Robust Secure Transmission in MISO Channels with Imperfect ECSI

This paper studies robust transmission schemes for MISO wiretap channels with imperfect channel state information (CSI) for the eavesdropper link. Both the cases of direct transmission and cooperative jamming with a helper are investigated. The error in the eavesdropper´s CSI is assumed to be norm-bounded, and robust transmit covariance matrices are obtained based on worst-case secrecy rate maximization, under both individual and global power constraints. Numerical results show the advantage of the proposed robust design. In particular, under a global power constraint, although cooperative jamming is not necessary for optimal transmission with perfect eavesdropper´s CSI, we show that robust jamming support can increase the secrecy rate in the presence of channel mismatch.