Channel Occupancy Time Based TCP Rate Control for Improving Fairness in IEEE 802.11 DCF

In the IEEE 802.11 distributed coordination function (DCF), the basic service set (BSS) suffers from two unfairness issues: 1) performance anomaly and 2) uplink/downlink unfairness. In this paper, to solve these issues, we propose a window control scheme in the Transmission Control Protocol (TCP) for the IEEE 802.11 DCF mode. The proposed scheme is called channel occupancy time based rate control for TCP (COTRC-TCP). COTRC-TCP controls the maximum window size based on the throughput estimated at the TCP layer so that each station can use the wireless channel for equal duration. The throughput estimation is based on the number of active stations and the channel occupancy period used by each station in the BSS, which are monitored at the Medium Access Control (MAC) layer. The proposed scheme forms a cross-layer approach that involves both MAC and transport layers. The performance of COTRC-TCP over multirate IEEE 802.11 DCF is evaluated and compared with that of previous works through extensive simulations. Simulation results show that COTRC-TCP exhibits fairness in terms of channel-occupancy time among the competing stations, which accordingly remedies the unfairness problems. The proposed scheme also improves the transmission efficiency.