Model Physical Model Propagation Model Modulation Model Packet Error Time of Packet Reception

Underwater acoustic networks have the potential to support a wide variety of applications from facilitating communication between autonomous underwater vehicles to supporting the remote monitoring of underwater mining equipment or environmental conditions [1]. Even though underwater acoustics has been studied for many years, and communications technologies exist for underwater scenarios, interest on networking and protocol design in this environment is just beginning. As such, there is currently no standard underwater simulation module for any of the major network simulators. To accurately model underwater communication, channel, propagation, and interface models are required. Since the underwater environment is different from its terrestrial counterpart [1, 7], it is likely that existing wireless modules cannot be easily reused, and specific underwater extensions will be needed. The underwater environment differs from the terrestrial radio environment both in terms of its modem energy costs, and in terms of the channel propagation phenomena. The underwater channel is characterized by long propagation times and frequency-dependent attenuation that is highly affected by the distance between nodes [7] as well as by the link orientation. The main contribution of this work is an underwater propagation, channel, and interface model for the widely-used ns2 network simulator [5]. In this abstract, we give a brief description of its functionality and refer the reader to [3]. A challenge in building such a model lies in the fact that many of the features of the channel, such as bandwidth, depend on the distance between the two nodes and the orientation of the link. However, in ns2, the bandwidth is usually assumed to be fixed and used by layers higher than the propagation and channel model. Therefore, in underwater scenarios, bandwidth information has to be calculated and returned to the upper layers of the simulator, which is not the case for other radio models. The ns2 simulator divides the layers below the MAC layer into four components: Propagation, Channel, Physical, and Modulation. We provide modules for each layer, allowing protocol developers to concentrate efforts on the higher layers of the network protocol stack.