Optimal Coordinated Beamforming with Artificial Noise for Secure Transmission in Multi-Cell Multi-User Networks

This paper investigates how to achieve secure information transmission in multi-cell multi-user networks, where artificial noise (AN) aided multi-cell coordinated beamforming (MCBF) is designed to guarantee the authorized users' QoS requirements while avoiding the information being intercepted by unauthorized users. To realize the green communication target, we formulate an optimization problem to minimize the total transmit power by jointly optimizing the beamforming and AN vectors at all BSs. Since the problem is nonconvex and not easy to be solved by using existing solution methods, we then solve it by applying semi-definition relaxation (SDR) and prove that our proposed method can guarantee the global optimal solution under full channel state information (CSI). Moreover, we further design a distributed AN-aided MCBF for the system by using alternating direction method of multipliers (ADMM), with which each BS can calculate the beamforming and AN vectors with its local CSI. Simulation results demonstrate our analysis, which show that our proposed distributed algorithm converges to the optimal results obtained by the centralized one. It is also observed that for the same secure transmission requirement, the total power consumed by our proposed AN-aided MCBF decreases with the increment of transmit antennas, where less part of the power is used by AN and more part is used for information beamforming.