Underwater Communication Enabled by Visible Light Semiconductors: Toward Beyond 5G

To support seamless network coverage in the Beyond 5G (B5G) era, this paper proposes three practical approaches to extending terrestrial access networks into underwater environments using Underwater Optical Wireless Communication (UOWC) based on visible light semiconductors. First, a Radio-over-UOWC (RoUOWC) method enables low-power LPWA signals in the 920MHz band to be transparently transmitted underwater. Second, the application of G.hn technology facilitates gigabit-class optical wireless links exceeding 500Mbps using commercial OFDM-based chipsets. Third, a novel PON-UOWC hybrid architecture is proposed to support multi-terminal underwater access while retaining compatibility with existing OLT/ONU systems. These results demonstrate the feasibility of a cost-effective, scalable, and protocol-transparent underwater extension of terrestrial networks. The proposed methods offer promising pathways for future applications in smart aquaculture, marine infrastructure monitoring, and blue economy initiatives.