Journal Articles
Permanent URI for this collectionhttps://idr.nitk.ac.in/handle/123456789/19884
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Item Variable speed wind turbine for maximum power capture using adaptive fuzzy integral sliding mode control(2014) RAJENDRAN, S.; Jena, D.This paper presents a nonlinear control approach to variable speed wind turbine (VSWT) with a wind speed estimator. The dynamics of the wind turbine (WT) is derived from single mass model. In this work, a modified Newton Raphson estimator has been considered for exact estimation of effective wind speed. The main objective of this work is to extract maximum energy from the wind at below rated wind speed while reducing drive train oscillation. In order to achieve the above objectives, VSWT should operate close to the optimal power coefficient. The generator torque is considered as the control input to achieve maximum energy capture. From the literature, it is clear that existing linear and nonlinear control techniques suffer from poor tracking of WT dynamics, increased power loss and complex control law. In addition, they are not robust with respect to input disturbances. In order to overcome the above drawbacks, adaptive fuzzy integral sliding mode control (AFISMC) is proposed for VSWT control. The proposed controller is tested with different types of disturbances and compared with other nonlinear controllers such as sliding mode control and integral sliding mode control. The result shows the better performance of AFISMC and its robustness to input disturbances. In this paper, the discontinuity in integral sliding mode controller is smoothed by using hyperbolic tangent function, and the sliding gain is adapted using a fuzzy technique which makes the controller more robust. © 2014, The Author(s).Item High-speed and reliable Underwater Wireless Optical Communication system using Multiple-Input Multiple-Output and channel coding techniques for IoUT applications(Elsevier B.V., 2020) Naik, P.N.; Acharya Udupi, S.; Krishnan, P.In this paper, we investigate the performance of an Underwater Wireless Optical Communication (UWOC) system employing on–off keying modulation at a data-rate of 500 Mbps over a link-range of 30 m. Transmit/receive diversity schemes, namely Multiple-Input to Single-Output (MISO), Single-Input to Multiple-Output (SIMO) and Multiple-Input to Multiple-Output (MIMO) techniques with and without RS-coding have been employed to mitigate the effects of weak oceanic turbulence and beam attenuation. The novel closed-form analytical Bit Error Rate (BER) expressions of Single-Input to Single-Output (SISO), SIMO, MISO and MIMO links for un-coded and RS-coded cases have been computed using the hyperbolic tangent distribution and validated with Monte-Carlo simulation results. The obtained BER results show that the use of (63,51) RS-coded 4 × 5 MIMO UWOC system offers at-least 35 dB of transmit power gain compared with the un-coded SISO UWOC system at a BER of 10?5. Emerging technologies like the fifth-generation (5G) networks and the Internet of Underwater Things (IoUT) will have a high impact on UWOC as these systems require a high degree of information integrity, high data rates and energy efficiency when employed in conjunction with data transfer between underwater vehicles and objects. The proposed RS-coded MIMO UWOC system offers high reliability and power efficiency and it has the potential to be gainfully employed in IoUT applications. © 2020 Elsevier B.V.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 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.