Optimization of LED Semi-Angle in Multipath Indoor Visible Light Communication Links

Indoor visible light communication (VLC) combines illumination and data transmission, thereby facilitating green and sustainable energy solutions. However, due to the diffuse nature of white light emitting diodes (LEDs), the received optical power is spatially non-uniform which degrades the link performance. These spatial variations in power can be diminished by using LEDs with larger semi-angle but this increases the number of wall reflections leading to higher losses. Hence the average value of received power falls down resulting in a trade-off situation. In order to address this issue, we obtain an optimum value of semi-angle at which the received optical power has low spatial variations and a high average value in multipath VLC links. We discuss a recursive multipath channel model and show that it is sufficient to model up to second order reflections to adequately emulate the multipath effect in the optimization technique. We simulate the multipath VLC channel and study the effect of several practical factors like the order of reflections, transmitter configuration, wall reflectivity, transmitter-receiver separation and different optimization conditions. The results and analyses presented herein provide critical insights into the modelling of LED transmitters for indoor VLC.