Faculty Publications
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Item Multi-hop convergent FSO-UWOC system to establish a reliable communication link between the islands(Elsevier B.V., 2020) Bhargava Kumar, B.K.; Krishnan, P.Most part of the earth is filled with water. Oceans hold around 97% of this water, and hence they are the heart of mother earth. People use these oceans for traveling, edibles, and communication. Many islands in this world consist of a large number of sub-islands. Establishing a communication link or a network between these sub-islands is highly challenging one. In this paper, we proposed a decode-and-forward multi-hop convergent free space optical — underwater wireless optical communication (FSO-UWOC) system for establishing high-speed network connectivity between the islands. The closed form expressions of outage probability of the differential phase shift keying (DPSK) based FSO-UWOC system over a Malaga distributed FSO channel and Gamma–Gamma distributed UWOC channel is derived. The results are analyzed and plotted for different weather conditions, turbulences and pointing errors of FSO and UWOC, respectively. The simulated results show that the proposed system will be useful in design of convergent UWOC-FSO system in coastal environments where the weather changes frequently such as clear, rain, haze etc. © 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 Bit error rate analysis of ground-to-high altitude platform free-space optical communications using coded polarization shift keying in various weather conditions(Springer, 2022) Nallagonda, V.; Krishnan, P.High altitude platforms (HAPs) aided free-space optical (FSO) communication, a future emerging technology for next-generation communication systems. HAP aided FSO communication systems, contributing significantly to data hunger applications. Weather conditions, angle of arrival fluctuations, blockages, and pointing error loss due to the HAP’s hovering state are some of the limitations to establishing an efficient link. In this paper, we proposed for the first time a Ground-to-HAP FSO communication system based on polarization shift keying to improve performance under hovering fluctuations. We also improved the proposed system’s performance by employing BCH and repetition coding schemes. The proposed system’s average bit error rate performance is expressed in closed form, and the results are analysed under various weather conditions such as rain (light and heavy) and fog (light and moderate). The results for coded and uncoded cases are compared. The achieved coding gain is 28.5 dB. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Item RoFSO system based on BCH and RS coded BPSK OFDM for 5G applications in smart cities(Springer, 2022) Kumar, A.; Krishnan, P.The radio over the free space optical (RoFSO) communication system has become a popular research topic in 5G communication in recent years. Atmospheric turbulence typically degrades the performance of the RoFSO system. Multiple input multiple output, aperture averaging, error-correcting codes, and robust modulation are standard mitigation techniques used to reduce the effects of atmospheric turbulence. In this paper, Reed Solomon (RS) and Bose-Chaudhuri-Hocquenghem (BCH) coded binary shift keying (BPSK) orthogonal frequency division multiplexing (OFDM) based RoFSO system is proposed for 5G applications. We introduced RS and BCH coding techniques for the first time in this proposed RoFSO system, and achieved an average bit error rate (ABER) of 10 - 6, at 40 dB, 17 dB, and 4 dB carrier to noise plus distortion ratio (CNDR) for the uncoded, RS coded, and BCH coded systems, respectively, under weak turbulence conditions. That is, when compared to the uncoded system, the proposed RS and BCH coded system provide transmit power gains of 13 dB and 34 dB, respectively. The ABER performance of the proposed coded RoFSO system is investigated and compared to an uncoded system under various turbulence, weather, and pointing error cases. In all turbulence regimes, weather conditions, and pointing error scenarios, the BCH coded system outperforms the RS coded and uncoded systems. The proposed RS and BCH coded system is energy efficient and may be useful in 5G implementation. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Item Performance analysis of radio-over-free-space optical communication system with spatial diversity over combined channel model(Springer, 2022) Kumar, A.; Krishnan, P.Radio over Free Space Optical (RoFSO) communication is accepted as one of the promising technologies in communication systems that can fulfill the demands of high bandwidth and high data rate because it has an inherent quality of transmission capacity significantly more than what is provided by radio transmission technologies. It is a low power, high data rate, unlicensed spectrum, and large bandwidth wireless technology. Nevertheless, the full potential of the RoFSO communication system can be utilized only by overcoming the adverse effects of the atmospheric channel, which are scattering, absorption, and turbulence. Pointing error is also another factor responsible for the deterioration of the performance of the RoFSO system. In this paper, spatial diversity at the transmitting and receiving ends is used to improve the performance of the RoFSO system in various turbulence and weather conditions. The Malaga distribution has been used to model atmospheric turbulence. For single input single output (SISO), single input Multiple output (SIMO), multiple input single output (MISO), multiple input multiple output (MIMO) configurations, closed form expressions for average bit error rate (BER) have been estimated. To improve the performance of the proposed system, the two combining techniques, Optimal Combining and Equal Gain Combining, are being considered. The results obtained are compared to various configurations such as SISO, SIMO, MISO, and MIMO cases. The result shows that MIMO offers better average BER performance compared with SISO, SIMO and MISO cases. The 4 × 4 MIMO case has an average BER of 10 - 9 at an average SNR of 25 dB, but the SISO case has an average BER of 10 - 1 at the same average SNR. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Item Performance analysis of multi-hop FSO convergent with UWOC system for security and tracking in navy applications(Springer, 2022) Bhargava Kumar, B.K.; Naik, R.P.; Krishnan, P.The Navy is ubiquitous in every major geographic area of the world. It is estimated that 60% of global goods are transported by sea. The Navy plays a vital role in offering protection of the sea lanes and the trade transportation, preserves territorial ocean borders and the right to the resources contained in them, and facilitates the response to natural disasters and other disasters. In this paper, we proposed for the first time a multi-hop free-space optical (FSO)—underwater wireless optical communication (UWOC) converging system. It is useful for the secure transport and tracking of goods and missiles through cargo ships for the navy and marine applications. The end-to-end average bit error rate (ABER) and outage probability performance of multi-hop FSO transmission systems converged with UWOC is analysed. The outage and ABER expression of the proposed system was obtained and the results were plotted for different weather conditions, turbulence regimes, pointing error and number of FSO hop scenarios. A case study is done on the extent to which the speed and height of the ship, the wind speed and the links between the ships affect the end-to-end outage performance of the proposed triple hop FSO converging UWOC system. This study is performed in Surathkal, which is located 20 km north of Mangalore. We assumed in this case study that the ships are located near surathkal in the Arabian Sea (GPS coordinates: N 13∘0′38.0988′, E 74∘47′17.4876′), Karnataka, India. Computational complexity of proposed cumulative distribution functions (CDF) have been evaluated with the existing CDF in the literature. In addition to that the expected cost analysis of the proposed communication system provided. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Item High-speed long-range multihop underwater wireless optical communication convergent with free-space optical system for optical internet of underwater things and underwater optical wireless sensor network applications(SPIE, 2022) Bhargava Kumar, B.K.; Naik, R.P.; Krishnan, P.We propose a multihop underwater wireless optical communication (UWOC) convergent with free-space optical (FSO) system for an optical internet of underwater things (O-IoUT) and underwater optical wireless sensor network (UOWSN) applications. A closed-form expression of outage probability was derived for the proposed system using the cumulative distribution functions gamma-gamma and hypertangent log-normal for FSO link and UWOC link, respectively. The outage performance of the proposed multihop UWOC convergent with FSO system was analyzed over various oceanic water types (clear ocean, coastal ocean, and turbid harbor) and different FSO weather conditions (clear air, haze, drizzle, and light fog). The results also depict the end-to-end system performance for different pointing errors (strong, moderate, and weak) and varying the number of hops. The maximum link range of ∼2.5 km, which includes 2 km of FSO link and 450 m of multihop UWOC link (nine hops with each of 50 m clear ocean), is considered. © 2022 Society of Photo-Optical Instrumentation Engineers (SPIE).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.Item Enhancing Smart City Connectivity: Implementing Channel-Adaptive Strategies for FSO-Based Drone-Assisted Mobile Access Networks in Urban Environments(Institute of Electrical and Electronics Engineers Inc., 2025) Aarthi, G.; Bhargava Kumar, L.; Vaidya, M.; Nema, S.; Krishnan, P.; Sangeetha, A.; Natarajan, R.; Karthikeyan, K.The global surge in urbanization has catalyzed the evolution of smart city infrastructures, characterized by expansive interconnected networks spanning vast urban landscapes. To address the connectivity challenges inherent in smart city environments, this study advocates for the utilization of autonomous aerial vehicles (AAVs) as an alternative to traditional mobile air base stations. Leveraging Free-Space Optical (FSO) links for downlink transmission from AAVs to users, the proposed system confronts atmospheric turbulence and pointing loss impairments. In this context, the study explores the average spectral efficiency (ASE) performance of the proposed FSO-based Drone-Assisted system employing various channel adaptive techniques, including Optimal Rate Adaptation, Channel Inversion with Fixed Rate, Optimal Power and Rate Adaptation, and Truncated Channel Inversion with Fixed Rate. Additionally, the investigation underscores the impact of factors such as link range, coverage distance, AAV orientation fluctuation standard deviation, AAV position vibration standard deviation, and beam divergence on system performance. By elucidating these aspects, the research aims to contribute valuable insights into the optimization of smart city connectivity, paving the way for enhanced communication infrastructure in urban environments. Notably, the study achieved a maximum ASE of 101 bits/s/Hz using the TIFR adaptation scheme, underscoring the efficacy of the proposed approach. © 2013 IEEE.