Effects of LED Non-linear Response and Waveform Settings on Multi-Cell VLC System Deployments

Abstract

Visible light communication (VLC) offers the opportunity to provide services with new requirements, when compared to the ones offered so far by radio wireless technologies almost exclusively. The idea behind VLC is to re-use the light signal, currently utilized for illumination purposes only, to transfer information wirelessly. Light-emitting diodes (LEDs), which are the natural sources of light for VLC due to their fast time response and high energy-efficiency, are devices with a notable non-linear response. A current trend to improve the achievable data rate of the VLC links relies on the use of linear waveforms, instead of just using On-Off Keying, which is robust against LED non-linearities but difficult to adapt to the variable VLC link conditions. Since having a linear transfer function is important when using efficient waveforms such as orthogonal frequency division multiplexing (OFDM), this paper starts by modelling the voltage-versus-current response of commercial LEDs. Then, the derived model is used to identify the guidelines that new VLC prototypes should fulfill. In particular, this paper focuses on the strength of the communication signal, compared to the light source optical power, and shows the way in which these parameters affect the coverage range of a multi-cell VLC system. The effect that these key design parameters have on the VLC link are identified, based on a real experimental setting, as they are difficult to model accurately due to the complex non-linear nature of LEDs when working in highly energy-efficient regimes.