Department of Electrical and Electronics Engineering
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Item Exact sum distribution of alpha-eta-kappa-mu fading channels for statistical performance analysis of rrs-based wireless transmission(2025-02) Zafaruddin, S.M.Reconfigurable refractive surface (RRS) is an efficient alternative to holographic multiple input multiple outputs (HMIMO) systems that can serve as a transmission unit operating in the signal refraction mode. RRS transmissions experience near-field propagation due to the proximity of the transmission feed and far-field propagation for the user located farther from the transmitting unit. There is limited research on the effect of channel fading on far-field users in RRS-based transmissions. In this paper, we conduct an exact statistical analysis of RRS-based transmission considering alpha-eta-kappa-mu fading model for the far-field user and the near-field effect of transmission feed. First, we show the exact statistical analysis for the RRS transmission over alpha-eta-kappa-mu fading model consisting of multiple infinite-series representations with multivariate Fox-H function. Next, we develop a novel approach to derive the density and distribution functions for the resultant fading channel of the RRS system in terms of multivariate Fox-H functions without involving infinite series approximations for tractable performance analysis. We present the exact outage probability and average bit-error-rate (BER) performance of single-element and multiple-element RRS systems to validate the proposed analysis further. We also obtain the diversity order of the system by analyzing the outage probability at a high signal-to-noise ratio (SNR). Computer simulations demonstrate the relevance of the developed statistical results for RRS-based wireless systems over the generalized fading model for a comprehensive performance evaluation.Item Performance Analysis of Outdoor THz Wireless Transmission Over Mixed Gaussian Fading with Pointing Errors(Springer, 2023-07) Zafaruddin, S.M.This paper presents the performance analysis for THz transmissions by considering a novel channel fading model for outdoor THz transmission with the combined effect of zero-boresight pointing error. We consider the recently proposed Gaussian mixture fading for outdoor THz transmissions to model the small-scale fading. We derive the probability density function of the channel fading with zero-boresight pointing errors. Using the derived PDF, we derived the outage probability and the average bit error rate (BER) of the considered system. We validate the derived analytical expressions with Monte Carlo simulations and demonstrate the effect of various system and channel parameters on the performance for single THz wireless communications.Item Intelligent Connectivity Through RIS-Assisted Wireless Communication: Exact Performance Analysis With Phase Errors and Mobility(IEEE, 2023-06) Zafaruddin, S.M.The current research offers only approximations for evaluating the performance of wireless systems that use reconfigurable intelligent surfaces (RIS) over generalized fading channels with phase error caused by imperfect phase compensation at the RIS. This article presents an exact analysis of RIS-assisted vehicular communication considering uniformly distributed phase error and generalized fading channels with a coherent combining of received signals reflected by RIS elements and direct transmissions from the source terminal. We use a generalized- K shadowed distribution for the direct link and asymmetrical channels for the RIS-assisted transmission with κ - μ distribution for the first link and double generalized Gamma (dGG) distribution for the second link, combined with a statistical random waypoint (RWP) model for the moving vehicle. We employ a novel approach to represent the probability density function (PDF) and cumulative distribution function (CDF) of the resultant channel in terms of a single univariate Fox-H function and use the multivariate Fox-H approach to develop an exact statistical analysis of the end-to-end signal-to-noise ratio (SNR) for the RIS-assisted system. We also use the inequality between the arithmetic and geometric means to simplify the statistical results of the considered system in terms of the univariate Fox-H function. Our analysis also provides exact, upper bound, and asymptotic expressions of the outage probability and average bit-error-rate (BER) performance using the derived density and distribution functions. We conduct computer simulations in various practically relevant scenarios to assert that mitigating phase errors is achievable by augmenting the number of elements in the RIS module and employing a higher quantization level.Item Performance of Integrated IoT Network With Hybrid mmWave/FSO/THz Backhaul Link(IEEE, 2024-01) Zafaruddin, S.M.Establishing end-to-end connectivity of Internet of Things (IoT) network with the core for collecting sensing data from remote and hard-to-reach terrains is challenging. In this article, we analyze the performance of an IoT network integrated with a wireless backhaul link (BHL) for data collection. We propose a solution that involves a self-configuring protocol for aggregate node (AN) selection in an IoT network, which sends the data packet to an unmanned aerial vehicle (UAV) over radio frequency (RF) channels. We adopt a novel hybrid transmission technique for wireless backhaul employing opportunistic selections combining (OSC) and maximal ratio combining (MRC) that simultaneously transmits the data packet on mmWave (mW), free space optical (FSO), and terahertz (THz) technologies to take advantage of their complementary characteristics. We employ the decode-and-forward (DF) protocol to integrate the IoT and BHLs and provide physical layer performance assessment using outage probability and average bit-error rate (BER) under diverse channel conditions. We also develop simplified expressions to gain a better understanding of the system’s performance at a high-signal-to-noise ratio (SNR). We provide computer simulations to compare different wireless backhaul technologies under various channel and SNR scenarios and demonstrate the performance of the data collection using the integrated linkItem Outage Probability Analysis for UOWC System Over Oceanic Turbulence With Pointing Errors(IEEE, 2023-09) Zafaruddin, S.M.This letter proposes a combined underwater optical wireless communication (UOWC) system consisting of maximum ratio combining (MRC)-based direct link and optical intelligent reflecting surface (OIRS)-assisted indirect link. Oceanic turbulence is modeled by the mixture exponential–generalized gamma (EGG) distribution. We evaluate the system performance using the outage probability. An exact outage probability expression is derived for these links under EGG oceanic turbulence and pointing errors (PEs). Moreover, we derive the asymptotic expression for the outage probability to present an analytical expression of the system’s diversity order. We demonstrate that the Monte Carlo simulation results perfectly match the derived expressions, and closely align with the asymptotic expression at high signal-to-noise ratio (SNR) values. Hence, the proposed system ameliorates the connectivity of the high-speed UOWC under different underwater channel conditions.Item Random Access Protocols for Cell-Free Wireless Network Exploiting Statistical Behavior of THz Signal Propagation(2023-11) Zafaruddin, S.M.The current body of research on terahertz (THz) wireless communications predominantly focuses on its application for single-user backhaul/fronthaul connectivity at sub-THz frequencies. First, we develop a generalized statistical model for signal propagation at THz frequencies encompassing physical layer impairments, including random path-loss with Gamma distribution for the molecular absorption coefficient, short-term fading characterized by the α-η-κ-μ distribution, antenna misalignment errors, and transceiver hardware impairments. Next, we propose random access protocols for a cell-free wireless network, ensuring successful transmission for multiple users with limited delay and energy loss, exploiting the combined effect of random atmospheric absorption, non-linearity of fading, hardware impairments, and antenna misalignment errors. We consider two schemes: a fixed transmission probability (FTP) scheme where the transmission probability (TP) of each user is updated at the beginning of the data transmission and an adaptive transmission probability (ATP) scheme where the TP is updated with each successful reception of the data. We analyze the performance of both protocols using delay, energy consumption, and outage probability with scaling laws for the transmission of a data frame consisting of a single packet from users at a predefined quality of service (QoS)Item An Exact Statistical Representation of α−η−κ−μ Fading Model for THz Wireless Communication(IEEE, 2023-12) Zafaruddin, S.M.The α−η−κ−μ is one of the most generalized and flexible channel models having an excellent fit to experimental data from diverse propagation environments. The existing statistical results on the envelope of α−η−κ−μ model contain an infinite series, prohibiting its widespread application in the performance analysis of wireless systems. This paper employs a novel approach to derive density and distribution functions of the envelope of the α−η−κ−μ fading channel without an infinite series approximation. The derived statistical results are presented using a single Fox's H-function for tractable performance analysis, especially for high-frequency mmWave and terahertz wireless transmissions. We also develop an asymptotic analysis using the Gamma function, which converges to the exact values within a reasonable range of channel parameters. To further substantiate the proposed analysis, we present the exact outage probability and average bit-error-rate (BER) performance of a wireless link subjected to the α−η−κ−μ fading model using a single trivariate Fox's H-function. We obtain the diversity order of the system by analyzing the outage probability at a high signal-to-noise (SNR) ratio. We use simulations to demonstrate the significance of the developed statistical results compared with the existing infinite series representation of the α−η−κ−μ model.Item Path Loss Modeling for RIS-Assisted Wireless System with Direct Link and Elevation Factors(2024-02) Zafaruddin, S.M.The present path loss models for wireless systems employing reconfigurable intelligent surfaces (RIS) do not account for the elevation of the transmitter, receiver, and RIS module. In this paper, we develop an analytical model for path loss of a wireless system utilizing an NxM-element RIS module positioned above the ground surface with elevated transmitter and receiver configurations. Furthermore, we integrate the direct link into the path loss model to enhance its applicability, a crucial aspect often neglected in previous research. We also present simplified analytical expressions for path loss under various configurations, including near-field and far-field scenarios. These expressions elucidate the impact of elevation factors on path loss, facilitating more accurate signal quality estimation at the receiver. Simulation results corroborate that accounting for elevated RIS modules and transceiver units can yield improved deployment strategies for RIS-based wireless systems.Item A Generalized Statistical Model for THz Wireless Channel with Random Atmospheric Absorption(IEEE, 2024) Zafaruddin, S.M.Current statistical channel models for Terahertz (THz) wireless communication primarily concentrate on the sub-THz band, mostly with α−μ and Gaussian mixture fading distributions for short-term fading and deterministic modeling for atmospheric absorption. In this paper, we develop a generalized statistical model for signal propagation at THz frequencies considering random path-loss employing Gamma distribution for the molecular absorption coefficient, short-term fading charac-terized by the α−η−κ−μ distribution, antenna misalignment errors, and transceiver hardware impairments. The proposed model can handle various propagation scenarios, including indoor and outdoor environments, backhauVfronthaul situations, and complex urban settings. Using Fox's H-functions, we present the probability density function (PDF) and cumulative distribution function (CDF) that capture the combined statistical effects of channel impairments. We analyze the outage probability of a THz link to demonstrate the analytical tractability of the proposed generalized model. We present computer simulations to demonstrate the efficacy of the proposed model for performance assessment with the statistical effect of atmospheric absorption.Item Statistical Results of Multivariate Fox-H Function for Exact Performance Analysis of RIS-Assisted Wireless Communication(IEEE, 2024) Zafaruddin, S.M.Existing research provides statistical results on the sum of single-variate Fox-H functions to analyze the performance of diversity receivers and reconfigurable intelligent surfaces (RIS) based wireless systems. There is a research gap in exact performance analysis when more than a single-variate Fox-H function represents the statistical characterization of wireless systems. In this paper, we propose a novel approach to obtain the distribution of the sum of independent and non-identically distributed (i.ni.d) random variables characterized by the multi-variate Fox-H function. Further, we develop a general framework for an exact analysis of the ergodic capacity when the multivariate Fox-H function characterizes the statistics of signal-to-noise ratio (SNR). We apply the derived results to conduct an exact performance analysis of outage probability and ergodic capacity, taking an example of RIS-assisted communication over Rician fading channels with phase errors. We conduct computer simulations to validate the exact analysis and demonstrate performance of the RIS-assisted system under various practically relevant scenarios for a better performance assessment.