Path-loss Analysis and Link Design for Optical Wireless Communication Between Underwater and Aerial Drones

The common and well-accepted architectures for monitoring underwater (UW) environments involve UW drones for collecting information and fixed buoys to relay the information outside the water. Fixed buoys lead to some disadvantages, such as their high cost and limited coverage of UW devices. To address these problems, new architectures are considered in the literature, where the buoys are eliminated and instead aerial drones are used for collecting data from the UW ones. These architectures potentially lead to improved and more flexible UW monitoring and control. The existing literature for these novel architectures includes some channel models for optical wireless communication through the water-air (W-A) interface. The primary drawback of these models lies in the fusion of the received rays. Furthermore, the mathematical analysis is mostly carried out in 2D and then extended to 3D, leading to reduced modeling accuracy. In this paper, an accurate 3D ray-tracing solution is proposed for channel modeling and simulation of communication through W-A, where the rays observed at the receiver through multi-path are properly combined. Numerical analysis reveals insights and suggestions on optical channel gain variation over time, and also some conclusions on the overall communication system design, such as the best depth of UW devices and the best height of aerial drones.