Fine-grained spectral-efficient adaptive DMIM-OFDM for VLC via non-power-of-two constellation design

To address the issue of channel resource wastage caused by coarse spectral efficiency (SE) granularity in adaptive visible light communication (VLC) systems, this Letter proposes a fine-grained SE adaptive DMIM-OFDM scheme via non-power-of-two constellation design. Specifically, a concentric-circle-based non-power-of-two dual-mode constellation is designed to achieve integer SEs. Combined with conventional power-of-two constellations, it reduces the adaptation granularity from 1 bit/s/Hz to 0.5 bit/s/Hz, enabling more precise signal-to-noise ratio matching. Simulation and experimental results demonstrate that the proposed fine-grained scheme consistently outperforms the 1 bit/s/Hz granularity scheme, achieving a transmission rate gain of up to 7.45%.