Three-Dimensional Transmission Based UOWC in Complex Underwater Environments

The burgeoning demand for underwater optical wireless communication (UOWC) necessitates robust and high-speed transmission links capable of complex underwater environments characterized by turbidity and turbulence. Previous research was mainly focused on static or simulated underwater channels, which do not adequately give the dynamic nature of real-world underwater environments. This work presents a comprehensive experimental demonstration of a three-dimensional (3D) transmission system equipped with wavelength division multiplexing (WDM), polarization multiplexing (PolMux), and orthogonal frequency division multiplexing (OFDM), designed to withstand the challenges posed by bubble-induced turbulence and different levels of turbidity. Specifically, two novel pairwise coding (PWC) techniques, i.e., joint frequency-domain PWC (JF-PWC) and 3D-PWC considering frequency, wavelength, and polarization domains, are proposed to balance the signal-to-noise ratio (SNR) discrepancies among subcarriers and wavelength/polarization subchannels caused by the impact of bubble turbulence and turbid water conditions. The experimental results demonstrate the robustness of 3D-PWC and JF-PWC against challenging underwater transmission environments, showing a significant advancement in the UOWC field and paving the way for reliable and efficient underwater communications.