Yingqiang Wang | Searcharxiv

arXiv2025

Raspi$^2$USBL: An open-source Raspberry Pi-Based Passive Inverted Ultra-Short Baseline Positioning System for Underwater Robotics

Precise underwater positioning remains a fundamental challenge for underwater robotics because global navigation satellite system (GNSS) signals cannot penetrate the sea surface. This paper presents Raspi$^2$USBL, a Raspberry Pi-based passive inverted ultra-short baseline (piUSBL) positioning system that provides a low-cost, accessible, and reproducible platform for underwater robotic research. The system consists of a passive acoustic receiver and an active beacon. The receiver integrates a hydrophone array, multichannel preamplifier, oven-controlled crystal oscillator (OCXO), Raspberry Pi 5, and MCC-series data acquisition (DAQ) board. The beacon integrates a matching network, power amplifier, and transmitting transducer. An open-source C++ framework supports clock synchronization and triggering for one-way travel-time (OWTT) messaging, while performing matched filtering, array beamforming, and adaptive gain control to estimate the time of flight (TOF) and direction of arrival (DOA). The system was validated in an anechoic tank, a freshwater lake, and open-sea trials. Results demonstrate a slant-range accuracy better than 0.1%, a bearing accuracy within 0.1{\deg}, and stable performance over distances up to 1.3 km. These findings show that low-cost, system-level reproducible hardware can deliver research-grade underwater positioning accuracy. By releasing the software framework and providing a reproducible hardware architecture, Raspi$^2$USBL offers a reference platform that lowers the entry barrier for underwater robotics laboratories and promotes reproducible research in underwater acoustic navigation and swarm robotics.

cs.RO↗

arXiv2025

Precise Time Delay Measurement and Compensation for Tightly Coupled Underwater SINS/piUSBL Navigation

In multisensor systems, time synchronization is particularly challenging for underwater integrated navigation systems (INSs) incorporating acoustic positioning, where time delays can significantly degrade accuracy when measurement and fusion epochs are misaligned. This article introduces a tightly coupled navigation framework that integrates a passive inverted ultrashort baseline (piUSBL) acoustic positioning system, a strapdown inertial navigation system (SINS), and a depth gauge under precise time synchronization. The framework fuses piUSBL azimuth and slant range with depth measurements, avoiding poor vertical-angle observability in planar arrays. By combining synchronized timing with acoustic signal processing, the proposed method transforms delay from an unobservable error into a measurable parameter, enabling explicit quantification of both acoustic propagation and system processing delays. Field experiments demonstrate that the proposed approach reduces position RMSE by 44.02% and maximum error (MAXERR) by 40.79% compared to the uncompensated baseline while achieving further RMSE reductions of 37.66% and 35.82% in horizontal directions relative to filter-based delay compensation. The results confirm that explicit delay measurement outperforms filter-based estimation though instantaneous performance remains sensitive to acoustic signal quality, emphasizing the need for robust signal processing alongside accurate time synchronization in latency-sensitive multisensor systems.

cs.RO↗