Bias Point Optimisation in LiFi for Capacity Enhancement

In this paper, we investigate methods to optimise the bias point of an LED to benefit from increasing bandwidth at higher driving current while minimising the resulting signal distortion. The approaches are based on allowing for some nonlinear distortion or to reduce signal swing/signal-to-noise ratio while benefiting from higher bandwidth at higher driving currents. A framework is presented to estimate the attainable capacity under both conditions. We also experimentally validate the optimisation with a PAM-4 based VLC system. The experimental results show that for a $40\,\mathrm{mA}$ dynamic range VLMB1500 LED used, the optimum bias point is not in the middle of the dynamic range but at $31\,\mathrm{mA}$ .