Demo: Coding with Superposed Reflection Light for LED-Camera Communication

As a popular approach to implementing Visible Light Communication (VLC) on commercial-off-the-shelf devices, LED-Camera VLC has attracted substantial attention recently. While such systems initially used reflected light as the communication media, direct light becomes the dominant media for the purpose of combating interference. Nonetheless, the data rate achievable by direct light LED-Camera VLC systems has hit its bottleneck: the dimension of the transmitters. In this demo, we revisit the reflected light approach and propose a novel modulation mechanism, ReflexCode, which converts the potentially destructive interferences into collaborative transmissions. Essentially, our ReflexCode system codes information by superposing light emissions from multiple transmitters. It combines traditional amplitude demodulation with slope detection to "decode" the grayscale modulated signal, and it tunes decoding thresholds dynamically depending on the spatial symbol distribution. In addition, ReflexCode re-engineers the balanced codes to avoid flicker from individual transmitters. We implement ReflexCode as a prototype and demonstrate that it can achieve a promising throughput.