iSonar: Software-defined Underwater Acoustic Networking for Amphibious Smartphones

Recent technological advances have brought to the end-user market smartphones that are able to remain fully-functional even when submerged under water. This capability will soon enable the commercialization of a plethora of exciting smartphone apps, including life-saving systems such as real-time monitoring of scuba divers breathing. On the other hand, it becomes paramount to empower smartphones with end-to-end underwater communication capabilities. In this paper, we propose iSonar, the first system implementing reliable software-defined acoustic networking between water-proof smartphones. Specifically, iSonar transforms off-the-shelf smartphones into ultrasonic software "radios" that implement an orthogonal frequency division multiplexing-based communication system to exchange data under water. To this end, iSonar sends and receives information through the AUX interface and by implementing a lightweight network stack entirely in software. We have implemented a fully-functional hardware/software prototype of iSonar on Android smartphones and off-the-shelf electronic equipment, and extensively evaluated its performance through several experiments in a tank testbed. Results show that iSonar is able to achieve packet error rate (PER) of 10-3, which is significant considering the low audio sampling rate and the strong multipath effect induced by the water tank environment.