Real-time UWOC miniaturized system based on FPGA and LED arrays and its application in MIMO

In order to alleviate the impact of turbulence on the performance of underwater wireless optical communication (UWOC) in real time, and achieve high-speed real-time transmission and low cost and miniaturization of equipment, a 2 x 2 real-time multiple-input and multiple-output (MIMO) high-speed miniaturized UWOC system based on a field-programmable gate array (FPGA) and a high-power light-emitting diode (LED) array is designed in this Letter. In terms of multiplexing gain, the imaging MIMO spatial multiplexing and high-order modulation for the first time are combined and the real-time high-speed transmission of PAM-4 signal based on the LED array light source in 12 m underwater channel at 100 Mbps rate is implemented, which effectively improves the throughput of the UWOC system with a high-power commercial LED light source. In light of diversity gain, the system employs the diversity of repeated coding scheme to receive two identical non-return-to-zero on-off keying (NRZ-OOK) signals, which can compensate the fading or flickering sublinks in real time under the bubble-like simulated turbulence condition, and has high robustness. To our knowledge, this is the first instance of a high rate and long-distance implementation of a turbulence-resistant real-time MIMO miniaturized UWOC system based on FPGA and high-power LED arrays. With spatial diversity or spatial multiplexing capabilities, its low cost, integrity, and high robustness provide the system with important practical prospects.