Dynamic MAC Parameters Configuration for Performance Optimization in 802.11e Networks

Quality of service support in wireless LAN is a theme of current interest. Several solutions have been proposed in literature in order to protect time-sensitive traffic from best-effort traffic. According to the EDCA proposal, which is a completely distributed solution, the service differentiation is provided by giving probabilistically higher number of channel accesses to stations involved in real-time applications. To this purpose, the MAC parameter settings of each contending stations can be tuned dynamically. In this paper, we face the problem of tuning the EDCA MAC parameters in common scenarios in which a given number of low-rate delay-sensitive traffic flows share the channel with some stations involved in data transfer. Our contribution is threefold. First, we show that, whenever possible, the delay constraints of the high priority class can be satisfied in both the cases of contention windows differentiation and inter-frame space differentiation. However, these mechanisms have different side effects in terms of bandwidth availability for the best effort stations. Second, we propose to exploit the MAC parameter dynamic settings of EDCA in order to probabilistically guarantee the delay requirements and to jointly maximize the aggregated throughput of the network. Finally, we suggest a very simple solution to automate these parameter settings in a real scenario, where traffic flows can be activated/deactivated dynamically, by simply monitoring the channel activity. The proposed solution is very robust, since it does not require any a priori traffic model or any network load estimator.