Filter-and-forward distributed relay beamforming for cognitive radio systems

In this paper, the problem of distributed beamforming for cognitive radio systems with frequency-selective channel is studied. Our proposed scheme is based on the filter-and-forward (FF) relay beamforming approach and aims to maximize the received signal to interference plus noise ratio (SINR) at the secondary destination, while suppressing the interference introduced to the primary user. This scheme is further extended to accommodate a relay node output power constraint. Under certain conditions, the extended scheme can be transformed into two sub-schemes with lower computational complexity, where their closed-form solutions are derived. Simulation results are provided to show the performance of the proposed schemes.