Robust Beamforming Design for Covert Communications

TL;DR

This paper develops robust beamforming strategies for covert communication, maximizing the covert rate to Bob while avoiding detection by Willie, under perfect and imperfect channel knowledge scenarios.

Contribution

It introduces novel beamformer designs using semidefinite relaxation, zero-forcing, and robust optimization for covert communications with imperfect channel information.

Findings

Proposed beamformers achieve higher covert rates.

Robust design effectively handles imperfect channel knowledge.

Numerical results validate the effectiveness of the methods.

Abstract

In this paper, we consider a common unicast beamforming network where Alice utilizes the communication to Carol as a cover and covertly transmits a message to Bob without being recognized by Willie. We investigate the beamformer design of Alice to maximize the covert rate to Bob when Alice has either perfect or imperfect knowledge about Willie's channel state information (WCSI). For the perfect WCSI case, the problem is formulated under the perfect covert constraint, and we develop a covert beamformer by applying semidefinite relaxation and the bisection method. Then, to reduce the computational complexity, we further propose a zero-forcing beamformer design with a single iteration processing. For the case of the imperfect WCSI, the robust beamformer is developed based on a relaxation and restriction approach by utilizing the property of Kullback-Leibler divergence. Furthermore, we derive the optimal decision threshold of Willie, and analyze the false alarm and the missed detection probabilities in this case. Finally, the performance of the proposed beamformer designs is evaluated through numerical experiments.