This letter proposes a novel design of reconfigurable intelligent surface (RIS) to enhance the physical layer security (PLS) in the RIS-aided non-orthogonal multiple access (NOMA) network. Under the design of the RIS, the problem of increasing the number of RIS elements damaging the secrecy performance is solved. Besides, it also ensures that the networks can use traditional channel coding schemes to achieve secrecy. Our results show that the novel design of the RIS is ready for enhancing secrecy performance.

Intelligent reflective surface (IRS) technology is emerging as a promising performance enhancement technique for next-generation wireless networks. Hence, we investigate the physical layer security of the downlink in IRS-aided non-orthogonal multiple access networks in the presence of an eavesdropper, where an IRS is deployed for enhancing the quality by assisting the cell-edge user to communicate with the base station. To characterize the network's performance, the expected value of the new channel statistics is derived for the reflected links in the case of Nakagami- $m$ fading. Furthermore, the performance of the proposed network is evaluated both in terms of the secrecy outage probability (SOP) and the average secrecy capacity (ASC). The closed-form expressions of the SOP and the ASC are derived. We also study the impact of various network parameters on the overall performance of the network considered. To obtain further insights, the secrecy diversity orders and the high signal-to-noise-ratio (SNR) slopes are obtained. We finally show that: 1) the expectation of the channel gain in the reflected links is determined both by the number of IRS elements and by the Nakagami- $m$ fading parameters; 2) If the Nakagami- $m$ parameter is no less than 2, the SOP of both User 1 and User 2 becomes unity, when the number of IRS elements tends to infinity; 3) The secrecy diversity orders are affected both by the number of IRS elements and by the Nakagami- $m$ fading parameters, whereas the high-SNR slopes are not affected by these parameters. Our Monte-Carlo simulations perfectly demonstrate the analytical results.

In recent years, the reconfigurable intelligent surface (RIS) has garnered considerable interest for its remarkable advancements in spectral efficiency (SE) and energy efficiency (EE). To further enhance the performance of cellular networks, we propose a novel RIS-aided multi-input multi-output (MIMO) non-orthogonal multiple access (NOMA) architecture. To mitigate both inter-cell and inter-cluster interferences, we introduce a signal-cancellation-based (SCB) design specifically tailored for the RISs. By strategically deploying the RIS in suitable locations and adjusting the reflection coefficient (RC) of its elements, we achieve effective interference mitigation. The passive beamforming at the RISs is meticulously designed, and we assess how many RIS elements are necessary to implement the SCB design. To gain insights into system performance, we analyze the outage probability and the ergodic rate, providing valuable information on the high signal-to-noise ratio slopes and diversity orders for the users in the network. The numerical results reveal: 1) in comparison to the zero-forcing and maximum-ratio-transmission precoding matrices, the identity precoding matrix at the BS offers superior performance; 2) an optimal number of RIS elements exists in order to maximize both SE and EE.

In this paper, we consider a downlink non-orthogonal multiple access (NOMA) system over Nakagami-m channels. The single-antenna base station serves two single-antenna NOMA users based on statistical channel state information (CSI). We derive the closed-form expression of the exact outage probability under a given decoding order, and we also deduce the asymptotic outage probability and diversity order in a high-SNR regime. Then, we analyze all the possible power allocation ranges and theoretically prove the optimal power allocation range under the corresponding decoding order. The demarcation points of the optimal power allocation ranges are affected by target data rates and total power, without an effect from the CSI. In particular, the values of the demarcation points are proportional to the total power. Furthermore, we formulate a joint decoding order and power allocation optimization problem to maximize the sum throughput, which is solved by efficiently searching in our obtained optimal power allocation ranges. Finally, Monte Carlo simulations are conducted to confirm the accuracy of our derived exact outage probability. Numerical results show the accuracy of our deduced demarcation points of the optimal power allocation ranges. And the optimal decoding order is not constant at different total transmit power levels.

Intelligent reflecting surface (IRS) has been considered a promising technology to be applied to mobile edge computing (MEC) systems, especially when offloading links are blocked or weak. However, most existing works are restricted to narrow-band channel and ideal IRS reflection model, which is not practical and may lead to significant performance degradation. Thus, we consider an IRS-enhanced wideband MEC system with practical IRS reflection model. Our objective is to minimize the weighted latency of all devices by jointly optimizing the offloading data volume, edge computing resources, BS receiving vector, and IRS basic phase shift (BPS). Since the formulated problem is non-convex, we employ the block coordinate descent (BCD) technique to decouple it into two subproblems to alternatively optimize computing and communication resources. In particular, the computing resource optimization subproblem is solved based on Karush-Kuhn-Tucker (KKT) conditions and bisection search method. While the communication resource optimization subproblem is first transformed into a weighted sum-rate maximization problem based on LDR technique and KKT conditions. Then leveraging the equivalence between sum-rate maximization and MSE minimization, it is converted into a multi-variable problem that can be effectively solved using BCD technique. Simulation results show that the proposed schemes can reduce latency by 16% compared to baseline schemes when the number of IRS elements is 100, confirming the effectiveness of considering practical IRS reflection model for wideband MEC systems.

Near-field (NF) communications have attracted considerable interest, particularly with the implementation of extremely large-scale antenna arrays (ELAAs). Additionally, the increase in communication frequencies and the expansion of reconfigurable intelligent surface (RIS) apertures contribute to this growing field. This article investigates the synergy of simultaneously transmitting and reflecting (STAR)-RIS and nonorthogonal multiple access (NOMA) for secure transmission under hybrid far-field (FF) and NF scenarios. The secrecy sum rate (SSR) maximization problem is formulated by joint optimization of the power allocation, the beamforming at access point (AP), and the transmission/reflection coefficients (TRCs). Specifically, we consider the transmit power budget, unit-norm conditions, coupled phase shifts (CPSs), quality of service requirements, and decoding order. To tackle this extremely challenging problem, we combine the successive convex approximation (SCA), Riemannian exact penalty method via smoothing, and penalty dual decomposition (PDD) and successfully develop an efficient iterative algorithm. Simulation results reveal that the proposed design exhibits superior effectiveness when compared to other traditional benchmarks.