Evaluation of In-Car Communication Systems - Digital Signal Processing for In-Vehicle Systems and Safety - page 68

Chapter 5
Evaluation of In-Car Communication Systems
Gerhard Schmidt, Anne Theiß, Jochen Withopf, and Arthur Wolf
Abstract Due to high background noise and sound absorbing materials, commu-
nication between front and rear passengers inside a vehicle is often difficult. In-car
communication (ICC) systems distribute the seat-dedicated microphone signals via
the car's sound system in order to improve speech intelligibility and communica-
tion quality. Due to interfering signals and the closed loop operation of ICC
systems, various signal processing techniques are required to reduce feedback,
echo, and noise, as well as, to prevent system instability.
In this chapter, a basic overview about the involved signal processing schemes
and some ideas for a methodical evaluation of the processing units as well as of the
overall ICC system are presented. The evaluation considers different requirements
for both talking and listening passengers. The evaluation is performed using four
different types of systems and setups. The first one is an ideal ICC system. Here, a
simulated system without any noise or feedback problems is computed in real time
and is presented to listeners and to the measurement equipment. This ideal system is
used to obtain upper performance levels or thresholds such as the maximum desired
gain. Furthermore, a real ICC system is evaluated in order to analyze the achieved
speech intelligibility and system quality. Some measurements are based on the
assumption of linear time-invariant systems. This assumption is usually violated by
real ICC systems. For that reason, ICC systems should freeze some of their
algorithmic components to allow LTI-based measures to obtain suitable results.
Usually, this is possible only for research ICC systems but not for commercially
available ones. Finally, the measurements should be performed without any ICC
system to obtain a basis for comparison.
G. Schmidt ( * ) • A. Theiß • J. Withopf
University of Kiel, Kiel, Germany
e-mail: [e-mail] ; [e-mail] ; [e-mail]
A. Wolf
SVOX Deutschland GmbH, Ulm, Germany
e-mail: [e-mail]