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IEEE Access

Covert Communications Over Non-Orthogonal Multiple Overt Channels

Hien Quang Ta, Khuong Ho‐Van, Daniel Benevides da Costa, Sang Wu Kim, Hoon Oh

Published Jan 1, 2022• 16 citations
Publisher

Abstract

The paper exploits overt information of non-orthogonal multiple access (NOMA) systems for camouflage to hide covert information. The optimum strategy of hiding information at the transmitter, accounting for the probability of the warden’s detection error and the resulting spectral efficiency of the covert information under the covertness requirement, is determined. The results show that the optimum strategy of hiding the covert information is to superimpose it onto the overt NOMA information which is hardest-decoded, increasing to 1 the probability of detection error at the warden when the number of NOMA users accretes. This indicates that the multiplicity of NOMA users can be leveraged to hide the covert information in NOMA systems. In addition, various results prove the increase in the covert spectral efficiency with increasing the number of NOMA users while guaranteeing the probability of the warden’s detection error close to 1.

DOI
10.1109/access.2022.3223357

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The paper exploits overt information of non-orthogonal multiple access (NOMA) systems for camouflage to hide covert information. The optimum strategy of hiding information at the transmitter, accounting for the probability of the warden’s detection error and the resulting spectral efficiency of the covert information under the covertness requirement, is determined. The results show that the optimum strategy of hiding the covert information is to superimpose it onto the overt NOMA information which is hardest-decoded, increasing to 1 the probability of detection error at the warden when the number of NOMA users accretes. This indicates that the multiplicity of NOMA users can be leveraged to hide the covert information in NOMA systems. In addition, various results prove the increase in the covert spectral efficiency with increasing the number of NOMA users while guaranteeing the probability of the warden’s detection error close to 1.
This paper pioneers the exploitation of power domain superposition to embed covert messages within overt ones in a two-user uplink Non-Orthogonal Multiple Access (NOMA) system. This eliminates the need for a dedicated covert trans-mitter, enhancing practicality. Our method thwarts conventional radiometer detection at Willie, necessitating Likelihood Ratio Testing (LRT), which we evaluate under optimized overt transmission rates and imperfect Successive Interference Cancellation (SIC) scenarios at Willie. We then minimize Willie's detection error probability by optimizing his detection thresholds and subsequently maximize his minimum DEP by exploiting the user's transmit power and overt-covert power allocation. We show that covert communication is safe if the warden, Willie, doesn't decode any overt message and converges to 1 under high transmission power at users.
This letter proposes a joint covert and secure transmission scheme in the non-orthogonal multiple access (NOMA) networks against internal eavesdropping and external monitoring. In the network, the strong user wiretaps the signals of the weak user while an external warden monitors the communication behaviors of the strong user. To address the issue, a random artificial noise (AN) based beamforming is adopted, which not only reduces the eavesdropping rate of the strong user but also confuses the warden. We consider the worst case, where the warden can minimize the detection error probability (DEP) by optimizing its detection threshold. Further, we characterize the closed-form expressions of the average minimum DEP of the warden, the connection outage probabilities of the NOMA users and the secrecy outage probability of the weak user under the imperfect successive interference cancellation (SIC). To improve the performance, an effective covert rate maximization problem is formulated, under the constraints of the covertness, reliability and secrecy, which is analytically solved. Numerical results validate the superiority of the proposed scheme.
It is challenging to covert communication under channel distribution information (CDI) uncertainty caused by limited feedback and rapid-changing channels. This letter investigates covert communication in uplink non-orthogonal multiple access (NOMA) systems under CDI uncertainty, where a covert user (CU) and reliable user (RU) transmit messages to a legitimate receiver (Bob) threatened by a warden (Willie). RU not only transmits its public messages but also helps CU to send private messages against Willie’s detection. To protect CU’s transmission with imperfect CDI, we first study the worst case for NOMA users and obtain a lower bound of the worst-case detection error probability (DEP). In addition, both closed-form expressions for RU and CU’s connection outage probabilities are derived. Constrained by the DEP and connection outage probability, we maximize the expected covert rate (ECR) and derive the optimal power settings for RU and CU under imperfect CDI. Numerical results show that the proposed robust power setting scheme achieves a positive maximum ECR despite CDI uncertainty causing the reduction of covertness 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.
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.
We consider the situation where a transmitter communicates with a legitimate receiver and at the same time aims to send a covert message to a covert receiver while ensuring that the covert message is non-detectable at a third receiver, referred to as the warden. The considered system belongs to the class of non-orthogonal multiple access (NOMA) systems. For the considered NOMA system, we show that it is possible to achieve complete covertness, i.e., the error detection probability at the warden to be one, using artificial noise generated at the transmitter. Depending on the power of the artificial noise, there is a trade-off between the data rate achieved at the legitimate receiver and the covert data rate achieved at the covert receiver, while ensuring complete covertness.