Improving the modulation designs for visible light communications with signal-dependent noise

This article reviews the recent investigations on improving modulation designs for visible light communication (VLC) systems subject to signal-dependent noise (SDN). The existence of signal-dependent noise degrades the system performance and leads to modulation deficiency issues due to the constellation distortion caused by the SDN. For single-carrier systems, a joint constellation and threshold design was recently proposed to compensate the SDN, and it is re-analyzed in this article together with an improved design criterion based on the rotated minimum Euclidean distance (MIN-ED) that was employed to enhance modulation efficiency in multi-carrier systems. These design criteria are further ameliorated by optimizing the distance-range. Performance comparisons between improved and MIN-ED-based designs for VLC-SDN systems under communications and lighting constraints are also presented to illustrate the major limitations of current modulations. This article concludes with critical implementation challenges and future research opportunities.