Multiple Access for Downlink Multi-User VLC System: NOMA or OMA User Pairing?

Non-orthogonal multiple access (NOMA) is regarded as one of the primary enabling candidates for fifth-generation cellular systems. In this letter, we compare NOMA with orthogonal multiple access (OMA) for visible light communication (VLC) systems, and show that the relationship between NOMA and OMA in VLC is different from that in radio frequency (RF) systems, since the traditional Shannon formula is not suitable for expressing the system capacity of VLC. Moreover, we propose a hybrid NOMA and OMA scheme for VLC according to two user pairing guidelines. In order to maximize the achievable sum rate, a permutation-based genetic algorithm with low complexity is proposed to optimize user pairings in the hybrid NOMA and OMA scheme. Simulation results demonstrate that considerable performance gains can be achieved by the proposed genetic algorithm compared to other baseline schemes.