Covert Communication with Channel-State Information at the Transmitter

TL;DR

This paper derives the maximum covert communication rates over state-dependent channels with transmitter channel-state information, showing that CSI can enable positive covert capacity where it would otherwise be zero.

Contribution

It provides closed-form formulas for covert capacity with causal and noncausal CSI, and demonstrates the importance of CSI for covert communication over AWGN channels.

Findings

Covert capacity is positive with CSI at the transmitter for AWGN channels.

Without CSI, the covert capacity for certain channels is zero.

Lower bounds on secret key rates needed for achieving covert capacity.

Abstract

We consider the problem of covert communication over a state-dependent channel, where the transmitter has causal or noncausal knowledge of the channel states. Here, "covert" means that a warden on the channel should observe similar statistics when the transmitter is sending a message and when it is not. When a sufficiently long secret key is shared between the transmitter and the receiver, we derive closed-form formulas for the maximum achievable covert communication rate ("covert capacity") for discrete memoryless channels and, when the transmitter's channel-state information (CSI) is noncausal, for additive white Gaussian noise (AWGN) channels. For certain channel models, including the AWGN channel, we show that the covert capacity is positive with CSI at the transmitter, but is zero without CSI. We also derive lower bounds on the rate of the secret key that is needed for the transmitter and the receiver to achieve the covert capacity.