DarkVLP: “Lights-Off” Visible-Light Positioning

Visible-light positioning (VLP) has been considered as a promising indoor positioning technology due to its high precision and low cost. However, current VLP techniques are greatly limited by the assumption that lights have to be turned on to emit shining light beams, which is not applicable to scenarios that do not need the illumination all the time. In this article, we design and implement a novel VLP system, DarkVLP, to achieve high-precision positioning when lights are “turned off.” The “turn off” state means lights emit the extremely low luminance that is imperceptible to human eyes. In order to realize such a system, we have to tackle nontrivial challenges in data encoding/decoding, modulation/demodulation, and positioning algorithm. Specifically, we propose the sliding rheostat-based modulation scheme to eliminate the need of a complex signal synchronization mechanism and landmark recognition algorithm at the receiver. We also propose the dual-photodiode-based positioning algorithm, which effectively mitigates effects of substantial signal strength fluctuation, to reliably achieve VLP. In the end, we design novel circuits and prototype our system DarkVLP on commercial off-the-shelf devices. The results of extensive experiments demonstrate that our DarkVLP system could achieve submeter precision under the extremely low luminance, which greatly broadens application scenarios of VLP.