INTEGRATION OF VISIBLE LIGHT COMMUNICATIONS TRANSCEIVERS INTO SWITCHED-MODE POWER SUPPLIES

Abstract

The rise of IoT devices has increased RF spectrum demand, causing congestion and interference issues. As a solution, Optical Wireless Communications (OWC) uses unregulated IR, visible, and UV wavelengths. Visible Light Communication (VLC) is a practical OWC subset, benefiting from LEDs used in lighting due to their energy efficiency, affordability, long lifespan, and dimming capabilities. Integrating VLC into luminaires should not compromise these LED features and must meet optical communication wireless standards. An effective VLC system requires both downlink and uplink capabilities, compatibility with standards, and support for fronthauling and backhauling. Implementing this in LED luminaires while preserving light quality is challenging.

This thesis addresses this process by proposing a general approach to integrate VLC functionality into the LED drivers (power converters) present in all luminaires. Firstly, this work proposes the replacement of Schottky diodes conventionally found in a buck/boost converter with LEDs. These devices are referred to as light-emitting commutating diodes (LECD). The LECDs enable data transmission through simple modulation techniques such as pulse position modulation (PPM) or overlapping pulse position modulation (OPPM) while also contributing to the total light output of the luminaire. Importantly, since only the LECDs are modulated for data transmission, the lifespan of the LEDs used for illumination is extended, and the risk of color shift is reduced. As a result, this approach successfully integrates a VLC transmitter into the LED driver while improving the efficacy of the boost converter up to 15\% in comparison with a conventional boost converter.

Secondly, the integration of the VLC transmitter into LED drivers is further improved by utilizing the metal-oxide-semiconductor field-effect transistor (MOSFET) in a boost LED driver as both an amplifying and switching device. Specifically, the gate signal of the MOSFET is modified to bias it into saturation when the MOSFET is off, allowing it to function as an amplifier. Despite this modification, the MOSFET remains off from the perspective of the LED driver, ensuring that its operation is not disrupted. This approach eliminates the need for an inefficient linear power amplifier, allowing the data to be amplified and injected into the system directly through the MOSFET. This method supports advanced modulation schemes specified in current standards such as orthogonal frequency division multiplexing (OFDM) while maintaining simplicity and efficiency, thus outperforming current methods without requiring complex control schemes or additional components. The prototype of the proposed topology achieves a data rate of 3.84 Mbps using 64-QAM ACO-OFDM with 256 subcarriers, delivering an efficacy improvement of 6.25\% compared to conventional VLC-enabled luminaires.

Finally, the thesis addresses the uplink channel and optical fronthauling and backhauling in VLC systems by developing an optical wireless repeater integrated into a luminaire. This is achieved by replacing the diodes of a multiphase boost converter with photodiodes which develops a power converter specifically for VLC applications. This system enables amplification and retransmission of received optical signals while simultaneously addressing uplink and fronthauling and backhauling. A prototype featuring 7 LEDs and 1 photodiode in each phase of a 2-phase boost converter is implemented, demonstrating an optical amplification factor of 8.5 dB for infrared signals with a mean optical power of 1–10 mW. Unlike previous approaches which handle these functions separately, this configuration integrates them into a single system, thereby simplifying the overall design by consolidating multiple functions into one.