Performance Analysis of a Dual-Hop FSO–Vertical UOWC Link for Seamless Air-to-Underwater Connectivity

In this paper, an analytical model is proposed for a dual-hop Free Space Optical (FSO) and vertical Underwater Optical Wireless Communication (UOWC) system designed to achieve seamless connectivity between air and underwater environments. Novel closed-form expressions are derived for the average bit error rate (ABER) and outage probability (OP), and their accuracy is verified through Monte-Carlo simulations. The FSO link is modeled using the Malaga distribution, while the vertical UOWC link, influenced by temperature and salinity-induced multilayer turbulence variations, is modeled using the hyperbolic tangent log-normal (HTLN) distribution under weak underwater turbulence and the Gamma–Gamma (GG) distribution under moderate to strong underwater turbulence. The effects of pointing errors and attenuation losses in both atmospheric and underwater media are incorporated into the channel model. The proposed dual-hop optical wireless communication framework enables high-speed, reliable data transmission using a relay at the air–water interface, making it suitable for communication between aerial and underwater vehicles.