Software modems for underwater sensor networks

The prohibitive monetary cost and high power consumption of existing acoustic hardware represent an obstacle for underwater sensor network deployment efforts. To address this issue, we propose underwater networks that rely on widely available speakers and microphones in electronic devices, coupled with software modems, to establish acoustic communication links. In this paper, we analytically and empirically explore the potential of this acoustic communication system for the underwater environment with a generic PC microphone as a receiver and with the Tmote Invent sensor module speaker as a transmitter. After waterproofing the components with elastic membranes that provide suitable coupling with the water, our experiments profile the hardware communication capability in a controlled aquatic environment. The medium profiling results expose the favorable frequencies of operation for the hardware, enabling us to design a software FSK modem. The experiments to evaluate the data transfer capability of our 8-frequency FSK software modem in the underwater channel yield an error-free channel capacity of 24 bps, and they also demonstrate that the system supports data rates up to at least 48 bps within a transmission range of 17 m.