  The auditory system of humanoid robots has gained increased attention in
recent years. This system typically acquires the surrounding sound field by
means of a microphone array. Signals acquired by the array are then processed
using various methods. One of the widely applied methods is direction of
arrival estimation. The conventional direction of arrival estimation methods
assume that the array is fixed at a given position during the estimation.
However, this is not necessarily true for an array installed on a moving
humanoid robot. The array motion, if not accounted for appropriately, can
introduce a significant error in the estimated direction of arrival. The
current paper presents a signal model that takes the motion into account. Based
on this model, two processing methods are proposed. The first one compensates
for the motion of the robot. The second method is applicable to periodic
signals and utilizes the motion in order to enhance the performance to a level
beyond that of a stationary array. Numerical simulations and an experimental
study are provided, demonstrating that the motion compensation method almost
eliminates the motion-related error. It is also demonstrated that by using the
motion-based enhancement method it is possible to improve the direction of
arrival estimation performance, as compared to that obtained when using a
stationary array.
