ABSTRACT
This chapter provides an overview of the modulation schemes applied in visible light communications (VLC) systems. The description includes baseband modulations, multicarrier modulations, and special color-shift keying (CSK) for VLC. The baseband modulation schemes can be classified into: (i) pulse amplitude, (ii) pulse position, and (iii) pulse interval modulation depending upon the method used to encode information into the optical carrier. Variable pulse position modulation (VPPM) supports simultaneously illumination with dimming control and communication. It is a combination of pulse amplitude modulation (PAM) and pulse width modulation schemes. The chapter compares the different baseband modulation schemes in terms of power and bandwidth efficiencies. Orthogonal frequency division multiplexing (OFDM) signal is sensitive to nonlinear distortions, which cause intermodulation between the subcarriers. CSK is a special modulation method in VLC systems. Most VLC systems use a blue light-emitting diode (LED) and a yellow phosphor layer on LED which converts the blue light into white.
