Department of Electrical and Electronics Engineering

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    Channel Estimation-Based Rate Maximization for IRS-Aided UAV Wireless Communication Systems
    (IEEE, 2024-08) Joshi, Sandeep; Chaubey, Vinod Kumar
    In this paper, we provide a channel estimation-based optimization technique for maximizing the weighted sum rate (WSR) of an intelligent reflecting surface (IRS)-aided unmanned aerial vehicle (UAV). The model considers an IRS mounted on a UAV to predict the channel between the multi-input base station (BS) for the multi-user system using mobile IRS-aided wireless channels. We optimize the UAV position and then employ a compressive sensing-based technique that exploits the sparsity of the wireless channel, specifically, we utilize the Bayesian iterative group approximate message passing (BIG-AMP) algorithm. The strategy involves mobile IRS for efficient message passing and estimation of the channel state information between the BS and users. Using these channel estimates, we maximize the WSR for all the users by optimizing the precoding matrix at the BS and also the phase matrix at the mobile IRS.
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    Multihop Optical Wireless Communication Over F-Turbulence Channels and Generalized Pointing Errors With Fog-Induced Fading
    (IEEE, 2022-10) Zafaruddin, S.M.; Chaubey, Vinod Kumar
    Multihop relaying is a potential technique to mitigate channel impairments in optical wireless communications (OWC). In this paper, multiple fixed-gain amplify-and-forward (AF) relays are employed to enhance the OWC performance under the combined effect of atmospheric turbulence, pointing errors, and fog. We consider a long-range OWC link by modeling the atmospheric turbulence by the Fisher-Snedecor F distribution, pointing errors by the generalized non-zero boresight model, and random path loss due to fog. We also consider a short-range OWC system by ignoring the impact of atmospheric turbulence. We derive novel upper bounds on the probability density function (PDF) and cumulative distribution function (CDF) of the end-to-end signal-to-noise ratio (SNR) for both short and long-range multihop OWC systems by developing exact statistical results for a single-hop OWC system under the combined effect of F -turbulence channels, non-zero boresight pointing errors, and fog-induced fading. Based on these expressions, we present analytical expressions of outage probability (OP) and average bit-error-rate (ABER) performance for the considered OWC systems involving single-variate Fox's H and Meijer's G functions. Moreover, asymptotic expressions of the outage probability in high SNR region are developed using simpler Gamma functions to provide insights on the effect of channel and system parameters. The derived analytical expressions are validated through Monte-Carlo simulations, and the scaling of the OWC performance with the number of relay nodes is demonstrated with a comparison to the single-hop transmission.
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    Opportunistic Scheduling in IRS-Aided UAV Multi-User Wireless Communication Systems: Modeling and Analysis
    (IEEE, 2024-11) Joshi, Sandeep; Chaubey, Vinod Kumar
    In this paper, we present the performance analysis of an opportunistic scheduling-based intelligent reflecting surface (IRS)-aided unmanned aerial vehicle (UAV) multi-user wireless communication system. We consider an IRS mounted on a UAV and the communication links between transmitter and receiver to be Rician faded. The considered IRS-aided UAV communication system performs opportunistic scheduling for user selection and transmission, assuming the practical limitation of outdated channel state information (CSI). We provide an analytical framework for the IRS-aided UAV wireless communication system and derive expressions for outage probability, asymptotic outage probability, ergodic capacity, effective capacity, and symbol error rate (SER) considering M-ary phase shift keying modulation. We show the performance variations with the CSI parameter, the number of reflecting elements, the Rician factor, and the delay constraint. We observe that a lower delay constraint value results in higher effective capacity. Furthermore, the analytical results are verified through system simulations.
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    Outage Analysis of an IRS-Assisted 5G and Beyond Wireless Communications System
    (IEEE, 2023-06) Joshi, Sandeep; Chaubey, Vinod Kumar
    In this work, we present an outage analysis of an intelligent reflecting surface (IRS)-assisted wireless communications system considering direct and indirect communication links between the transmitter and the receiver. We derive the probability density function and cumulative distribution function for the combined communication link between the transmitter, IRS, and the receiver. Furthermore, we derive the closed-form expressions for the outage probability, considering the direct link between the transmitter and the receiver as Nakagami-m faded, and the indirect communication link via IRS is considered to be under Rician fading. The analytical results are verified by simulations and give insight into modeling and analysis of N element IRS-assisted wireless communications system. We observe that the performance of the considered IRS- assisted wireless communications system significantly improves with an increase in the number of reflecting elements.
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    Outage Analysis of IRS-Assisted Dual-Hop Mixed RF-UWOC Network
    (IEEE, 2023-06) Joshi, Sandeep; Chaubey, Vinod Kumar
    In this work, we derive the outage analysis of an intelligent reflecting surface (IRS)-assisted dual-hop mixed radio frequency (RF)-underwater wireless optical communication (UWOC) network. For diverse underwater operations such as surveillance, excursions, and climate monitoring, UWOC is a promising solution for transferring high-speed information. IRS is a revolutionary low-cost technique to improve the received signal strength and system performance. The use of IRS is advantageous in improving wireless communication over long distances by providing a line-of-sight path and making it reliable. We investigate a communication scenario where a source located underwater transmits signals to the relay using an underwater wireless optical link, which, assisted by the IRS, provides an alternate path to the receiver through an RF link. We consider generalized κ-µ fading for the relay-IRS and IRS-receiver RF communication links, mixed intensity-modulation direct detection (IM-DD) with exponential generalized Gamma distribution for the source-relay UWOC link.
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    Unified Performance Assessment of Optical Wireless Communication Over Multi-Layer Underwater Channels
    (IEEE, 2022-10) Zafaruddin, S.M.; Chaubey, Vinod Kumar
    In this paper, we model the multi-layer vertical underwater link as a cascaded channel and unify the performance analysis for the underwater optical communication (UWOC) system using generalized Gamma (GG), exponential GG (EGG), exponentiated Weibull (EW), and Gamma-Gamma ( ΓΓ ) oceanic turbulence models. We derive unified analytical expressions for probability density function (PDF) and cumulative distribution function (CDF) for the signal-to-noise ratios (SNR) considering independent and non-identical (i.ni.d.) turbulent models and zero bore-sight model for pointing errors. We develop performance metrics of the considered UWOC system using outage probability, average bit error rate (BER), and ergodic capacity with asymptotic expressions for outage probability and average BER. We develop the diversity order of the proposed system to provide a better insight into the system performance at a high SNR. We also integrate a terrestrial OWC (TOWC) subjected to the combined effect of generalized Malága atmospheric turbulence, fog-induced random path gain, and pointing errors to communicate with the UWOC link using the fixed-gain amplify-and-forward (AF) relaying. We analyze the performance of the mixed TWOC and multi-layer UWOC system by deriving PDF, CDF, outage probability, and average BER using the bivariate Fox H-function. We use Monte-Carlo simulation results to validate our exact and asymptotic expressions and demonstrate the performance of the considered underwater UWOC system using measurement-based parametric data available for turbulent oceanic channels.