Downlink-Uplink Symmetry in Mobile Battery-Free Retro-Reflective VLC: Enabling Sensing-Assisted Communications

• Main Authors: Shao, Sihua, Salustri, Adrian, Heusser, Alexander, Khaniani, Hassan, Hassanalian, Mostafa, Roghanchi, Pedram
• Format: Conference Proceeding
• Language: English
• Subjects: backscatter communication; battery-free; Conferences; Curve fitting; Downlink; drone-assisted mine rescue; mobility; Photovoltaic cells; Prototypes; Sensing-assisted communication; Sensors; Uplink; visible light communication
• ISSN: 2694-2941
• DOI: 10.1109/ICCWorkshops59551.2024.10615381

Designing a mobile retro-reflective visible light communication (R-VLC) system presents significant challenges due to the rapid and substantial changes in uplink channel gain. These changes occur when the retro-reflective tag, crucial for the system's operation, is worn by a person in motion. Consider a scenario where an intelligent rescue drone is leading the assisted-escape for miners trapped due to an accident. The drone, equipped with a searchlight, facilitates duplex communication with the trapped miners via a batteryless R-VLC system. Despite the retro-reflective tag's unique ability to support self-alignment in the VLC system, the tag's orientation changes quickly as a miner moves. This movement induces significant variations in the uplink channel gain, which requires a fast adaptive modulation and coding scheme. In response to this challenge, our work involves prototyping an R-VLC system powered by photovoltaic cells. Based on Manchester-coded on-off keying, the communication distance achieves up to 6 meters. Through channel characterization and experimental validation, we demonstrate that the prototype can leverage the downlink photovoltaic cell sensing output to directly estimate the strength of the uplink retro-reflected signal. The symmetry between downlink and uplink allows for symbol-wise adaptation, crucial for effective sensing-assisted communication.