Faculty Publications
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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 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 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.