Spectrum sensing improvement by SNR maximization in cognitive two-way relay networks

In this paper, we consider a cognitive two-way relay network consisting of two primary transceivers and some cognitive radio (CR) terminals forming the secondary network. Assuming no direct link between the two primary transceivers, CR terminals play the relaying role when the primary transceivers are in operation to provide a two-step two-way relaying scheme for primary transmission. A cognitive base station (CBS) uses the received signal in the second step of relaying to detect the presence of the primary transmission. With the aim of increasing the accuracy of spectrum sensing at the CBS (trough signal-to-noise ratio maximization), we perform beamforming at CR terminals while satisfying the quality of service requirements at primary transceivers. This optimization problem is firstly relaxed to the semidefinite form and then solved iteratively. Simulation results demonstrate the superiority in terms of sensing performance for the proposed technique in comparison with conventional beamforming methods.