Explicit solution of worst-case secrecy rate for MISO wiretap channels with spherical uncertainty

A multiple-input single-output (MISO) wiretap channel model is considered, that includes a multi-antenna transmitter, a single-antenna legitimate receiver and a single-antenna eavesdropper. Assuming a spherical uncertainty model for for both the legitimate and the eavesdropper channels, the problem of finding the optimal input covariance that maximizes the worst-case secrecy rate subject to a power constraint is considered, and an explicit expression for the maximum worst-case secrecy rate is provided.