In this work, we investigate the use of reconfigurable intelligent surface (RIS) partitioning and transmit power allocation for terahertz (THz) enabled spectrum-sharing underlay device-to-device (D2D) communication, assuming that instantaneous channel state information (CSI) for co-channel interference (CCI) links is unavailable. We first derive closed-form expressions for the ergodic rate (ER) based on statistical CSI using the moment matching technique and Gaussian–Chebyshev quadrature approximation, while accounting for generalized fading and pointing errors. We then develop a low-complexity particle swarm optimization (PSO) algorithm based solution to jointly partition the RIS and allocate transmit powers, aiming to maximize the ER of the D2D user. Analytical findings are validated via extensive Monte Carlo simulations, which provide key system design insights and performance comparisons with both non-RIS systems and benchmark optimization schemes.

In recent years, reconfigurable intelligent surfaces (RIS) have emerged as a promising technology for enhancing link reliability in wireless communication systems. This paper introduces a novel RIS-assisted terahertz (THz) communication system utilizing the spatial modulation (SM) technique. We derive the closed-form expressions for the probability density function (PDF) and moment generating function (MGF) of the SM-based RIS-assisted THz system over α-μ fading. Leveraging these derived channel statistics, we obtain an upper bound on the average bit error rate (BER) and a lower bound on the ergodic capacity to evaluate the performance of the proposed system. The asymptotic BER is analyzed to determine the system’s diversity gain. The numerical results validate the theoretical findings and provide valuable insights into the system’s performance. The analysis shows that the SM-based RIS-assisted THz system outperforms the existing traditional systems. Lastly, a trade-off between average BER performance and spectral efficiency is observed.

In this paper, we investigate a full-duplex underlay device-to-device (D2D) communication system, where multiple D2D pairs exchange information with the assistance of a single reconfigurable intelligent surface (RIS). We begin by deriving analytical expressions for the outage probability of the users, and subsequently for ergodic rate. The analysis is carried out over a generalized Nakagami-m fading channel and incorporates several practical impairments, including residual self-interference (RSI), hardware imperfections (HI), and co-channel interference (CCI) from both cellular and D2D users. Assuming only statistical channel state information (CSI) is available for the CCI links, we formulate a joint optimization problem for D2D transmit power allocation and RIS partitioning, with the objective of maximizing the ergodic sum rate of the network. This optimization problem is efficiently solved using the particle swarm optimization (PSO) algorithm. Simulation results validate the effectiveness of the proposed system, demonstrating superior performance over conventional half-duplex systems and highlighting the advantages of the proposed optimization framework compared to benchmark schemes.

This paper explores a full-duplex underlay D2D communication system, where multiple D2D pairs exchange data with the help of a single RIS through RIS partitioning. Closed-form expressions for outage probability and ergodic rate are derived over generalized Nakagami-m fading, considering practical impairments such as residual self-interference, hardware imperfections, and co-channel interference (CCI). Assuming only statistical channel state information (CSI) availability for the CCI links, we formulate and solve a joint optimization problem for transmit power allocation and RIS partitioning using particle swarm optimization. Simulation results show significant performance gains over half-duplex systems and comparative benchmarks schemes.

Reconfigurable intelligent surfaces (RISs) hold great potential for addressing the challenges in terahertz (THz) communication. However, a single RIS cannot sufficiently overcome the high path loss of THz frequencies. This paper proposes a beam routing scheme for multi-RIS-assisted sixth-generation (6G) networks, employing a dynamic programming algorithm to optimize the propagation environment through multiple RISs for efficient multi-hop communication. A closed-form expression for ergodic capacity is derived. Simulation results demonstrate significant enhancements in throughput and reliability, highlighting the advantages of this approach over traditional methods and supporting the deployment of THz networks for future wireless applications.

This study explores a hybrid framework that merges terahertz (THz) and free space optics (FSO) technologies in a backhaul network. The combined FSO and THz systems leverage reconfigurable intelligent surfaces (RIS) and employ maximal ratio combining (MRC) at the receiver. Specifically, the closedform expressions for cumulative distribution function (CDF) of channel and signal-to-noise ratio (SNR) for RIS-assisted FSO and THz channels are derived by assuming the impediments such as atmospheric turbulence, fading, pointing errors, and pathloss. Using these statistics, outage probability, average symbol error rate (SER), and outage capacity are computed for the proposed RIS-assisted hybrid FSO/THz system. Numerical results compare the proposed hybrid FSO/THz system against various wireless systems, including RIS-assisted FSO, RIS-assisted THz, and hybrid FSO/THz systems without RIS.

Intelligent reflecting surface (IRS) technology is a promising solution for addressing the limitations of terahertz (THz) systems, including blockage effects and tremendous path loss. This paper investigates a novel IRS-assisted hybrid framework that seamlessly combines both THz and radio frequency (RF) technologies using a selection combining (SC) scheme, thereby enhancing system reliability. The study incorporates the deterministic and statistical properties of IRS in both RF and THz domains employing a sophisticated spatial scattering chan-nel model across generalized α - µ fading channels. Specifically, the exact closed-form expressions for the probability density function (PDF) and cumulative distribution function (CDF) of the output signal-to-noise ratio (SNR) are derived for both THz and RF links. From this, the outage probability and average symbol error rate (SER) are derived. Furthermore, asymptotic expressions are evaluated for outage and average SER, offering insights into diversity gain of the system. Simulation results reveal a significant enhancement in system performance and power savings for the proposed IRS-aided hybrid THz/RF system. These findings provide valuable insights into the practical implementation of IRS-assisted hybrid networks, contributing to the ongoing efforts for future wireless networks.

Intelligent reflecting surfaces (IRS) have emerged as a promising technology for addressing the inherent challenges associated with terahertz (THz) bands, thereby enhancing system performance and offering immense potential for future wireless systems. However, existing single and multi-IRS-aided wireless systems often overlook crucial IRS-related factors such as IRS unit-cell dimensions, IRS gain, and inter-IRS collaboration, potentially limiting system performance. To mitigate these limitations and to leverage the unique advantages of THz band, this study investigates a multi-IRS-empowered THz system, that incorporates design parameters such as, the transceiver antenna gains, operation frequency, link distances, molecular absorption losses, beam misalignment, transceiver hardware imperfections, and statistical characteristics of the THz channel. By utilizing a sophisticated channel model that integrates the joint effects of these parameters with IRS properties and inter-IRS collaboration, this study demonstrates a significant enhancement in system performance and power savings. Moreover, exact closed-form expression and asymptotic approximation for outage probability are derived to quantify the effects of the deterministic and statistical channel parameters. These findings provide valuable insights into the practical implementation of multi-IRS-assisted THz networks, contributing to the ongoing efforts to unlock the potential of THz band for future wireless applications.

Terahertz (THz) wireless communication has emerged as a front-line technology for substantially improving the data rates for 6G networks. However, they suffer from tremendous path-attenuation that limits the communication distance. Intelligent reflecting surface (IRS) is an excellent cost-effective technology for enabling THz wireless systems. This article presents comprehensive analysis of an IRS-empowered THz system, incorporating a detailed channel model encompassing deterministic IRS channel gain, THz molecular absorption losses, and the characteristics of sum of double$\alpha -\mu $fading. The analysis considers IRS-specific parameters, such as unit-cell dimensions, gain, radiation pattern, and array factor, for accurate received signal power characterization. For statistical analysis, the probability density function, cumulative distribution function, and moments are characterized using programmable multivariate Fox’s H-functions. Using these derived statistical results, the exact closed-form solutions for outage probability, average bit error rate, and ergodic capacity are reported. Additionally, asymptotic approximations are presented for deeper insights. Finally, to validate the accuracy of analytical results, extensive Monte-Carlo simulations are conducted. Multiple results investigate various design aspects of the proposed system. The findings demonstrate that significant performance gains and power savings thereby making THz communication feasible and highly promising for future wireless networks.

Recently, reconfigurable intelligent surfaces (RISs) have emerged as a highly promising technology within the realm of wireless communication systems, as they offer the potential to minimize obstructions, enhance reliability, and establish alternative paths for signal propagation. This article presents the performance of a free space optics (FSOs) system empowered by multiple optical reflecting surfaces (ORSs) over a Gamma-Gamma turbulence-induced fading channel with pointing errors by considering imperfections in channel state information (CSI). The expressions for probability density function (PDF) of the end-to-end FSO channel considering both perfect and imperfect CSI cases are derived. Further, the unified PDF and cumulative distribution function (CDF) of instantaneous signal-to-noise ratio (SNR) are determined under two detection schemes, i.e., intensity modulation/ direct detection and heterodyne detection for both perfect and imperfect CSI cases. Utilizing the derived CDFs, the closed-form expressions for outage probability and average symbol error rate (ASER) of the proposed multiple ORSs system are obtained along with performing asymptotic analysis. Finally, the numerical results indicate that the performance of ORS-assisted FSO systems is significantly degraded by severe turbulence, pointing errors, and imperfect CSI. However, the inclusion of ORSs and increasing their number improves the performance of ORS-assisted FSO systems in the presence of turbulence, pointing errors, and imperfect CSI, compared to FSO systems without ORSs.

This paper investigates a hybrid framework that combines free space optics (FSO) and terahertz (THz) technologies for a backhaul network. In this hybrid configuration, the FSO and THz systems are empowered by reconfigurable intelligent surface (RIS) and are combined at the receiver using either maximal ratio combining (MRC) or selection combining (SC). The performance of the RIS-assisted hybrid FSO/THz system is evaluated under multiple impairments for FSO and THz links. The exact closed-form expressions for probability density function (PDF), cumulative distribution function (CDF), and moment-generating function (MGF) of the output signal-to-noise ratio (SNR) of both RIS-assisted FSO and THz links are derived. Leveraging these SNR statistics, we compute the outage probability and the average symbol error rate (SER) of the proposed hybrid FSO/THz system with MRC and SC schemes. Additionally, this paper conducts an asymptotic analysis at high SNR levels, yielding asymptotic expressions for outage and average SER, which not only reduce computational complexity but also provide insights into the system’s diversity gain. In the numerical results, the performance of the proposed hybrid FSO/THz system is compared against other state-of-the-art wireless systems, including direct link FSO without RIS, RIS-aided FSO, and the hybrid FSO/THz systems without RIS using diversity combining techniques.

Free space optics (FSO) communication offers various advantages like higher bandwidth, higher data rates, etc., when compared with its counterpart, i.e. radio frequency (RF) communication. Despite that the FSO link is adversely affected due to atmospheric turbulence, obstructions between transmitter and receiver, and pointing errors. In this work, we propose a mixed FSO/RF system based on decode-and-forward (DF) relaying technique consisting of a FSO-based transmitter node (i.e. source), a relay node, which is capable of receiving FSO signal and transmitting RF signal, and an RF-based receiver node (i.e. destination). Furthermore, both FSO and RF links are aided with intelligent reflecting surfaces (IRS). The main goal of the proposed system model is to increase the coverage and overall system reliability of the existing mixed FSO/RF system. Specifically, we investigate the performance of the proposed system by deriving the closed-form expressions for outage probability and average bit error rate (BER) in terms of multivariate Fox’s H-function without using central limit theorem. Moreover, the numerical results are shown along with some insightful discussions. From numerical results, it is deduced that IRS-assisted mixed FSO/RF system performs better than the existing mixed FSO/RF systems without IRS. Finally, analytical results are verified by performing Monte-Carlo simulations.

The deployment of intelligent reflecting surfaces (IRSs) in wireless communication systems have recently garnered much attention due to its potential to reduce blockages by providing an alternate propagation path and improving reliability. This paper reports the performance analysis of multiple optical reflecting surfaces (ORSs)-assisted free space optics (FSO) communication. Specifically, the performance is investigated by utilizing the selection of the best ORS from the multiple available ORSs. Firstly, we have derived the exact probability density function (PDF) of the end-to-end maximum instantaneous signal-to-noise ratio (SNR) among multiple ORSs-aided FSO links. Further, using the above PDF statistics, the outage and average symbol error rate (SER) expressions of the considered multiple ORSs system are derived in closed-form. Additionally, the asymptotic expressions, which are mathematically more tractable, for both outage and average SER are presented with the diversity gain analysis. Finally, numerical results along with Monte-Carlo simulation results are provided to corroborate the derived analytical results.

Recently, the use of reconfigurable intelligent surfaces (RIS) has gained popularity and is emerging as a promising technique to provide improved link reliability and enhanced coverage area. In this paper, we propose an optical reflecting surface (ORS)-assisted free space optics (FSO) communication system, which is based on optical space shift keying (OSSK) technique. Specifically, the closed-form expression for probability density function (PDF) of the ORS-assisted FSO channel is derived over Malaga turbulence model. Further, we have obtained the moment generating function (MGF) of the instantaneous signal-to-noise ratio (SNR) of the overall OSSK-based multiple-input multiple-output (MIMO)-FSO system. Using the derived channel statistics, an upper bound expression for the average bit error rate (BER) and a lower bound for the ergodic capacity are derived. Further, the asymptotic BER is utilized to calculate the diversity gain of the system. Numerical results are provided to corroborate the theoretical analysis of the system, along with insightful discussions. It is observed from the numerical results that the atmospheric turbulence and pointing errors have a negligible effect on the performance of the proposed system. Finally, a trade-off is noticed with respect to the average BER performance versus the spectral efficiency of the proposed system.

This study deals with the performance analysis of adaptive combining‐based hybrid free‐space optics (FSO)/radio‐frequency (RF) system in a terrestrial communication scenario with and without pointing errors. Here, outage probability and average symbol error rate (SER) are used as the performance metrics. Adaptive combining is a switching scheme in which the FSO link is active throughout, whereas the RF link is activated based on the transmission reliability of the FSO link and maximal‐ratio‐combining (MRC) of RF and FSO links is performed at the destination. The small‐scale fading in RF and atmospheric turbulence induced fading in FSO links have been characterised by Nakagami‐ m and Gamma–Gamma distributions, respectively. In addition, the radial displacement between the beam centre and detector centre, which induces pointing errors, is modelled using Rayleigh distribution. The exact closed form expressions for the outage and average SER have been derived along with their corresponding asymptotic expressions. Diversity gain of the system has also been determined using the asymptotic expressions. Further, the variation in the performance of the system has been analysed with respect to various parameters including link distance, fading severity parameter, average signal‐to‐noise of the RF link, and the pointing errors parameter.