Underwater Visible Light Mobile Communication Using a Gain Feedback Control Method With Dynamic Threshold

In underwater visible light communication (UVLC) systems, it is important to support mobility of transceivers and enhance both the dynamic range of communication distance and the field of view (FOV) because the received optical power experiences significant variations when the transmission distance changes due to substantial intrinsic absorption of water. In this paper, we propose an UVLC system with mobility of transceivers using a gain feedback control (GFC) method with dynamic threshold, which obtains significant improvements in both the dynamic range of communication distance and FOV. In experiments, we achieved duplex mobile video transmission at a data rate of 5.0 Mb/s while moving at a speed of 0.21 m/s. Real-time duplex video transmission with a resolution of 800 × 600 pixels was realized at a distance ranging from 1.3 m to 5.6 m. The dynamic range of communication distance can be increased by a factor of 10.0 and 10.5 in comparison with the system without GFC at forward bias currents of 0.3 A and 0.35 A, respectively. In addition, the receiving FOV angle of the system is increased by a factor of 1.9.