Achieving Temporal Fairness in Multi-Rate 802.11 WLANs with Capture Effect

This paper proposes new MAC layer transmission opportunity (TXOP) adaptation algorithms for achieving temporal fairness in multi-rate 802.11 WLANs, which take underlying capture effect into account. Due to capture effect, a frame with the strongest received signal strength can be correctly decoded at the receiver even in the presence of transmission collisions from multiple contending stations. This effect introduces significant imbalance in channel access probabilities, and consequently the use of equal TXOP for each contending station cannot achieve temporal fairness. We develop a centralized and a distributed TXOP adaptation algorithm that compensate the stations with less channel access opportunities by giving them larger TXOPs. In the proposed centralized scheme, the access point estimates the successful TXOP acquisition probability of each associated station and allocates appropriate TXOPs to the contending stations. In the proposed distributed algorithm, each station estimates its own share of channel occupation time and adjusts its TXOP individually. We present the conditions that ensure the convergence of the distributed algorithm. Simulation results show that our proposed schemes can effectively achieve "true" temporal fairness.