PNC-Aided Robust Secure Beamforming Design for Two-Way Relay Networks with Artificial Noise

In this paper, we study a two-way relay network (TWRN), in which eavesdroppers' channel state information is imperfect, and all the eavesdroppers collude to form joint receive beamforming for enhanced receptions. To ensure the robustness of the TWRN, we design the transmit beamforming and establish two secure beamforming design formulations, which combines the physical layer network coding with artificial noise technique at the relay. One secure beamforming design formulation is to minimize the total transmit power in the TWRN, and the other one is to guarantee a maximum secrecy sum rate (SSR) in the worst-case. With the help of approximation techniques, the former optimization problem is converted into a convex problem, whose semidefinite relaxation solution is rank-one. However, due to the maximum available power limit of the system, the power optimization problem may be infeasible. To overcome this problem, the SSR optimization formulation is presented, and the optimization problem is decoupled into two subproblems that can be transformed into the convex forms. Finally, it is verified by the numerical results that the proposed schemes are effective.