Hiding Communications in AWGN Channels and THz Band with Interference Uncertainty

TL;DR

This paper explores covert communication strategies in noisy wireless environments, demonstrating how interference uncertainty can enhance covert throughput in AWGN and THz bands, with novel reflection-based schemes for detection avoidance.

Contribution

It introduces a new covert communication scheme utilizing interference uncertainty and reflection techniques, extending covert communication theory to noisy wireless networks and THz bands.

Findings

Interference uncertainty benefits covert communication in AWGN channels.

Achieves higher spatial throughput despite lower covert throughput in AWGN.

Reflection-based schemes improve covert detection resistance in THz bands.

Abstract

Covert communication can prevent an adversary from knowing that a wireless transmission has occurred. In additive white Gaussian noise (AWGN) channels, a square root law is found that Alice can reliably and covertly transmit $\mathcal{O}(\sqrt{n})$ bits to Bob in $n$ channel uses. In this paper, we consider covert communications in noisy wireless networks, where the receivers not only experience the background noise, but also the aggregate interference from other transmitters. Our results show that uncertainty in interference experienced by the adversary Willie is beneficial to Alice. In AWGN channels, when the distance between Alice and Willie $d_{a,w}=\omega(n^{1/(2\alpha)})$ ($\alpha$ is the path loss exponent), Alice can reliably and covertly transmit $\mathcal{O}(\log_2\sqrt{n})$ bits to Bob in $n$ channel uses. Although the covert throughput is lower than the square root law, the spatial throughput is higher. In THz (Terahertz) Band networks,covert communication is more difficult because Willie can simply place a receiver in the narrow beam between Alice and Bob to detect or block their LOS (Line-of-Sight) communications. We then present a covert communication scheme that utilizes the reflection or diffuse scattering from a rough surface to prevent being detected by Willie. From the network perspective, the communications are hidden in the interference of noisy wireless networks, and what Willie sees is merely a "shadow" wireless network.