Adaptive medium access mechanisms for quality of service support over wireless local area networks

This dissertation investigates adaptive medium access mechanisms to provide Quality of Service (QoS) over Wireless Local Area Networks (WLANs) thereby enabling end-to-end QoS over current heterogeneous Internet. Our main purpose is to study the impact and benefit of introducing adaptive mechanisms into wireless Medium Access Control (MAC) protocols. Our work is based on previous efforts of QoS enhancing mechanisms for wireless MAC protocols. In particular, we consider the MAC protocols defined in the upcoming IEEE 802.11e standard.; First, we demonstrate via simulations that although service differentiations can be achieved by assigning different Channel Access Parameters (CAPS) to different traffic classes at the MAC layer, the assignment of fixed CAP values is not sufficient to provide guaranteed QoS for real-time applications because of the dynamic nature of traffic load and channel conditions. We proposed SEDCA (Smart Enhanced Distributed Channel Access) to enhance the QoS support of EDCA mode which was proposed in 802.11e standard draft.; Second, since we found that channel utilization could also be enhanced by adapting CAPS, we proposed a new framework called HARMONICA to efficiently manage the resources of 802.11 WLANs. By introducing a novel Link-layer Quality Indicator (LQI) for the Access Point (AP) to easily measure the QoS experienced by traffic flows in different QoS classes, we proposed two adaptive algorithms to adapt CAPs for each traffic class to best match the required QoS requirements and the channel conditions. We also designed a simple admission control mechanism to avoid congestion. Through extensive simulations, we demonstrated that under an interference-free environment, HARMONICA can guarantee the QoS for all traffic classes, while simultaneously achieving quasi-optimal channel utilization.; Third, we address the issues of extending parameterized QoS support to WLANs. We proposed Wireless Subnet Banwidth Manager (Wireless SBM) protocol which support the signaling between WLAN components and RSVP/SBM daemons. We discussed the design issues of Wireless SBM focusing on synchronization between the HCCA (HCF Controlled Channel Access) signaling process and the RSVP/SBM protocol. The QoS mapping between them is also investigated. We evaluated the performance of HCCA mode to investigate its benefits on resource scheduling and management. Our simulations revealed that a simple HCCA scheduler is efficient to make parameterized QoS reservation for Constant Bit Rate (CBR) application flows. However, the design of an efficient scheduler for Variable Bit Rate (VBR) traffic flows remains a challenge, and a good scheduler for VBR flows should be able to adapt to the bursty traffic of VBR applications.