Experimental Validation of Inverse M-PPM Modulation for Dimming Control and Data Transmission in Visible Light Communications

A hybrid-coding scheme based on Multi-Pulse Position Modulation (M-PPM) and Pulse Width Modulation (PWM) is proposed and experimentally validated for simultaneous control of illumination and data transmission in a visible light communication system VLC (Visible Light Communications). The implemented VLC system complies with the dual functionality of indoor lighting and data transmission using low cost components. The codification implemented allows data transmission at a constant speed despite the lighting levels supported by the VLC system. The proposed and experimentally validated coding solves the problem of the interdependence between the data transmission rate and the variation of the lighting levels. Such interdependence is caused by the variation of the useful cycle available for data transmission after the lighting control performed by PWM.In this work, the feasibility of the implementation of the proposed scheme is demonstrated using low cost elements and commercial photodetectors. A constant transmission speed of 30 kbit/s was obtained with two 10W RGB LEDs at 0.9 meters from the OPT101 photodetector from Texas Instruments, with a range of illumination ranging from 25\% to 85\% of the possible luminous power of the LED sources.