  In this paper, we propose a method to estimate the proximity of an acoustic
reflector, e.g., a wall, using ego-noise, i.e., the noise produced by the
moving parts of a listening robot. This is achieved by estimating the times of
arrival of acoustic echoes reflected from the surface. Simulated experiments
show that the proposed nonintrusive approach is capable of accurately
estimating the distance of a reflector up to 1 meter and outperforms a
previously proposed intrusive approach under loud ego-noise conditions. The
proposed method is helped by a probabilistic echo detector that estimates
whether or not an acoustic reflector is within a short range of the robotic
platform. This preliminary investigation paves the way towards a new kind of
collision avoidance system that would purely rely on audio sensors rather than
conventional proximity sensors.
