Covert Communication Gains from Adversary's Uncertainty of Phase Angles

TL;DR

This paper demonstrates that in IRS covert communication, leveraging the adversary's uncertainty of phase angles can double the covertness gain, which saturates at N=2 and does not improve further with more phase angle pairs.

Contribution

It reveals that the maximum covert gain from phase uncertainty is achieved at N=2, providing new insights into phase-based covert communication strategies.

Findings

Achieves a covertness gain of 2 using phase uncertainty.

The gain saturates at N=2 and does not increase with larger N.

The approach enhances covert communication effectiveness over AWGN channels.

Abstract

This work investigates the phase gain of intelligent reflecting surface (IRS) covert communication over complex-valued additive white Gaussian noise (AWGN) channels. The transmitter Alice intends to transmit covert messages to the legitimate receiver Bob via reflecting the broadcast signals from a radio frequency (RF) source, while rendering the adversary Willie's detector arbitrarily close to ineffective. Our analyses show that, compared to the covert capacity for classical AWGN channels, we can achieve a covertness gain of value 2 by leveraging Willie's uncertainty of phase angles. This covertness gain is achieved when the number of possible phase angle pairs $N=2$. More interestingly, our results show that the covertness gain will not further increase with $N$ as long as $N \ge 2$, even if it approaches infinity.