  We propose a combined uplink/downlink opportunistic scheduling algorithm for
infrastructure WLANs. In the presence of both uplink and downlink flows, an
infrastructure WLAN suffers from the uplink/downlink unfairness problem which
severely decreases the throughput of the access point (AP). We resolve the
unfairness by maintaining a separate queue and a backoff timer for each
associated mobile station (STA) at the AP. We also increase the system
throughput by making the backoff time a function of the channel gains. This
reduces the collision probability also. We theoretically analyze the
performance of the system under symmetric statistics for all users and validate
the analysis by extensive simulations. Simulation results show increase in
system throughput by over 40% compared to the 802.11 MAC.
