The incorporation of reconfigurable intelligent surfaces (RISs) and unmanned aerial vehicles (UAVs) presents considerable potential for improving the functionality of ground-based terrestrial Internet of Things (IoT) networks. This paper introduces a novel UAV deployment and aerial RIS partitioning mechanism for the uplink non-orthogonal multiple access (NOMA)-based IoT networks under practical hardware constraints. The low-cost hardware of IoT devices results in imperfect successive interference cancellation (SIC) and distortion noise due to transceiver hardware impairments (T-HIs). Specifically, we have optimized the aerial RIS partitioning and its deployment to maximize the minimum rate under the impact of imperfect SIC and T-HIs. The numerical results show that the proposed scheme outperforms the benchmark. Through extensive simulations, we prove that the proposed UAV-based aerial RIS-aided uplink NOMA network significantly enhances the max-min fair rate.

The integration of reconfigurable intelligent surfaces (RISs) and grant-free non-orthogonal multiple access (GF-NOMA) has emerged as a promising solution for enhancing spectral efficiency and massive connectivity in future wireless networks. This paper proposes a GF-NOMA communication network enabled by simultaneously transmitting and reflecting RISs (STAR-RIS). In the proposed GF-NOMA, all user equipments (UEs) have instantaneous access to resource blocks (RBs) without the need for grant acquisition and power control as in the traditional grant-based NOMA schemes. Specifically, we have considered two regimes of interest: 1) the max-min fair (MMF) regime and 2) the max-sum throughput (MST) regime. To achieve the required power disparity, a two-level power control mechanism is proposed; initially, the UEs are clustered according to their channel gains. Additionally, we introduce a multi-level GF-NOMA (MGF-NOMA) scheme that adjusts the transmit power levels for each UE in the cluster. The second level of power disparity is achieved through the assignment of STAR-RISs to the clusters and optimal partitioning of STAR-RIS to support each of the cluster members. Specifically, we have also derived the closed-form equations for the optimal partitioning of STAR-RIS within the clusters for both regimes of interest. Simulation results demonstrate that the proposed STAR-RIS-aided MGF-NOMA yields a gain of 60% and 20% in the MST regime with active and passive RIS realization, respectively. Furthermore, the active and passive RIS-based MGF-NOMA achieve nearly the equivalent fairness that can be obtained through optimal power control in the MMF regime. The finding emphasizes the potential of integrating STAR-RIS with GF-NOMA as a robust and promising solution for future wireless communication systems.

The integration of reconfigurable intelligent surfaces (RISs) and grant-free non-orthogonal multiple access (GF-NOMA) has emerged as a promising solution for enhancing spec-tral efficiency (SE) and massive connectivity in future wireless networks. This paper proposes a novel virtual RIS partitioning mechanism for GF-NOMA, where all user equipments (UEs) within a specific NOMA cluster have instantaneous access to resource blocks (RBs) without the need for grant acquisition and power control as in the traditional grant-based NOMA schemes. To achieve the required power disparity, RIS portions are allocated to the UEs in a manner that increases the reception power disparity. We derive closed-form equations for optimal RIS portions in two regimes of interest: 1) max-min fair regime and 2) maximum throughput regime. Simulation results demonstrate that the proposed RIS-assisted GF-NOMA yields a gain of 28% and 15% in terms of max-sum rate and max-min rate, respectively, outperforming existing grant-based approaches. The study highlights the potential of combining RIS with GF-NOMA as a powerful solution for future wireless communication systems.

Reconfigurable intelligent surfaces (RISs) have sparked a renewed interest in the research community envisioning future wireless communication networks. In this study, we analyzed the performance of RIS-enabled non-orthogonal multiple access (NOMA) based device-to-device (D2D) wireless communication system, where the RIS is partitioned to serve a pair of D2D users. Specifically, closed-form expressions are derived for the upper and lower limits of spectral efficiency (SE) and energy efficiency (EE). In addition, the performance of the proposed NOMA-based system is also compared with its orthogonal counter-part. Extensive simulation is done to corroborate the analytical findings. The results demonstrate that RIS highly enhances the performance of a NOMA-based D2D network.

Vehicle-to-everything (V2X) connectivity in 5G-andbeyond communication networks supports the futuristic intelligent transportation system (ITS) by allowing vehicles to intelligently connect with everything. The advent of reconfigurable intelligent surfaces (RISs) has led to realizing the true potential of V2X communication. In this work, we propose a dual RIS-based vehicle-to-infrastructure (V2I) communication scheme. Following that, the performance of the proposed communication scheme is evaluated in terms of deriving the closed-form expressions for outage probability, spectral efficiency and energy efficiency. Finally, the analytical findings are corroborated with simulations which illustrate the superiority of the RIS-assisted vehicular networks.

Reconfigurable intelligent surfaces (RISs) have recently been envisioned to provide an adaptable channel for futuristic wireless communication networks. In this work, we investigate a downlink RIS-aided non-orthogonal multiple access (NOMA) wireless networks, where a RIS is deployed to enhance users’ performance communicating with the base station (BS) in the presence of a non-ideal transceiver. Specifically, closed-form expressions for the outage, spectral efficiency (SE) and energy efficiency (EE) are derived. The results demonstrate that the non-ideal transceiver has a detrimental impact on the performance of the RIS-aided NOMA system. The proposed analysis also shows that for a RIS-aided NOMA system with a non-ideal transceiver, there exists an upper bound on SE that is independent of the transmit power and the number of reflecting elements in the RIS. Additionally, the performance of the NOMA system is compared with its OMA counterpart, where the results show that for a non-ideal transceiver-based system, the RIS-aided NOMA outperforms OMA.

An intelligent reflecting surface (IRS) comprises of an array of discrete reflective elements (REs) possessing re-configurable scattering properties. IRS has the capability to beamform and relays the received radio signal from the transmitter to the desired receiver. This has made the IRS a promising candidate technology for the beyond fifth-generation (5G) cellular standards. In this work, the performance of an IRS-assisted wireless communication system is investigated and compared with the full-duplex (FD) relay-assisted system in the presence of non-ideal transmitters. Specifically, the performance is compared in terms of channel capacity and energy efficiency (EE). The results show that the IRS can never achieve more capacity than the ideal FD relaying, in the presence of a non-ideal transmitter, irrespective of the placement of IRS and relay. Further increasing the number of REs, the capacity saturates with an upper bound that equals to the capacity provided by the relay-assisted system. However, increasing the number of REs results in the reduction of the EE for IRS-assisted systems, which are otherwise known to be highly energy-efficient.

Energy efficiency (EE) and spectral efficiency (SE) are among the key performance metrics for any wireless standards. In this work, we study the trade-off between EE-SE for supporting the downlink data rate as well as opportunistically harvesting the ambient radio frequency (RF) energy. The goal is to maximize EE while maintaining the requisite data rate for the downlink. We consider a case of downlink full duplex multi-input single-output (MISO) system where the transmitter having multiple antennas is transmitting to a user equipped with single antenna. At the transmitter, few antennas are reserved for selfenergy recycling (S-ER) while the remaining antennas are utilized for information transmission. S-ER enhances the EE of the system at the expense of SE due to loss in the array gain. In order to improve the SE, we incorporate the adaptive S-ER scheme which utilizes selection of antennas corresponding to higher gains for information transmission. This compensates the loss in the SE along with the increase in EE of the system. Both linear and nonlinear transmitter cases have been considered for analyzing the trade-off and the simulation results are shown by obtaining the outage probability.