A Power and Spectrum Efficient NOMA Scheme for VLC Network Based on Hierarchical Pre-Distorted LACO-OFDM

Recently, a hybrid multiple access (MA) scheme, non-orthogonal MA (NOMA) combined with orthogonal frequency-division MA (OFDMA), has attracted significant attention in the fifth-generation (5G) wireless communication due to its superior spectrum efficiency. However, the advantage of the hybrid MA scheme cannot be fully realized in visible light communication (VLC) networks, since current optical orthogonal frequency-division multiplexing (OFDM) technologies are unable to provide high spectrum efficiency and power efficiency at the same time. In this paper, a hierarchical pre-distorted layered asymmetrically clipped optical OFDM (HPD-LACO-OFDM) scheme is proposed for NOMA, which offers superior spectrum efficiency as well as high optical power efficiency. In HPD-LACO-OFDM, multiple layers of asymmetrically clipped optical OFDM (ACO-OFDM) signals are generated to fill the odd subcarriers successively, and the inter-layer interference is eliminated with successive signal pre-distortion. A comparison of the bit-error-rate (BER) performance between the traditional dc-biased optical OFDM (DCO-OFDM), the layered ACO-OFDM (LACO-OFDM), and the proposed HPD-LACO-OFDM scheme is experimentally performed. The results show that with the same signal power, the HPD-LACO-OFDM-based NOMA-VLC network shows the best BER performance, whereas the demand for direct current voltage is reduced by half of the signal voltage compared to the traditional DCO-OFDM-based NOMA-VLC network.