Advanced Modulation Formats in Phosphorous LED VLC Links and the Impact of Blue Filtering

A theoretical model for transmission of advanced modulation schemes [pulse amplitude modulation (PAM), carrierless amplitude-phase (CAP), and discrete multitone (DMT)] in visible light communications (VLC) link using white phosphorescent LEDs is presented. The model extends and adapts the Randel et al., framework for advanced modulation format transmission in intensity-modulated direct-detection for the VLC channel. The main contributions are: CAP modulation, effect of transmit signal spectral shaping in PAM and CAP, analytical calculation of crest factor for CAP, and analysis of inter-symbol and cross-carrier interference due to an insufficient cyclic-prefix in DMT. Based on this model, the impact of blue filtering at the receiver is studied in the context of spectrally efficient modulation formats. The results indicate that blue filtering has a marginal effect on the performance for all the investigated modulation formats, while PAM with decision feedback equalizer shows the best performance. Without blue filtering, slightly higher data rates can be achieved, but at a price of extensive signal processing.