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. For the scenario in which spherical uncertainty for both the legitimate and the eavesdropper channels is included, 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. 
Jiangyuan Li and Athina P. Petropulu
cs.IT math.IT