There are many applications requiring the propagation of acoustic signals through an underwater channel from a mobile transmitter to a mobile receiver, for example from a diver or autonomous vehicle to a surface vessel, or vice versa. For a diver, the information can represent depth or physiological parameters such as heart rate, breathing rate and body temperature. For an autonomous vehicle it
... [Show full abstract] can represent depth, control commands or scientific data. During transmission, the signals can be corrupted by noise from many sources. They can also be reflected and scattered at the surface, and refracted by variations in acoustic velocity; these effects cause multipath interference at a receiver. Here, we describe a diving application to illustrate design problems associated with a low-rate telemetry system. Then we consider the constraints of extending it to a high-rate system, including effects limiting its range.