In this paper, we investigate covert communications under multiple-antenna eavesdropping, and explore the impact of the channel state information (CSI) at the adversary on the covertness of the system with noise uncertainty. We first analyze the detection performance of the adversary without the CSI of the eavesdropping channel. Specially, the generalized likelihood ratio (GLR) detection is adopted to handle this scenario. Then, a more practical scenario with the uncertain noise power at the adversary is considered, and the covertness of the system is analyzed. In addition, the optimal transmit power at the legitimate transmitter is derived theoretically to maximize the covert throughput. Finally, we present numerical results to compare the covert throughputs when the adversary knows or doesn't know the CSI. The results demonstrate the significance of unknown CSI at the adversary when considering the covert throughput of the system.
In this paper, we investigate covert communications under multiple-antenna eavesdropping, and explore the impact of the channel state information (CSI) at the adversary on the covertness of the system with noise uncertainty. We first analyze the detection performance of the adversary without the CSI of the eavesdropping channel. Specially, the generalized likelihood ratio (GLR) detection is adopted to handle this scenario. Then, a more practical scenario with the uncertain noise power at the adversary is considered, and the covertness of the system is analyzed. In addition, the optimal transmit power at the legitimate transmitter is derived theoretically to maximize the covert throughput. Finally, we present numerical results to compare the covert throughputs when the adversary knows or doesn't know the CSI. The results demonstrate the significance of unknown CSI at the adversary when considering the covert throughput of the 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 paper considers the problem of covert communication over a multiple-input single-output channel (MISO) in the case of the imperfect channel state information. The transmitter wants to communication with the receiver while the eavesdropper detects the existence of the transmission. We first study the scenario that the accurate channel state information (CSI) is known and show that the condition achieving the positive rate by the beamforming vector. However, because of the non-cooperation between the transmitter and the eavesdropper, we consider the CSI is imperfect. There are estimation errors for the transmitter. When the positive rate can not be achieved, the objective is to maximize the communication rate. We discuss the deterministic bounded CSI errors for the covert communication. Robust beamforming and the transmitter power is investigated, which can be transformed as a second order cone programming (SCOP) problem. We consider the line-of-sight (LoS) channel and the linear array antenna model. Comparing with the perfect CSI, the results show that the strategy of the transmitter is more conservative under the imperfect CSI. The capacity declines by the estimation errors.
Proactive eavesdropping is an effective method for government to monitor suspicious users who are deemed to misuse communication systems for illegal activities. In this paper, considering that a legitimate full-duplex (FD) eavesdropper tries to monitor a dubious multi-antenna system, we propose a covert pilot spoofing attack (PSA) scheme to enhance the legitimate eavesdropping performance by taking the channel training phase into consideration. For the proposed covert PSA scheme, the total error detection probability and optimal detection threshold of suspicious source are derived as the worst case for the considered monitoring system. Given the optimal detection threshold, the closed-form expressions of effective eavesdropping rate are also derived based on the results of detection at suspicious source. Furthermore, an optimal power allocation algorithm to maximize the effective eavesdropping rate is proposed under the covert PSA and transmission power constraints. Simulation results illustrate that the adversary's uncertain about channel state information (CSI) before channel estimation process, can be exploited by legitimate eavesdropper to cover the PSA without being detected. Therefore, the proposed covert PSA scheme can achieve a better performance with respect to effective eavesdropping rate and effectively combat with a suspicious multi-antenna system.
Covert communication enforces the transmitted signal to be indistinguishable from other signals under wireless environment, making it difficult for an eavesdropper to detect and intercept the message. The most common approach within covert systems is the augmentation of artificial noise (AN), ensuring reliable transmission. However, this strategy becomes problematic when the eavesdropper's position is uncertain, as continuous amplification of interference power can precipitate a substantial decline in covert communication capacity. In this paper, we investigate the covert communication between legitimate transmitter (i.e., Alice) and full duplex receiver (i.e., Bob) in the presence of the location uncertainties of the eavesdropper (i.e., Willie). We first derive the sufficient condition for achieving covert communication through robustness analysis. Then, we derive the effective throughput to measure the covert communication capacity. Afterward, by using joint optimization technology, the optimal AN power of Bob and the number of antennas for Alice are jointly designed to maximize the effective throughput subject to a covertness constraint. Theoretical analysis indicates that reducing the AN power while increasing the number of antennas helps to improve the system capacity, the effective throughput between Alice and Bob is inversely proportional to the distance between them. Finally, the validity of our analytical approach is corroborated by simulation results.
This letter investigates the robust beamforming design for an integrated sensing and covert communications system, where the transmitter (Alice) performs some sensing task and simultaneously communicates with multiple legitimate users (Bobs) covertly, evading detection by the eavesdropper (Willie). Considering the impact of imperfect channel state information (CSI) of Alice-to-Bobs and Alice-to-Willie links, we formulate a robust beamforming optimization problem to minimize the Cramér-Rao bound for sensing parameter while satisfying the total transmit power, the signal-to-interference-plus-noise ratio and covertness constraints for communication. An iterative algorithm, employing semi-definite programming and successive convex approximation, is proposed to address this challenging problem. Numerical results validate the effectiveness of the proposed scheme, highlighting the robustness of the optimized beamforming design under imperfect CSI.
A wireless legitimate surveillance system is studied for a proactive eavesdropping scheme, where a full- duplex legitimate monitor eavesdrops a suspicious link by injecting artificial noise (AN) towards the suspicious receiver. Different from the existing work, the suspicious receiver is assumed to be capable of detecting the presence of AN. Once such receiver detects the AN, it stops transmission. Hence, to improve the surveillance performance, AN should be transmitted covertly with low detection probability by the suspicious receiver. To achieve this goal, an optimal problem is first formulated to maximize the eavesdropping rate under covert constraint. Then, according to the derived detection error probability, the optimal detection threshold is determined under Rayleigh fading channels. A novel scheme is proposed to solve the optimization problem under both perfect and imperfect channel state informations (CSIs). Finally, simulation is performed to verify the analyses. It is shown that the imperfect CSI of the suspicious link can benefit the surveillance performance.