Call admission control with Soft-QoS based spectrum handoff in cognitive radio networks

In Cognitive Radio (CR) networks, spectrum handoff is an important functionality to guarantee the reliability and continuity of the communications of Secondary Users (SUs). In this paper, we integrate soft-QoS based spectrum handoff mechanism into the framework of Call-Admission-Control (CAC) for CR networks. By doing so, the proposed CAC strategy has in-built capability to deal with resilient services of wireless applications, and hence obviously improves the QoS and spectrum utilization of CR networks. We adopt Markov chain model to describe the procedures of the proposed CAC and spectrum handoff strategy. After that, the problem is formulated as a nonlinear optimization where the dropping probability is minimized under the constraint of blocking probability. The method of branch-and-bound is employed to make the optimization problem tractable. The proposed CAC strategy is evaluated through simulation experiments. The numerical results indicate that the proposed CAC strategy outperforms two traditional CAC strategies. It achieves a much better tradeoff in dropping and blocking probabilities, and meanwhile significantly enhances the spectrum utilization of CR networks.