On the Secrecy Degrees of Freedom of Multi-Antenna Wiretap Channels with Delayed CSIT

TL;DR

This paper investigates the secrecy degrees of freedom in multi-antenna wiretap channels with delayed channel state information, revealing positive SDoF guarantees and optimal strategies for secure communication.

Contribution

It characterizes the SDoF in MISO wiretap and broadcast channels with delayed CSI, introducing optimal artificial noise schemes for secure transmission.

Findings

Positive SDoF guaranteed with delayed CSI

Optimal SDoF of 2/3 with delayed CSI on both channels

Artificial noise schemes achieve the optimal SDoF region

Abstract

The secrecy degrees of freedom (SDoF) of the Gaussian multiple-input and single-output (MISO) wiretap channel is studied under the assumption that delayed channel state information (CSI) is available at the transmitter and each receiver knows its own instantaneous channel. We first show that a strictly positive SDoF can be guaranteed whenever the transmitter has delayed CSI (either on the legitimate channel or/and the eavesdropper channel). In particular, in the case with delayed CSI on both channels, it is shown that the optimal SDoF is 2/3. We then generalize the result to the two-user Gaussian MISO broadcast channel with confidential messages and characterize the SDoF region when the transmitter has delayed CSI of both receivers. Interestingly, the artificial noise schemes exploiting several time instances are shown to provide the optimal SDoF region by masking the confidential message to the unintended receiver while aligning the interference at each receiver.