Dynamic Contention Window Control to Achieve Fairness Between Uplink and Downlink Flows in IEEE 802.11 WLANs

This paper considers a fairness issue between uplink and downlink flows in IEEE 802.11 wireless LANs, where uplink flows dominate over downlink flows in terms of wireless bandwidth usage. As a solution to this unfairness, the authors propose modifying the IEEE 802.11 MAC protocol at access points (APs). Our scheme dynamically controls the minimum contention window size at APs and provides an ample opportunity for them to acquire the transmission right. Because the control is based only on the number of downlink flows, APs can easily find the optimal window size to achieve per-flow fairness. Note that the proposed scheme does not require any modifications in the MAC protocol at wireless terminals. Through simulation experiments with UDP flows, the authors show that the proposed scheme can achieve fairness between uplink and downlink flows.