Smartphone users are often grouped to exchange
files or perform collaborative tasks when meeting together.We argue
that the location information of group members is critical to
many mobile applications. Existing localization solutions mostly
rely on anchor nodes or infrastructures to perform ranging
and positioning. These approaches are inefficient for ad hoc
scenarios. In this paper, we propose AMIL, an Acoustic Mobility-
Induced TDoA (Time-Difference-of-Arrival)-based Localization
scheme for smartphones. In AMIL, a smartphone user can use
simple gestures (e.g., hold the phone and draw a triangle in the
air) to quickly obtain the relative coordinates of neighboring
mobile devices. We have implemented and evaluated AMIL on
off-the-shelf smartphones. The field tests have shown that our
scheme can achieve less than three degree orientation errors and
can successfully build a simple map of 12 people in an office
room with average error of 50cm.