We explore leveraging the multiplicity of overt (public) messages, destined for different receivers through different channels, for hiding the transmission of a covert (private) message. The transmitter hides the covert message against a warden by superimposing it onto an overt message. We determine the optimum rule for choosing the overt message to maximize the total detection error probability (sum of the probability of false alarm and missed detection) at the warden. In addition, the channel variation is exploited to minimize the throughput loss on the overt message caused by the superimposition of the covert message. We show that the maximum total detection error probability converges fast to 1 as the number of overt messages (channels) increases; the total detection error probability is independent of the transmission power; and that a positive covert rate (bits per channel use) can be achieved while keeping the total detection error probability arbitrarily close to 1. These findings indicate that the multiplicity of overt messages (channels) and channel variations can be exploited to achieve a positive covert rate.

This paper investigates short-packet communications (SPCs) of a cooperative non-orthogonal multiple access (NOMA) Internet-of-Things (IoT)-based cellular network where an IoT master node acts as: (1) a relay for the cellular system and (2) a source for the IoT system. Accurate and asymptotic closed-form expressions for the average block error rates (BLERs) of cellular user (CU) and IoT user (IU) are derived in the presence of imperfect successive interference cancellation (SIC) and channel state information (CSI). Notably, numerical results show that: (i) IUs' performance is significantly improved by exploitation of NOMA technique and is not dominated by decode-and-forward (DF) or amplify-and-forward (AF) relaying protocol; (ii) CUs' performance may not perform well compared with orthogonal multiple access (OMA)-based systems for both AF and DF protocols; (iii) higher antenna configuration at the cellular transmitter results in a rapid BLER convergence for CU.

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 presents an analytical study on wireless systems employing partial Non-Orthogonal Multiple Access (PNOMA) combining energy harvesting technique. In the proposed system, which includes one information source, two destinations, one power beacon, and one eavesdropper, we conduct an analysis of reliability and security. We derive closed-form and asymptotic expressions for outage probability (OP), intercept probability (IP) for the system. In addition, the ergodic and security capacities for the system’s two secure schemes, i.e., full transmission information (FTI) and partial transmission information (PTI), where the eavesdropper is aware of the bandwidth region for signal transmission, are also calculated for evaluation. The results indicate that the bandwidth division ratio must be meticulously selected based on the beacon’s transmit power to ensure the superior performance, i.e., both reliability and security, of the PNOMA scheme over the NOMA scheme. Moreover, the findings demonstrate that employing PNOMA enhances the outage performance of the near destination, while the far destination retains the same level of performance as observed with the NOMA scheme. Additionally, the performance of the PNOMA scheme is superior to that of the Orthogonal Multiple Access scheme in terms of OP. For security aspect, the performance of the destination in the PTI scheme is the best in terms of IP. Specifically, the system performance benefits from the PNOMA scheme when the beacon transmits at lower power levels.

The paper proposes a joint semi-blind algorithm for simultaneously cancelling the self-interference component and estimating the propagation channel in 5G Quasi-Cyclic Low-Density Parity-Check (QC-LDPC)-encoded short-packet Full-Duplex (FD) transmissions. To avoid the effect of channel estimation processes when using short-packet transmissions, this semi-blind algorithm was developed by taking into account only a small number (four at least) pilot symbols, which was integrated with the intended information sequence and used for the feedback loop of the estimation of the channels. The results showed that this semi-blind algorithm not only achieved nearly optimal performance, but also significantly reduced the processing time and computational complexity. This semi-blind algorithm can also improve the performances of the Mean-Squared Error (MSE) and Bit Error Rate (BER). The results of this study highlight the potential efficiency of this joint semi-blind iterative algorithm for 5G and Beyond and/or practical IoT transmission scenarios.