Passive visible light networks: Taxonomy and opportunities

Artificial lighting has been used mainly for illumination for more than a century. Only recently, we have started to transform our lighting infrastructure to provide new services such as sensing and communication. These advancements have two key requirements: the ability to modulate light sources (for data transmission) and the presence of photodetectors on objects (for data reception). These requirements assume that the system has direct control over the transmitter and receiver, as in any traditional communication system. But not all lights can be modulated, and most objects do not have photodetectors. To overcome these limitations, researchers are developing novel networks that (i) exploit passive light sources that cannot be directly modulated, such as the sun, and (ii) leverage reflections from the external surfaces of objects to create a new generation of sensing and communication networks with visible light that is sustainable and does not require active control over the system. In this survey, we propose a taxonomy to analyze state-of-the-art contributions. We also identify the overarching principles, challenges, and opportunities of this new rising area.