Hybrid visible light communication for cameras and low-power embedded devices

Abstract

Visible light communication (VLC) between LED light bulbs and smart-phone cameras has already begun to gain traction for identification and indoor localization applications. To support detection by cameras, the frequencies and data rates are typically limited to below 1kHz and tens of bytes per second (Bps). In this paper, we present a technique for transmitting data from solid-state luminaries, used for interior ambient lighting, simultaneously to both cameras and low-power embedded devices in a manner that is imperceptible to occupants. This allows the camera communication VLC channel to also act as a higher speed downstream link and low-power wakeup mechanism for energy-constrained devices. Our approach uses Manchester encoding and Binary Frequency Shift Keying (BFSK) to modulate the high-speed data stream and applies duty-cycle adjustment to generate the slower camera communication signal. We explore the trade-off between the performance of the two communication channels. Our hybrid communication protocol is also compatible with existing IR receivers. This allows lights to communicate with low-cost commodity chipsets and control home appliances such as TVs, AV receivers, AC window units, etc. We show that we are able to reliably simultaneously transmit low-speed data at 1.3 Bps to camera enabled devices and higher-speed data at 104 Bps to low-power embedded devices. Since the majority of energy in many RF communication protocols often goes towards media access and receiving, VLC-triggered wakeup can significantly decrease system energy consumption. We also demonstrate a proof-of-concept wakeup circuit that consumes less then 204uA and can be triggered in less then 10ms.