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A novel portable underwater acoustic modem is proposed in this paper for covert communication between divers or underwater unmanned vehicles (UUVs) and divers at a short distance. For the first time, real dolphin calls are used in the modem to realize biologically inspired Covert Underwater Acoustic Communication (CUAC). A variety of dolphin whistles and clicks stored in an SD card inside the modem helps to realize different biomimetic CUAC algorithms based on the specified covert scenario. In this paper, the information is conveyed during the time interval between dolphin clicks. TMS320C6748 and TLV320AIC3106 are the core processors used in our unique modem for fast digital processing and interconnection with other terminals or sensors. Simulation results show that the bit error rate (BER) of the CUAC algorithm is less than 10 − 5 when the signal to noise ratio is over ‒5 dB. The modem was tested in an underwater pool, and a data rate of 27.1 bits per second at a distance of 10 m was achieved.

For decades, underwater acoustic communication has been restricted to the point-to-point long distance applications such as deep sea probes and offshore oil fields. For this reason, previous acoustic modems were typically characterized by high data rates and long working ranges at the expense of large size and high power consumption. Recently, as the need for underwater wireless sensor networks (UWSNs) has increased, the research and development of compact and low-power consuming communication devices has become the focus. From the consideration that the requisites of acoustic modems for UWSNs are low power consumption, omni-directional beam pattern, low cost and so on, in this paper, we design and implement an omni-directional underwater acoustic micro-modem satisfying these requirements. In order to execute fast digital domain signal processing and support flexible interfaces with other peripherals, an ARM Cortex-M3 is embedded in the micro-modem. Also, for the realization of small and omni-directional properties, a spherical transducer having a resonant frequency of 70 kHz and a diameter of 34 mm is utilized for the implementation. Physical layer frame format and symbol structure for efficient packet-based underwater communication systems are also investigated. The developed acoustic micro-modem is verified analytically and experimentally in indoor and outdoor environments in terms of functionality and performance. Since the modem satisfies the requirements for use in UWSNs, it could be deployed in a wide range of applications requiring underwater acoustic communication.