Device-Free Visible Light Sensing: A Survey

The latest advancements in visible light communication (VLC) technology have greatly facilitated the evolution of wireless sensing based on visible light, commonly referred to as visible light sensing (VLS) systems. Similar to other wireless sensing technologies, these systems can be categorized into two primary types: device-based (or active) and device-free (or passive), depending on whether targets, such as people or objects of interest, are equipped with an optical receiver (e.g., a photodiode or camera). By reusing the existing Light-emitting diode (LED) lighting infrastructure as transmitters in indoor environments, device-free VLS (DF-VLS) systems can help address the growing energy demands of ubiquitous sensing and communication in Sixth-Generation Wireless Networks (6G). This survey meticulously explores the landscape of DF-VLS technology, proposing a redefinition of the classification of VLS systems and delving into the existing literature in this domain. We conduct a comprehensive analysis of various DF-VLS sensing techniques, focusing on their diverse applications in the Internet of things (IoT). By closely examining the integration and utility of DF-VLS in IoT environments, we highlight the potential of this technology. Furthermore, we underscore critical open challenges that demand attention for the effective development of efficient DF-VLS systems. Finally, the paper outlines a future roadmap for DF-VLS systems, shedding light on potential directions this field may embark upon.