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, in which a multi-antenna source communicates with a single-antenna destination in the presence of one single-antenna eavesdropper. It is assumed that both the channel to the destination and the channel to the eavesdropper contain spherical uncertainty. The problem of finding the optimal input covariance that maximizes the worst-case secrecy rate subject to a sum power constraint is studied, and an explicit expression for the maximum worst-case secrecy rate is provided.