Real-time FPGA-based half-duplex underwater wireless optical communication system with high-loss link

Underwater wireless optical communication (UWOC) is a promising technology because of its high transmission rate, low latency, and small volume advantages. Therefore, it has drawn a lot of attention for real-time underwater wireless communication (UWC), especially for large-capacity transmission under short and medium distances. In this paper, we designed a real-time UWOC system with blue/green light sources and high-sensitive multi-pixel photon counters (MPPC), which can achieve an 8-Mbps half-duplex UWOC link in a standard 50-m swimming pool. Specifically, orthogonal frequency division multiplexing (OFDM) modulation was deployed and realized using a field programmable gate array (FPGA) to complete real-time signal processing. Moreover, we have also analyzed the transmission stability under misalignment of the optical axis. Under an inclination no more than 2° for the blue-light receiver or an inclination no more than 7° for the green-light receiver, the 8-Mbps communication link was always steady, and the measured bit error ratios (BER) were both below 1×10⁻⁴. The results reveal that the proposed scheme can be beneficial to the real deployment of UWOC.