Spectrum Sensing and Access in Cognitive Radio Networks

With tremendous growth in wireless services, the demand for radio spectrum has significantly increased. However, spectrum resources are scarce and most of them have been already licensed to existing operators. Recent studies have shown that despite claims of spectral scarcity, the actual licensed spectrum remains unoccupied for long periods of time. Thus, cognitive radio (CR) systems have been proposed in order to efficiently exploit these spectral holes, when licensed primary users (PUs) are not present. CRs or secondary users (SUs) are wireless devices that can intelligently monitor and adapt to their environment, hence, they are able to share the spectrum with the licensed PUs, operating when the PUs are idle. In this chapter, we discuss spectrum sensing and access in cognitive radio networks. Depending on the nature of the activities in the network, different categories of MAB problems have been formulated. Solutions and regret bounds are provided.