Providing secrecy when the eavesdropper channel is arbitrarily varying: A case for multiple antennas

Despite recent attempts with compound channel settings, guaranteeing information theoretically secure communication rates with no knowledge of the eavesdropper channel states has been elusive to date. In this work, we address this problem, and consider the worst case scenario where the eavesdropper's channel is arbitrarily varying, and is known only by itself. We show that it is possible to provide non-zero secure communication rates with the aid of multiple antennas. Under the mild assumption that the number of antennas at the eavesdropper is limited, we provide the strong secrecy rate for the MIMO wiretap channel. Specifically, it is proved that there exists a universal coding scheme that secures the confidential message against any sequence of channel states experienced by the eavesdropper. We show that the result is tight in terms of secure degrees of freedom.