Maximization of worst-case secrecy rates in MIMO wiretap channels

We study a multi-antenna wiretap channel, where the transmitter does not have perfect knowledge about the channels to the eavesdropper. The transmitter only knows that the logical location of the eavesdropper is drawn from a certain set. We characterize the worst-case secrecy rate in this scenario for given transmit strategies and derive an upper and a lower bound for the worst-case secrecy rate that is maximized under a sum power constraint at the transmitter. Finally, we discuss strategies for the high and low SNR regime and illustrate our results.