Faculty Publications
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Item 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 GmbHItem 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.Item Performance analysis of RoFSO links with spatial diversity over combined channel model for 5G in smart city applications(Elsevier B.V., 2020) Kumar, A.; Krishnan, P.The smart city concept improves the lives of citizens and optimizes the efficiency of city operations, services through the integration of information and communication technology with the help of the internet of things (IoT) and 5G techniques. The bandwidth demand for 5G, smart city, and IoT applications are fulfilled with wireless optical communications. Particularly, radio over free space optical (RoFSO) communication establishes a very attractive choice for interconnecting central base stations with remote antenna units. In this paper, we consider the transmission of orthogonal frequency division multiplexing (OFDM) radio signals with quadrature amplitude (QAM) modulation format through a free space optical link using spatial diversity mitigation technique. The atmosphere is modeled as the combined channel model which takes into account atmospheric attenuation, turbulence, and pointing errors. The atmospheric turbulence and pointing errors are modeled by Malaga, Beckmann, and Rayleigh distributions. The novel closed form BER expressions are derived for the proposed QAM OFDM RoFSO link with spatial diversity. The results are analyzed and plotted for different weather conditions (clear, haze, light fog), turbulence regimes (weak, moderate, strong), misalignment (weak, enhanced), the order of QAM and number of transceivers. The proposed RoFSO system is highly useful for 5G in smart city applications. © 2020 Elsevier B.V.Item Bit error rate analysis of polarization shift keying based free space optical link over different weather conditions for inter unmanned aerial vehicles communications(Springer, 2021) Nallagonda, V.; Krishnan, P.The increasing availability of unmanned aerial vehicles (UAVs) is an exciting part of future emerging technology with advanced scientific and industrial interests. Free space optical (FSO) communications’ ability to offer very high data rates and the mobility of unmanned aerial vehicle (UAV) flying platforms make the delivery of Fifth-Generation (5G) wireless networking services appealing to FSO-UAV-based solutions. UAVs play a greater role in end-to-end delivery in next- generation wireless networking systems, serving as a base station, capacity enhancement, high data access, and other disaster management systems. To establish a link between unmanned aerial vehicles and ground stations, FSO can be applied. But, the different weather conditions liken rain, fog effects on the performance of the FSO link, contributing to the loss of the signal. In this paper, we proposed polarization shift keying (POLSK) modulated FSO link based UAV–UAV communication system for 6G beyond applications. We examine the effect of different weather conditions such as rain, fog on the bit error rate (BER) performance of the proposed system. Novel closed-form expressions for UAV–UAV based FSO propagation channel are derived, and BER performance is investigated under different weather conditions. Fog and rain are the main limiting factors mitigated in this paper by suitable mitigation techniques by increasing receiver field of view. © 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 enhancement of FSO communication system using machine learning for 5G/6G and IoT applications(Elsevier GmbH, 2022) Kumar, L.J.S.; Krishnan, P.; Shreya, B.; Sudhakar, S.6G networks will provide extremely high capacity and will support a wide range of new applications in the future, but the existing frequency bands may not be sufficient. Furthermore, because traditional wireless communications are incapable of providing high-speed data rates, 6G enables superior coverage by integrating space/air/underwater networks with terrestrial networks. 5G-and-beyond (5 GB) and 6G networks have been mandated as a paradigm shift to take the enhanced broadband, massive access, and ultra-reliable and low latency services of 5G wireless networks to an even more advanced and intelligent level, to meet the ever-growing quantities of demanding services. In 5G and 6G wireless communication systems, artificial intelligence (AI), particularly machine learning (ML), has emerged as an essential component of fully intelligent network orchestration and management. 5 GB and 6G communication systems will also rely heavily on a tactile Internet of Things (IoT). The diverse nature of heterogeneous traffic and the established service quality parameters in 5 GB networks will present numerous challenges. Many other wireless technologies, including free space optics (FSO), look promising for meeting the demands of 5 GB systems. FSO has been identified as a promising technology for achieving higher data rates while consuming less power. However, attenuation due to weather, pointing errors, and turbulences limits its performance. Traditional Maximum likelihood decoding techniques require prior channel information to decode the signals. in this paper, first time we proposed a novel decoding technique for decoding on–off keying (OOK) modulated FSO signals using support vector machines (SVM). The model is tested under various atmospheric weather conditions such as fog, rain, and snow, as well as turbulence and pointing errors. Simulated numerical results demonstrate that the proposed SVM-based decoding schemes are capable of mitigating attenuation, pointing error, and turbulent channel impairments. © 2021 Elsevier GmbHItem 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.Item A Low-Complexity Solution for Optimizing Binary Intelligent Reflecting Surfaces towards Wireless Communication(Multidisciplinary Digital Publishing Institute (MDPI), 2024) Janawade, S.A.; Krishnan, P.; Kandasamy, K.; Holla, S.S.; Rao, K.; Chandrasekar, A.Intelligent Reflecting Surfaces (IRSs) enable us to have a reconfigurable reflecting surface that can efficiently deflect the transmitted signal toward the receiver. The initial step in the IRS usually involves estimating the channel between a fixed transmitter and a stationary receiver. After estimating the channel, the problem of finding the most optimal IRS configuration is non-convex, and involves a huge search in the solution space. In this work, we propose a novel and customized technique which efficiently estimates the channel and configures the IRS with fixed transmit power, restricting the IRS coefficients to (Formula presented.). The results from our approach are numerically compared with existing optimization techniques.The key features of the linear system model under consideration include a Reconfigurable Intelligent Surface (RIS) setup consisting of 4096 RIS elements arranged in a 64 × 64 element array; the distance from RIS to the access point measures 107 m. NLOS users are located around 40 m away from the RIS element and 100 m from the access point. The estimated variance of noise (Formula presented.) is 3.1614 (Formula presented.). The proposed algorithm provides an overall data rate of 126.89 (MBits/s) for Line of Sight and 66.093 (MBits/s) for Non Line of Sight (NLOS) wireless communication. © 2024 by the authors.