Performance Comparison of 2 x 120 OAM Polarized Hybrid Multiplexed FSO System in Heavy Rain and Wet-Snow Weather Conditions

Recently, different research articles have given more emphasis to the design of high-speed free space optical (FSO) links using various multiplexing techniques to achieve optimum long reach under adverse weather conditions. This research paper presents a spectral-efficient, robust design of a novel, 2 x 120 Gb/s, hybrid multiplexed FSO system based on orthogonal frequency division multiplexing (OFDM). The 16-QAM modulated multiplexed data is sent over the helical structure of the orthogonal laser modes to increase the optical link's capacity, whereas OFDM is used to mitigate the fading induced by the atmospheric turbulence. The in-phase (I) and quadrature phase (Q) based optical modulators, along with the digital signal processing (DSP) unit, are used at the receiver to take care the high-speed data below the acceptable FEC limit. The system performance is evaluated in terms of scatter plot, link distance, optical signal-to-noise ratio (OSNR), and received optical power under strong turbulence, heavy rain and snow conditions to achieve the maximum transmission range of 2.5 km for an acceptable threshold bit error rate of <=\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\le $$\end{document} 2 x 10-3. The simulation results illustrate the receiver sensitivity of - 21.71 dBm and OSNR requirements of 32.98 dB for the B2B case under clear weather conditions.