Journal Articles
Permanent URI for this collectionhttps://idr.nitk.ac.in/handle/123456789/19884
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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 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 Reconfigurable intelligent surface-assisted free-space optical communication system under the influence of signal blockage for smart-city applications(Optica Publishing Group (formerly OSA), 2022) Naik, R.P.; Krishnan, P.; G.D., G.D.G.Atmospheric turbulence and pointing errors represent substantial hurdles to free-space optical communications (FSOs), impeding their practical design. The reconfigurable intelligent surface (RIS) is an emerging technology that enables reflective radio transmission conditions for next-generation 5G/6G wireless frameworks by intelligently adjusting the beam in the desired direction using low-cost inactive reflecting elements. In this paper, we proposed an RIS-assisted FSO system for mitigating the effects of atmospheric turbulence, pointing errors, and communication system signal blockage. The probability density function and cumulative distribution functions of an FSO system composed of N-RIS elements are evaluated in a free-space environment that contains obstructions. We derived closed-form expressions for the proposed system's bit error rate (BER), outage probability, and channel capacity. The proposed system's performance is analyzed in terms of BER, outage probability, and channel capacity under various weather conditions, pointing errors, and signal blockage. The results are plotted as a function of number of RIS elements and average signal-to-noise ratio. The proposed system will be beneficial in smart-city applications since it will provide reliable connectivity in urban environments with a high population density and high-rise buildings. © 2022 Optica Publishing GroupItem Performance analysis of a RIS-assisted RoFSO communication system over Malaga distribution for smart city applications(Optica Publishing Group (formerly OSA), 2023) Kumar, A.; Krishnan, P.; Raj, A.A.B.Radio over free space optics (RoFSO) is one of the potential technologies that can satisfy the requirements of 5G services in a smart city. However, as RoFSO is line-of-sight (LOS) communication, one of its limitations is the occurrence of a skip zone in the targeted areas. In this work, a reconfigurable intelligent surface (RIS) is proposed as the solution to overcome this connection difficulty, which prevents signal blocking by generating LOS connections. These RIS modules extend the communication channel coverage, making it more intelligent and controllable. The performance analysis based on outage probability, ergodic channel capacity, and bit error rate has been performed using heterodyne detection. Malaga distribution has been used to model atmospheric turbulence. The exact closed-form expressions of the probability density function and cumulative distribution function of the end-to-end signal-to-noise ratio are derived. Exploiting these derived statistics, system performance is investigated through the ergodic channel capacity, outage probability, and average bit error rate for M-ary quadrature amplitude modulation and two binary modulation schemes: non-coherent binary frequency-shift keying and coherent binary phase-shift keying. Numerical results are compared among different turbulence conditions, link lengths, and scattering errors. The results show that the proposed RIS-assisted RoFSO technology has the potential to be effective for 5G smart city applications. © 2023 Optica Publishing Group.