Spectrum sharing based on detection thresholds for cognitive radio with cooperative relay

Cognitive radio can greatly improve spectrum utilization by access spectrum licensed to the primary user. Spectrum-sharing problem of a basic cognitive network consisting of a primary user (PU) link and a secondary user (SU) link was studied, and a novel spectrum-sharing scheme in which transmission diversity of PU is formed by SU actively acting as its cooperative relaying through orthogonal space-time block coding (OSTBC) was proposed. A four-state Markov chain based on detection thresholds was used to model PU's state transition process and the closed-form expression of PU and SU link's throughput was derived. The simulation results show PU's probability of outage is reduced and the SU's available idle slots are increased significantly through SU appropriately choosing its transmission power, which can finally result in a higher throughput for SU when compared to direct relaying and without relaying.