In this paper, we focus on investigating the link-layer rate within a non-orthogonal multiple access (NOMA) system operating in the finite blocklength (FBL) regime, specifically designed for short-packet communications. By leveraging the effective capacity (EC) framework, latency and reliability in FBL, encompassing parameters such as the block error probability and the delay outage probability, are analyzed for two scenarios, namely, system operation with multiple NOMA pairs and the two-user NOMA operation. Closed-form expressions for the EC in the two cases are derived by assuming that transmissions are subject to Rayleigh fading and adopting a practical path-loss model. Numerical results are provided to validate the analytical findings, and to highlight the impact of the transmit signal-to-noise ratio, the blocklength, the delay exponent, and the block error probability, on the EC and the delay outage probability. Furthermore, various pairing configurations are investigated and demonstrate that the paired NOMA set attains the highest total EC for users experiencing substantial differences in their channel conditions.

This paper investigates the use of simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) to assist the communication with multiple devices distributed according to a Poisson point process. First, using rate-splitting multiple access (RSMA) transmission scheme, the downlink STAR-RIS multi-user system is studied, and its fundamental statistics are provided. Then, by leveraging stochastic geometry tools, and adopting an approach based on the cumulative distribution function, the outage probability is obtained for the two types of devices, i.e., the ones in the transmission zone and those in the reflection zone. For such, the distributions of the channel gains and the devices’ distances are also characterized. The closed-form expressions with Meijer-G functions for the outage probability are provided in two cases for the STAR-RIS operation, energy splitting and mode switching. Simulation results and comparisons are provided, and the impact of various system parameters on the outage performance is analyzed. In particular, it is shown that as the RIS size, the RSMA power splitting factor, and the devices’ density, increase, the STAR-RIS aided RSMA helps achieve enhanced performance in both operation cases, i.e., energy splitting and mode switching.

This paper proposes a joint broadcast-unicast downlink communication framework implementing layered-division multiplexing (LDM) and aerial reconfigurable intelligent surface (RIS), and develops a corresponding design with a focus on energy efficiency. Maximization of the energy efficiency is achieved by jointly designing the optimal active beamforming at the base station and the passive beamforming at the aerial RIS. The non-convex optimization is solved using a two-stage algorithm. The active beamforming is designed by using low-complexity zero-forcing for the unicasting service and successive convex approximation based on the first-order Taylor series expansion for the broadcasting service, and the RIS phase shifting is designed with semi-definite programming. Comparative results are provided, and show that the proposed LDM-based RIS-assisted joint broadcast-unicast communication framework is more energy efficient than the joint broadcast-unicast via time-division multiplexing or amplify-and-forward relaying.

In this contribution, a novel framework for joint broadcast-unicast downlink transmissions using dual-polarized aerial reconfigurable intelligent surface (RIS) is proposed. The objective is to maximize the energy efficiency by jointly designing the active beamforming at the base station and the passive beamforming at the RIS. The optimization problem to maximize the system’s energy efficiency is formulated and solved using a two-stage algorithm. To tackle the non-convex nature of the problem, an alternating technique, where the optimization is decomposed into two sub-problems, is proposed. In the first stage, the passive beamforming matrix of the dual-polarized aerial RIS is designed based on the Gaussian randomization method, which relaxes the inhomogeneous non-convex quadratically constrained quadratic program (QCQP) into a semi-definite program. In the second stage, the active beamforming at the base station is designed based on a dual-structured beamforming approach, in which the interior point method is used to obtain the prebeamforming matrix, and the beamforming matrices pertaining to the unicasting and broadcasting are obtained based on low-complexity zero-forcing and successive convex approximation, respectively. Numerical results and comparisons are provided. In particular, it is shown that the polarization-based communication system yields higher energy efficiency gains as compared to a system implementing layered division multiplexing.

This paper investigates the wireless power coverage in a network where intelligent reconfigurable surfaces (RISs), distributed according to a homogeneous Poisson point process, cooperate in the energy transfer from the power beacon to the harvesting devices. First, using energy beamforming and maximum ratio transmission, the harvested energy at a typical device is obtained. Then, leveraging stochastic geometry tools, and adopting an approach based on the moment generating function, the power coverage probability is obtained. For such, we also characterize the distributions of the channel gains and the device distances. Novel closed-form expressions for the coverage probability are provided for the cases when the wireless power transfer is assisted by multiple RISs, deployed in cascaded or distributed configurations, as well as when the power beacon is aided by a single RIS. The impact of the main network parameters on performance is analyzed. In particular, comparative results show the significant gains that can be achieved in the network coverage when multiple RISs cooperate in the wireless power transfer, as compared to the non-cooperative scheme.

This paper investigates the power coverage probability in cooperative wireless powered communication networks, where multiple access points collaborate to meet the energy demands of low-power devices. Based on the theory of Poisson-Delaunay triangulation, the probability density functions (PDF) of the Euclidean distance between the access points of the Poisson-Delaunay triangular cell and typical devices are derived. By using the theory of stochastic geometry and the obtained PDFs, the closed-form expressions of the wireless power coverage probability are obtained for three typical locations of the devices. As the wireless power coverage probability expressions involve the extended generalized multivariate MeijerG function (EGMMGF), a new implementation enabling numerical calculation of the EGMMGF is also proposed. The impacts of the main network parameters on the performance of the proposed framework are analyzed. In particular, comparative results show the significant gains that can be achieved in the wireless power coverage when multiple access points participate in the wireless power transfer or when the density of the network’s access points is increased, as compared to the non-cooperative scheme.

Wireless communications via reconfigurable intelligent surfaces (RIS) are envisioned to offer unprecedented spectral efficiency gains by smartly inducing phase shifts on the impinging electromagnetic waves at the RIS to reconfigure the underlying propagation environment. This work investigates a multi-user downlink communication system in which the access point, equipped with multiple antennas, serves its associated single-antenna users equipments (UE) with the help of RIS. The proposal is a leakage-based design in which the transmit precoding, the power allocation, and the phase shifts of the RIS, are designed to maximize the minimum signal-to-Ieakage-plus-noise power ratio (SLNR) of the UEs subject to the constraint on the power budget of the access point. The merits of the SLNR-based approach are highlighted, e.g., reduced complexity, and simulation results show that the RIS-aided design can achieve massive MIMO gains with much fewer number of active antennas in the access point as compared to conventional relaying.

In this paper, we present a resource allocation framework for uplink communication in cellular networks aided with aerial intelligent reflecting surface (IRS). The main focus is on maximizing the energy efficiency by jointly optimizing the transmit powers of the users, the active beamforming at the base stations, and the passive beamforming at the IRS, while maintaining the users' minimum rates and adhering to the power constraints. The formulated problem is a highly intractable non-convex one, with the optimization variables coupled with each other in an intricate manner. To tackle this, an iterative solution based on alternating techniques is proposed. In particular, the transmit beamforming and the phase-shift matrix are obtained by minimum mean square error and semidefinite relaxation techniques, respectively. Numerical results are provided and show that using aerial IRS has remarkable advantages compared to the system operation with conventional aerial relaying. In particular, significant energy efficiency gains are achieved when optimal transmit power and a large number of reflecting elements are implemented.

This paper investigates the wireless power coverage and the transmission probability in a network where multiple access points, distributed according to a homogeneous Poisson point process, cooperate in the energy transfer towards harvesting devices. Using distributed energy beamforming and maximum ratio transmission, and leveraging stochastic geometry tools, the power coverage probability and the transmission probability are obtained in closed-form for three types of devices, namely, inner-cell, cell-edge, and vertex-cell. Exact formulae for the coverage and transmission metrics when devices are serviced by single energy sources are also provided. The impact of the main network parameters on performance is analyzed. In particular, comparative results show the significant gains that can be achieved in the coverage and transmission probabilities when multiple access points participate in the wireless power transfer, as compared to the non-cooperative scheme.