Faculty Publications
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Publications by NITK Faculty
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Item Comparison of OMP and SOMP in the reconstruction of compressively sensed hyperspectral images(2011) Aravind, N.V.; Krishnan, K.; Acharya, V.V.; Sumam David, S.In this paper, we present a novel method for the acquisition and compression of hyperspectral images based on two concepts - distributed source coding and compressive sensing. Compressive sensing (CS) is a signal acquisition method that samples at sub Nyquist rates which is possible for signals that are sparse in some transform domain. Distributed source coding (DSC) is a method to encode correlated sources separately and decode them together in an attempt to shift complexity from the encoder to the decoder. Distributed compressive sensing (DCS) is a new framework suggested for jointly sparse signals which we apply to the correlated bands of hyperspectral images. We compressively sense each band of the hyperspectral image individually and can then recover the bands separately or using a joint recovery method. We use the Orthogonal Matching Pursuit (OMP) for individual recovery and Simultaneous Orthogonal Matching Pursuit (SOMP) for joint decoding and compare the two methods. The latter is shown to perform consistently better showing that the Distributed Compressive Sensing method that exploits the joint sparsity of the hyperspectral image is much better than individual recovery. © 2011 IEEE.Item Remote Triggered Laboratory for Boost Converter Using LabVIEW(Springer Science and Business Media Deutschland GmbH, 2021) Ansal, V.; Remya, V.K.; Jagadeesh, V.K.; Krishnan, K.This paper aims to provide remote access to laboratories in power electronics to all levels from under graduate to research. The platform is focused on learning aspect as much as performing the experiments. Remote triggered power electronics laboratory for boost converter experiments has been developed using National Instruments(NI) data acquisition device myRIO and LabVIEW software package which has an extensive support for interfacing devices and instruments. LabVIEW software is used to access the data using myRIO which has both the processor and Field Programmable Gate Array (FPGA). Through Graphical User Interface (GUI), a user in remote location is able to vary parameter pertaining to boost converter circuit which is transmitted to laboratory PC that has NI LabVIEW installed in it. The input is further fed to circuit, and then, output is fed back to LabVIEW through NI myRIO which ultimately is returned to user’s PC using web-publishing tool and can be viewed through GUI. Remote Triggered (RT) power electronics laboratories can be effectively used to give laboratory demonstrations to large number of learners. © 2021, Springer Nature Singapore Pte Ltd.Item BER Performance Analysis of Optical Wireless Communication System over Weak and Strong Underwater Turbulence Channels(Springer Science and Business Media Deutschland GmbH, 2023) Naik, R.P.; Shripathi Acharya, U.S.; Bhargava Kumar, L.B.; Krishnan, K.; Chung, W.-Y.In this paper, we have investigated the performance of an underwater wireless optical communication (UWOC) link employing single-input and single-output (SISO) and selection combining (SC) as receiver diversity for varying link-ranges. As the the link-range increases, then strength of turbulence between the underwater optical entities also increases. It is assumed that the distribution of light propagation in weak and strong turbulence UWOC channel as log-normal (LN) and gamma-gamma (GG) density functions, respectively. The analytical bit error rate (BER) equations of on–off keying modulated UWOC link have been derived for SISO and SC receiver diversity using hyperbolic tangent distribution for LN and power series for GG density functions. The analytical BER results are validated with the Monte Carlo simulations. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.Item Outage Probability Analysis of Variable and Fixed Gain Relay-Assisted Dual-Hop RF-FSO Links Using Space–time Block Code Users(Springer Science and Business Media Deutschland GmbH, 2023) Naik, R.P.; Bhargava Kumar, L.B.; Krishnan, K.; Chung, W.-Y.In this paper, we have implemented an analytical study on a relay-assisted dual-hop system using fixed and variable gains for the radio-frequency (RF) and free-space optical communication (FSO). RF and FSO links are realized using the Rayleigh and Malaga distribution functions. Simulation results shows that pointing errors become severe, system performance deteriorates, and conjointly that the RF users exploiting space–time block coding (STBC) will enhance the performance of the end-to-end system. Outage probability of the end-to-end communication link operated with the STBC using the variable and fixed gain system implemented and plotted with respect to average SNR. From the obtained results, fixed gain relay-based communication link performs better efficient than the variable gain relay system. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.Item Switchable Wideband phase Gradient Beam Steering Reflector/Absorber for Applications such as Intelligent Reflecting Surfaces(Institute of Electrical and Electronics Engineers Inc., 2023) Janawade, S.A.; Krishnan, K.; Kandasamy, K.A miniaturized dual functional phase gradient meta-structure for beam steering and simultaneous RCS reduction is proposed in this work. A unit cell is designed, which generates a complete phase profile from -90° to 90° to direct the incident beam in all directions. The novelty in the proposed work is that the realized unit cell can reflect incident EM waves with 99.9% efficiency over a wide range of frequencies from 1 Hz to 40 GHz. Also, when the unit cell is loaded with lumped elements like a resistor and capacitor, it acts as an absorber. The magnitude of absorption is controlled by resistor, which can be varied from 79.17% to 99.97%, whereas the frequency at which absorption occurs can be tuned by varying capacitance. This unit cell configuration could achieve beam steering at sub 6 GHz, K and Ka-band frequencies. The dimensions of the proposed meta-atom is 8.4x8.4x1.56 mm3 and formulated on Rogers RT duroid 5880. © 2023 IEEE.Item Asymptotic bit-error rate analysis of quadrature amplitude modulation and phaseshift keying with OFDM RoFSO over M turbulence in the presence of pointing errors(Institution of Engineering and Technology journals@theiet.org, 2018) Krishnan, K.; Jana, U.; Kumar, B.K.In case where installation of optical fibre is not practically reliable, the new generation wireless communication popularised as free-space optics (FSO) systems can be used to transmit radio-frequency (RF) signals. FSO technology can efficiently transfer multiple RF signals, and this new technique is commonly referred as radio-on-FSO (RoFSO). The major challenges in this technology are atmospheric turbulence and pointing errors. In this study, the authors analysed the performance of RoFSO links employing the orthogonal frequency division multiplexing (OFDM) scheme under both modulation formats namely quadrature amplitude modulation and phase shift keying in the newly developed Málaga or M distribution turbulent channel model. The performance is evaluated with consideration of both scintillation and pointing errors in M distribution channel for higher values of the carrier-to-noise plus distortion ratio. M distribution channel serves as an effective generalised model which unifies all other available statistical channel models. The novel expressions of average bit-error rate has been derived and performance comparison has been done between the two modulation formats. This study identifies the crucial parameters that deteriorate the efficiency of the OFDM signal over FSO link which can be helpful in designing an optimal system. © The Institution of Engineering and Technology 2018.Item Design of Collision Detection System for Smart Car Using Li-Fi and Ultrasonic Sensor(Institute of Electrical and Electronics Engineers Inc., 2018) Krishnan, K.The 21st century is defined as the era of technological development. With drastic increase in population, automation is becoming the need of the hour in order to make life more comfortable and easy. Due to the advancement and development in the field of automation and embedded system, the notion of smart car has become very popular. Smart cars are modernizing trends in the traditional automobile industry. Companies across the globe have been investing a huge amount of resources on the production and design of smart cars. Every technological development needs to overcome certain obstacles, and hence, in this paper, a design of a collision detection system for smart car using light fidelity (Li-Fi) and ultrasonic sensor on the Arduino platform is proposed. This design consists of an ultrasonic sensor, an Arduino processor, and a Li-Fi circuit. The ultrasonic is used for measurement of distance between vehicles, and Arduino processes the data and makes decisions accordingly. Data transmission between vehicles is ensued using a Li-Fi transmitter circuit and a Li-Fi receiver circuit. The transmitter circuit is mounted on the tail lights of the leading car and the receiver circuit is mounted on the front side of the car that follows. Using visible light communication, the transmitter circuit transmits the calculated speed and the information is received by the receiver circuit of the second car. On the basis of the information received, the speed of the second car is changed in order to avoid collision. In this paper, a system that can detect and thus avoid collision between vehicles and prevent accidents is proposed and studied. © 1967-2012 IEEE.Item Highly birefringent photonic crystal fiber with hybrid cladding(Academic Press Inc. apjcs@harcourt.com, 2019) Krishnan, K.; Malavika, R.A highly birefringent hybrid cladding photonic crystal fiber (PCF) is proposed in this article. The guiding properties of the proposed PCF are numerically investigated using the finite element method (FEM). This fiber exhibits very high birefringence in the order of10-2 at communication wavelengths. In addition, low confinement loss of 6.1 × 10?3 dB/km, lower negative dispersion of -274.5ps/nm/km and higher nonlinearity of 76.41W-1km-1 is achieved at the same wavelengths compared with the exist literature. The proposed simple cladding structure is easy for fabrication. Moreover, effective mode area and nonlinear coefficient are analyzed and optimized. The proposed fiber can prove its applications in sensing, telecommunication and non-linear technologies. © 2018 Elsevier Inc.Item Analysis of M-QAM Modulated Underwater Wireless Optical Communication System for Reconfigurable UOWSNs Employed in River Meets Ocean Scenario(Institute of Electrical and Electronics Engineers Inc., 2020) Uppalapati, A.; Naik, R.P.; Krishnan, K.In this paper, the bit error rate (BER) performance of underwater wireless optical communication system employing with M-ary quadrature amplitude modulation is proposed for underwater optical wireless sensor networks (UOWSN) in river meets ocean scenario. The underwater channel degradation effects such as absorption, scattering and oceanic turbulence is taken into account. The oceanic turbulence is modelled by the Gamma-Gamma distribution. The first time, we proposed re-configurable UOWSN for the real time scenario of the river meets the ocean and derived the novel closed form analytical BER expressions of the proposed system over Gamma-Gamma turbulence with attenuation effects. The impact of oceanic turbulence parameters such as the variations of temperature, kinetic energy, viscosity, salinity, link range and the water type of system performance is investigated for river water, mixed water (river and ocean water) and ocean water. The proposed system and the related analysis will be highly useful in UOWSN and the Internet of underwater thing (IoUT) applications. © 1967-2012 IEEE.Item Photonics radar based LSS targets’ postures’ m-D and cadence frequency imaging using empirical wavelet transform technique(Taylor and Francis Ltd., 2024) Akhter, N.; Raj, A.A.B.; Krishnan, K.Developing a photonics radar to detect the combined multiple simultaneous-behaviours/postures of low-slow-small (LSS) aerial targets and appropriately extracting their Doppler profile have become significant to enable air surveillance/security and guidance for unmanned aviation. A CW photonic radar of 5.3 GHz, and an empirical wavelet transform (EWT) based radar signal processing algorithm are developed and their sensing/measurement capabilities are tested with representative LSS target models: two/three blades propeller systems, a warhead-like cone-shaped target and a bionic bird. Open field experiments with different simultaneous-behaviours of these LSS targets are conducted, and performance validation of radar, in terms of micro-Doppler signature extractions, cadence frequency imaging and targets' behavioural parameters measurement, is analysed, quantitatively investigated and the results are presented. All the measurement results keep an average of 99% of agreement with the standard measurement values that evidence the compatibility of developed photonics radar for precision sensing of multiple simultaneous-behaviours/postures of LSS aerial targets. © 2023 The Royal Photographic Society.