Differentiation of downlink 802.11e traffic in the virtual collision handler

A number of analytical models have been proposed to describe the priority schemes of the enhanced distributed channel access (EDCA) mechanism of the IEEE 802.11e standard. EDCA provides a class-based differentiated quality of service (QoS) to IEEE 802.11 WLANs. Many have used a multiple number of nodes to study the differentiation behaviour of the model. However, in many real-life usage scenarios Internet traffic is often asymmetric with much downlink traffic from the access point to the stations and little traffic in the reverse direction. Hence, most of the overall traffic differentiation will happen in the virtual collision handler (VCH) of the access point. If the access point uses EDCA, it should know the characteristics of the VCH to be able to control the differentiation of the downlink traffic. The main contribution of this paper opposed to other works is that it demonstrates how a generic channel model of 802.11e can be modified to predict the performance behaviour of the VCH with a remarkably good accuracy. In doing so, we first introduce virtual collision handling into the generic model. We also show how to derive a closed-form solution for the performance. We observe good match between the analytical model and simulations