Low-power based coherent acoustic modem for emerging underwater acoustic sensor networks

Smart, small, inexpensive sensor nodes are used to construct underwater acoustic sensor networks. In addition, with the recent increase in the importance of underwater applications, the need for underwater communication has become more important. Hence, an acoustic modem capable of effective underwater communications has become more necessary for the sensor nodes to obtain underwater data. To develop an acoustic modem for effective underwater communications, some limitations must be overcome, such as the very short transmission range of radio waves, limited power supply, and high cost of commercial acoustic modems. Recently, low-power, low-cost acoustic modems have been developed. However, the data rates of these modems are so slow that sensor nodes cannot perform energy-efficient protocols. The objective of this work is to develop an acoustic modem capable of supporting high data rates. We introduce a coherent acoustic modem that uses waterproof ultrasonic sensors to process acoustic waves. The proposed modem is based on a low-power, low-cost, short-range concept, and it also supports a high data rate for energy-efficient MAC and routing protocols. Underwater experiments are conducted to evaluate the performance improvements of our modem. Experimental results show that our modem has the best performance among all recently developed low-power modems and that it is preferable to develop a coherent modem able to perform effective underwater communications.