On Fairness Enhancement for CSMA/CA Wireless Networks

Location dependency and its associated exposed receiver problem create the most severe unfairness scenario in CSMA/CA protocol. To address this issue, we develop an analytical model to study 1) the likelihood of the exposed receiver problem and how this likelihood varies with the carrier sensing and the transmission ranges; 2) the probabilities of successful RTS receptions and of successful RTS/CTS handshakes of the disadvantaged link under the typical exposed receiver scenario. Based on the analytical insights, we propose a receiver assistance feature as addition to the CSMA/CA protocol so that the receiver of a disadvantaged link can help the sender to contend for channel access. In terms of compatibility with the existing 802.11 protocol, the proposed feature requires only one bit of modification in the packet header. Simulation results show that the proposed feature not only significantly improves the fairness of the CSMA/CA protocol, but also increases the overall throughput, all accomplished without creating other side effects, such as aggravation of the hidden terminal problem.