Faculty Publications

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Author: search.filters.author.Naik, R.P.Subject: search.filters.subject.Intelligent systems

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    Performance investigation of underwater wireless optical system for image transmission through the oceanic turbulent optical medium
    (Springer, 2022) Naik, R.P.; Shripathi Acharya, U.S.; Lal, S.; Krishnan, P.
    The importance of resources contained in the sea and on the sea floor is increasing with each passing day. Hence, exploration of the sea and sea floor has become a very important requirement. Underwater imaging is a science that has gained importance over the past two decades. Underwater images indicate the state of sea floor and transmitting such images through the harsh and turbulent oceanic medium can cause deterioration of the information contained in the image due to diminished color reproduction, low contrast and blur. In this paper, we have performed the simulation studies to understand perturbations induced during the transmission of sea floor images using high-speed optical signaling through the underwater channels. The transmitted irradiance often suffers from underwater turbulence and beam attenuation. The bit error rate (BER) of the system proposed to transmit information through channels has been determined through analytic means and validated through Monte-Carlo simulation. Comparison between the transmitted and received images in the presence of turbulence and attenuation have been presented. The BER performance of the proposed system is evaluated in the presence of beam attenuation and underwater turbulence. The turbulence induced errors are minimized using the transmit/receive diversity and multiple input multiple output (MIMO) techniques. In addition to the diversity techniques, median and adaptive median filters used to minimize the distortion in the received image. The BER results show that the 4 × 5 MIMO system gains 19.50 dB of transmit power at BER of 10 - 5, when compared with the single input single output system. Similarly, an improvement of at-least 18 dB peak signal to noise ratio obtain using the adaptive median filter based system over the un-filter based system. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
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    Performance analysis of underwater vertical wireless optical communication system in the presence of weak turbulence, pointing errors and attenuation losses
    (Springer, 2023) Savidhan Shetty, S.C.S.; Naik, R.P.; Shripathi Acharya, U.S.; Chung, W.-Y.
    In this paper, we have investigated the performance of underwater vertical wireless optical communication (UVWOC) link employing on–off key modulation in the presence of underwater turbulence, pointing errors and attenuation losses. The turbulence of the medium (assumed to be weak turbulence) has been modeled by employing the hyperbolic tangent log normal (HTLN) distribution. Temperature, pressure and salinity are parameters which can bring about variation of optical transmission characteristics with respect to depth of the ocean/sea. An in-depth study of optical transmission through vertical oceanic links requires the the underwater medium to be modeled as comprising of non-identical turbulent layers. Each of these independent and non-identical turbulence layers are modeled using the HTLN distribution function. The pointing error due to misalignment between source and detector is modeled using Rayleigh displacement pointing error. A novel closed-form expression to quantify the average bit error rate (BER) has been derived for single input single output (SISO) communication link. This expression has then been further generalized to make it applicable to the case of receive diversity schemes such as selection combining, majority logic combining and maximum ratio combining. The expression for the average BER associated with the UVWOC link for different pointing errors, different data rates and different types of ocean water has been determined. Novel closed-form expressions quantifying the outage probability and ergodic channel capacity have been derived for SISO and SC receive diversity schemes. The accuracy of all of the closed-form expressions derived in this paper have been validated using Monte-Carlo simulations. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
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    Performance analysis of underwater vertical wireless optical communication links using selection combining
    (Optica Publishing Group (formerly OSA), 2023) Savidhan Shetty, S.C.S.; Naik, R.P.; Shripathi Acharya, U.S.
    In this paper, we have investigated the performance of underwater vertical wireless optical communication (UVWOC) links employing on–off key modulation for selection combining based receive diversity schemes in the presence of underwater turbulence, pointing errors, and attenuation losses. Due to variations in temperature and salinity along the ocean’s depth, turbulence-induced fading affects the performance of the underwater vertical wireless optical link. The vertical link of the underwater medium influenced by a strong turbulence regime is modeled using cascaded gamma–gamma distribution considering multiple non-identical layers along with attenuation losses and pointing errors. We have derived closed-form expressions for the average bit error rate (BER) and outage probability (OP) for the link employing multiple detectors at the receiving end. The accuracy of all of the closed-form expressions derived in this paper has been validated using Monte Carlo simulations. © 2023 Optica Publishing Group.
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    Performance Analysis of MIMO-EGC System for the Underwater Vertical Wireless Optical Communication Link
    (Institute of Electrical and Electronics Engineers Inc., 2023) Savidhan Shetty, S.C.S.; Naik, R.P.; Shripathi Acharya, U.S.; Chung, W.-Y.
    In this paper, we have investigated the performance of an underwater vertical wireless optical communication (UVWOC) link employing multiple input-multiple output (MIMO) operating in conjunction with equal gain combing (EGC) techniques perturbed by weak and strong turbulence in the presence of pointing errors and attenuation losses. Vertical underwater turbulence, which varies from layer to layer due to temperature and salinity variation connected to depth, is modeled using hyperbolic tangent log-normal (HTLN) distribution in the case of weak underwater turbulence and gamma-gamma (GG) distribution in the case of strong underwater turbulence. Novel closed-form expressions quantifying the average bit error rate (BER) have been derived for the UVWOC MIMO EGC system for weak and strong turbulence regimes. The expression for the average BER associated with the UVWOC link for different values of pointing error, differing vertical layer depth, modulation types, and differing numbers of sources and detectors have been determined. In addition, closed-form expressions for the outage probability (OP) and ergodic channel capacity (ECC) have been derived for the UVWOC MIMO EGC system. The accuracy of all closed-form expressions derived in the paper has been verified using Monte Carlo simulations. © 2013 IEEE.
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    Multiuser Data Transmission Aided by Simultaneous Transmit and Reflect Reconfigurable Intelligent Surface in Underwater Wireless Optical Communications
    (Institute of Electrical and Electronics Engineers Inc., 2024) Naik, R.P.; Salman, M.; Bolboli, J.; Savidhan Shetty, C.S.; Chung, W.-Y.
    Recent research in the wireless communications field has focused on the reconfigurable intelligent surface (RIS), which can enhance energy and spectrum efficiency by reconfiguring radio waves to propagate in a specific direction. In this study, we applied the simultaneous transmit and reflect (STAR)-RIS to an underwater wireless optical communication (UWOC) system. In contrast to a conventional RIS, a STAR-RIS allows multiple users to transfer data simultaneously in all directions by obtaining a UWOC channel despite underwater turbulence, beam attenuation, blockage, and pointing errors. Underwater turbulence-induced fading was obtained by using exponential and generalized Gamma distributions, and numerical analysis were performed to evaluate the outage probability, bit error rate (BER), and channel capacity of a direct UWOC channel, conventional RIS assisted UWOC channel, and STAR-RIS assisted UWOC channel. The BER performance was also evaluated according to the number of reflective elements, type of modulation scheme, impact of pointing errors, blockage levels, and varying the transmit-reflection coefficient. Monte-Carlo simulations were performed to validate the analytical results for the BER and outage probability with respect to the average signal-to-noise ratio. Experiments were performed to demonstrate the received luminous intensity performance with respect to the incident beam luminous intensity of the proposed STAR-RIS assisted UWOC channel. © 1967-2012 IEEE.