Multi-User Broadcast Acoustic Positioning System

This paper describes work to investigate a true multi-user underwater acoustic positioning network based on the continuous broadcast of low power, spread spectrum signals from 3 or more surface nodes synchronised by Global Positioning System (GPS) reception. The ultimate goal is to provide position update rate of at least 1 Hz to any number of underwater receivers, without the requirement for precise clock synchronisation underwater, whilst minimising the peak power of the broadcasts. Simultaneous reception of multiple signals requires Code Division Multiple Access (CDMA) processing gain combined with adaptive cancellation techniques. Results from simulation and initial field experiments demonstrate the feasibility of this approach. The technique used in this paper will offer an approach to more biofriendly acoustic modem devices for use in regions with sensitive fauna and/or increasingly strict environmental controls[1].