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IEEE Wireless Communications Letters

Adaptive Power Control for Cooperative Covert Communication With Partial Channel State Information

Rongrong He, Guoxin Li, Haichao Wang, Yutao Jiao, Jihao Cai

Published May 5, 2022• 25 citations
Publisher

Abstract

In jammer-assisted covert communication scenarios, jamming signals also degrade the communication between legitimate users. Considering that it is difficult for a transmitter to obtain all the required channel state information (CSI), we propose an adaptive power control strategy with partial CSI, which decreases the outage probability while bringing more uncertainty to a warden. Specifically, we adopt an upper confidence limit to estimate the unknown CSI from the jammer to the receiver. Under warden’s optimal detector, we analyze the maximum covert throughput by optimizing the upper confidence limit. A closed-form expression of the optimized upper confidence limit is derived in certain cases. The numerical results validate the effectiveness of the proposed strategy and guide the estimation of unknown CSI.

DOI
10.1109/lwc.2022.3172683

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In jammer-assisted covert communication scenarios, jamming signals also degrade the communication between legitimate users. Considering that it is difficult for a transmitter to obtain all the required channel state information (CSI), we propose an adaptive power control strategy with partial CSI, which decreases the outage probability while bringing more uncertainty to a warden. Specifically, we adopt an upper confidence limit to estimate the unknown CSI from the jammer to the receiver. Under warden’s optimal detector, we analyze the maximum covert throughput by optimizing the upper confidence limit. A closed-form expression of the optimized upper confidence limit is derived in certain cases. The numerical results validate the effectiveness of the proposed strategy and guide the estimation of unknown CSI.
In covert communication, adaptive power control can help balance reliability and covertness, particularly when working with a cooperative jammer. Recent studies considering adaptive power control in covert communications typically assume perfect channel estimation at the transmitter. However, channel estimation is imperfect in practice, resulting in inaccurate power allocation with degraded covertness performance. This paper investigates the effect of channel estimation error on jammer-assisted covert communication. We model channel estimation error in covert communication and analyze its impact on the covertness throughput. Simulation results show that estimation uncertainty leads to degraded throughput compared to perfect channel state information (CSI).
This study investigates covert communication in the presence of a half-duplex amplify-and-forward (AF) relay, while accounting for transceiver hardware impairments. A cooperative jamming strategy and channel uncertainty are employed to achieve covertness. For a trusted relay, informed jammers mitigate the effect of artificial noise (AN) at the legitimate receiver and increase the warden’s uncertainty, thereby enhancing the covert rate. For an untrusted relay, the jammer must emit AN while the data signal is transmitted toward the untrusted relay to reduce the untrusted relay’s signal-to-interference-plus-noise ratio (SINR), which poses a challenge for deploying an informed jammer. The results show that, in both trusted and untrusted relay scenarios, increasing the transmit power yields only marginal performance gains due to hardware impairments, highlighting the importance of high-quality transceivers and compensation algorithms. Notably, under specific conditions, impairments in the legitimate receiver’s transmitter can slightly enhance performance in the trusted relay case, while in untrusted relay scenarios, impairments in any legitimate node degrade covert communication performance. Differences in hardware equipment quality between the transmitter (or retransmitter) and its associated jammer also affect the warden’s ability to detect the transmission.
Covert communication is achieved if a transmitter (Alice) sends a message to a legitimate receiver (Bob) without being detected by an attentive warden (Willie). Recent work has taken an outage approach that considers an infinite blocklength and analyzes the probability that channel conditions are such that communication is reliable and/or covert. Power adaptation via truncated channel inversion (TCI) has been examined in previous work in an attempt to minimize outage under the covertness constraint. However, the optimality of TCI was not established, and the associated parameters in the TCI scheme were only found numerically. We provide the exact optimal power adaptation schemes under different covertness constraints and with different channel models: 1) when the channel between Willie and an uninformed jammer is AWGN; and 2) when the channel is a Rayleigh fading channel. We also examine the performance improvement of these schemes over standard approaches. This establishes that TCI is optimal in some, but not all, scenarios of interest.
In this letter, we consider the covert wireless communication (CWC) against a jamming-assisted proactive detector in two scenarios corresponding to whether Alice utilizes the jamming to hide the communication signals. Specifically, for the both scenarios, we first obtain Alice’s communication strategy by exploiting the statistic channel state information (CSI) of the detecting link. Then, we propose the covertness outage probability (COP) as a new covert communication measure proposed in this letter and derive its closed-form expression which indicates that the lower tolerance value or the longer channel uses are likely to cause communication outage. Numerical results indicate that, against a jamming-assisted proactive detector, hiding the communication signals in the noise is more favorable than exploiting the detector’s jamming for achieving covertness, since the latter raises the transmit power at Alice and thus leads to larger COP.
To address the inherent openness of wireless communication environments, covert communication has emerged as a promising approach to protect legitimate transmissions from unauthorized detection. This paper investigates a UAVassisted wireless covert communication system, where channel uncertainty is exploited to enable covert information transmission in the presence of active wardens acting simultaneously as jamming sources. We first model the indirect communication strategy between legitimate parties and characterize the detection behavior of an active warden. To achieve both covertness and communication efficiency, the transmit power of the devices and the hovering positions of UAVs are jointly optimized, subject to the dual constraints of maintaining a sufficient covert communication rate and ensuring a high detection error probability at the warden. Closed-form expressions for the wardens detection error probability and the achievable covert communication rate are derived. Furthermore, numerical optimization is employed to maximize the achievable rate under covertness constraints. Simulation results corroborate the theoretical analysis and demonstrate the effectiveness of the proposed scheme in enabling covert communication in jamming-assisted active warden scenarios.
In this work, we consider a system of covert communication with the aid of a full-duplex (FD) receiver to enhance the performance in a more realistic scenario, i.e., only the channel distribution information (CDI) rather than channel state information (CSI) is known to a warden. Our work shows that transmitting random AN can improve the covert communication with the infinite blocklength. Specifically, we jointly design the optimal transmit power and AN power by minimizing the outage probability at Bob, and we find that the outage probability decreases and then increases as the maximum allowable AN power increases. Intuitively, once AN exceeds an optimal value, the performance will become worse because of the self-interference. The simulation results also show that the performance behaviors of CDI and CSI are different. When Willie only knows CDI, there is an optimal AN power that minimizes Bob's outage probability. However, when Willie knows CSI, the outage probability monotonically decreases with AN power.