An Ultrasonic Sensor Based Low-Power Acoustic Modem for Underwater Communication in Underwater Wireless Sensor Networks

Applications of underwater sensor networks involve environmental monitoring, disaster prevention, and resource detection. As the importance of these applications has recently grown, underwater sensor networks made up of sensor nodes have to be further investigated. However, little research has been performed to develop an underwater sensor node with communication functionality. In an underwater environment, typical RF-based communication is not appropriate because of two facts. One fact is that radio waves require large antennae and high transmission power. The other fact is that the Berkeley Mica 2 Motes have been reported to have a transmission range of 120cm underwater. Consequently, we have concluded that underwater communication has to use an acoustic or ultrasonic wave rather than a radio wave. The objective of our work is to develop an acoustic modem for underwater communication, where we have to consider an energy-aware acoustic modem. This is because the battery can not easily be recharged underwater as well as in a terrestrial environment. As a consequence, an acoustic modem has to be designed with low-power. In this paper, we describe our implementation of an energy-aware acoustic modem and its performance in underwater experiments.