Software Acoustic Modems for Underwater Sensor Networks

Recent technological improvements and application opportunities have fueled increased interest in the development and deployment of underwater acoustic sensor networks. Deployment efforts have been impeded by the prohibitive monetary cost and high power consumption of existing acoustic hardware. Alternately, we propose underwater networks that rely on widely available speakers and microphones in electronic devices, coupled with software modems, to establish acoustic communication links. The proposed acoustic communications system paves the way for cheap and easily deployable underwater acoustic sensor networks through the use of audio hardware built in to sensor nodes, namely the Tmote Invent modules. In this paper, we explore the potential of the acoustic communication system for both aerial and underwater environments with the generic PC microphone as a receiver and with two transmitter types: (1) generic PC speakers; and (2) Tmote Invent speakers. We follow a systematic experimental approach that first profiles the hardware communication capability in air. We then repeat the profiling in water after waterproofing the components with elastic membranes. Subsequently, our experiments evaluate the data transfer capability of the underwater channel with 8-frequency FSK software modems. The data transfer experiments reveal that within a communication range of 17 m the Tmote Invent speakers can transfer between 6 and 48 bps with respective bit error rates of 5% to 21%.