Signal Processing Volume 86, Issue 6,
Gerhard Schmidt, Tim Haulick
Due to a large amount of background noise the communication within a car driving at high or even moderate speed is often difficult. This is especially true if one of the communication partners is the driver and the other is one of the backseat passengers. As a result of the high noise level the backseat passengers often lean towards the front passengers. Furthermore, all speakers increase their loudness. Even if both reactions enhance the quality of the “communication channel” it is rather exhausting and uncomfortable for the passengers.
The situation can be improved by using in-car communication systems. These systems record the speech of each passenger by means of a single microphone or with an array of microphones. The recorded signals of the currently speaking passengers are processed by the system and played back via those loudspeakers which are located close to the non-active passengers. Comparable to public address systems, in-car communication systems operate within a closed electro-acoustic loop. Thus, signal processing is required to guarantee stable operation so as to avoid acoustic feedback such as howling or whistling.
In this contribution we describe the basic processing units of an in-car communication system. Those units contain mostly standard algorithms such as beamforming, echo cancellation, and loss control. However, these methods cannot be applied and controlled as in applications like hands-free telephones or preprocessing for speech recognition systems. Here, the problem is that the excitation signals and the distorting components are highly correlated—leading to convergence problems of adaptive algorithms. Furthermore, in-car communication systems have very restrictive demands on the tolerable processing delay.Read/download now