Filter-and-forward relay design in cognitive two-way relay networks

In this paper the filter-and-forward (FF) strategy is developed for an overlay cognitive radio (CR) network with frequency selective channels. The system comprises two primary users (PUs) and two secondary users (SUs). One of the SUs is a multi-antenna node which is employed for two-way relaying between PUs and spectrum sharing is achieved by superposing the secondary signal to filtered signals of PUs. We propose an alternating optimization algorithm to joint design of beamforming filter and power allocation in secondary relay node. The relay design is based on maximizing SINR of secondary receiver while ensuring quality of service (QoS) requirements of PUs and the maximum allowable relay transmit. Simulation results show that the proposed FF approach improves performance of system compared with traditional AF relaying strategy.