Researchers at Boston University have developed a technique to increase visible light communication (VLC) data transmission rates by 20 megabits per second. Using an approach called overlapping pulse-position modulation to control dimming and data transmission, John E. Gancarz, Hany Elgala, and Thomas D.C. Little found that this novel approach resulted in a gain of data throughput over similar, two-level schemes, according to an article just published in the Journal of Solid State Lighting.

The synthesis of visible light communication (VLC) and lighting state control necessitates data-light modulation that can accommodate intensity control. A number of techniques that enable both optical wireless data transmission and intensity control of light-emitting diodes (LEDs) have been proposed as a response to this need. Relevant schemes leverage amplitude modulation (AM)/continuous current reduction (CCR) and/or pulse-width modulation (PWM) for dimming capability. In this paper, the authors survey and compare the most commonly-investigated two-level techniques: on-off keying with compensation time (OOK + CT), variable pulse position modulation (VPPM), and multiple pulse position modulation (MPPM).

They then propose a novel approach towards dimming and data transmission through the variation of codeword weights in overlapping pulse-position modulation (OPPM). The proposed approach has comparatively high spectral efficiency. Using realistic constraints of a practical VLC system, their analysis reveals that OPPM can increase data rates by more than 20Mbps over expected performance of related, two-level schemes, when using LEDs suitable for lighting that have relatively low modulation bandwidths.

Full details of the study are here.