Date of Award


Document Type

Master Thesis

Degree Name

Master of Engineering (Research)


Electronic Engineering

First Advisor

Dr. Dirk Pesch


The growing demand for mobile computing worldwide has led to the increasing deployment and use of Wireless Local Area Networks (WLANs) in the last number of years. During this time, user requirements have evolved, resulting in a more diverse mix of services being carried over the wireless medium. In particular, delay sensitive real-time applications such as streaming multimedia and voice over IP are growing in importance. The widely accepted IEEE 802.11b standard, however, was not designed with sufficient Quality of Service (QoS) constraints for such applications. A new draft of the standard named 802.1 le has been proposed that deals with QoS issues for WLANs. The 802.1 le enhancement has been shown to provide an improved QoS for time-bounded services. The higher priority traffic receives the highest throughput and lower access delay at the MAC layer. However, the nature of the medium access strategy defined for 802.11 WLANs means that during periods of congestion, large delays are experienced at the MAC layer, causing a degradation in the QoS provided to the active real-time sessions.

Load balancing is seen as an effective approach to deal with this problem. Some users could be handed off to neighbouring, lightly loaded access points (APs) lessening the load at the overloaded AP, thus improving the QoS for all sessions. The contribution of this thesis is a load balancing procedure called cell breathing. Based on QoS measurements in each Basic Service Set Area (BSSA), an AP will determine its loading state. An AP in a congested state will reduce its transmit power and request neighbours to increase theirs to ensure seamless network coverage. Adjustment of transmit powers has the effect of changing the coverage pattern of AP's, thus allowing overloaded AP's to shed users, resulting in a more even balance of the load in local spheres of the network.


Submitted to the Higher Education & Training Awards Council, August 2005.

Access Level