An overview of the ASIMOV acoustic communication system

In the framework of project ASIMOV, an autonomous underwater vehicle and an autonomous surface craft cooperate to jointly carry out complex missions at sea. Exchange of positioning data between the two vehicles ensures that they remain vertically aligned, so that communication using underwater acoustic modems is most effective. Given the widely-varying speed and reliability requirements of traffic between the two vehicles, two distinct communication links were installed. One of them uses robust non-coherent modulation, but achieves at most 400 bps. The other is a high-speed coherent link that operates at 30 kbps, but can only be used in near-vertical configurations. This paper analyses the overall design constraints and options which ensure that the underwater vehicle may be contacted at all times. It also describes the hardware structure, as well as equalization, synchronization and coding algorithms that were used in the high-speed link.