The receiver works just like a GPS receiver. It determines the distance between its self and the transmitters by knowing how long it takes for the sound to travel to it. All it needs is a good time source, a good edge triggered timing circuit and the right programming to get the distances.
There are three possible market segments here. One involves one GPS receiver and two dumb buoys that are located at a fixed distance. Without the GPS component, this could still provide a high degree of navigation information.. The second market involves having a number of smart buoys that all communicate with each other using some form of radio and or sonar. This would be useful on large archaeological sites where the range may need to be extended. The last market is on large recreational dive areas. For this, the transponders are put in known locations that can be surveyed. They don
One other feature of this is that the receivers and emit a pulse and be detected by the buoys which can then fix the location and retransmit it. This would aid underwater teams in keeping their locations relative to each other or for dive masters keeping track of recreational divers.
One other feature of this system is for position along underwater caves. One one transmitters needed and the receiver can just display the relative distance from the transponder and the direction of travel.