Analog Underwater Backscatter: Networked Underwater Sensing at Microwatt Power Levels

Abstract

We present Analog Underwater Backscatter (AUB), the first technology for microwatt-level underwater wireless sensor networks. AUB departs from past underwater backscatter technologies in that it encodes sensor data directly into the physical layer through analog (frequency) modulation. Our design introduces multiple innovations that enable it to address challenges in practical underwater environments arising from mobility (Doppler shift) and the low-frequency carrier, which makes it vulnerable to small hardware imperfections. AUB’s design also introduces the first ultra-low-power wakeup receiver for underwater backscatter, enabling it to operate for a long time on small batteries. We built an end-to-end prototype of AUB and evaluated it in a river. Our evaluation demonstrates that AUB consumes 5.9 µW, 46× lower power than state-of-the-art past underwater backscatter systems. We also demonstrate AUB’s ability to sense two of the most important oceanographic vitals: temperature and depth.