Ping-pong: Using smartphones to measure distances and relative positions

Abstract

A novel system for real-time range and geometry estimation of a group of smartphones co-located in a shared physical space is presented. The system uses off-the-shelf devices and employs audible signals to estimate inter-device (pair-wise) distances. Coordinated sound synthesis and processing of a pair of pitched sounds allows to estimate the distance between two devices based on the travel time. By independently analyzing different harmonics of the sounds used in the measurement, a more robust and precise distance estimation is achieved. To overcome the absence of a centralized clock to coordinate measurements, a synchronous communication channel was used. When four or more devices are present, it is possible to estimate their relative positions in a three-dimensional space, by minimizing an equation error norm. The system works both on closed and open spaces. We believe that such system opens the possibility for new ways of interaction that could benefit musical expression, social interaction and gaming.