Search

In this paper, we investigate the possibility and condition of exploiting wireless-powered signals as a cover for conducting covert communications in unmanned aerial vehicle (UAV) networks. Specifically, we aim to design the hovering altitude of a UAV and its prior transmission probability to strike a balance between energy replenishment and covert communications. We derive the necessary condition for guaranteeing communication covertness subject to an energy replenishment constraint, under which the UAV’s optimal hovering and the prior transmission probability are determined. Our simulation shows that varying the prior transmission probability can significantly improve the achievable communication covertness under the energy replenishment constraint, relative to a baseline scheme with a fixed prior transmission probability. [ABSTRACT FROM AUTHOR]

In this letter, we jointly investigate packet generation and covert communication in delay-intolerant status update systems. For the first time, we establish a bridge between the prior transmission probability and the finite block-length in covert communication by modeling the stochastic status packet generation as a Poisson process. Considering a general prior transmission probability model, we derive closed-form expressions for the covertness constraint, the average packet error probability, and the effective covert throughput (ECT) to reveal the non-trivial tradeoff between the communication covertness and reliability. An optimization problem to maximize ECT is also formulated, and then the optimal transmit power and block-length are obtained, respectively. In contrast to exiting results, our examination shows that the longest block-length and the widely adopted equal prior probabilities are generally suboptimal when jointly considering the packet generation and covert communication. [ABSTRACT FROM AUTHOR]

This work tackles the joint optimization of a unmanned aerial vehicle's (UAV's) three-dimensional (3D) placement and transmit power for covert communications with the objective to maximize the communication covertness subject to a constraint on communication quality. We analytically prove that the optimal horizontal location of the UAV must be on the straight line connecting the legitimate receiver and the warden, while its optimal height is the minimum allowable flying altitude. Subsequently, we derive closed-form expressions to characterize the UAV's optimal 3D location and its optimal transmit power, taking into account the impact of finite blocklength coding. Our numerical results show that the developed optimal design can achieve a better covertness performance compared with an optimal two-dimensional (2D) UAV deployment, especially when the warden is close to the receiver. Besides, we show that, for a given requirement on the communication quality, communication covertness does not always improve as the number of channel uses increases. [ABSTRACT FROM AUTHOR]

In this paper, we consider covert communications for bistatic backscatter systems, where a tag transmits information passively to a reader by reflecting incident carrier signals with artificial noise (AN) generated from a dedicated carrier emitter (CE) under the supervision of a warden. By exploiting the channel uncertainty introduced by CE, we analytically derive the warden's minimum sum of error probabilities to evaluate communication covertness. We find that communication covertness can be improved by reducing the tag's reflection coefficient, but is not affected by the CE's transmit power. Therefore, in order to achieve energy-efficient design, we optimize the tag's reflection coefficient to minimize the CE's transmit power under the constraints of communication covertness and reliability. Our analysis shows that the minimum CE's transmit power can be further reduced with a minor loss of the achievable covert rate. [ABSTRACT FROM AUTHOR]

In this work, we adopt channel inversion power control (CIPC) to achieve covert communications aided by a full-duplex receiver. Specifically, the transmitter varies the power and phase of transmitted signals as per the channel to the receiver, such that the receiver can decode these signals without knowing the channel state information. This eliminates the required feedback from the transmitter to the receiver, which aids hiding the transmitter from a warden. The truncated CIPC and conventional CIPC schemes are proposed and examined, where for truncated CIPC covert transmission ceases when the channel quality from the transmitter to the receiver is low, while for conventional CIPC covert transmission always occurs regardless of this channel quality. We examine their performance in terms of the achieved effective covert throughput (ECT), which quantifies the amount of information that the transmitter can reliably convey to the receiver, subject to the constraint that the warden's detection error probability is no less than some specific value. Our examination shows that the truncated CIPC scheme can outperform the conventional CIPC scheme due to this constraint. [ABSTRACT FROM AUTHOR]

Covert communication hides the transmission of a message from a watchful adversary, while ensuring reliable information decoding at the receiver, providing enhanced security in wireless communications. In this work, covert communication in the presence of a multi-antenna adversary and under delay constraints is considered. Under the assumption of quasi-static wireless fading channels, we analyze the effect of increasing the number of antennas employed at the adversary on the achievable throughput of covert communication. It is shown that in contrast to a single-antenna adversary, a slight increase in the number of adversary's antennas drastically reduces the covert throughput, even for relaxed covertness requirements. [ABSTRACT FROM AUTHOR]

URLLC is one category of service to be provided by next-generation wireless networks. Motivated by increasing security concerns in such networks, this article focuses on physical layer security in the context of URLLC. The physical layer security technique mainly uses transmission designs based on the intrinsic randomness of the wireless medium to achieve secrecy. As such, physical layer security is of a lower complexity and incurs less latency than traditional cryptography. In this article, we first introduce appropriate performance metrics for evaluating physical layer security in URLLC and investigate the trade-off between latency, reliability, and security. We then identify the key challenging problems for achieving physical layer security in URLLC, and discuss the role that channel state information can have in providing potential solutions to these problems. Finally, we present our recommendations on future research directions in this emerging area. [ABSTRACT FROM AUTHOR]

This paper examines the possibility, performance limits, and associated costs for a self-sustained relay to transmit its own covert information to a destination on top of forwarding the source’s information. Since the source provides energy to the relay for forwarding its information, the source does not allow the relay’s covert transmission and to detect it. Considering the time switching (TS) and power splitting (PS) schemes for energy harvesting, where all the harvested energy is used for transmission at the self-sustained relay, we derive the minimum detection error probability $\xi ^{\ast }$ at the source based on which we determine the maximum effective covert rate $\Psi ^{\ast }$ subject to a given covertness constraint on $\xi ^{\ast }$. Our analysis shows that $\xi ^{\ast }$ is the same for the TS and PS schemes, which leads to the fact that the cost of achieving $\Psi ^{\ast }$ in both the two schemes in terms of the required increase in the energy conversion efficiency at the relay is the same, although the values of $\Psi ^{\ast }$ in these two schemes can be different in specific scenarios. For example, the TS scheme outperforms the PS scheme in terms of achieving a higher $\Psi ^{\ast }$ when the transmit power at the source is relatively low. If the covertness constraint is tighter than a specific value, it is the covertness constraint that limits $\Psi ^{\ast }$ , and otherwise, it is upper bound on the energy conversion efficiency that limits $\Psi ^{\ast }$. [ABSTRACT FROM AUTHOR]