Experimental demonstration of positioning the cooperation terminal for underwater wireless optical communication based on visual navigation

Abstract

Underwater wireless optical communication (UWOC) is a useful way to transmit a large volume of data in ocean engineering. In application, one of the UWOC terminals is usually carried on an underwater robot to actively adjust its orientation and position to establish an optical link, which requires the mobile terminal to locate the cooperation partner. At a short communication distance, visual navigation is a preferred method to measure the position. In this method, a camera is installed on the mobile terminal while several light-emitting diodes (LEDs) are in the cooperation one. In the image of the camera, by capturing the pattern formed of LEDs light spots, the relative position and orientation between terminals could be calculated. However, in a UWOC system, visual navigation is interfered with by the UWOC transmitter since it forms an additional light spot in the camera’s image. To solve this issue, we present a UWOC-compatible visual navigation method, in which the UWOC light spot is distinguished with the hue, saturation, and value (HSV) color model. Then, we experimentally demonstrate the effectiveness of the method in a pool, applying signals with different bitrates and power on the transmitter. The results show that, while the distance between terminals is within 350 cm and the yaw angle is within 5°, the measured errors are within 1.77 cm and 0.92°, respectively, which is accurate enough for most UWOC applications. The method presented in this paper is simple, pragmatic, and useful for establishing a UWOC link.