Challenges in Covert Wireless Communications with Active Warden on AWGN channels

TL;DR

This paper investigates how an active, multi-antenna warden can detect covert wireless transmissions over AWGN channels, revealing limitations of existing laws and highlighting the importance of warden mobility and capabilities.

Contribution

It analyzes the impact of an active, multi-antenna warden on covert communication detection, challenging the square root law and providing new insights into detection strategies.

Findings

Active warden can detect transmission via trend tests using samples from different locations.

The square root law does not hold when the warden is active and mobile.

Multiple antennas make the warden more effective and reduce detection time.

Abstract

Covert wireless communication or low probability of detection (LPD) communication that employs the noise or jamming signals as the cover to hide user's information can prevent a warden Willie from discovering user's transmission attempts. Previous work on this problem has typically assumed that the warden is static and has only one antenna, often neglecting an active warden who can dynamically adjust his/her location to make better statistic tests. In this paper, we analyze the effect of an active warden in covert wireless communications on AWGN channels and find that, having gathered samples at different places, the warden can easily detect Alice's transmission behavior via a trend test, and the square root law is invalid in this scenario. Furthermore, a more powerful warden with multiple antennas is harder to be deceived, and Willie's detection time can be greatly shortened.