Due to the presence of the "hidden terminal" and the "exposed terminal" problems

the applications for radio Ad hoc networks have greatly been restricted.Furthermore

with the characteristics of the underwater acoustic channel

such as low available bandwidth

highly varying multipath

and large propagation delays

the designing of underwater acoustic Ad hoc networks is a more challenging task.In this paper

we propose a new multiple access control (MAC) protocol for underwater acoustic Ad hoc networks

namely

the parallel transmission multiple access (PTMA) protocol.This protocol is based on the following ideas:to resolve collision

the reservation for multiple channels is m

ade

thus data packets may parallelly be transimitted on multiple channels;to reduce the time for waiting for the clear

-

to

-

send (CTS) packets

we begin to transmit data packets as soon as the request

-

to

-

send (RTS) packets have been sent without the receipt of the CTS packets.Simulation results

which were obtained by using the OPNET Modeler/Radio

show that the proposed PTMA protocol can provide higher throughput performance and lower end-to-end propagation delay than those that are suitable for radio Ad hoc networks within the underwater acoustic environment.