PCAP: Proportional Channel Access Probability Fairness in Multi-rate IEEE 802.11 DCF

The 802.11 standard supports multiple data transmitting rates. The "throughput fairness" characteristic of the standard DCF appears undesirable, because of the high rate nodes has same channel access probability with the low rate ones. COT-based fairness is proposed with the purpose of guaranteeing fairness and improving the aggregate throughput, but the COT fairness is achieved by adjusting stations\´ packet length and sending multiple back-to-back packets at one time, it not suitable for all applications. The main contribution of this paper is the proposal of a PCAP(Proportional Channel Access Probability) fairness index. The index evaluate the fairness by the CAP which is in proportion to the nodes\´ transmission rates. This paper also proposed a PCAP-based fairness algorithm. With our algorithm, the stations in WLAN can achieve PCAP-based fairness which is independent with nodes\´ packet length. Through exclusive simulations, we show that the PCAP-based fairness index and algorithm leads to significant improvements in aggregate throughput and all stations have proportional fairness under multi-rate condition.