On the Optimality of the Stationary Solution of Secrecy Rate Maximization for MIMO Wiretap Channel

To achieve perfect secrecy in a multiple-input multiple-output (MIMO) Gaussian wiretap channel (WTC), we need to find its capacity and optimal signaling, which involves solving difference of convex functions program known be non-convex for the non-degraded case. deal with this, class existing solutions have been developed but only local optimality is guaranteed by standard convergence analysis. Interestingly, our extensive numerical experiments shown that these optimization methods indeed global optimality. In this letter, provide an analytical proof observation. show Karush-Kuhn-Tucker (KKT) conditions rate maximization problem admit unique solution both degraded cases. Motivated also propose low-complexity algorithm stationary point. Numerical results are presented verify theoretical