Dimming and Modulation for VLC-Enabled Lighting

Abstract

Advances in high brightness light emitting diode (LED) technology are enabling myriad applications in lighting including visible light communications (VLC) technology that has the potential to complement RF technology to provide wireless data access for indoor coverage. This chapter reviews various dimming techniques suitable for VLC, and presents an LED driver circuit architecture incorporating digitally controlled analog circuit blocks to deliver concurrent dimming control and data transmission for VLC-enabled lighting. To achieve this target, a bi-level pulse-width modulation (PWM) driving scheme is applied to enable data transmission during the “off” period of the LED drive current while concurrently providing dimming control. The proposed architecture is compatible with digital baseband modulation schemes and implements a mechanism for ease of integration with commercial off-the-shelf (COTS) LED drivers for VLC system realization. This chapter also discusses a dimming compatible analog baseband modulation scheme. The reverse polarity optical orthogonal frequency-division multiplexing (RPO-OFDM) is a recent approach to realize compatibility between any format of an analog OFDM signal suitable for optical transmission and the concept of a digital pulse-width modulation (PWM) technique for dimming control. We also describe an implementation of the RPO-OFDM approach as part of a wireless access testbed. Experiments reveal that bit-error and bit-rate performances are maintained over a wide range of dimming.