Cooperative Beamforming in Cognitive Radio Network with Two-Way Relay

This paper investigates the cooperative beamforming in the amplify-and-forward-based cognitive relay network. Beamforming coefficients are designed to maximize the sum rate of the secondary users with a total transmit power constraint of the relays and an interference power constraint at the primary receiver. The sum rate maximization problem is firstly solved by characterizing the achievable rate region. This method is optimal but of great complexity. Then, an iteration algorithm based on semidefinite programming (SDP) and the first order Taylor polynomial which has lower complexity but comparable performance is introduced. Simulation results confirm the feasibility of these two methods for the sum rate maximization problem in the cognitive relay network and demonstrate that the lower complexity method finds the global optimum of the problem just as the rate region method does.