Opportunistic Spectrum Access in Multiple-Primary-User Environments Under the Packet Collision Constraint

Cognitive radio (CR) technology has great potential to alleviate spectrum scarcity in wireless communications. It allows secondary users (SUs) to opportunistically access spectrum licensed by primary users (PUs) while protecting PU activity. The protection of the PUs is central to the adoption of this technology since no PU would accommodate SU access to its own detriment. In this paper, we consider an SU that must protect multiple PUs simultaneously. We focus on the PU packet collision probability as the protection metric. The PUs are unslotted and may have different idle/busy time distributions and protection requirements. Under general idle time distributions, we determine the form of the SU optimal access policy and identify two special cases for which the computation of the optimal policy is significantly reduced. We also present a simple algorithm to determine these policies using principles of convex optimization theory. We then derive the optimal policy for the same system when an SU has extra "side information" on PU activity. We evaluate the performance of these policies through simulation.