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 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.
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.
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.
In this paper, we consider a covert communication system with a multi-antenna full-duplex (FD) receiver to enhance covert performance. More precisely, the receiver Bob (i.e., multiple antennas) selects the best antenna to receive the covert message, and then it sends artificial noise (AN) to the warden Willie causing uncertainty by utilizing an antenna among the remaining antennas. In order to take full advantage of multi-antenna technology, we consider two cases: (1) Willie does not know which antenna Bob chooses to send AN, and Willie knows only part of the channel information. (2) Willie knows which antenna Bob chooses to send AN, and Willie knows all the channel information. Based on the analysis of the optimal detection threshold, we derive the minimum detection error probability of the two cases. Furthermore, given the pre-determined convert constraints, the closed-form expression of the maximum effective convert rate is derived. When the power of AN sent by Bob is greater than that of covert message sent by the sender Alice, surprised research results are shown: (1) the detection error rate of case 1 is higher than that of case 2. (2) the effective covert rate of case 1 is always lower than that of case 2. The simulation results show that the proposed scheme is more conducive to sending covert messages for Alice; in addition, the numerical results imply that the maximum effective covert rate of the system using the multi-antenna FD receiver is significantly higher than that of the traditional dual-antenna FD receiver system.
In this paper, we investigate covert communications under multi-antenna detection, and explore the impacts of the warden's channel state information (CSI) availability and the noise uncertainty on system covert capability. The detection performance at warden is analyzed in two cases under the perfect and statistical CSI at warden, respectively. In particular, for the former one, the warden utilizes the likelihood ratio (LR) detector, while for the latter one, the generalized likelihood ratio (GLR) detector is adopted. We first consider the scenario where the blocklength is finite, and demonstrate that the covert rate under both cases asymptotically goes to zero as the blocklength goes to infinity. Subsequently, we take the noise uncertainty at the warden into account which leads to positive covert rate, and characterize the covert rate for infinite blocklength. Specially, we derive the optimal transmit power for the legitimate transmitter that maximizes the covert rate. Besides, the rate gap under two cases, with different CSI availability at the warden, can be presented in closed form. Finally, numerical results validate the effectiveness of our theoretical analysis and also demonstrate the impacts of the factors studied on the system covertness.
This letter considers hiding messages into overt transmissions with a Full-Duplex receiver, which emits Artificial Noise to secure its transmission connection while a transmitter opportunistically sends a covert message to a covert user. The warden’s uncertainties of decoding the overt message and Artificial Noise received power are exploited to hide messages. Then, the covert throughput accompanied with the warden’s average detection error probability are determined. The results show that increasing the transmit power of Artificial Noise will improve the covert performance. The results also show that the covert performance is improved when the self-interference cancellation is improved at the Full-Duplex receiver or the warden is located close to the Full-Duplex receiver, indicating the positive impact of the overt performance on the covert performance.
This letter considers hiding messages into overt transmissions with a Full-Duplex receiver, which emits Artificial Noise to secure its transmission connection while a transmitter opportunistically sends a covert message to a covert user. The warden’s uncertainties of decoding the overt message and Artificial Noise received power are exploited to hide messages. Then, the covert throughput accompanied with the warden’s average detection error probability are determined. The results show that increasing the transmit power of Artificial Noise will improve the covert performance. The results also show that the covert performance is improved when the self-interference cancellation is improved at the Full-Duplex receiver or the warden is located close to the Full-Duplex receiver, indicating the positive impact of the overt performance on the covert performance.