Performance analysis of a relay-aided cognitive radio network with multiple secondary links

In this paper, we propose a cooperative cognitive radio (CR) network, where several secondary sources can simultaneously transmit their information to the destinations via a relay network. We efficiently exploit an optimal cooperative beamforming (CBF) method for the investigated CR network and show that the secondary sources can simultaneously communicate with the secondary destinations irrespective of whether the primary link is idle or not. The proposed CBF can simultaneously maximize the received signal to interference plus noise ratio (SINR) at the secondary destinations while keeping the interference plus noise power at the primary destination below a predefined threshold. To investigate the efficiency of our proposed model, we increase the number of secondary links and consider the received SINR at the secondary destinations and interference plus noise power at the primary destination. We optimize the proposed CBF vector by solving a convex semidefinite problem (SDP) using the bisection search algorithm. Moreover, we investigate the performance of the proposed system model by increasing the channel occupancy probability of the primary user (PU) link. Outage probability is also another key event of our interest which is investigated. Numerical results show the efficiency and robustness of our strategy.