Underwater Omnidirectional SLIPT for Integrated Space-Air-Ground-Ocean 6G Networks

Integrating the ocean segment is essential to realizing the sixth-generation (6G) vision of space-air-ground-ocean (SAGO) networks, yet progress remains constrained by limited connectivity and poor energy sustainability. To address these challenges, we develop an underwater omnidirectional simultaneous lightwave information and power transfer (SLIPT) architecture with two coupled components. First, we propose a harmonic-roundness framework for omnidirectional SLIPT cellular architecture, linking array geometry to coverage uniformity, capacity, and fairness. Second, using a photovoltaic-receiver model that characterizes energy harvesting and small-signal communication, we derive the energy-harvesting and communication Pareto frontier and its achievability proof. Together, these two components enable a practical underwater SLIPT cellular architecture for alignment-free simultaneous energy and data transfer. Experimentally, a hexagonal omnidirectional transmitter used as a cellular base station attains 98.15% roundness. With the omnidirectional base station and a photomultiplier tube receiver, a 5-m underwater link delivers 142.3 Mbps. With a 450-nm laser and a photovoltaic panel, a 5-m link achieves 100 Mbps while simultaneously harvesting 67.75 mW, an order-of-magnitude improvement over prior work.With the omnidirectional base station and a photovoltaic panel over a 0.5-m underwater channel, the link simultaneously sustains 13 Mbps and harvests 0.02 mW. An orthogonal frequency division multiple access (OFDMA) demon-stration with two users yields a Jain’s index of 0.85, providing initial experimental support for equitable multiuser performance. These results support harmonic-roundness-driven SLIPT with photovoltaic receivers as a promising cellular architecture for self-power underwater networking and as a potential building block for future SAGO 6G networks.