On the Multi-Antenna Wiretap Channel with Delayed CSI at the Transmitter

Abstract

The multi-input single-output (MISO) Gaussian wiretap channel with delayed channel state information (CSI) available at the transmitter and at the eavesdropper is investigated. This scenario may occur when the legitimate receiver sends its channel state to the transmitter via a delayed feedback link which can be also overheard by an eavesdropper. We show that delayed CSI, even completely outdated, offers the opportunity to ensure the secrecy. Namely, by aligning the artificial noise at the legitimate receiver, a secrecy degrees of freedom (SDoF) of 1/2 can be achieved. It turns out that the result is irrelevant to whether the transmitter knows the legitimate channel or the eavesdropper channel with a delay and both cases yield the equivalent opportunity. The artificial noise scheme can be further extended to the case of broadcast channel with two confidential messages.