Optimal Modulation Technique for Underwater Visible Light Communication Using Rolling-Shutter Sensor

The visible light communication (VLC) technique using a rolling-shutter sensor-based commercial camera has an advantage in that the LED and camera mounted on an underwater device (e.g., drone, sensor) can be effectively used as a transmitter (Tx) and a receiver (Rx), respectively, under water. On the other hand, a suitable modulation technique has not been well considered to realize a VLC system using a rolling-shutter sensor in an underwater channel that includes high ambient light conditions. In this paper, we design VLC systems using phase-shift keying (PSK), non-return-to-zero on- off keying (NRZ-OOK), and orthogonal frequency division multiplexing (OFDM), and evaluate them through simulations and experiments. The results suggested that the VLC system using PSK or OFDM is more resilient than that using NRZ-OOK in an underwater channel with low-frequency ambient light, and that a VLC system using PSK or NRZ-OOK is more tolerant than that using OFDM in environments with high ambient light, resulting in pixel saturation. In conclusion, the present study has demonstrated that PSK is the most suitable modulation technique for a VLC system using a rolling-shutter sensor in an underwater channel that includes high ambient light conditions.