The Investigation of Underwater Wireless Optical Communication Channel Fading in Multi-size particles, bubbles, and turbulence

Underwater wireless optical communication (UWOC) has emerged as a high-bandwidth, low-latency technology for marine applications, such as sensor networks, autonomous underwater vehicles (AUVs), and the Internet of Underwater Things (IoUT). However, the underwater channel faces severe impairments from absorption, scattering, turbulence due to temperature and salinity gradients, and bubbles from wave breaking or biological activity. These cause beam wandering, scintillation, beam spreading, link misalignment, inter-symbol interference (ISI), and signal loss, limiting effective ranges in turbid waters. Accurate modeling of these combined effects is vital for optimizing modulation, error correction, and system reliability. This study combines experimental and numerical approaches to evaluate the performance of UWOC channels under the influence of bubbles, turbulence, absorption, and scattering. Experimentally, small bubbles are produced via microporous ceramics, while turbulence is induced by propeller rotation to mimic real disturbances. Numerically, a composite model employs Monte Carlo simulations and ray tracing, integrating phase screen methods and Mie theory to simulate scattering from multi-size particles in turbulent conditions. UWOC systems are tested with intensity modulation/direct detection (IM/DD) using OOK, BPSK, QPSK, and 16-QAM modulations. Findings show synergistic degradation: turbulence exacerbates scattering by changing photon angular distributions, heightening scintillation and path distortion. Bubbles have a more pronounced impact than turbulence, leading to higher channel unreliability. The study quantifies how parameters like bubble count, turbulence strength, scattering level, distance, and aperture size affect scintillation index and bit error rate (BER). These results provide critical insights for enhancing underwater optical networks, wake tracking, and IoUT in harsh environments.