Underwater Acoustic Modem for a MOrphing Distributed Autonomous Underwater Vehicle (MODA)

In the last ten years several simulation studies on Autonomous Underwater Vehicle (AUV) swarm fleet formation have been performed, and some preliminary sea demonstrations of proof-of-concept prototypes were carried out. However, their actual realization is hindered on one side by the high cost of acoustic modems, whose price can easily exceed that of small AUVs, and, on the other side, by the difficulties of keeping track of the vehicles' positions due to the long latency required by traditional round trip time ranging measures. One-way travel-time (OWTT) halves the latency, at the cost of a high precision oscillator, such as an atomic clock or an oven controlled crystal oscillator, installed in the modem processing unit. In this work we present the design of a low-cost software-defined acoustic modem developed with off-the-shelf components and a low-complexity integration. We also present an analysis on how to perform OWTT depending on the mission duration and the requirements in ranging precision. The results obtained from a tank test of the modem proof-of-concept prototype proved the effectiveness of the design choices, encouraging us to move towards further implementation and realize a prototype with a higher technology readiness.