  Modern cars provide versatile tools to enhance speech communication. While an
in-car communication (ICC) system aims at enhancing communication between the
passengers by playing back desired speech via loudspeakers in the car, these
loudspeaker signals may disturb a speech enhancement system required for
hands-free telephony and automatic speech recognition. In this paper, we focus
on speech zone detection, i.e. detecting which passenger in the car is
speaking, which is a crucial component of the speech enhancement system. We
propose a model-based feedback estimation method to improve robustness of
speech zone detection against ICC feedback. Specifically, since the zone
detection system typically does not have access to the ICC loudspeaker signals,
the proposed method estimates the feedback signal from the observed microphone
signals based on a free-field propagation model between the loudspeakers and
the microphones as well as the ICC gain. We propose an efficient recursive
implementation in the short-time Fourier transform domain using convolutive
transfer functions. A realistic simulation study indicates that the proposed
method allows to increase the ICC gain by about 6dB while still achieving
robust speech zone detection results.
