Optimal Admission Control For Secondary Users In Cognitive Radio Systems

The optimal admission strategy for secondary users (SUs) in a cognitive radio (CR) system with two types of primary users (PUs) is investigated in this paper. When an SU comes to the system, it will decide to either enter the system or give up its service and leave the system based on the current state (number of PUs and SUs) of the system. SUs can access the spectrum in an opportunistic way without interfering with the PUs. When any PU arrives, however, if the band is occupied by a SU, the SU's service on the band is interrupted and this SU is placed back to the waiting queue. Admitting each SU would bring a reward to the system provider but holding each US in the system would also incur some expenses (or cost) to the provider. We concentrate on the optimization problems of when to admit or reject a SU when all bandwidth are being used in order to achieve the maximum total discounted expected reward for any initial state. By developing a continuous time Markov decision process model, we verify that the optimal policy for admitting SUs is a state-related control limit policy. Our numerical results explained in both tables and diagrams are consistent with our theoretic results.