A cognitive rate separation IEEE 802.11b MAC with airtime fairness

The maximum throughput is limited by the slowest transmitting station in IEEE 802.11 distributed coordination function (DCF) medium access control (MAC), giving rise to the rate anomaly problem. This limitation is carried into a cognitive IEEE 802.11b DCF MAC. In our paper, we propose airtime fairness in a cognitive rate separation IEEE 802.11b MAC. Stations are grouped according to their transmission rates for transmitting their packets in different data transmission periods (DTPs) for the different groups of stations. A sensing period is used to sense for primary transmissions. The analytical framework is formulated for N stations, including an access point (AP). The state transition diagram is modeled by a two-dimensional discrete-time Markov chain. The saturated throughput is approximated by the sum of the product of a weighted ratio of the throughput of the DTP under consideration and the throughput of the DTP minus the period necessary to transmit a packet before the end of the current DTP, the probability of the number of devices in the DTP, the number of DTPs and the probability of false alarm. The DTPs to achieve airtime fairness are formulated as non-linear equations, which are solved using Newton-Raphson method with Jacobian functions. Numerical results of the saturated throughput corresponding to typical parameter values are presented. The advantage of the proposed cognitive rate separation IEEE 802.11b MAC with airtime fairness is shown through achieving airtime fairness and high saturated throughput.