Subcarrier and Power Allocation in OFDM-NOMA VLC Systems

We propose a novel subcarrier and power allocation method to improve both the throughput and user fairness in orthogonal frequency division multiplexing non-orthogonal multiple access visible light communication (OFDM-NOMA VLC) systems. The proposed method considers various constraints in practical VLC systems, including bandwidth limitation, non-negative optical signal, peak power for eye safety, and quality of service. The method adopts the log utility function to improve the user fairness and is applicable to cases where the number of multiplexed users on each subcarrier is not equal to the total user number due to the decoding complexity of NOMA. The problem is generalized as a non-convex one and is solved by the genetic algorithm. Monte Carlo simulations show that at a signal to interference noise ratio of 2.5 dB, the throughput of the proposed method is 11%, 22%, and 125% higher than the conventional enhanced power allocation, the fixed power allocation, and the gain ratio power allocation algorithms, while the fairness is improved by 23%, 30%, and 49%, respectively.