Abstract

Can we build a battery-free underwater GPS? While underwater localization is a long-studied problem, in this paper, we seek to bring it to battery-free underwater networks. These recently introduced networks communicate by simply backscattering (i.e.,reflecting) acoustic signals. While such backscatter based communication enables them to operate at net-zero power, it also introduces new and unique challenges for underwater localization. We present the design and demonstration of the first underwater backscatter localization (UBL) system. Our design explores various challenges for bringing localization to underwater backscatter, including extreme multipath, acoustic delay spread, and mobility. We describe how an adaptive and context-aware algorithm may address some of these challenges and adapt to diverse underwater environments (such as deep vs shallow water, and high vs low mobility). We also present a prototype implementation and evaluation of UBL in the Charles River in Boston, and highlight open problems and opportunities for underwater backscatter localization in ocean exploration, marine-life sensing, and robotics.