A Strategy for Reducing Interference in Underwater Optical Multi-beam Systems Based on NOMA

To address the severe issues of inter-beam and intra-beam interference in underwater multi-beam NOMA systems, we propose an adaptive transmit diversity strategy. We design an algorithm for adaptive selection and merging beams based on the degree of interference between beams in space, which merges LED beams with high interference. Diversity technology is used to reduce interference between beams, and spatial multiplexing is still performed between LED groups with low interference. Within the same beam, we use OFDM-NOMA scheme to match and group the users and send the signals of different user groups through different sub-carriers to improve the resource utilization. This enhances access capacity while reducing NOMA inter-user interference. Simulation results demonstrate that the adoption of the adaptive transmit diversity strategy in multi-beam NOMA systems effectively reduces interference and yields better bit error rate (BER) performance compared to multi-beam NOMA systems without interference management. Furthermore, we analyzed the BER performance of the system in a multi-user scenario, confirming the feasibility of this strategy for multi-user communication in multi-beam NOMA systems.