Bandwidth efficient multi-level MPPM encoding decoding algorithms for joint brightness-rate control in VLC systems

A number of binary modulation schemes are proposed for LED based Visible Light Communication (VLC) systems to jointly achieve data transmission and brightness control. These binary modulation based solutions are spectrally inefficient because they consider the LED light source as single device. We observe that most of the commercial LED lights use more than one LED per light source and the possibility of individual current control of these LEDs would provide better brightness control resolution as well as higher data transmission rates. To achieve this we propose multi-level multi-pulse position modulation block coding scheme to jointly control multiple LEDs providing flicker free VLC link. The brightness level of the light source is controlled based on the number of LEDs switched on simultaneously. New algorithms are developed for symbol encoding/decoding as well as to enumerate the maximum number of symbols that can be encoded for the selected brightness level and the number of levels. Improvement in spectral efficiency is analyzed and compared with the contending binary modulation schemes.