Faculty Publications

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Author: search.filters.author.Krishnan, P.Subject: search.filters.subject.Bit error rate

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    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.
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    Analysis of beam divergence on free space optical link using polarization shift keying technique
    (SPIE spie@spie.org, 2019) Rajeev, M.; Mathew, G.A.; Krishnan, P.
    Beam diverging is an indispensable phenomenon on the quality and bit error rate (BER) performance of the free space optical (FSO) communication system. The role of an efficacious modulation technique that mitigates the combined effect of beam diverging and atmospheric attenuation is highly relevant. The weak depolarizing property of the atmosphere advances the use of polarization shift keying (PolSK) modulation. We are subjected to investigate the quality and feasibility of the communication link, considering the impact of beam divergence on the PolSK modulation under various weather conditions. It is shown that PolSK subdues the effects of increase in beam divergence, attenuation factor, and further extends the communication range. A comparison with on off keying and PolSK-based FSO links considering the divergence angle is discussed. Moreover, BER and quality factor graphs are plotted against link distance and beam divergence using PolSK, which improves the performance analysis. © 2019 Society of Photo-Optical Instrumentation Engineers (SPIE).
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    Analysis of FSO Systems with SISO and MIMO Techniques
    (Springer New York LLC barbara.b.bertram@gsk.com, 2019) Krishnan, P.
    Free space optics (FSO) is a form of line of sight communication technology that uses the help of LASERS and photodetectors to give optical connections from one place to another without the use of an optical fiber. The major hindrance to an FSO communication system comes in the form of atmospheric turbulences characterized by haze, rain, snow, storms among others. In this paper, the bit error rate performance of single input single output and multiple input multiple output based FSO system is analyzed and compared. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.
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    Modelling of OFDM based RoFSO system for 5G applications over varying weather conditions: A case study
    (Elsevier GmbH, 2019) Pati, P.S.; Krishnan, P.
    From the perspective of spectrum scarcity, Radio-on-FSO (RoFSO)system is the best available option as it operates at unlicensed optical frequencies with the salient features of high bandwidth, cost effectiveness, lower transmit power, immunity to electromagnetic interference and easy deployment. To cater to the high data rate requirement of 5G applications in the near future, RoFSO systems will definitely be the best assisted alternative technology to the conventional wireless systems. However, the atmospheric conditions and non-linearity of the optical link have got a bearing on the efficiency of the system. In this work, we have presented an analytical model for transmitting phase shift keying (PSK)modulated orthogonal frequency division multiplexing (OFDM)signals through free space optics (FSO)links. RL is the load resistor of the photo detector an Considering optical noises, nonlinear distortion resulting from laser diode and the atmospheric turbulence effect modelled by gamma-gamma distribution, we have derived a closed form closed-form bit error rate (BER)and outage probability expression for the aforementioned transmission system. Pointing error is also factored in for more accurate and appropriate analysis of the system performance. Better system performance was observed through use of aperture averaging technique. A case study has been undertaken for analyzing the FSO system performance with reference to BER for various seasons for the year 2016 over IIIT Bhubaneswar area by considering the wind speed and altitude at different floors of the building of the institute. © 2019 Elsevier GmbH
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    Performance enhancement of BPSK-SIM- and DPSK-SIM-based FSO downlink over atmospheric turbulence using aperture averaging and receiver diversity
    (Springer New York LLC barbara.b.bertram@gsk.com, 2019) Krishnan, P.; Jha, G.K.; Walia, A.
    In this paper, we evaluate the bit error rate (BER) performance of a free-space optical satellite downlink by considering the atmospheric turbulence effects using binary shift keying subcarrier intensity modulation and differential phase shift keying subcarrier intensity modulation (DPSK-SIM). The performance of the link is enhanced using aperture averaging and receiver diversity. The closed form mathematical expressions of BER for BPSK-SIM and DPSK-SIM schemes are derived and analyzed. It is observed that on varying the turbulence level, the performance of the link degrades when the turbulence level increases. The improved BER of 10?12 and 10?10 at signal-to-noise ratio of 30 dB of the link for both BPSK-SIM and DPSK-SIM is obtained by using aperture averaging (aperture diameter, D = 10 cm) and receiver diversity with optimal combining. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.
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    High-speed and reliable Underwater Wireless Optical Communication system using Multiple-Input Multiple-Output and channel coding techniques for IoUT applications
    (Elsevier B.V., 2020) Naik, P.N.; Acharya Udupi, S.; Krishnan, P.
    In this paper, we investigate the performance of an Underwater Wireless Optical Communication (UWOC) system employing on–off keying modulation at a data-rate of 500 Mbps over a link-range of 30 m. Transmit/receive diversity schemes, namely Multiple-Input to Single-Output (MISO), Single-Input to Multiple-Output (SIMO) and Multiple-Input to Multiple-Output (MIMO) techniques with and without RS-coding have been employed to mitigate the effects of weak oceanic turbulence and beam attenuation. The novel closed-form analytical Bit Error Rate (BER) expressions of Single-Input to Single-Output (SISO), SIMO, MISO and MIMO links for un-coded and RS-coded cases have been computed using the hyperbolic tangent distribution and validated with Monte-Carlo simulation results. The obtained BER results show that the use of (63,51) RS-coded 4 × 5 MIMO UWOC system offers at-least 35 dB of transmit power gain compared with the un-coded SISO UWOC system at a BER of 10?5. Emerging technologies like the fifth-generation (5G) networks and the Internet of Underwater Things (IoUT) will have a high impact on UWOC as these systems require a high degree of information integrity, high data rates and energy efficiency when employed in conjunction with data transfer between underwater vehicles and objects. The proposed RS-coded MIMO UWOC system offers high reliability and power efficiency and it has the potential to be gainfully employed in IoUT applications. © 2020 Elsevier B.V.
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    Experimental demonstration and analysis of underwater wireless optical communication link: Design, BCH coded receiver diversity over the turbid and turbulent seawater channels
    (John Wiley and Sons Inc. P.O.Box 18667 Newark NJ 07191-8667, 2020) Naik, P.N.; Udupi, S.A.; Krishnan, P.
    In this article, we demonstrate an experimental underwater wireless optical communication (UWOC) system in the presence of air bubbles and weak turbulence for varying turbidity levels of the aquatic optical medium. The major limiting factors of the UWOC system are: absorption, scattering, and beam fluctuations; these effects can be mitigated by employing transmitter/receiver diversity schemes and channel codes. In this proposed system, we have employed receiver diversity (selection combining (SC), majority logic combining (MLC), and equal gain combining (EGC)) techniques augmented with Bose-Chaudhuri-Hocquenghem (BCH) codes to improve the performance of on-off keying modulated UWOC system. The bit error rate (BER) expressions are derived for the proposed system and results are validated using analytic and experimental means. The results show that the proposed system, that is, the receiver employing SC, MLC, and EGC receiver combining techniques augmented with the BCH code provides a transmit power gain of 4, 6, and 8 dB respectively, when compared with the uncoded single-input single-output system, at a BER of 10?5. © 2020 Wiley Periodicals, Inc.
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    Co-operative RF-UWOC link performance over hyperbolic tangent log-normal distribution channel with pointing errors
    (Elsevier B.V., 2020) Naik, P.N.; Udupi, S.A.; Krishnan, P.
    In this paper, we have proposed an analytic model and determined the outage probability and average bit error rate (BER) performance of a co-operative radio frequency ? underwater wireless optical communication (RF?UWOC) system. In recent years, UWOC has attracted attention as a useful enabler of underwater activities such as climate and ocean monitoring, surveillance, ocean exploration, underwater wireless optical sensor networks (UWOSN) and internet of underwater things (IoUT) because of its high speed, ease of deployability and wide bandwidth availability which is free of licensing fees. The proposed co-operative RF–UWOC system is designed to establish a connection between an underwater vehicle inside the ocean to a terrestrial ground station using decode?forward and amplify?forward relays. The RF link between the terrestrial ground station to relay is modeled as a Rayleigh distributed channel. The UWOC link between the relay to the underwater vehicle is modeled as being perturbed by the hyperbolic tangent log-normal (HTLN) distribution. To the best of our knowledge, it is for the first time that the perturbations due to weak oceanic turbulence have been modeled using HTLN distribution. This distribution is a member of the class of log-normal distributions derived from hyperbolic tangent distribution. Novel closed-form expressions have been derived for the outage probability and average BER for various modulation techniques that can be employed in this system. The analytical results are evaluated and validated with Monte-Carlo simulations in the presence and absence of pointing errors. The results show that the impact of pointing errors in the RF-UWOC system is to impose an additional SNR penalty of at-least 10 dB to obtain a BER of 10?6 when compared with the system operating without pointing errors. © 2020 Elsevier B.V.
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    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).
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    Performance analysis of FSO based inter-UAV communication systems
    (Springer, 2021) Nallagonda, V.R.; Krishnan, P.
    Recently unmanned aerial vehicles (UAVs) gained considerable attention for recent potential applications like 6G, internet of things, disaster management applications etc. Especially inter UAV communications have an increased interest in low, medium, and high altitude platforms. Free space optical (FSO) communication plays a vital role in UAV communication to offer a high data rate, wider bandwidth, and secure transmission. In this paper, first time we introduced heterodyne detection (HD) in FSO based inter UAV communication. The outage and average bit error rate (BER) performance of the proposed system is analyzed and the results are compared with the existing Intensity modulation direct detection (IM/DD). We studied the impact of turbulence and pointing errors on BER and outage performance of the proposed system. The results are plotted for different system parameters such as Rytov Variance, field-Of-view, Transmitter UAV orientation ; receive UAV orientation, link range, and Beam width. The analytical results are validated with the monte-carlo simulations. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.