系統(3G)的延伸，使其無線通訊系統更能達到更強大的功能。而其中對於無線區域網路，能提供多媒體傳輸服務品質保證(QoS)就變成一個非常重要的議題。在這篇論文中，我們針對兩個不同等級的服務，在無線區域網路中延伸式分散協調式功能(EDCF)，提出一個能達到公平比例分配頻寬的方法。我們針對兩個不同的等級的服務，利用排隊模型做行為上的分析，並且分析的結果和電腦模擬來比較，由模擬結果可顯示我們可達到公平比例分配頻寬的目標，藉由依照不同的比例目標，調整不同的仲裁訊框間隔 (Arbitration Inter Frame Space) 及競爭視窗 (contention window) 可以公平比例分配頻寬。 再者，在無線區域網路中，我們提出一個在混合協調式功能(HCF)中，整合語音及數據服務的方案，結合輪詢模式(polling-based)及競爭模式(contention-based)的演算法，稱做需求輪詢機制 (on-demand polling)。藉由需求輪詢機制，我們可以在無線區域網路中，保證語音延遲的服務品質，並且有效提升數據服務的總傳輸量。

There is an increasing demand for “mobile information” that everyone can access to the Internet at high speed but with low cost whenever they are. Recently, wireless local area network (WLAN) has been considered as a complement technology for 3rd Generation (3G) technology. The quality of service (QoS) assurance is then becoming an important issue for supporting wireless multimedia services in WLAN. In this thesis, we propose a method to achieve weighted fairness for two classes of services operating under the enhanced distributed coordinator function (EDCF) mode of 802.11e. A queueing model is proposed to analyze the behavior of the two classes. The analytical results have been verified by computer simulation. Simulation results showed that the weighted fairness is achieved by adjusting the Arbitration Inter Frame Space (AIFS) and the contention window (CW) according to the assigned weights for different wireless multimedia services. Moreover, we consider to support integrated services, such as interactive voice and non-real-time data service, in WLAN. We propose a combination of polling-based and contention-based algorithm based on HCF mode, called on-demand polling (ODP) scheme. The ODP scheme can guarantee the delay requirement of voice and increase the aggregate throughput of non-real-time data service efficiently.