Performance Analysis of a High-Speed Hybrid UOWC-SMF-FSO System for Long-Distance IoUT Applications

The need for high-bandwidth, low-attenuation communication in underwater environments is driving the development of new technologies. The Internet of Underwater Things (IoUT) addresses this need by enabling underwater devices to communicate, sense, and transmit data. Hybrid optical communication systems, combining Underwater Optical Wireless communication (UOWC), Single-Mode Fiber (SMF), and Free-Space Optics (FSO), have emerged as promising solutions to overcome these challenges and achieve high-speed, long-distance transmission. In this study, we propose a hybrid UOWC-SMF-FSO system utilizing a Photodetector, Remodulate, and Forward Relay (PRFR) for efficient wavelength conversion from 532 nm (visible spectrum) to 1550 nm (infra-red spectrum) at the water-fiber-air interface. System performance is evaluated under varying underwater distances, data rates, and water types. Key metrics such as Bit Error Rate (BER), Quality-factor (Q-factor), and eye diagrams are used to analyze the robustness and reliability of the proposed system. The results demonstrate that the hybrid system achieves at BER below threshold <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(3.8\times 10^{-3})$</tex> an overall transmission range of up to 2035 m (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$35\mathrm{m}$</tex> underwater range + 1000 m SMF length <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$+1000\mathrm{m}$</tex> FSO range) in Pure Seawater (PW) at 10 Gbps, with decreasing ranges for Clear Ocean (CL) and Coastal Ocean (CS) water types due to higher attenuation. These findings pave the way for the development of high-capacity underwater sensor networks and contribute significantly to the advancement of IoUT application.