Retro-VLC: Enabling Battery-free Duplex Visible Light Communication for Mobile and IoT Applications

The ubiquity of the lighting infrastructure makes the visible light communication (VLC) well suited for mobile and Internet of Things (IoT) applications in the indoor environment. However, existing VLC systems have primarily been focused on one-way communications from the illumination infrastructure to the mobile device. They are power demanding and not applicable for communication in the opposite direction. In this paper, we present RetroVLC, a duplex VLC system that enables a battery-free device to perform bi-directional communications over a shared light carrier across the uplink and downlink. The design features a retro-reflector fabric that backscatters light, an LCD modulator, and several low-power optimization techniques. We have prototyped a working system consisting of a credit card-sized battery-free tag and an illuminating LED reader. Experimental results show that the tag can achieve 10kbps downlink speed and 0.5kbps uplink speed over a distance of 2.4m. We outline several potential applications and limitations of the system.