Faculty Publications
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Publications by NITK Faculty
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Item Performance analysis and mitigation of turbulence effects using spatial diversity techniques in FSO systems over combined channel(Institution of Engineering and Technology, 2019) Krishnan, P.[No abstract available]Item Nisp: A multi-lingual multi-accent dataset for speaker profiling(Institute of Electrical and Electronics Engineers Inc., 2021) Kalluri, S.B.; Vijayasenan, D.; Ganapathy, S.; Rajan, M.; Krishnan, P.Many commercial and forensic applications of speech demand the extraction of information about the speaker characteristics, which falls into the broad category of speaker profiling. The speaker characteristics needed for profiling include physical traits of the speaker like height, age, and gender of the speaker along with the native language of the speaker. Many of the datasets available have only partial information for speaker profiling. In this paper, we attempt to overcome this limitation by developing a new dataset which has speech data from five different Indian languages along with English. The metadata information for speaker profiling applications like linguistic information, regional information, and physical characteristics of a speaker are also collected. We call this dataset as NITK-IISc Multilingual Multi-accent Speaker Profiling (NISP) dataset. The description of the dataset, potential applications, and baseline results for speaker profiling on this dataset are provided in this paper. © 2021 IEEE.Item Performance analysis of FSOC system over generalized turbulence channel with pointing errors using Po1SK signalling technique(Institute of Electrical and Electronics Engineers Inc., 2021) Palliyembil, V.; Krishnan, P.; Jagadeesh, V.K.; Muthuchidamdaranathan, P.; Ekpo, S.Optical Wireless communication (OWC) is used to provide high speed wireless connectivity to end users. OWC along the outdoor environment is called Free Space optical Communication (FSOC). Along with the high speed performance of this technology, it is cheap, secure and easy to install. In this work, the performance analysis of an FSOC system employing Polarization shift keying (PoISK) modulation over Málaga (M)-distributed channel is carried out. The communication channel is also considered as inducing pointing error fading. The closed-form expressions for BER and channel capacity for this proposed system are derived to quantitatively analyse the performance. © 2021 IEEE.Item Analysis and Enhancement of Spectral Efficiency of UWOC System for IoUT Applications(Institute of Electrical and Electronics Engineers Inc., 2023) Mitra, A.; Kumar, A.; Krishnan, P.Underwater wireless optical communication (UWOC) has engrossed significant attention in diverse fields, such as defence, military applications, environmental monitoring, and scientific research. The growing number of interconnected devices in underwater environments has increased the importance of UWOC capacity analysis. It will be instrumental in underwater optical wireless sensor networks (UOWSNs) and the Internet of Underwater Things (IoUT). Understanding the concept of underwater channel capacity is crucial as it determines the maximum volume of reliable information that can be sent through the underwater communication channel. This work focuses on analyzing the performance of a UWOC system that facilitates communication between a surface source (ship) and an autonomous underwater vehicle (AUV) as the intended recipient. The investigation considers explicitly heterodyne detection and models the channel with Exponential Generalized Gamma (EGG) distribution. The study presents closed-form expressions for average channel capacity, employing Meijer's G function and derived average spectral efficiency (ASE) based on the derived channel capacity. Additionally, the paper delves into the influence of various factors, including pointing errors, bubble levels, water types, beam waist, and aperture radius, on the system's overall performance. © 2023 IEEE.Item Machine Learning Aided Signal Detection in Underwater Wireless Optical Communication for IoUT applications(Institute of Electrical and Electronics Engineers Inc., 2024) Kavitha, K.; Angayarkanni, V.; Paramanandham, N.; Yogarajan, G.; Krishnan, P.This study explores the effectiveness of the Machine Learning (ML) algorithms in addressing channel impairments in underwater Wireless Optical Communication (UWOC) systems employing On-Off Keying (OOK) modulation. The simulation takes into account underwater challenges such as signal attenuation, scattering, and absorption by using the Gamma-Gamma distribution to model fading and scintillation effects. The ML algorithm's performance is assessed by comparing its bit error rate (BER) against the signal-to-noise ratio (SNR) in comparison to the ideal scenario with perfect channel state information (CSI). The simulation covers various underwater scenarios, including ocean water, harbor water, clear water, coastal water, and oligotrophic water, showcasing the algorithm's adaptability in diverse environmental conditions. The results indicate that the SVM algorithm closely approaches the BER performance achieved with CSI, demonstrating its potential to improve communication reliability in UWOC systems under realistic channel conditions. This study provides valuable insights into the application of machine learning for signal detection in UWOC, offering prospects for enhanced underwater communication performance. © 2024 IEEE.Item Outage Probability Analysis of Dual Hop FSO Convergent with RF-UWOC Hybrid Link for SAGSIN in 6G-IoT Systems(Institute of Electrical and Electronics Engineers Inc., 2024) Rajeshwari, V.; Ishana Chellam, S.; Yukta Sri, C.K.; Kavitha, K.; Suveetha Dhanaselvam, P.; Karthikeyan, B.; Krishnan, P.This paper analyses the effectiveness of a novel hybrid communication system designed for a space-air-ground-sea integrated network (SAGSIN) within 6G Internet of Things (6G-IoT) environments. The system employs a dual-hop mechanism, featuring a free-space optical (FSO) link with a Malaga distribution for communication between ground and ships, along with a hybrid Radio Frequency - Underwater Wireless Optical Communication (RF-UWOC) link characterized by Nakagami-m and exponential generalized Gamma distributions for ship-to-underwater Autonomous Vehicle (AUV) communication. In this configuration, the ship serves as a Decode-and-Forward relay, where the RF link bolsters system reliability, and the UWOC link ensures secure communication. To optimize overall performance, the system implements a selection combining technique to identify the best signal from both RF and UWOC links. The paper evaluates the end-to-end cumulative distribution function (CDF) of the channel through the Meijer-G hypergeometric function. It also examines the outage probability of the proposed system across various weather conditions in the FSO channel, the effects of the Nakagami fading parameter m, and variations in salinity in the UWOC link. © 2024 IEEE.Item Energy Harvesting Optimization in FSO Communication with SLIPT Using Advanced Splitting Methods(Institute of Electrical and Electronics Engineers Inc., 2025) Angayarkanni, V.; Sheeba, A.; Dharshini V, M.; Suvetha, P.; Kavitha, K.; Suveetha Dhanaselvam, P.; Karthikeyan, B.; Krishnan, P.This paper presents an analysis of Simultaneous Lightwave Information and Power Transfer (SLIPT) in FreeSpace Optical (FSO) communication systems, incorporating key techniques such as AC-DC Separation (ADS), Power Splitting (PS), Time Switching (TS), and a hybrid Time Switching-Power Splitting (TS-PS) scheme. Closed-form expressions for the average harvested energy are derived, considering FSO turbulence channels modeled using the Málaga distribution. Furthermore, the analysis evaluates the impact of various turbulence conditions, including clear air, heavy rain, drizzle, and light fog, as well as the influence of receiver aperture size and other system and channel parameters. The primary focus of the result is to assess the energy harvesting performance under these diverse operating conditions. © 2025 IEEE.Item Performance Analysis of Triple Hop RF-RIS Convergent with FSO and UWOC System(Institute of Electrical and Electronics Engineers Inc., 2025) Sheeba, A.; Dharshini V, M.; Suvetha, P.; Kavitha, K.; Suveetha Dhanaselvam, P.; Karthikeyan, B.; Angayarkanni, V.; Krishnan, P.This paper proposes a hybrid communication system for integration within the space-air-ground-sea network (SAGSIN) architecture, tailored for 6G Internet of Things (6GIoT) applications. The system employs a triple-hop link combining Reconfigurable Intelligent Surface (RF-RIS), Free Space Optics (FSO), and Underwater Wireless Optical Communication (UWOC), facilitating communication between a base station, a lighthouse, a ship, and Underwater Aerial Vehicles (UWAVs). The architecture, using differential phaseshift keying, is ideal for Underwater Optical Wireless Sensor Networks (UOWSNs) and Internet of Underwater Things (IoUT). Performance analysis models RF-RIS with Nakagamim distribution, the FSO link with the Malaga distribution, and the UWOC link using the Exponential Generalized Gamma (EGG) distribution. The system's end-to-end cumulative distribution function (CDF) is evaluated via the Meijer-G function, while outage probability is examined under varying conditions, including atmospheric turbulence, fading parameters, and salinity levels. This system shows promise for coastal environments with changing weather conditions like rain, haze, and fog. © 2025 IEEE.Item A Review–Unguided Optical Communications: Developments, Technology Evolution, and Challenges(MDPI, 2023) Raj, A.A.B.; Krishnan, P.; Darusalam, U.; Kaddoum, G.; Ghassemlooy, Z.; Abadi, M.M.; Majumdar, A.K.; Ijaz, M.This review paper discusses the complete evolution of free-space optical (FSO) communication, also known as unguided optical communication (UOC) technologies, all the way back to ancient man’s fire to today’s machine-learning-supported UOC systems. The principles, significance, and developments that have happened over the past several decades, as well as installation methodologies, technological limitations, and today’s challenges of UOCs are presented. All the subsets of UOC: FSO communication, underwater optical wireless communication (UOWC), and visible light communication (VLC), with their technology/system developments, potential applications, and limitations are reviewed. The state-of-the-art developments/achievements in (i) FSO channel effects and their mitigation techniques; (ii) radio-over-FSO techniques; (iii) wavelength division multiplexing and sub-carrier multiplexing techniques; (iv) FSO for worldwide interoperability for microwave access applications; (v) space optical satellite communication (SOSC); (vi) UWOC; (vii) photoacoustic communication (PAC); (viii) light-fidelity; (ix) VLC; (x) vehicular VLC (V2LC); and (xi) optical camera communication are reviewed. In addition, the current developments on emerging technologies such as artificial intelligence (to improve the performance of UOC systems), energy harvesting (for the effective utilization of UOC channels), and near-future communication network scenarios (mandatory for secured broadband digital links) are covered. Finally, in brief, to achieve the full potential of UOC systems, challenges that require immediate research attention are summarized. © 2023 by the authors.Item Performance Analysis of Hybrid RF/FSO System Using BPSK-SIM and DPSK-SIM Over Gamma-Gamma Turbulence Channel With Pointing Errors for Smart City Applications(Institute of Electrical and Electronics Engineers Inc., 2018) Krishnan, P.The flourishing technology in wireless communication-free space optics (FSO) offers lots of merits over radio frequency (RF) links due to its license free bandwidth, ease of installation, high security features, and viable cost for short distance communication. It's high speed data rate and immunity against electromagnetic interference makes FSO the emerging technology of today. But, FSO is not always reliable especially during atmospheric conditions, such as fog, rain, mist, and snow. Hence, in account a new technique of hybrid FSO/RF, this includes advantages of both FSO and RF technologies. Through this paper intend to perform an extensive analysis of the error and misalignment effects encountered in line of sight communication. Pointing error and turbulence effects are the main drawback parameters for our analysis. For this purpose I have taken into consideration different modulation techniques-binary phase shift keying-subcarrier intensity modulation, differential phase shift keying-subcarrier intensity modulation communication system with reference to on-off keying (OOK) modulation. The novel expressions for outage probability and BER for both FSO and RF system are derived which uses Rician channel and 16QAM modulation scheme alongside hybrid FSO/RF system for weak, moderate, and strong turbulence regimes using Meijer-G function. © 2013 IEEE.