On the Spectral Performance of Dimming-based Multilevel Modulation Schemes for VLC Systems

Dimming support is an essential feature of any practical visible light communication (VLC) system. In this paper, we study the spectral performance of two multilevel dimming-based modulation schemes, namely multiple pulse position modulation (MMPM) and overlapping pulse position modulation (OPPM). We quantify the bandwidth (BW) required by these schemes based on their power spectral densities (PSDs) derived in this work. We compare the different types of definitions used to quantify the BW requirement and determine the most precise definition that can be used for practical implementation of these schemes. We also obtain the number of symbols that can be transmitted using these schemes at different dimming levels. Moreover, we analyze the effect of dimming and number of slots on the PSDs and BW requirements of these schemes.