Throughput Analysis of Cognitive Radio with OSTBC between Primary and Secondary Users

Cognitive radio can effectively improve spectrum utilization by allowing the secondary user to access spectrum licensed to the primary user. According to cognitive radio principle, the secondary user can access the channel only when sensed idle. In this paper, we study the spectrum-sharing problem of a basic cognitive network consisting of a primary user (PU) link and a secondary user (SU) link, and propose a novel spectrum-sharing scheme in which transmission diversity of the primary user is formed by the secondary user actively acting as its cooperative relaying through orthogonal space-time block coding (OSTBC). We show by SU appropriately choosing its transmission power the primary user´s probability of outage is reduced and the SU´s available idle slots are increased significantly when compared to direct relaying. We use a Markov chain to model PU´s state transition process which is formed due to interference and cooperation from SU and derive the closed-form expression of the secondary user link´s throughput in our proposed scheme and compare it with that in existed scheme by numerical simulation; results show our proposed scheme can achieve a higher throughput.