In this paper, we investigate the performance of a non-orthogonal multiple access (NOMA)-enhanced active reconfigurable intelligent surface (RIS)-assisted integrated sensing and communication (ISAC) system under a non-terrestrial network (NTN) framework. The performance is analyzed in terms of outage probability, ergodic capacity, beampattern gain, and probability of detection (PoD). To this end, the end-to-end equivalent channel distribution under maximum ratio transmission beamforming is derived and modeled as a Gamma distribution. Based on this, a closed-form expression for the outage probability (OP) is obtained in terms of Meijer G-functions. The accuracy of the analytical results is validated through Monte Carlo simulations. To provide further insight, we derive the asymptotic expression of the OP and the corresponding diversity order. Additionally, an approximate expression for the ergodic capacity is derived using the method of moments, along with its upper and lower bounds. To evaluate the impact of the active RIS in mitigating the impact of multiplicative fading through amplification of the incident signal, its performance is compared against a baseline passive RIS scheme, revealing significant performance improvements. In particular, the outage probability is improved by approximately 72.94% and 73.33% for the weak user (D1) and strong user (D2), respectively, when employing an active RIS compared to a passive RIS at a transmit SNR of 22 dBm. The influence of practical impairments, including hardware impairments, imperfect channel state information, and imperfect successive interference cancellation, is also examined. The results show that increasing the number of RIS elements and the number of antennas at the satellite can effectively alleviate the adverse effects of these impairments. On the sensing side, the proposed ISAC system is compared with a conventional radar system in terms of the PoD for aerial targets located at various positions, and it additionally demonstrates beampattern gain. The results are obtained under the assumptions of ideal RIS phase configuration and line-of-sight (LoS) between the satellite and targets, representing key limitations of the analysis.

This study analyzes the performance of a two-hop communication system that integrates free-space optical (FSO) transmission with intelligent reflecting surface (IRS)-aided radio frequency (RF) transmission. This analysis focuses on the transmission within a non-orthogonal multiple access (NOMA) system over heterogeneous channels: the source-to-relay FSO channel follows a Fisher-Snedecor$F$distribution, the relay-to-users RF channels are modeled as Rayleigh distributions, the relay-to-IRS and IRS-to-users RF channels are characterized by Rician distributions. A closed-form expression for the outage probability has been derived and approximated as a Gamma distribution using the moment-generating function under imperfect successive interference cancellation. Notably, the outage probability expressions and their approximation closely align with our simulation results, thus validating the accuracy of our findings. Additionally, an asymptotic expression for the outage probability has been derived, particularly in the FSO transmit SNR regime, and the corresponding diversity order is evaluated. The impact of various system parameters, such as turbulence, on the rate of decay of the outage probability is explained through the diversity order.

Backscatter communication (BackCom) holds immense potential for enhancing the capabilities of energy-constrained Internet of Things (IoT) devices and supporting a wide range of applications. Nonorthogonal multiple-access (NOMA) schemes are advantageous for meeting the demands of massive connectivity in next-generation communication networks, and NOMA-aided BackCom can leverage the benefits of both BackCom and NOMA. This article covers the basics of BackCom, explores different types of BackCom systems, and explains how NOMA can be integrated with BackCom, where various crucial issues, including design principles, channel state information (CSI) estimation, node pairing schemes, and reflection coefficient (RC) designs, are illustrated. Furthermore, this survey evaluates the effectiveness of different network architectures for NOMA-aided BackCom, especially in IoT networks, and identifies potential research directions and future trends in this area. The key considerations for designing and optimizing NOMA-aided BackCom systems in real-world scenarios are also highlighted in this survey. In addition, by reviewing the existing literature and research on NOMA-aided BackCom, this article provides valuable insights for researchers and practitioners interested in this emerging wireless communication technique.

This article characterizes the performance of mixed free-space optical (FSO)/active intelligent reflecting surface (IRS)-aided nonorthogonal multiple access (NOMA) communication in the presence of imperfect channel state information (CSI) and imperfect successive interference cancelation (SIC). The detrimental effects of atmospheric turbulence on the FSO communication link, which affects end-to-end communication, are also presented. Considering practical implementation, we illustrate the impact of phase quantization error, imperfect SIC, and imperfect CSI on the outage performance. Our numerical analysis indicates that the outage performance can be significantly improved by utilizing multiple transmit apertures through transmit aperture selection at the base station and employing multiple transmit antennas via maximum ratio transmission at the relay. In addition, the numerical results demonstrate that performance improvements are achieved by mitigating double path loss through an active IRS compared to a passive IRS. The closed-form expression for the outage probability is derived using methods of moments and then verified through Monte Carlo simulations. To gain more valuable insights, asymptotic expressions are also provided for high RF transmit power and high FSO transmit power scenarios. Consequently, diversity orders are derived for an asymptotic study of the outage performance of the considered NOMA network.

The paper evaluates the ergodic sum capacity, outage performance for communication users, and the detection probability, beampattern gain for sensing targets in a simultaneous transmitting and reflecting intelligent reflecting surfaces (STAR-IRS) aided integrated sensing and communication (ISAC) system. The rate splitting multiple access (RSMA) technique and maximal ratio transmit beamforming at the multi-antenna base station have been explored. Closed-form expressions for the ergodic sum capacity and outage probability of the STAR-IRS-aided RSMA ISAC system are derived through moment methods. The derived expressions are validated through Monte Carlo simulations. Additionally, to provide deeper insights into the diversity orders of the RSMA ISAC system, we conduct an asymptotic outage probability analysis in the high signal-to-noise ratio regime. The effect of the number of base station antennas and STAR-IRS elements on outage performance has been demonstrated, along with an explanation of the underlying reasons through diversity gain. Furthermore, it shows that the implementation of STAR-IRS significantly boosts the system’s ergodic sum capacity compared to traditional reflecting-only IRS. Additionally, the RSMA technique delivers more substantial performance improvements than the non-orthogonal multiple access (NOMA) in high transmit SNR conditions while demonstrating comparable performance in low transmit SNR scenarios. A comparison between energy splitting and mode switching STAR-IRS has been conducted under both ideal and random phase shift conditions. A trade-off analysis between communication and sensing rates is presented. Additionally, the accuracy of target sensing is evaluated by measuring the mean square error (MSE) in beampattern gain matching. The impact of quantization levels for phase shift of STAR-IRS on outage probability has also been addressed. Finally, the effects of power allocation for sensing on detection probability and beam pattern gain are also presented.

The paper explores hybrid free-space optical (FSO) and active intelligent reflecting Surface (IRS)-aided radio frequency (RF) transmission in non-orthogonal multiple access (NOMA) networks to improve outage performance of internet of things (IoT) devices under imperfect channel state information (imCSI) and imperfect successive interference cancellation (imSIC). The superposed signal is transmitted from the source to the relay over FSO link exploiting the line of sight (LOS) path modeled as Gamma-Gamma distribution. Whereas RF signals transmission from the relay to IoT devices are boosted through an active-IRS. The multiplication factor of path-loss is prominent in the presence of a direct path from the relay to IoT devices. The active-IRS can mitigate the issue. In this paper, the direct path is modeled using a Rayleigh distribution, while the indirect paths via the Active-IRS are modeled using a Rician distribution. The paper demonstrates the impact of active noise introduced by the Active-IRS on outage performance. The closed-form expression for outage probability is derived under imCSI and imSIC, taking into account active-IRS noise. Additionally, it conducts an asymptotic analysis in a high signal-to-noise ratio (SNR) regime. The analytical results closely align with Monte Carlo simulation results, validating the accuracy of the findings.

In this paper, we analyze throughput and delay performance of clustered Machine Type Communication (MTC) devices which access an eNodeB utilizing a primary spectrum in underlay mode. We assume that the MTC devices form two clusters and there is an optimal preamble allocation between the two clusters to maximize the throughput. We further investigate the impact of the tolerable interference threshold on throughput, successful preamble decoding probability, and delay. Then, the impact of the preamble partition factor and the access barring factor on throughput and delay is analyzed. Finally, we evaluate the impact of the number of devices, retransmission requests, and preamble partitions on the delay.

In this study, a relay assisted order energy harvesting‐based non‐orthogonal multiple access (NOMA) network is considered where the relay harvests energy from radio frequency signal of the source. A transmit antenna selection scheme is considered at the source under imperfect channel state information (CSI). The outage probability of order NOMA network is analysed and a closed‐form expression of it is obtained. A comparative performance study is carried out with perfect and imperfect successive interference cancellation at the receiver. The impact of a number of antennas available at the source on outage performance and the effect of imperfect CSI on the outage performance are also presented in this work. The upper limit of the order of the NOMA network to be supported for a given threshold signal to interference plus noise ratio (SINR) is also estimated.

In this study, a multihop transmission scheme in cognitive environment is investigated. Several number of decode and forward relays are deployed between the secondary source and the secondary destination. All the nodes harvest energy using a time splitting‐based relaying scheme from radio‐frequency signal of a primary beacon (PB). All the nodes use harvested energy to transmit data from a node to its next node. The maximum transmit power of any secondary node is limited by interference constraint at a primary receiver. The presence of PB is considered in the form of a regular periodic pattern. An expression for signal‐to‐noise ratio and ergodic capacity at each secondary node in the multihop network are derived. A closed form expression for the outage probability (OP) of the secondary network is derived for transient and steady‐state condition in two different scenarios of arrival time period of PB ( ). The closed‐form expression for the OP of the secondary network is validated with the simulation results for different system parameters such as harvesting efficiency, harvesting time, the number of SRs, the transmission power of PB. An optimum value of the presence duration of PB within the time period is also estimated. Further, impact of imperfect channel state information (CSI) of interfering links between secondary transmitting nodes and primary receiver is investigated on secondary OP and compared with the case of perfect CSI.