On the LED Illumination and Communication Design Space for Visible Light Communication

Visible light communication (VLC) is a promising application for short-range wireless digital communications, presenting itself as a breakthrough for future lighting systems. The use of light emitting diodes (LEDs) as transmitters by modulating their light intensity requires the correct design from both illumination and communication perspectives. However, in face of worldwide efforts for efficient energy consumption, the modulation of light imposes an energy cost that VLC cannot avoid. It has been shown that the modulation of light intensity brings unavoidable extra power expense. Thus, this paper brings a deeper analysis of the LED concerning its operating limits and efficacy with joint illumination and VLC intended modulations. The study uses a static photometrical, electrical, and thermal model of the LEDs, in order to perform an analytical analysis regarding illumination and communication. Base modulation strategies supported by the IEEE 802.15.7 standard (PHY I and PHY II) were compared side-by-side with other classical modulation schemes, such as pulse amplitude modulation, phase shift keying, frequency shift keying, quadrature amplitude modulation, and orthogonal frequency division multiplexing, from an energy conversion point of view. The results mark the design space connecting a set of possible modulation schemes with the desired average total light flux. This analysis guides the selection of the modulation technique according to the available power for a VLC system when efficacy is constrained. Moreover, the results show that the thermal effects not only reduce LED efficacy, but also constrict possible operating conditions regarding VLC in terms of communication signal power.