Adaptive Transmission Control for Uplink/Downlink Fairness in Unsaturated CSMA Networks

In carrier sensing multiple access (CSMA)-based IEEE 802.11 systems, it is important for an access point (AP) and multiple stations to have access opportunity proportional to their traffic load, ensuring fairness between uplink (UL) and downlink (DL). This letter proposes an adaptive backoff algorithm based on estimation for the UL/DL backlog sizes in unsaturated CSMA networks. Based on the UL/DL backlog estimation, the optimal UL and DL transmission probabilities are derived as a function of the UL/DL backlog sizes. The proposed algorithm not only improves the overall system performance but also provides the near-perfect UL/DL fairness.