IEEE 802.11e無線區域網路中支援服務品質的機制之研究

Abstract

IEEE 802.11 wireless LAN is widely deployed currently. With the ever increase of transmission bandwidth, there is a growing demand on multimedia applications for such a wireless network. Therefore, how to support the quality of service(QoS) in IEEE 802.11 networks has became a hot research topic for the past few years. IEEE working group has thus proposed a new standard, IEEE 802.11e, recently to provide QoS capability for multimedia traffic in the IEEE 802.11 wirelss network. In this thesis, we proposed two QoS provisioning mechanisms to be employed in the IEEE 802.11e EDCA scheme. These two mechanisms contain the contention-based call admission control function and the adaptive contention window adjustment capability, respectively. With the contention-based call admission control function, the Quality of Service Access Point (QAP) decides whether to accept a new traffic stream request based on the access category of the new request as well as the current traffic statistics of established traffic connections. The call admission control method can not only guarantee the QoS of established connections of higher priority Access Category traffics but also protect the minimum reserved bandwidth for lower priority Access Category traffics. In addition, the adaptive contention window adjustment algorithm can dynamically adjust the maximum and minimum contention window size of each AC according to the established connection number of different ACs. Such an approach can decrease the collision probability effectively to reduce the packet delay significantly. Performance results via simulations have demonstrated the advantages of employing these two mechanisms in the IEEE 802.11 wireless networks.