Tangential Power Allocation in NOMA-Based Visible Light Communications

Visible light communications (VLC) are considered a promising technology for the next generation of wireless communications. In this sense, non-orthogonal multiple access (NOMA) is one of the proposed transmission schemes for the fifth generation (5G) of communications and beyond to enhance the spectral efficiency and also to reduce interference. Due to the characteristics of VLC scenarios, the power allocation plays a major role in power-domain NOMA, in which the symbols intended to two or more users are transmitted in the same transmission resource, time and frequency, allocating distinct power to them. In this paper, we propose a novel power allocation strategy for VLC-NOMA referred to as tangential power allocation (TPA). Basically, the power allocation is calculated from the NOMA rate region based on the tangential point to the line parallel to the orthogonal multiple access (OMA) region. Simulation results show that the proposed TPA improves the relation between sum-rate and fairness among users in comparison with traditional power allocation for NOMA schemes.