FMAC for Coexisting Ad Hoc Cognitive Radio Networks

Media access control plays a critical role in cognitive radio networks (CRNs). In our previous work, we have proposed a fairnessoriented media access control (FMAC) protocol to achieve fair and efficient coexistence of infrastructure-based CRNs. In this paper, we enhance FMAC to be used for coexisting ad hoc CRNs, where no centralized base stations exist, and secondary users (SUs) access channel independently. In FMAC, the contention window size is essential to network performance such as throughput. We first derive the optimal contention window size, which can then be used by SUs to achieve optimal throughput. However, the optimal contention window size is closely related to the total number of users of all CRNs, which is typically unknown to each individual SU of coexisting ad hoc CRNs. We attack this problem by building a bridge between the average number of consecutive idle time slots and optimal contention window size, since the average number of consecutive idle time slots can be easily observed by each individual SU. Hence, SUs can independently adjust their contention window size by observing their current average number of consecutive idle time slots and eventually approach the optimal contention window without the information of the total number of SUs. Extensive simulations are conducted and the results verify that the enhanced FMAC is able to significantly improve the fairness among coexisting ad hoc CRNs while maintaining good throughput.