Faculty Publications
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Item Performance Analysis of Relay-Assisted Free-Space Optical Communication (FSO) Under Gamma-Gamma Atmospheric Turbulence Channels with Pointing Errors(Springer Science and Business Media Deutschland GmbH, 2023) Tarimo, C.P.; Kulkarni, M.The use of infrared and visible spectrum parts in the electromagnetic spectrum has made great changes in communication because of its higher data rate, high security, and larger bandwidth. This technology can be implemented using guided media; that is optic fiber cable or unguided media such as free-space optical communication (FSO). In this work, gamma-gamma distribution with relay-assisted transmission as the main fading mitigation tool for FSO systems under different atmospheric conditions is proposed. The performance was evaluated by considering signal-to-noise ratio (SNR) and BER for a link with different atmospheric conditions using amplify and forward method for the relay transmission, in which geometrical losses and pointing errors were considered. Further, the output power versus distance was analyzed using multiple-input multiple-output (MIMO) technology. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.Item Co-operative RF-UWOC link performance over hyperbolic tangent log-normal distribution channel with pointing errors(Elsevier B.V., 2020) Naik, P.N.; Udupi, S.A.; Krishnan, P.In this paper, we have proposed an analytic model and determined the outage probability and average bit error rate (BER) performance of a co-operative radio frequency ? underwater wireless optical communication (RF?UWOC) system. In recent years, UWOC has attracted attention as a useful enabler of underwater activities such as climate and ocean monitoring, surveillance, ocean exploration, underwater wireless optical sensor networks (UWOSN) and internet of underwater things (IoUT) because of its high speed, ease of deployability and wide bandwidth availability which is free of licensing fees. The proposed co-operative RF–UWOC system is designed to establish a connection between an underwater vehicle inside the ocean to a terrestrial ground station using decode?forward and amplify?forward relays. The RF link between the terrestrial ground station to relay is modeled as a Rayleigh distributed channel. The UWOC link between the relay to the underwater vehicle is modeled as being perturbed by the hyperbolic tangent log-normal (HTLN) distribution. To the best of our knowledge, it is for the first time that the perturbations due to weak oceanic turbulence have been modeled using HTLN distribution. This distribution is a member of the class of log-normal distributions derived from hyperbolic tangent distribution. Novel closed-form expressions have been derived for the outage probability and average BER for various modulation techniques that can be employed in this system. The analytical results are evaluated and validated with Monte-Carlo simulations in the presence and absence of pointing errors. The results show that the impact of pointing errors in the RF-UWOC system is to impose an additional SNR penalty of at-least 10 dB to obtain a BER of 10?6 when compared with the system operating without pointing errors. © 2020 Elsevier B.V.Item Performance enhancement using multiple input multiple output in dual-hop convergent underwater wireless optical communication-free-space optical communication system under strong turbulence with pointing errors(SPIE, 2021) Bhargava Kumar, B.K.; Naik, R.P.; Krishnan, P.For the first time, we propose a dual-hop multiple input multiple output (MIMO)-based convergent underwater wireless optical communication (UWOC)-free-space optical (FSO) system. The UWOC and FSO links are Gamma-Gamma (GG) distributed. Closed-form expression for the average bit error rate (ABER) is derived for the proposed MIMO-based dual-hop UWOC-FSO convergent system using the GG cumulative distribution function. The end-to-end system performance analysis is carried out by considering the turbulence, attenuation, and pointing error effects for UWOC and FSO links. For the UWOC link, different oceanic conditions, such as the clear ocean, coastal ocean, and turbid harbor, are considered. Various atmospheric effects, such as clear air, fog, rain, drizzle, and haze, are considered for the FSO link. The analytical results of the proposed MIMO-based convergent system are compared with single-input single-output (SISO) system. As a result, it is observed that the proposed MIMO 2 × 3 scheme offers an improvement of 35 dB in the average signal-to-noise ratio compared with the SISO system at ABER of 10-5 in the case of weak pointing error. © 2021 Society of Photo-Optical Instrumentation Engineers (SPIE).Item Wireless-optical-communication-based cooperative IoT and IoUT system for ocean monitoring applications(The Optical Society, 2021) Naik, R.P.; G.D., G.D.G.; Krishnan, P.This paper proposes the idea of a new cooperative communication between the Internet of Things (IoT) and the Internet of Underwater Things (IoUT) using wireless optical connectivity for ocean monitoring applications.We considered IoT communication using a hybrid radio frequency (RF)/free space optical (FSO) link and IoUT using a underwater wireless optical communication (UWOC) link. Channel models for RF, FSO, and UWOC links are considered to be Rayleigh,Malaga with pointing errors, and hyperbolic tangent log-normal distributions, respectively. The outage probability and the bit error rate (BER) expressions for the proposed system are derived over the combined channel model, which includes the effects of attenuation, turbulence, and pointing errors. The BER results are plotted for various binary digital modulation schemes such as on-off keying, binary phase-shift keying, binary frequency-shift keying, and differential phase-shift keying over UWOC, hybrid RF/FSO and RF-UWOC, FSO-UWOCwith end-to-end systems.BERresults are extended for various turbulence regions and pointing errors of theFSOlink.MonteCarlo simulation results authenticate the correctness of the results. © 2021 Optical Society of America.Item Performance enhancement of FSO communication system using machine learning for 5G/6G and IoT applications(Elsevier GmbH, 2022) Kumar, L.J.S.; Krishnan, P.; Shreya, B.; Sudhakar, S.6G networks will provide extremely high capacity and will support a wide range of new applications in the future, but the existing frequency bands may not be sufficient. Furthermore, because traditional wireless communications are incapable of providing high-speed data rates, 6G enables superior coverage by integrating space/air/underwater networks with terrestrial networks. 5G-and-beyond (5 GB) and 6G networks have been mandated as a paradigm shift to take the enhanced broadband, massive access, and ultra-reliable and low latency services of 5G wireless networks to an even more advanced and intelligent level, to meet the ever-growing quantities of demanding services. In 5G and 6G wireless communication systems, artificial intelligence (AI), particularly machine learning (ML), has emerged as an essential component of fully intelligent network orchestration and management. 5 GB and 6G communication systems will also rely heavily on a tactile Internet of Things (IoT). The diverse nature of heterogeneous traffic and the established service quality parameters in 5 GB networks will present numerous challenges. Many other wireless technologies, including free space optics (FSO), look promising for meeting the demands of 5 GB systems. FSO has been identified as a promising technology for achieving higher data rates while consuming less power. However, attenuation due to weather, pointing errors, and turbulences limits its performance. Traditional Maximum likelihood decoding techniques require prior channel information to decode the signals. in this paper, first time we proposed a novel decoding technique for decoding on–off keying (OOK) modulated FSO signals using support vector machines (SVM). The model is tested under various atmospheric weather conditions such as fog, rain, and snow, as well as turbulence and pointing errors. Simulated numerical results demonstrate that the proposed SVM-based decoding schemes are capable of mitigating attenuation, pointing error, and turbulent channel impairments. © 2021 Elsevier GmbHItem Reconfigurable intelligent surface-assisted free-space optical communication system under the influence of signal blockage for smart-city applications(Optica Publishing Group (formerly OSA), 2022) Naik, R.P.; Krishnan, P.; G.D., G.D.G.Atmospheric turbulence and pointing errors represent substantial hurdles to free-space optical communications (FSOs), impeding their practical design. The reconfigurable intelligent surface (RIS) is an emerging technology that enables reflective radio transmission conditions for next-generation 5G/6G wireless frameworks by intelligently adjusting the beam in the desired direction using low-cost inactive reflecting elements. In this paper, we proposed an RIS-assisted FSO system for mitigating the effects of atmospheric turbulence, pointing errors, and communication system signal blockage. The probability density function and cumulative distribution functions of an FSO system composed of N-RIS elements are evaluated in a free-space environment that contains obstructions. We derived closed-form expressions for the proposed system's bit error rate (BER), outage probability, and channel capacity. The proposed system's performance is analyzed in terms of BER, outage probability, and channel capacity under various weather conditions, pointing errors, and signal blockage. The results are plotted as a function of number of RIS elements and average signal-to-noise ratio. The proposed system will be beneficial in smart-city applications since it will provide reliable connectivity in urban environments with a high population density and high-rise buildings. © 2022 Optica Publishing GroupItem 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.Item 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.Item Reconfigurable intelligent surface-assisted free-space optical communication link for the Satellite-Internet of Things(Optica Publishing Group (formerly OSA), 2023) Naik, R.P.; G.D., G.D.G.; Bhargava Kumar, L.B.; Krishnan, P.The Satellite-Internet of Things (S-IoT) is envisaged as one of the promising technological enhancements in this decade due to its outright connectivity, especially in the areas of terrestrial communication andweather forecasting. Invariably, turbulent atmospheric conditions and varied terrain profiles are hindrances for satellite based freespace optical (FSO) communication, and immensely disrupt signal levels. Recently, a new technological invention called a reconfigurable intelligent surface (RIS) empowered radio transmission environments for next generation wireless/optical technology has emerged. Elements of RIS are used to intelligently tune the striking beam towards desired locations. In this paper, we propose an RIS based FSO link to manueuver S-IoT. The challenges of pointing errors and turbulent atmospheric connectivity froma satellite to ground station and vice versa with the cooperation of RIS have been derived and substantiated with closed form solutions. The proposed system's performance has been analyzed using packet and bit error rates, and outage probability over atmospheric turbulence, pointing errors, and signal blockage scenarios.Results are evaluated for different RIS elements as a function of average signal to noise ratio. The proposed system is extremely productive, since this scheme has the capability to provide dependable connectivity in rural, urban, and suburban environments where reliable connectivity is difficult in spite of traditional infrastructures. ©2023 Optica Publishing Group.Item Performance of Spatially Coupled LDPC Codes over the Underwater Wireless Optical Channel with Strong Turbulence and Pointing Errors(Institute of Electrical and Electronics Engineers Inc., 2024) Padala, S.K.; D'Souza, J.The major problems in an underwater wireless optical communication (UWOC) link are turbulence induced fading and pointing errors. In this paper, we have investigated the bit error rate (BER) performance of spatially coupled low-density parity-check (SC-LDPC) coded horizontal UWOC link over a strong turbulent channel model with pointing errors. The performance of this link for different channel and code parameters has been studied using simulations. It has been observed that a rate 1/2 ARJA protograph based SC-LDPC code with graph lifting factor of 256 gives a coding gain of 47 dB at a BER of 10^-4 for strong turbulence channel model with pointing errors. An analytical BER expression for an uncoded UWOC link under strong turbulence with pointing errors for the On-Off Keying modulation technique has been derived. A multidimensional protograph based extrinsic information transfer algorithm has been developed to obtain the decoding thresholds for different channel parameters and code rates. We have also studied the SC-LDPC coded vertical UWOC link performance for some specific strong turbulence channel parameters with pointing errors and observed that as the link length increases from 20 m to 40 m , the performance gap between the hypothetical and cascaded channel models increases from 1.1 dB to 5.5 dB. © 2013 IEEE.