PSK modulation for Underwater Communication and One-Way Travel-Time Ranging with the Low-Cost Subsea Software-Defined Acoustic Modem

What limits most the use of low-cost underwater unmanned vehicles is the lack of affordable and low-power acoustic modems and positioning systems able to provide satisfying performance, such as accurate distance measurement, a transmission range of at least several hundreds of meters, and datarate of a few kilobits per second. In fact, although low-cost modems are now available in the market, they usually provide a datarate of a few hundreds bits per second and may not be able to perform complex task such as One-Way Travel-Time (OWTT) ranging or adapt their communication parameters such as modulation and coding schemes. In contrast, the Subsea underwater acoustic software-defined Modem (SuM), recently developed by the University of Padova and SubSeaPulse SRL, is a flexible platform composed of a newly developed Raspberry Pi HAT analog frontend for underwater acoustic data transmissions and positioning. In this paper we present its inaugural sea trial campaign in fresh and salt water, where its ranging and communication abilities have been significantly tested. Results prove that the developed system is mature enough to be used in sea trials and provides good performance up to a range of several hundred meters when equipped with low-cost transducers, and of a few kilometers when used with professional transducers.