Power-Constrained Optimal Cooperative Jamming for Multiuser Broadcast Channel

Optimal cooperative jamming (CJ) is studied for multiuser multiple-input multiple-output (MU-MIMO) broadcast channel to enhance the physical layer security with the help of a friendly jammer (FJ). We first derive a necessary and sufficient condition to achieve the asymptotically perfect security and propose an optimal CJ scheme to minimize the maximum signal-to-interference-plus-noise ratio (SINR) at the eavesdropper subject to a power constraint at the FJ. Then we derive an achievable lower bound of the eavesdropper´s SINR and propose an asymptotically optimal CJ scheme achieving the lower bound. Numerical results demonstrate that the proposed schemes are effective.