This paper investigates simultaneous wireless information and power transfer (SWIPT) for a decode-and-forward (DF) full-duplex relay (FDR) network. A battery group consisting of two batteries is applied to utilize the relay-harvested energy for FDR transmission. The virtual harvest-use model and the harvest-use-store model are considered, respectively. By switching between two batteries for charging and discharging with the aid of power splitting (PS), concurrent source and relay transmissions can overcome spectral efficiency loss compared with half-duplex relay (HDR)-assisted PS-SWIPT. The outage probability for the virtual harvest-use model is presented in an exact integral form and the optimal PS (OPS) ratio that maximizes the end-to-end signal-to-interference-plus-noise ratio (e-SINR) is characterized in closed form via the cubic formula. The fundamental tradeoff between the e-SINR and recycled self-power is quantified. The OPS ratios and the corresponding outage probabilities in noise-limited and interference-limited environments are also derived. In the harvest-use-store model, a greedy switching (GS) policy is implemented with energy accumulation across transmission blocks. The OPS ratio of the GS policy is presented and the corresponding outage probability is derived by modeling the relay's energy levels as a Markov chain with a two-stage state transition. Numerical results verify the performance improvement of the proposed scheme over HDR-assisted PS-SWIPT in terms of outage probability and average throughput.

In this work, we investigate a novel covert communication system, where the legitimate transmitter attempts to communicate with a covert user in the presence of a warden and the public user covertly. Specifically, the legitimate transmitter employs non-orthogonal multiple access (NOMA) and rate-splitting (RS) to communicate with users aided by a reconfigurable intelligent surface (RIS). In this context, we investigate key performance indicators of covert communication, namely the detection error probability and the covert communication rate. Meanwhile, we consider the physical layer security (PLS) of the proposed system in the presence of an eavesdropper, and derive the approximate secrecy outage probability (SOP) expression. Also, an asymptotic analysis of the SOP is also carried out. Various numerical results are presented that demonstrate the usefulness of the proposed analysis, which are complemented by simulated ones, verifying the correctness of the theoretical framework. From these results, it becomes evident that the use of RS, NOMA, and RIS can improve the performance of covert communication. Finally, it is also depicted that under the condition of high signal-to-noise ratio, the SOP of the system tends to be a constant value.

This paper investigates a cooperative non-orthogonal multiple access system, in which a base station communicates with two far users with the aid of a decode-and-forward (DF) relay. Three cooperative relaying schemes, namely, the fixed relaying (FR), the selective DF with coordinated direct and relay transmission (SDF-CDRT), and the incremental-selective DF (ISDF) relaying are proposed to enhance the outage performance for the two far users by utilizing both the direct and relay links. Taking into account the received signal-to-noise ratio (SNR) events at the relay, the SDF-CDRT scheme adaptively forms an orthogonal transmission branch with respect to the direct link or keeps silent to reduce error propagation. Besides considering the relay detection results, the ISDF scheme further exploits the limited feedback of the received SNR events from two users, so that error propagation can be avoided and unnecessary relaying can be reduced. Analytical expressions for the outage probabilities and average throughputs of the paired users are derived in closed-form for the three cooperative relaying schemes. Asymptotic expressions for the outage probabilities are derived in the high SNR region. It is shown that the FR and SDF-CDRT schemes achieve a diversity order of one for both users, while the ISDF scheme achieves a diversity order of two for both users. The superior system performance achieved by the proposed schemes over those of the existing methods is verified by Monte Carlo simulations.

In this article, we investigate covert communication in simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS)-assisted networks with rate-splitting multiple access (RSMA). Specifically, a legitimate transmitter employs RSMA to send messages over the STAR-RIS to a pair of legitimate users located on both sides of the STAR-RIS, where the user on the transmitting surface is equipped with a full-duplex (FD) receiver with two antennas. In particular, one of the receiver’s antennas is used to receive signals and the other is used to transmit jamming signals to confuse the warden’s detection. In order to evaluate the covert performance of the considered system, we derive closed-form expressions for the detection error probability (DEP), the outage probability, and the covert rate. Then, the effects of the maximum signal interference power of the FD, the power distribution coefficient, and the reflection coefficient of the STAR-RIS elements on the covert performance are presented. The numerical results indicate that increasing the maximum signal interference power of the FD enhances the value of DEP, but reduces its outage performance. Additionally, it is observed that the impact of the reflection coefficient of the STAR-RIS elements on the covert performance is related to the transmit power, and the DEP is a monotonically increasing function of the reflection coefficient when the transmit power is sufficiently high.

In this paper, we propose a novel architecture for a multi-layer active-passive cascade transmitting reconfigurable intelligent surface (RIS)-aided receiver. We aim at enhancing the scalability of antenna dimensions and energy efficiency for user equipment (UE), as well as improving the amplitude freedom of antenna gain. This architecture integrates reflecting RIS for applications in both jamming and anti-jamming scenarios. We formulate a problem to maximize the worst-case spectral efficiency (SE) of the UE, based on imperfect channel state information (CSI) of the malicious device, thereby ensuring the SE of our UE while disrupting the signal reception of the illegal UE. To address the inherently non-convex nature of the formulated problem, we propose an alternating optimization framework, which decomposes the main problem into several subproblems. Specifically, we uniformly discretize the uncertain domains to obtain robust CSI, allowing us to determine an optimal receiver vector. To balance computational complexity and performance, we propose solutions for the subproblems of base station beamforming and coefficients with different patterns of RIS. Furthermore, to effectively disrupt malicious inter-device communication while avoiding detection and localization, we develop a collaborative interference pattern incorporating silent interference and non-interference protocols. Importantly, the pattern carefully balances performance with the overhead of CSI acquisition. Finally, simulation results validate the efficiency of the proposed algorithms, demonstrating that the proposed architecture achieves better jamming and anti-jamming performance.