Soft per-flow throughput guarantees in contention based WLANs

Abstract

The mandatory Medium Access Control(MAC) protocol for 802.11 wireless local area networks (WLANs) does not provide hard throughput guarantees for flows with strict throughput requirements because it is contention based. However its universal implementation by 802.11 equipment vendors is testimony to its popularity. Doe to this large installed base, there are potentially great benefits to the user base if improvements are made to the WLAN protocols to at least provide soft per flow throughput guarantees. Accordingly, this paper proposes some improvements to infrastructure WLANs for this purpose. The improvements are mainly at the Access Point (AP) in the form of per flow queues for real-time (RT), Weighted Fair Queueing (WFQ) scheduling and a new Contention Window(CW) adjustment algorithm. The AP will also perform rate estimation for admission control. Simulation results show that the CW adjustment algorithm is resilient even under saturation conditions. A simple traffic measurement technique we propose however guards against saturation conditions occurring.