Utilising power capture for service differentiation in wireless LANs

In recent years, wireless communication systems have become pervasive, allowing continuous connectivity for people on the move, at home and in the workplace. The advent of third generation (3G) systems with capabilities beyond traditional telephony, and the explosive uptake of wireless Local Area Networks (LANs) are but two factors that have contributed to this growth. By virtue of their appeal to the market, wireless LANs have proven to be a serious contender as the access technology of choice for traditional data as well as the emerging 3G networks. If wireless LANs are to be successful as an access technology, however, the issue of Quality of Service (QoS) support will need to be addressed. QoS support for wireless LANs is becoming increasingly important because applications requiring such support, e.g. voice and video, are becoming more common in today's hybrid wireless systems, with the trend expected to grow into the future. The dominant standard for wireless LANs is the IEEE's 802.11 of which the contention-based Medium Access Control (MAC) protocol; also known as the Distributed Coordination Function (DCF), is universally supported. While the DCF is widely supported, it provides no QoS support. In this work, we propose and study a new and different mechanism of achieving service differentiation in 802.11 wireless LANs. Our approach employs the capture effect as the vehicle for achieving QoS differentiation for the contention mode of the standard. This approach enriches current research efforts by providing another dimension to QoS provisioning in wireless LANs. Hitherto most proposals have focussed on the modification of some aspect of the protocol, such as the minimum contention window size (CWmin), the Distributed Inter-Frame Space (DIFS), or the maximum contention window size (CWmax), amongst others. Capture based service differentiation complements these efforts. It can be used alone or in conjunction with existing approaches to provide additional priority classes.In this thesis, the capture based service differentiation approach is proposed and studied through Markov chain modelling and simulation. From the study, the following conclusions were drawn. It was confirmed that capture based service differentiation is a feasible approach in wireless LANs and that it can be achieved with practical and sustainable power differences between the transmitters from different classes. A number of factors were found to influence the level of service differentiation, including the population ratios of hosts in the power classes, the power ratios of the transmitters as well as the capture threshold of the receiver. For practical considerations, a complete architectural framework is also proposed, including support functions such as Transmission Power Control (TPC), QoS Signalling and Admission Control