Scalable and Low Power Localization for Underwater Robots

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 SONARstyle (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 rangedoppler 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.