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ICT Express

Covert communications in a compress-and-forward relay system

Jihwan Moon

Published Aug 18, 2023• 7 citations
Publisher

Abstract

In this paper, we study covert communications strategies in a compress-and-forward (CF) relay system. Along with a public message to a destination node via a CF relay, a source node attempts to transmit a covert message while evading the surveillance of the CF relay. We identify the optimal power distribution between the public and covert messages and the optimal amount of compression that maximize the covert rate subject to the minimum detection error probability requirement. Our provided solutions also reveal that both the power distribution and the achievable covert rate are identical to that of an equivalent amplify-and-forward (AF) relay system if an adequate quantization codebook with the optimal compression is employed. The numerical results verify the effectiveness of the optimal solutions and confirm our analyses.

DOI
10.1016/j.icte.2023.08.005

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In this paper, we study covert communications strategies in a compress-and-forward (CF) relay system. Along with a public message to a destination node via a CF relay, a source node attempts to transmit a covert message while evading the surveillance of the CF relay. We identify the optimal power distribution between the public and covert messages and the optimal amount of compression that maximize the covert rate subject to the minimum detection error probability requirement. Our provided solutions also reveal that both the power distribution and the achievable covert rate are identical to that of an equivalent amplify-and-forward (AF) relay system if an adequate quantization codebook with the optimal compression is employed. The numerical results verify the effectiveness of the optimal solutions and confirm our analyses.
Covert communications have arisen as an effective communications security measure that overcomes some of the limitations of cryptography and physical layer security. The main objective is to completely conceal from external devices the very existence of the link for exchanging confidential messages. In this paper, we take a step further and consider a scenario in which a covert communications node disguises itself as another functional entity for even more covertness. To be specific, we study a system where a source node communicates with a seemingly receive-only destination node which, in fact, is full-duplex (FD) and covertly delivers critical messages to another hidden receiver while evading the surveillance. Our aim is to identify the achievable covert rate at the hidden receiver by optimizing the public data rate and the transmit power of the FD destination node subject to the worst-case detection error probability (DEP) of the warden. Closed-form solutions are provided, and we investigate the effects of various system parameters on the covert rate through numerical results, one of which reveals that applying more (less) destination transmit power achieves a higher covert rate when the source transmit power is low (high). Since our work provides a performance guideline from the information-theoretic point of view, we conclude this paper with a discussion on possible future research such as analyses with practical modulations and imperfect channel state information.
This paper investigates the covert communications in the wireless-powered two-way relay systems with energy harvesting. The primary task of the relay is to assist the source nodes on both sides in completing the legitimate communication. Based on this, relay attempt to transmit covert information to source nodes. With limited transmit power at the relay, a reliable transmission strategy is needed to against the warden, who detects whether the relay transmits the cover message or not. We first analyzed the detection error probability at the warden. Based on the detection performance of the warden, we propose a ratio-control transmit strategy for the relay, which can efficiently implement covert communication with the harvested energy while the warden has optimized the detection error probability.
This paper studies the covert and secure communications in a UAV-aided untrust relay system composed of an unmanned aerial vehicle (UAV), a base station (BS), a user and a warden (Willie). The UAV collects data from underground users, and then uploads it to the BS. The BS forwards it to the remote user. The UAV attempts to perform covert communication with the BS in the presence of Willie, while the untrust BS serving as a relay also intercepts the message from the UAV. To ensure the covert and secure communications, we first derive the average minimum detection error rate (DEP) at Willie’s location using the noise uncertainty model. We then formulate the average covert transmission rate maximization as an optimization problem with the constraints of covertness and security requirements. We further solve the optimization problem using a search method. Numerical results are provided to validate our theoretical analysis and also to illustrate the impact of power allocation factors on the covert and secure rate. Finally, we achieve maximization of the covert transmission rate in different scenarios.
In this paper, we investigate a covert communications system that consists of a source node communicating with a disguised full-duplex (FD) destination node. Supposedly receive-only, the destination node covertly transmits confidential messages to a hidden receiver while avoiding the surveillance of a warden node. Our specific focus is on the impact of the channel uncertainty of the warden node from the perspective of the destination node on covert communications. We take the expected minimum detection error probability (DEP) at the warden node into consideration and obtain the optimal public data rate and transmit power to maximize the covert rate. Numerical results verify that the covert rate increases as the availability of the channel state information (CSI) improves and highlight the importance of optimization regardless of the level of CSI based on comparisons with baseline schemes.
In this paper, we investigate covert communication where the relay and the jammer are jointly selected. It is demonstrated that the improvement of covert communication performance can be achieved under the proposed maximum-and-minimum-selection (MMS) scheme. Specifically, the relay with maximal channel gain to the legitimate destination (Bob) is selected to forward the covert signal when the jammer with minimal channel gain to Bob sends artificial noise to confuse the warden (Willie). We derive the expressions of detection error probability and effective covert rate in closed-form. Based on the derivations, the transmit power of relay is optimized to further improve the covert communication performance. The simulation shows that the effective covert rate cannot always be improved by increasing the number of relay, and there exists an optimal jamming power to maximize the effective covert rate.
This paper investigates the covert communication network assisted by the multi-antenna relay, by taking into account two typical scenarios of eavesdropping channel state information (ECSI). In this network, the relay operates in half-duplex amplify-and-forward (AF) relaying protocol, where the relay either forwards the Alice’s confidential signal to the Bob by designing the precoding matrix to enhance the communication performance or sends artificial noise (AN) to disrupt the warden’s detection. For this covert communication system with either instantaneous ECSI (I-ECSI) or statistical ECSI (S-ECSI), an optimization problem is formulated with the aim of maximizing the received signal-to-noise ratio (SNR) at the Bob while ensuring the constraints on the transmit power and covert performance. To solve the non-convex optimization problem, an alternating optimization method is proposed through jointly optimizing the transmit power at Alice and precoding matrix at the relay. Numerical results are provided to demonstrate the effectiveness of our proposed method. In particular, our method is superior to the conventional ones up to 49.6% with I-ECSI and 57.9% with S-ECSI.