The multi-input multi-output (MIMO) millimeter wave (mmWave) is a promising technology for beyond 5G communication systems, which provides high data rates, ultra-low latency, massive connectivity, and high spectral efficiency. However, a typical mmWave communication link is severely impaired by path loss, nonlinear device impairments, and non-Gaussian noise. Furthermore, MIMO mmWave channel exhibits sparseness due to blockage and scattering. The conventional orthogonal matching pursuit (OMP), zero-attracting least mean square (ZA-LMS), and their variants deliver suboptimal performance for nonlinear mmWave systems. To improve the estimation accuracy, we propose a random Fourier features (RFF) based sparsity-aware kernel maximum correntropy (SA-KMC) algorithm, which is robust for MIMO mmWave sparse channel estimation in the presence of nonlinear hardware impairments and non-Gaussian distortions. Simulations indicate that the proposed RFF-SA-MCC algorithm outperforms the existing state-of-art approaches.

In this paper, we investigate the performance of a full-duplex (FD) Internet-of-Things (IoT) network with hardware impairments (HIs) over generalized α − μ fading channels, where IoT devices transfer their information to the access point via a simultaneous wireless information and power transfer (SWIPT) enabled relay node. The α − μ fading channel explores the non-linearity of the propagation medium and includes Nakagami-m, Rayleigh, exponential, one-sided Gaussian, and Weibull fading channels as special cases. For SWIPT enabling, we consider a power splitting (PS) receiver at the relay node. Further, we consider a practical scenario where the system suffers from residual self-interference (RSI) due to imperfect self-interference cancellation. We derive the closed-form expressions of outage probability (OP), asymptotic OP, system throughput, and energy efficiency over α − μ fading channels. The diversity order of the considered network at high SNR is obtained. An optimal value of the PS factor is obtained which depicts optimum outage performance. We highlight the impact of HIs, RSI, PS factor, and other system parameters on the performance of the considered network. Finally, Monte-Carlo simulations validate the derived closed-form expressions.

In this work, a hybrid free-space optics (FSO)/ teraHertz (THz) based backhaul network is considered to provide high-data-rate reliable communication to the terrestrial mobile users (MUs) operating at millimeter-wave (mmWave) bands. The FSO link is affected by atmospheric turbulence and pointing error impairments. At the FSO receiver, both intensity-modulated direct detection and heterodyne detection techniques are considered. The multi-antenna THz link suffers from high path-loss, small-scale fading, and misalignment error. To minimize the effect of back-and-forth switching, soft switching method is introduced at the access point (AP) to select the signal coming through the hybrid FSO/THz link, and a comparison with hard switching method is presented. Selective decode-and-forward relaying is considered at the AP. In this context, we derive closed-form expressions of the individual link’s outage probability, end-to-end (E2E) outage probability, asymptotic outage probability, ergodic capacity, and generalized average bit-error-rate. Finally, we study the effect of different parameters such as atmospheric turbulence, pointing/misalignment errors, link distance, atmospheric attenuation/path-loss, fading parameters of the THz and access links, and number of antennas on the network performance. Our results indicate that, with a proper switching method, the joint implementation of FSO/THz links improves the rate/reliability of the backhaul links with limited switching overhead.

In this paper, we investigate the impact of nonlinear distortion on the overall system outage probability of simultaneous wireless information and power transfer enabled two-way amplify-and-forward relaying network by employing three different nonlinear power amplifier (NLPA) models such as traveling wave tube amplifier, soft envelope limiter, and solid-state power amplifier at the relay node. We consider a time-switching based protocol at the energy-constrained relay node to harvest energy and information transmission. We derive the closed-form expression of the system outage probability by utilizing the selection combining technique at the source nodes over Nakagami-m fading channels. System throughput and energy efficiency of the network are also investigated. The impact of NLPA, threshold data-rate, fading severity, and time-switching factor are highlighted on the network's performance. Finally, the derived analytical results are validated by the Monte Carlo simulations.

In this work, we study the effect of a non-linear power amplifier (NLPA) on the performance of simultaneous wireless information and power transfer (SWIPT) enabled two-way relay network with transceiver hardware impairments (HIs). We employ a hybrid receiver at the relay to process information and harvest energy through the radio-frequency signal. we derive the closed-form expressions of outage probability and asymptotic outage probability by using a selection combining technique at the destination node over Nakagami-m fading channels. The diversity order of the system is determined by using the asymptotic outage probability. We also investigate the throughput and energy efficiency of the system. Further, the impact of NLPA, transceiver HIs, fading severity, hybrid receiver, threshold data-rate, and overall system ceiling are highlighted on the network's performance. Finally, the derived closed-form expressions are verified through Monte Carlo simulations.

Simultaneous wireless information and power transfer (SWIPT) plays a vital role in power-constrained cooperative communication by harvesting energy at the relay node from the ambient radio frequency signals while transmitting information to the destination. In this work, we consider SWIPT based overlay device-to-device (D2D) multi-input and multi-output (MIMO) relay communications with outdated channel state information (CSI) overgeneralized Nakagami-m fading channels. Further, transmit antenna selection is employed in choosing the antenna which maximizes the received signal-to-noise ratio at the receiver to reduce the system complexity. Framework for outage probability and asymptotic outage probability for the SWIPT based D2D MIMO relay system with outdated CSI is developed. Impact of energy harvesting and outdated CSI over throughput is analyzed for the considered system model. Simulations are carried out to verify the correctness of the obtained analytical expressions.

In this study, the authors present an analytical approach to evaluate the performance of a two‐way multi‐relay system with direct link using a three‐phase analogue network coding and opportunistic relay selection scheme. Herein, the imperfect channel state information is considered over independent and non‐identically distributed Nakagami‐ m fading channels with integer‐valued fading parameter. For analysis, initially, the closed‐form expressions of cumulative distribution function and moment generating function (MGF) for the considered system are derived. Further, by using the MGF‐based approach, generalised expressions of average symbol error rate (ASER) for higher‐order quadrature amplitude modulation (QAM) schemes such as hexagonal QAM, rectangular QAM, and cross QAM are derived. They then analyse the asymptotic behaviour of ASER expression to evaluate the system's diversity order. Furthermore, a comparative analysis of the ASER performance for various QAM constellations is illustrated and impact of the number of relays, fading parameter, relay location, and channel estimation error are highlighted on the system's performance. Finally, all the analytical results are validated through Monte‐Carlo simulations.

In this work, a two-way multi-relay system using three phase analog network coding (3P-ANC) with opportunistic relay selection scheme is considered, and performance is analyzed over independent and non-identically distributed (i.n.i.d.) Nakagami-m fading channels with imperfect channel state information (CSI) and non-linear power amplifier (NLPA) at the relays. For this, closed-form expression of outage probability is derived and diversity order of the system is obtained with the help of asymptotic outage probability. Further, the impact of number of relays, fading parameter, channel estimation error and non-linear distortion are highlighted on the system's performance. Finally, theoretical expressions are validated through simulations.

This paper presents closed-form expression of average symbol error rate (ASER) for general order rectangular quadrature amplitude modulation (RQAM) with selection combining (SC) receiver in orthogonal frequency division multiplexing (OFDM)-based nonlinear amplify-and-forward (AF) relay network over independent and non-identically distributed (i.n.i.d.) frequency selective Nakagami-m fading channel for integer-valued fading parameter (m). The asymptotic ASER behavior is also investigated for the considered system model. Further, the impact of nonlinear distortion (NLD) of relay's amplifier is highlighted on the ASER performance for different constellation size and different signal-to-noise ratio (SNR) levels. The numerical results are compared with computer simulations, and accuracy of the derivations is verified.

In this paper, a 3-hop orthogonal frequency division multiple access (OFDMA) based variable- gain amplify and forward (AF) relaying network with selection combining receiver is considered, which is based on a scattered infrastructure known as shared user equipment (UE)-side distributed antenna system (SUDAS). The considered system model uses millimeter wave (mmWave) wireless links along with ultra high frequency (UHF) links, which can provide high data rate transmission (targeted for 5G systems). Wireless links are considered to be independent but non-identically distributed (i.n.i.d.), since Rician and Rayleigh distributions are preferred for mmWave and UHF links, respectively. In this work, closed-form expressions for the lower and upper bound of the outage probability are derived for the system under consideration. Derived analytical results are verified through Monte-Carlo simulations and impact of the Rician K-factor(s) of the considered links is also highlighted.

In this study, performance analysis of variable‐gain amplify‐and‐forward relaying orthogonal frequency division multiplexing‐based systems over independently but not necessarily identically distributed Nakagami‐ m fading channels using non‐linear power amplifier (PA) at the relay and maximal ratio combining scheme at destination. Specifically, novel closed‐form expressions of outage probability and asymptotic outage probability are investigated for the considered system model. Further, an average symbol error rate (ASER) expression is derived for general‐order rectangular quadrature amplitude modulation (RQAM) scheme using cumulative distribution function‐based approach, which is also the novel contribution of the work. Since the transfer function of PA used at relay is nonlinear, this introduces non‐linear distortion (NLD) in the considered system model. Thus, the impact of NLD and fading parameters on outage probability, diversity gain of the system and ASER performances are analysed. Further, the impact of NLD on constellation order for RQAM scheme is also discussed. The theoretical results are compared with computer simulations to verify the accuracy of the derivations. The derived expressions are generalised over variety of fading environments for integer‐valued fading parameter.