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 Asymptotic bit error rate analysis of convergent underwater wireless optical communication-free-space optical system over combined channel model for different turbulence and weather conditions with pointing errors(SPIE, 2020) Bhargava Kumar, B.K.; Krishnan, P.The differential phase-shift keying-based dual-hop underwater wireless optical communication-free-space optics (UWOC-FSO) convergent system is proposed for UOWSNs and Internet of Underwater Things (IoUT) applications. In the proposed system, the collected sensor data are transmitted to a decode-and-forward relay using underwater optical wireless communication links modeled as gamma-gamma distribution. The relay transmits the signal to the terrestrial destination using free-space optical link modeled as Malaga distribution. The end-to-end performance of the system (novel expression for asymptotic bit error rate) is derived and analyzed over combined channel model (including the effects of attenuation, turbulence, and pointing errors for both FSO and UWOC channels). The in-depth study is carried out for different weather conditions of FSO (attenuation - very clear, haze, rain, and fog; turbulence - weak and strong; and pointing error - weak and strong based on the g values 1, 2, and 6) and UWOC (attenuation - clear, coastal ocean, and turbid harbor; turbulence - weak, moderate, and strong; and pointing error - weak and strong based on the g values 1, 2, and 6), respectively. The proposed system is highly useful in coastal environments, where the climate is changing adequately as clear, rain, haze, and fog. © 2020 Society of Photo-Optical Instrumentation Engineers (SPIE).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 Underwater wireless optical communications based reconfigurable UOWSN for monitoring and discovering continental margin ore deposits(Optica Publishing Group (formerly OSA), 2022) Bhargava Kumar, B.K.; Naik, R.P.; Krishnan, P.; Majumdar, A.K.Changes in the environment, such as landslides, tsunamis, rising or falling sea levels in coastal oceans, and neighboring land surfaces, significantly impact the structure of the ocean and human life. These natural climate-change processes have unanticipated and deadly consequences for coastal areas. The continental margin part of the ocean has recently attracted the most attention because of the mineral sources and human activities such as exploration, navigation, recreation, and fishing. The continental margin stretches fromthe coastal mountains and plains to continental shelf, slope, and rise, where terrestrial and maritime means meet. In this paper, we propose a reconfigurable underwater optical wireless sensor network (UOWSN) based on underwater wireless optical communication (UWOC) to monitor and discover continental margin ore deposits. In this proposed system, a transceiver on the underwater wireless autonomous vehicle moving around the different regions of the continental margin collects information and transmits it to the seashore control station once it reaches the ocean surface. We investigated the outage probability and average bit error rate of the proposed system at the continental margin and used coding techniques to mitigate the effects of high turbulence in the continental shelf region. © 2022 Optica Publishing Group.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).