Performance Enhanced Dual-Mode Index Modulation Ofdm with Oct Precoding in Vlc Systems

In this paper, dual-mode index modulation orthogonal frequency division multiplexing (DMIM-OFDM) enabled by orthogonal circulant matrix transform (OCT) precoding is proposed and experimentally demonstrated in visible light communication (VLC) systems. Since all available subcarriers are active to convey information bits, DMIM-OFDM can achieve higher spectral efficiency (SE) and energy efficiency (EE) than index modulation OFDM (IM-OFDM). In addition, to mitigate the uneven frequency-selective fading between different subblocks, channel-independent OCT precoding is applied to all subblocks to equalize the overall signal-to-noise ratio (SNR). The experimental results show that the DMIM-OFDM with OCT precoding outperforms the traditional IM-OFDM, DMIM-OFDM without precoding, and with DFT precoding at different SEs. For DMIM-OFDM VLC system with SE of 4.5 bit/s/Hz, by using OCT precoding, the receiver sensitivity improvement of 3 dB can be achieved at the bit error rate (BER) of 3.8e−3 after 3.5-m free-space transmission.