Appeal No. 2002-1197
Application 09/131,167
BACKGROUND
The invention relates to echo cancelation in a
bi-directional communications link, such as a telephone system.
In such systems, speech of a near-end user is detected by a
near-end microphone for transmission over a communications link
to a far-end loudspeaker and speech of a far-end user is detected
by a far-end microphone and transmitted to a near-end loudspeaker
for reproduction and presentation to the near-end user. At
either end of the communications link, loudspeaker output
detected by a proximate microphone may inadvertently be
transmitted back over the communications link, resulting in
unacceptable feedback or "echo." This is especially a problem in
portable telephones of small size having a close distance between
the loudspeaker and microphone and with hands-free speaker
phones. Conventionally, echo suppression has been accomplished
with echo canceling circuits which employ adaptive filters.
According to appellant, practical experience has demonstrated
that adaptive filtering does not work well when the source signal
(i.e., the near-end microphone signal) becomes saturated. The
present invention overcomes the problem by updating the filter
coefficients of the adaptive filter only when the magnitude of
the source signal is within a predetermined range of possible
values less than the saturation level.
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