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Preemptive Opportunistic MAC Protocol in Distributed Cognitive Radio Networks

A preemptive opportunistic cognitive radio (CR) medium access control (MAC) protocol, which is called PO-MAC, is proposed for distributed CR networks. PO-MAC consists of three main phases: network initialization, reporting, and contention. The primary user (PU) channel exclusively assigned to each secondary user (SU) is sensed during the sensing period, and the sensing result is then reported to all other SUs without collisions during the reporting phase. Using the sensing results, SUs can preempt and make use of free channels via a contention method during the contention phase. It is demonstrated that PO-MAC outperforms existing CR MAC protocols in terms of the end-to-end delay and throughput performance. Further, it is shown that PO-MAC effectively operates when used in real-time services such as voice over Internet protocol.