Experimental Demonstration of High-Speed 4 × 4 Imaging Multi-CAP MIMO Visible Light Communications

In general, visible light communication (VLC) systems, which utilise white light-emitting diodes (LEDs), only offer a bandwidth limited to the lower MHz region. Therefore, providing VLC-based high data rate communications systems using VLC becomes a challenging task. To address this challenge, we propose a solution based on multiplexing in both the frequency and space domains. We experimentally demonstrate a 4 <inline-formula><tex-math notation="LaTeX"> ${\boldsymbol{\times }}$</tex-math></inline-formula> 4 imaging multiple-input multiple-output (MIMO) VLC system (i.e., space multiplexing) utilising multiband carrierless amplitude and phase (<italic>m</italic>-CAP) modulation (i.e., frequency multiplexing). Independently, both MIMO and <italic>m</italic>-CAP have separately shown the remarkable ability to improve the transmission speeds in VLC systems, and hence, here we combine them to further improve the net data rate. We investigate the link performance by varying the number of subcarriers <italic>m</italic> , link distance <inline-formula><tex-math notation="LaTeX">$\boldsymbol{L}$</tex-math></inline-formula>, and signal bandwidth <inline-formula><tex-math notation="LaTeX">$\boldsymbol{B_{\text{sig}}}$</tex-math></inline-formula>. From all the values tested, we show that a data rate of <inline-formula><tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula>249 Mb/s can be maximally achieved for <italic>m</italic> = 20, <inline-formula> <tex-math notation="LaTeX">$B_{\text{sig}}$</tex-math></inline-formula> = 20 MHz, and <inline-formula> <tex-math notation="LaTeX">$\boldsymbol{L}$</tex-math></inline-formula> = 1 m, at a bit error rate of <inline-formula><tex-math notation="LaTeX">${3.2\times 10^{-3}}$</tex-math></inline-formula> using LEDs with <inline-formula><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula>4 MHz bandwidth.