Sayed Saad Afzal, Jack Rademacher, Weitung Chen, Purui Wang, and Fadel Adib. 2025. Scalable and Low Power Localization for Underwater Robots. In Proceedings of the 31st Annual International Conference on Mobile Computing and Networking (ACM MOBICOM '25). Association for Computing Machinery, New York, NY, USA, 1075–1090. https://doi.org/10.1145/3680207.3765265

Abstract

Localization is a critical task for underwater robots, yet today's underwater localization systems are limited by their accuracy, scalability, and/or energy consumption (i.e., longevity). We present the design, implementation, and evaluation of EchoBLUE- an accurate, scalable, and low-power localization system for underwater robots.In EchoBLUE, an underwater robot transmits SONAR-style (FMCW) signals, and leverages ultra-low power underwater backscatter nodes as location anchors. EchoBLUE's design introduces two key innovations. The first is a novel doppler compensation mechanism that enables it to accurately self-localize under mobility: the technique employs a cross-chirp mechanism that exploits the quad-band nature of the resulting backscatter response to overcome the range-doppler ambiguity. Second, it introduces the first semi-active retrodirective underwater backscatter design and uses it for location anchors; this design achieves wide bandwidth to backscatter the full FMCW signal, enabling fine-grained localization.We implemented a proof of concept prototype of EchoBLUE by building a base station mounted on a BlueROV2 underwater robot and custom-designed low-power retrodirective location anchors deployed in a pool. Our evaluation across 700 real-world trials demonstrates that EchoBLUE achieves a median 3D localization accuracy of 28 cm and 90th percentile of 48 cm. Moreover, these anchors consume only 740 μW for semi-active backscatter, paving the way for truly low-power and scalable underwater localization.