一個無線區域網路上基於EDCA之串流排程保證機制

Abstract

IEEE 802.11e標準被制定用於無線區域網路以提供服務品質(QoS)，然而它依然無法在無線網路上滿足例如網際網路電話的多媒體應用。本篇論文的目的是透過一個簡單更改EDCA的方式對及時封包提供可靠的服務品質，包含時間顫動(jitter)、延遲(delay)、流通量(throughput)。我們提出一個中控式架構，在此架構內，基地台將根據服務品質需求的存取類別(Access Category)之數量，整體性地管理EDCA傳送參數，此參數包括AIFSN與競爭窗格(Contention Window)大小。基地台也將依據允許的延遲敏感封包的流量進行允入控制(admission control)。另外為了保證工作站之間的競爭遵守嚴謹的優先權，基地台會使用兩種EDCA參數設定組態以處理不同數量具服務品質需求的存取類別，一種是指定唯一的AIFSN(UAA)，另一種是競爭窗格分割(CWP)。我們提出的架構避免複雜的polling機制同時能大幅減少及時流量的時間顫動。模擬結果顯示使用我們之方法所得到時間顫動延遲的標準差將比使用標準802.11e EDCA的效果大幅改善50%以上。

IEEE 802.11e standard is developed for quality of service (QoS) provisioning in wireless local area networks. However, it is still difficult to achieve satisfactory quality for multimedia applications, such as voice over IP (VoIP). The motivation of this thesis is to provision reliable QoS, including jitter, delay and throughput, for real-time traffic through a simple modification to EDCA. We propose a centralized scheme in which access point (AP) globally manages EDCA transmission parameters, including arbitration interframe space number (AIFSN) and contention window (CW) size, based on number of active QoS access categories (AC), as well as performs admission control based on the volume of admitted delay-sensitive flows. Besides, in order to guarantee strict priority contention between stations, AP will work with two EDCA configurations, unique AIFSN assignment (UAA) and contention window partitioning (CWP), which can be applied to cope with different volume of QoS ACs. Our proposed scheme avoids complex polling mechanism and is able to reduce the jitter of real-time traffic significantly. The simulation results show that up to 50 percent reduction in standard deviation of jitter delay can be achieved comparing with using IEEE 802.11e EDCA.