Fairness-constrained sum-rate maximization in indoor MU-MISO VLC systems: a comparative study of RSMA, NOMA, and SDMA

Abstract

Visible light communication (VLC) has emerged as a strong candidate for beyond-5G and 6G systems due to its capability of providing both illumination and high-speed data transmission within the visible spectrum. Nevertheless, achievable rates in practical implementations are constrained by the modulation bandwidth limitations of light-emitting diodes (LEDs). To address the growing demand for higher data rates and efficient multi-user (MU) communication, advanced multiple access (MA) schemes must be investigated for indoor VLC systems. In this paper, sum-rate maximization problems are formulated for rate-splitting multiple access (RSMA), space-division multiple access (SDMA), and non-orthogonal multiple access (NOMA) by considering practical constraints such as fairness, providing a comprehensive fairness-constrained comparison that addresses a gap in the existing VLC literature for indoor MU-MISO systems. The resulting optimization problems are non-convex in nature. To solve these problems, particle swarm optimization (PSO) is utilized as a meta-heuristic approach. All numerical simulations are conducted in MATLAB. Numerical results demonstrate that RSMA achieves sum-rate performance comparable to NOMA while consistently outperforming SDMA, particularly in overloaded scenarios where SDMA cannot maintain reliable transmission. Furthermore, RSMA can achieve stable sum-rate performance under various fairness constraints, unlike NOMA and SDMA, whose performances fluctuate greatly depending on different fairness requirements and user distribution scenarios. Moreover, the performance gaps among RSMA, SDMA and NOMA can be more pronounced under different fairness constraints, which shows the robustness of RSMA for fairness-aware indoor MU-MISO VLC systems.