Adaptive coordination function for IEEE 802.11 wireless LANs

Multiple access control (MAC) protocols play a significant role in wireless LANs. The IEEE 802.11 MAC protocol specifies two coordination functions that are Distributed Coordination Function (DCF) and Point Coordination Function (PCF). While both DCF and PCF are available in a wireless cell, we propose a novel access mechanism called Adaptive Coordination Function (ACF) to support various classes of traffic. The ACF superframe comprises two periods, one TDMA period designed for real-time traffic and followed by an adaptive period which adaptively employs DCF or PCF to support non-real-time traffic. In this paper, we apply the theory of M/G/1 queues to analyze the performance of adaptive period in terms of queuing delay, end-to-end delay, and saturation throughput. With our analytic model, DCF or PCF can be invoked appropriately according to the number of stations, packet arrival rate, packet payload size, and effective channel bit rate. Analytical results are derived for an extensive throughput and delay performance evaluation of both DCF and PCF.