This paper introduces a relay-assisted solution for downlink communications in a mixed system of Radio Frequency (RF) and Underwater Optical Wireless Communications (UOWC) technologies. During the initial downlink phase, data transmission occurs via RF link between hovering Unmanned Aerial Vehicle (UAV) and the floating buoys at the water surface. As fixed buoy acts as amplify-and-forward relays, the second UOWC link represents downlink signal transmission from the floating buoy to the underwater device. Best relay selection is adopted, meaning that only the buoy with the best estimated RF-based UAV-buoy channel will perform signal transmission to an underwater device. Analytical expression for the outage probability is derived and utilized to examine the system's performance behaviour for various UOWC and RF channel conditions.

翻译：本文针对射频(RF)与水下光无线通信(UOWC)混合系统中的下行链路通信，提出了一种中继辅助解决方案。在下行链路初始阶段，数据传输通过悬停的无人机与水面浮动浮标之间的射频链路进行。固定浮标作为放大转发中继，第二条UOWC链路则实现从浮动浮标到水下设备的信号下行传输。系统采用最佳中继选择策略，即仅选择具有最佳估计射频无人机-浮标信道的浮标向水下设备执行信号传输。本文推导了中断概率的解析表达式，并利用该表达式研究了不同UOWC和RF信道条件下系统的性能表现。