Joint User-Subcarrier Pairing and Power Allocation for Uplink ACO-OFDM-NOMA Underwater Visible Light Communication Systems

Underwater visible light communication (UVLC) is a promising technique to provide high-speed data transmission in the water. Since it is quite difficult to supply power to the underwater devices in the complex and severe marine environment, energy consumption would be a main consideration in the practical deployment of UVLC system. In this article, we investigate an asymmetric clipped optical orthogonal frequency division multiplexing and non-orthogonal multiple access (ACO-OFDM-NOMA) scheme for the uplink UVLC system to realize energy saving and support massive device connectivity. A mixed integer nonlinear programming problem of jointly optimizing the user-subcarrier pairing and power allocation is formulated to maximize the system utility. To tackle this problem, we propose a low-complexity iterative algorithm to obtain an optimal solution. Simulation results verify that the proposed algorithm converges quickly, and the uplink ACO-OFDM-NOMA system using the proposed algorithm has better utility compared to the uplink ACO-OFDM-NOMA system using the greedy algorithm and the traditional uplink ACO-OFDM access (ACO-OFDMA) system.