Experimental Comparison of PAM and CAP Modulation for Visible Light Communication Under Illumination Constraints

In this paper, we study different modulation techniques for visible light communication (VLC), taking illumination constraints into account. Two modulation schemes are compared, namely pulse amplitude modulation (PAM) and carrierless amplitude and phase (CAP) modulation, through both simulations and experimental measurements. The data link under study is based on low-cost components comprising a white light-emitting diode (LED) and a silicon PIN photodiode. Moreover, the proposed VLC system complies with illumination standards and limits the brightness level to that of a typical office room. The impact of the roll-off factor parameter, which is directly related to the total occupied bandwidth, and the maximum achievable throughput for PAM and CAP are studied. Moreover, adaptive postdistortion based on a Volterra series expansion is implemented to mitigate the effects of LED nonlinearity in practice. We also demonstrate that 8-PAM can outperform 64-CAP and discrete multitone (DMT) when the LED nonlinearity is adequately compensated.