Self-localization application for iPhone using only ambient sound signals

We present a smartphone application to localize a group of networking devices in a mobile environment without the need of any further infrastructure. Ambient sound signals are the only information source. Time marks are assigned to the recorded audio stream for distinctive audio events, out of which we evaluate the time differences of arrival (TDOA) between the devices. In contrast to common multilateration approaches we do not need any positional anchor points - neither any predefined smartphone positions nor the positions of the environmental sounds. As an application scenario we can localize arbitrary devices using only the random environmental noise peaks, e.g. in crowded areas like market places or concerts with the usual soundscape, or for thunderstorm tracking. Especially, our solution becomes useful when established positioning systems (e.g. GPS) are too imprecise or fail, as during indoor self-localization. We use a Wi-Fi connection to synchronize the clocks of the devices and to exchange time marks. In our experiments we evaluated the audio information and synchronized the devices up to an order of 0.1 ms. This results in a positioning precision in the order of 10 cm.