One of the disruptive communication technologies for sixth-generation (6G) wireless networks is cell-free massive multiple-input multiple-output (CF-mMIMO), which is capable to control inter-cell interference in MIMO systems. This paper investigates the performance of a full-duplex (FD) CF-mMIMO systems with practical limited-capacity fronthaul links. The proposed system employs a large number of M distributed FD APs, arbitrarily distributed$K_{d}$downlink (DL) and$K_{u}$uplink (UL) half-duplex (HD) single-antenna equipped user terminals (UEs), and a central processing unit (CPU). To exploit the energy efficiency and potential throughput gains of FD systems, each AP is linked to the CPU through a fronthaul link with limited capacity that handles the quantized UL/DL data to/from the CPU. Each AP is expected to support K HD UEs on the same spectrum resource, where$K = (K_{u} + K_{d})$. Imperfect channel state information and the mobility of the UEs are also considered. A closed-form expression for the outage probability is derived using the optimal uniform quantization and maximum-ratio combining/maximum-ratio transmission considering the Welch-Satterthwaite approximation. Additionally, the asymptotic and infinite-M outage expressions for the proposed system are analytically studied and verified via Monte Carlo simulation. Simulation results demonstrate the relationship between the improved outage performance and uniform quality of service (QoS) for all UEs. Moreover, this analysis provides valuable insights into the behavior of FD-CF-mMIMO system and underscores the importance of providing a uniform QoS to all UEs in improving the overall performance of the system.

The cell-free massive multiple-input and multiple-output (CF-mMIMO) communication technology has the ability to handle inter-cell interference in MIMO systems, making it a potential candidate for sixth-generation (6G) wireless communication. A CF-mMIMO system is investigated in this paper for mission-critical ultra-reliable low latency communication (URLLC) applications involving a central processing unit (CPU), many distributed access points (APs), each with multiple antennas, and multiple single-antenna user equipment (UEs). In order to maximize energy efficiency (EE) and throughput gains, each AP is linked to the CPU through a fronthaul link with limited capacity, which handles the quantized uplink data to the CPU. We assume that each AP serves fewer UEs. Our approach has a minimal signal processing complexity and offers UEs uniform quality of service (QoS) as well as improved EE. Closed-form expression for outage probability (OP) in the uplink of the CF-mMIMO system considering Welch-Satterthwaite approximation is derived using a variety of Doppler power spectra (DPS) models that consider imperfect channel state information (CSI) and mobility of UEs. Our numerical simulations validate the correctness of the derived expressions.

Reconfigurable intelligent surface (RIS) is a break-through technology that enhances both energy efficiency (EE) and spectrum efficiency (SE) by artificial reconfiguration of the electromagnetic waves utilizing the reflective property of the metasurface elements. This work studies the optimization of the SE-EE trade-off using the deep reinforcement learning (DRL) algorithm in a RIS-assisted full-duplex multi-user multiple-input multiple-output (MIMO) communication system. We use partial channel state information to control the overhead signaling requirement and demand for energy supply to the system. We consider resource efficiency (RE), in which the RIS’s phase-shift design and power allocation at the nodes (i.e., node in BS in downlink (DL) and user in uplink (UL)) are jointly optimized, with the goal of investigating the SE-EE trade-off of the considered system using an appropriate performance metric. We adopt a DRL-based approach for the proposed system to tackle the challenges involved in optimization due to time-varying channels and exploitation in real-time applications. Additionally, simulation outcomes exemplify the efficiency and swift conver-gence rate of the proposed algorithm and demonstrate how different system characteristics, including co-channel interference (CCI), residual self-interference (RSI), and the number of RIS reflecting elements, affect the system’s performance.

With the advancement of wireless communication technologies, reconfigurable intelligent surfaces (RISs) have recently paved the way to augmenting the performance of wireless networks with the aid of multiple reflecting surfaces by efficiently attuning the signal reflection through a large number of low-cost passive elements. In this paper, we consider an RIS-aided full-duplex (FD) communication network consisting of a FD access point (AP) that communicates with an uplink and a downlink user simultaneously with the aid of an RIS as well as through the direct link between the AP and users. To evaluate the system performance under infinite blocklength (IBL) and finite blocklength (FBL) codes, we derive the analytical expressions for the outage probability and throughput in case of IBL, and for block-error rate (BLER) and goodput in the case of FBL, for both uplink and downlink transmission. Furthermore, the expressions for the maximum achievable rate under FBL and IBL transmission are derived. Next, we also extend the analysis of the single-user framework to a more practical scenario with multiple users utilizing non-orthogonal multiple access (NOMA) and derive analytical expressions for the outage probability and BLER at each downlink user and at the AP. The accuracy of the derived expressions is validated via simulation results, and insights are provided regarding the impact of the number of reflecting elements and imperfect channel state information (CSI) on the performance of the considered system. Finally, from the comparative analysis, it is shown that the RIS-aided system outperforms the system without RIS in both IBL and FBL scenarios, providing remarkable improvement in the outage probability and BLER.

The efficient and effective framework for next-generation (5G and beyond 5G) wireless networks should include mission-critical aspects such as ultralow latency ($\leq \!\!1$ms), ultrahigh reliability (99.999%), and enhanced data rate. Billions of ubiquitously connected devices are expected to serve various industrial applications in upcoming industry standards such as Industry 5.0. These industrial applications include mission-critical tasks such as smart grids, remote surgery, and intelligent transportation systems. This article considers an industrial Internet of Things (IIoT) environment in mission-critical ultrareliable low latency communication (URLLC) application where the main industrial unit or industrial control node (CN) sends messages to the target device (TD) with the aid of a cooperative device (CD). We investigate a novel transmission protocol and analyze the network’s performance. Considering the nonlinear energy harvesting (EH) mechanism at power-constrained nodes and direct and cooperative phase transmissions, the outage probability (OP) and block error rate (BLER) performances are evaluated for Rayleigh distributed fading channels. The analytical results are validated through Monte–Carlo simulations.

The reconfigurable intelligent surface (RIS)-assisted wireless communication system is studied in this paper, where two full-duplex (FD) users simultaneously communicate with each other. The reception at each user is facilitated through a dedicated RIS. Owing to the geometry and placements of meta-atoms, the analysis incorporates spatial-correlation among the channels related to RIS. Using moment-matching approach, a new analytical framework is presented for spatially-correlated channels considering the optimal phase-shifts from RIS meta-atoms. The effects of residual self-interference (RSI), self-reflections and interference from the RIS of transmitting user are considered in the analysis. The expressions are derived for the outage probability and ergodic capacity for infinite block-length transmission, and for finite block-length transmission, the expressions are obtained for block-error rate (BLER), ergodic capacity and system goodput. To gain further insights, the expression for the asymptotic outage probability is also derived. The finding of this paper confirms the ability of RIS-assisted communication to counter the detrimental effects of self-interference in FD scenario, even in presence of spatial-correlation. The derived expressions are validated using the Monte-Carlo simulations.

This paper investigates reconfigurable intelligent surface (RIS)-based multiple-destination downlink communication system under ultra-reliable low-latency communications (URLLC) constraints. A source communicates with multiple destinations with the aid of RIS and direct path transmissions. We consider the effect of spatial correlation arising due to the RIS geometry. Assuming that the source can communicate with only one destination in the given time-slot, we examine several scheduling schemes, such as random (RND), absolute (ABS) channel power based (CPB) and normalized (NRM) CPB. The expressions for the block-error rate (BLER) are derived for all the scheduling schemes and verified using the Monte-Carlo simulations. Effects of various parameters such as, channel uses, number of destinations, number of information bits, correlation are analyzed and the performance for the considered scheduling schemes is compared.

Nonorthogonal multiple access (NOMA) with a grant-free access has received a lot of attention due to its support to massive machine-type communication (mMTC) devices. The devices in grant-free systems are allowed to transmit information without undergoing an authentication process. Therefore, in such systems, the base station needs to distinguish between active and nonactive devices, called the active user detection (AUD) process. This process is challenging as the active device needs to be detected from the received signals that are superimposed. Furthermore, the identification of the Internet of Things (IoT) devices from these signals also poses a great challenge, which could help allocate resources in future generation communication systems. Motivated from the aforementioned facts, this article proposes a device detection and identification (DDI) architecture for joint AUD and IoT device identification from the received superimposed signals. The architecture extracts the Fourier patterns as the representative feature vector, which results in an improved detection and identification process. Experimental results show that the architecture not only outperforms the conventional schemes and deep neural network-based approaches in terms of success probability for the AUD task but also yields lower computational complexity. The evaluation of the DDI architecture for IoT device identification problems has also been performed and compared to various shallow learning methods to prove its efficacy.

The paper explores simultaneous transmitting and reflecting (STAR) reconfigurable intelligent surface (RIS)-aided rate-splitting multiple access (RSMA) communication. A base-station (BS) transmits information to the cell-edge users which are assisted by the STAR RIS in such a way that two users, one placed in front of and other behind the RIS, are served by reflection and transmission, respectively. The energy splitting (ES) and mode switching (MS) configurations of the STAR RIS are considered for analysis. Owing to the close-placement of RIS elements and rectangular geometry of RIS, the Rician distributed RIS channels are assumed to be spatially-correlated. The new expression for the joint moment of spatially-correlated Rician channels is derived. Both, infinite and finite block-length transmissions are analyzed in this work. For infinite block-length transmission, the expressions for outage probability and channel capacity are derived, whereas for finite block-length transmission, the expressions for block error rate (BLER), system goodput and channel capacity are derived. To get further insights, the expression for asymptotic outage probability is also derived. Furthermore, the effects of various parameters, including RSMA power splitting factor, reflection coefficients, inter-element spacing, distances between STAR RIS and users, finite block-length parameters, imperfect channel state information (CSI), etc., are examined.

This paper investigates unmanned aerial vehicles (UAVs)-assisted full-duplex (FD) non-orthogonal multiple access (NOMA) system based cellular network, aiming to improve overall sum-rate throughput of the system through dynamic user clustering, optimal UAV placement and power allocation. Since each UAV operates in FD mode, self-interference (SI), co-channel interference (CCI), inter-UAV interference (IUI) and intra-node interference (INI) dominate the system’s performance. Consequently, we propose an unconventional two-stage dynamic user clustering for user nodes (UNs) to reduce the cross-interference in multi-UAV aided FD-NOMA system. Particularly, all UNs are initially clustered into$K$clusters using k-means clustering in the first stage where each cluster is served by an UAV. Furthermore, each cluster is further divided into sub-clusters and each sub-clusters are operated in FD-NOMA scheme. Finally, to control interferences, a sum-rate throughput maximization problem is formulated for each UAV to jointly optimize uplink and downlink power allocation and UAV placement. The joint optimization problem is non-convex and difficult to solve directly, for which we decoupled the original problem by addressing UAV placement and power allocation separately. We first fix the UAV position and then solve the problem iteratively using successive convex approximation (SCA) method. By utilizing brute-force search algorithm, an optimal UAV placement is later performed which corresponds to maximum possible sum-rate throughput. Simulation results demonstrate that the proposed solution for the considered FD-NOMA system outperforms the conventional schemes.

We consider a full-duplex (FD)-enabled multi-user two-way communication system with adaptive amplify-and-forward (AF)/decode-and-forward (DF) relaying protocol. All the users are assumed to be mobile and to have FD abilities. The effect of mobility, which results in time-selective fading, is modeled using a first-order autoregressive (AR1) process. The fading channel-based approach characterizes the residual self-interference (RSI) at the FD relay, user nodes and is modeled as a Rician distributed random variable. This paper constitutes the most critical use case of 5G, i.e., ultra-reliable low latency communication (URLLC), which adopts short-packets finite blocklength (FB) codes to spin out into the mission-critical applications where strict latency and reliability requirements are highly desirable. The outage performance of the system is studied over independent and non-identically distributed complex Gaussian (Rayleigh envelope) channels with imperfect channel state information (CSI) for with and without URLLC use cases. The closed-form expressions for the outage probability and block error rate (BLER) are derived for the absolute channel power-based scheduling scheme considering the different Doppler power spectra models and the effect of co-channel interference (CCI). The expressions for the asymptotic outage probability are also derived. The presented analysis is compared with baseline schemes, e.g., the results derived with adaptive AF/DF relaying are also compared with both AF and DF relaying, and the performance of the FD transmissions is compared to that of half-duplex (HD) transmissions. The impact of node mobility, RSI, FBL, number of user pairs, and imperfect CSI on the system performance is investigated. Moreover, essential insights are obtained related to the performance gain and region of the superiority of the adaptive AF/DF relaying scheme. The derived analytic results are validated through Monte Carlo simulations. Furthermore, at high transmit power, the outage performance for the adaptive AF/DF protocol approaches the derived asymptotic floor.

We consider an Internet of things (IoT) environment where the base station (BS) sends messages to the target user (TU) with the help of a cooperative user (CU). The cooperative user is selected based on the instantaneous signal-to-noise ratio (SNR) of the BS- TU link. For the considered cooperative IoT model, we further propose a new transmission protocol that incorporates the performance of active users and non-linear energy harvesting (EH) into account. The EH is assumed at every node, and the performance of the considered framework is evaluated in terms of outage probability. Specifically, for Rayleigh distributed fading channels, the closed-form expression for the outage probability is derived. The analytical results are validated through Monte-Carlo simulations. We also illustrated the impact of the number of CU and other parameters on the system's performance.

Abstract In this paper, the physical layer security of an indoor visible light communication system, that consists of two transmission light‐emitting diodes to broadcast the information towards the legitimate user, is investigated. Further, a secure LED selection scheme is proposed to select an LED that can perform secure information broadcasting, in the presence of an active and/or passive eavesdropper. The probability of secure information broadcasting is obtained in terms of the positive secrecy rate which is defined under the constraints of known or unknown imperfect channel state information of both legitimate and eavesdropping links. The channel state information (CSI) knowledge of each transmitting link is estimated with the use of a minimum mean square error technique. The performance metrics of the system are defined in terms of the average secrecy capacity and secrecy outage probability parameters. Further, the performance of the system is compared with the conventional stand‐alone VLC system by varying various physical parameters. Further, analytical results are corroborated with the computer simulation results.

A reconfigurable intelligent surface (RIS)-assisted wireless communication system with non-linear energy harvesting (EH) and ultra-reliable low-latency constraints is considered for its possible applications in industrial automation. A distant data-center (DC) communicates with the multiple destination machines with the help of a full-duplex (FD) server machine (SM) and RIS. Assuming the deficiency of enough transmission power at the FD-SM, the SM is considered in the near vicinity of the destinations in the industry to forward the data received from the distant DC. The reception at SM is assisted by the RIS and a non-linear hybrid power-time splitting (PTS) based EH receiver architecture is adopted to extend the lifespan of SM, thus increasing network lifetime. The scheduling of multiple destinations is done by SM based on the considered selection criteria namely, random (RND) scheduling, absolute (ABS) channel-power-based (CPB) scheduling and normalized (NRM) CPB scheduling. The end-to-end performance of the considered FD RIS-assisted network is analyzed, and the expressions for the block error rate (BLER) for all scheduling schemes are derived. Moreover, the effects of number of RIS elements, packet size, channel uses on the system performance are analyzed for the considered ultra-reliable and low-latency communication (URLLC) network. The scheduling fairness of all the scheduling schemes is also analyzed to study the performance-fairness trade-off. The derived analytical results are verified through Monte-Carlo simulations.

In this paper, a multi-user full-duplex (FD) two-way relaying system with decode-and-forward protocol is considered where all the nodes are assumed to be mobile and to have FD abilities. The residual self-interference (RSI) at each node is modeled as a Rician distributed random variable and the effect of mobility is incorporated by adopting the first order auto-regressive (AR) model. Then, the signal-to-interference-plus-noise-ratio (SINR) based scheduling schemes namely random scheduling, absolute channel power-based (CPB) scheduling, hybrid scheduling, and normalized CPB scheduling, are modified and the user pair selection is carried out on the basis of instantaneous channel statistics. The performance of the considered framework is analyzed for the modified scheduling schemes in terms of error probability and average rate. Next, the closed-form expressions for the symbol error probability (SEP) and average rate are derived for independent and non-identically distributed Rayleigh fading channels. Also, the numerical analysis highlighting the impact of user mobility and imperfect channel estimation on the scheduling strategies, fairness is presented. Furthermore, the impacts of the degree of traffic asymmetry, scheduling fairness, user mobility, channel estimation errors and RSI on the system performance are investigated. Numerical results are validated through the Monte Carlo simulations.

In this study, the authors consider an indoor visible light communication (VLC) system with multiple light emitting diodes (LEDs) placed on the roof of a room. The location tracking algorithm for intelligent photo‐diode receiver (IPR) is proposed for the considered system which can rotate in both horizontal and vertical directions. The IPR can track its motion relative to its previous location and is able to calculate distance and angle at very high speed. Using IPR, the field of view (FOV) of the receiver is always made to face the LED and receive the signal normally. The algorithm for location tracking and rotation with accuracy has been analysed mathematically. Further, the switching/handoff criteria are also presented when the receiver crosses the coverage region of one LED and enters the coverage region of another LED. The authors also present the impact of FOV and rotation of receiver on the channel gain of the VLC link. Moreover, the effect of imperfect rotation of the receiver plane on the performance of the VLC system according to the location in the cell is also illustrated.

A cooperative cognitive radio network (CRN) with improved energy detection-based spectrum sensing is analyzed in various fading scenarios. Generalized multipath (Nakagami-m) fading and enriched multipath (Nakagami-q) fading models are considered along with two other general fading distributions, i.e., κ-μ and η-μ distributions. For spectrum sensing, instead of conventional power 2-based detection method, the arbitrary power p-based improved energy detector is used. The impact of the cognitive user mobility on the performance of the improved energy detector is investigated. Specifically, the statistics for the received signal are derived over various fading environments. The performance of the considered CRN system is evaluated in terms of probability of false alarm, probability of missed detection, and receiver operating characteristics (ROC) curves. Moreover, the area under the ROC curve is also obtained. Simulation results are provided to corroborate the theoretical results derived in this paper.

Device-to-device communication and energy harvesting are both key technologies to improve spectrum and energy efficiency. In this paper, we investigate the resource allocation problem for the energy harvesting-powered D2D communication underlaying cellular networks, where D2D pairs firstly harvest energy and then transmit information signals. The goal is to maximize the sum throughput via joint time scheduling and power control while satisfying the SINR requirement of cellular user and taking into account the energy constraint. The formulated non-convex problem is transformed into a nonlinear fractional programming problem with a tactful reformulation. Coupled with D.C. (difference of two convex functions) programming, a near optimal solution of the non-convex problem can be obtained by iteratively solving a sequence of convex problems. Then, a first-order algorithm is employed to solve these convex problems. Numerical simulations are conducted to validate the effectiveness of the proposed algorithm and evaluate the system throughput performance.

A cooperative cognitive radio (CR) network with multiple secondary users (or CRs) is considered. Each CR consists of an arbitrary M number of antennas. For spectrum sensing, at each CR, an improved energy detector with selection combining mechanism is assumed. Moreover, the impact of secondary user mobility on the performance of spectrum sensing is analysed. Specifically, the expression for received signal at destination is derived considering the imperfect channel state information in Rayleigh fading environment. The authors derive the expression for probability of false alarm and miss detection using arbitrary power p ‐based improved energy detector and analyse the error performance of the system. The area under receiver operating characteristics curve is also obtained. Simulation results are provided to verify the analysis presented in this study.

In this study, the performance of decode‐and‐forward relay‐assisted free‐space‐optical (FSO) communication systems under atmospheric turbulence‐induced fading and misalignment errors is investigated. To mitigate the adverse effects of the atmospheric turbulence, the aperture‐averaging receivers are considered both at the relay and destination sides. The atmospheric turbulence‐induced fading is modelled via the exponentiated‐Weibull distribution, which has recently been proposed to characterise an FSO link in the presence of finite‐sized receiver aperture. The expression for the moment generating function (MGF) of the instantaneous signal‐to‐noise ratio is derived. Furthermore, new closed‐form expression for the outage probability is obtained. Moreover, the new expression for the average symbol error rate of the subcarrier intensity‐modulated M ‐ary phase‐shift keying is obtained using the MGF‐based approach. Finally, numerical examples are discussed and all the derived analytical results are corroborated by Monte Carlo simulations.

In this paper, we analyze a free space optical (FSO) cooperative communication system utilizing the Gamma-Gamma fading optical links and a single decode-and-forward (DF) erroneous relay. We adopt the subcarrier intensity modulation (SIM) technique for transmitting the M-ary phase shift keying (M-PSK) modulated optical data over an FSO link. For the considered DF-FSO cooperative system, we derive an optimum maximum-likelihood (ML) decoder and a sub-optimal piecewise linear (PL) decoder in the destination of the system. The proposed PL decoder performs very close to the ML decoder and provides significantly reduced decoding complexity as compared to the optimal decoder. Both the ML and PL decoders incorporate the possibility of erroneous transmission by the DF relay and require the average statistics of the source-relay link for decoding the data of the source in the destination. We also derive the approximate average symbol error rate (SER) of the proposed PL decoder for M-PSK constellation.

The exponentiated Weibull (EW) distribution has been recently proposed for the modelling of free-space optical (FSO) links in the presence of finite sized receiver aperture. In this paper, the performance of FSO communication systems over EW is studied. Specifically, the probability density function (PDF) and cumulative distribution function (CDF) of the instantaneous signal-to-noise ratio (SNR), over EW turbulence fading, are studied. The derived statistics of the SNR is utilized to analyse the performance of an FSO communication system over a generalized communication environment with turbulence induced fading, misalignment errors and path loss. New expression for the outage probability is obtained, and exact expressions for the average bit error rate (BER) are derived for various binary modulation schemes. Finally, the obtained analytical results are verified via Monte Carlo simulations.

This paper investigates a free space optical (FSO) communication system with multiple user pairs sharing a single relay over atmospheric turbulence induced fading channels effected by path loss. Multiuser diversity is achieved by applying various scheduling schemes at the relay. The performance of various scheduling schemes based on selection combining (SC) diversity and switched diversity are evaluated for the considered dual-hop, bi-directional, half-duplex relay system with network coding. Closed form expressions for the outage performance for different scheduling schemes have been derived.

In this study, the authors derive the exact closed‐form expression of the outage probability for coded cooperation using power‐based approach. They consider a generalised system model with n relays ( n > 1) over Nakagami‐ m fading channels. They also obtain the optimal number of relays for the given outage performance. Furthermore, they find analytically the critical cooperation ratio at which the total outage probability is minimum.