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.