Optimal and Suboptimal Full-Duplex Secure Beamforming Designs for MISO Two-Way Communications

In this letter, we investigate full-duplex (FD) secure beamforming design problem for multiple-input-single-output two-way communication systems. Our objective is to maximize sum secrecy rate under sum transmit power constraint. We propose a globally optimal solution which solves the optimization problem by two-dimensional (2-D) search. In each iteration of 2-D search, a semidefinite programming is solved. To reduce computational complexity, we propose a null-space based suboptimal solution which solves the optimization problem by one-dimensional search. Furthermore, we also propose a closed-form low-complexity suboptimal solution. Simulation results demonstrate that all the proposed solutions for the FD secure beamforming achieve higher average sum secrecy ratethan the half-duplex one.