Development of the "Seatrac" miniature acoustic modem and USBL positioning units for subsea robotics and diver applications

As part of the EU FP7 project CADDY, an efficient and reliable acoustic communication network is required to connect a diver, autonomous underwater vehicle (AUV) and surface vehicle (ASV) working cooperatively. This paper describes the development of the modulation, receiver algorithms and miniature hardware platform for multi user communication and simultaneous positioning. Experiments using vehicles in the Adriatic, North Sea, enclosed docks and lakes have demonstrated reliable communication and positioning using a 100bps chirp based signaling scheme. Equally promising results are presented for experiments with a 1.4kbps direct sequence spread spectrum (DSSS) variant, currently being implemented on the same platform, which demonstrates remarkable tolerance of extreme multipath channels and noise using a relatively low complexity receiver algorithm.