Enhanced visible light communication modulators with dual feedback control

This paper presents a modulator for Optical Wireless Communication (OWC) via LEDs, controlled by a dual closed loop. While the potential communication speed and performance of OWC has received a lot of research attention, the design of appropriate modulator circuits has not been studied so widely. This paper addresses control aspects to minimize power losses and to ensure automatic adaptation to component spreads or aging, for ’high power’ LED emitters. We initially address a ’low bandwidth’ system, particularly suited for indoor camera-based detection and then a ’higher bandwidth’ one for LiFi data communication. In contrast to maximizing data throughput as it applies to high speed modulators, low speed modulators aim at high power and high efficiency in general lighting applications. Specifically, for the high-power modulator, we propose a control strategy that allows a wide range of combinations of LED types and LED power supplies. The power consumption of the modulator is minimized by voltage margin setting which is automatically adapt to the modulation and the LED type using the non-linear detector. The common industry practice is to use constant-current LED drivers for powering LEDs. After creating a theoretical framework of some generality to evaluate designs and control loops with rationals and verified models, we realize modulator designs that are supplied by constant current LED drivers and verify their performance by simulation and measurements.