Faculty Publications
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Publications by NITK Faculty
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Item Performance of QPSK modulation for FSO geo-synchronous satellite communication link under atmospheric turbulence(2013) Jokhakar Jignesh, D.; Sripati, U.; Kulkarni, M.In recent years, free space optical (FSO) communication has gained a considerable interest amongst the researchers due to certain benefits it has to offer over RF links such as availability of large unlicensed bandwidth, high data rates, negligible electromagnetic interference, ease of installation etc. However the conventionally used FSO systems use On-Off Keying (OOK) as the modulation technique. Such a link requires high levels of transmit power. In this paper, we have suggested the use of QPSK modulation technique which allows us to reap the benefits of coherent detection. Our calculations show that QPSK is more inert to the changes in atmospheric conditions like temperature, air pressure, humidity, aerosol concentration etc. © 2013 IEEE.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 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 BER performance enhancement for secure wireless optical communication systems based on chaotic MIMO techniques(2014) Abdulameer, L.F.; Jignesh, J.D.; Sripati, U.; Kulkarni, M.There has been a growing interest in the use of chaotic techniques for enabling secure communication in recent years. This need has been motivated by the emergence of a number of wireless services which require the channel to provide low bit error rates (BER) along with information security. The aim of such activity is to steal or distort the information being conveyed. Optical Wireless Systems (basically Free Space Optic Systems, FSO) are no exception to this trend. Thus, there is an urgent necessity to design techniques that can secure privileged information against unauthorized eavesdroppers while simultaneously protecting information against channel-induced perturbations and errors. Conventional cryptographic techniques are not designed for protecting information integrity when data is being transferred over a harsh communication medium. Hence, a separate channel coding protocol is often necessary to achieve this goal. Our work indicates that the use of a suitable Chaotic Shift Keying (CSK) map combined with an appropriate Space-Time Code (STC) can allow both requirements to be met. In this paper, we have concentrated on investigating the error rate performance of chaotic-wireless optical communication links operating over atmospheric channel, where the turbulence-induced fading is described by the Gamma-Gamma and log-normal distributions. The main aim of the paper is to assess the feasibility of employing Space-Time Coded chaotic communications over Multiple Input Multiple Output (MIMO) communication channels. Our simulations indicate that the combination of the STC and tent map provides the best BER performance in addition to security when compared to the choice of other maps. © 2013 Springer Science+Business Media Dordrecht.Item RIS Assisted Triple-Hop RF-FSO Convergent With UWOC System(Institute of Electrical and Electronics Engineers Inc., 2022) Bhargava Kumar, L.B.; Naik, R.P.; Krishnan, P.; Raj, A.A.B.; Majumdar, A.K.; Chung, W.-Y.The convergence of wireless optical communication (WOC) and radio-frequency (RF) systems is a promising technology that overcomes the shortcomings of standalone communication systems. By incorporating reconfigurable intelligent surfaces (RISs) on top of these WOC and RF communication systems, it is possible to circumvent the connection challenges associated with standard line of sight (LOS) communication links. Wireless communication systems with RIS assistance are a promising and evolving technology that enables more efficient and reliable link performance over long distances. The performance of the triple-hop RIS-assisted RF-FSO convergent with the underwater wireless optical communication (UWOC) system is investigated in this article. We considered the fading channel Nakagami-m over the RIS-RF connection and the fading channel Gamma-Gamma (GG) over the RIS-FSO and UWOC links. Then, the average bit error rate (ABER) and outage probability are determined using closed-form expressions. The ABER and outage probability performances of the triple-hop communication system is analysed by varying parameters such as turbulence, misalignment fading, and the number of RIS elements. The obtained results demonstrate an improvement in performance for low turbulence, low pointing error, and an increasing number of RIS elements. Additionally, the data demonstrate the accuracy of the analytical results. © 2013 IEEE.Item All-Optical UAV-Based Triple-Hop FSO-FSO-VLC Cooperative System for High-Speed Broadband Internet Access in High-Speed Trains(Institute of Electrical and Electronics Engineers Inc., 2023) Aarthi, A.; Bhargava Kumar, L.B.; Krishnan, P.; Natarajan, R.; Jayakody, D.N.K.In this paper, we proposed an unmanned aerial vehicle (UAV) based all optical triple hop mixed free space optical-free space optical-visible light communication (FSO-FSO-VLC) system for broadband internet access in high-speed train applications. The system consists of triple hops from gateway to the UAV, UAV to train and train to the end user. Two decode and forward relays are mounted on the UAV and train respectively to transmit the data between the gateway to the end-users. The first hop between gateway to UAV consist of FSO link which follows M-distribution. The second hop between the UAV to train consists of FSO link and is modelled using Gamma-Gamma distribution which takes into account both atmospheric turbulence and pointing errors due to position/orientation deviation. The third hop between the train and end user is connected using VLC link and it is mathematically modelled using Lambertian emission distribution. The relays map the incoming signal on the FSO links and send it down to the user inside the train via the VLC downlink. We derived the closed form expressions for average bit error rate and outage probability of the proposed system. This paper investigates the effects of atmospheric turbulence, field of view, beam divergence angle, displacement deviation variance, optical concentrator gain, number of access point, and modulation schemes on system performance. First time, we proposed all-optical system which offers high data rate and low transmission delay. © 2013 IEEE.