Experimental Demonstration of Multi-user OFDM-NOMA Based VLC Transmission

In multi-user visible light communication (VLC) systems, non-orthogonal multiple access (NOMA) combined with DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) is a promising method for improving spectral efficiency. This study presents the practical implementation of a two and three-user NOMA-OFDM-based VLC system, utilizing a laser diode (LD) as the transmitter and a avalanche photodiode (APD) as the receiver. In the three-user configuration, users positioned at $0.5 \mathrm{~m}, 1 \mathrm{~m}$, and 1.5 m are simultaneously served, while in the two-user configuration, users are positioned at $1 \mathbf{m}$ and 2 m from the transmitter. For the two-user case, net data rates of 48.18 Mbps and 96.36 Mbps were achieved using binary phase shift keying (BPSK) and quadrature amplitude modulation (QAM-4) respectively. In the three-user case, data rates of 72.27 Mbps and 144.54 Mbps were achieved using BPSK and QAM-4. For both scenarios, the bit error rate (BER) remained below the target threshold of $10^{-3}$. In the three-user configuration with QAM-4 modulation and a power allocation ratio of $\mathbf{0 . 7 2}$ for the far user, 0.18 for the middle user, and $\mathbf{0 . 0 5}$ for the nearest user, the required optical power levels to achieve the target BER are $-31 \mathrm{dBm},-29.5 \mathrm{dBm}$, and -28 dBm, respectively.