Appeal No. 2002-1197
Application 09/131,167
be sustained. We discuss this situation because of the dependent
claims and for the benefit of any further prosecution. Column 1,
lines 43-63, of Koski states:
Double-talking refers to the condition when the near
end subscriber (the user of the phone) and the far-end
subscriber talk simultaneously. When both parties talk
simultaneously, i.e. during double talk, the echo canceller
is no longer able to effectively block echo signals. This
is because the echo signals are included in the near-end
subscriber's signals to be transmitted, i.e. a desired
signal to be transmitted and an echo signal are
simultaneously applied to the send input. The super-
positioning of these signals causes distortion of the
adjustment of the echo canceller when it considers both the
echo signal and the desired signal to be transmitted. This
means that the replica produced by the echo canceller no
longer sufficiently cancels the current echo signal.
Accordingly, it is a current practice to provide a double
talk detector for preventing the disturbing influence of
double talk on echo canceller adjustment. This means that
the parameters of the adaptive filer performing the echo
cancellation are not updated during double talk. Echo and
double talk are problems especially in speaker phones and in
phones with hands-free equipment in which the far-end signal
from the speaker is captured by the microphone. [Emphasis
added.]
The superposition of the near-end and echo (far-end signals
coupled from the loudspeaker into the microphone) signals must
refer to superposition of signals to become the output signal of
the microphone, as noted by the examiner (e.g., FR3). The
superposition of the near-end and echo signals during double talk
creates an output signal that causes a distortion in the echo
canceller, and the need to prevent distortion suggests that the
resultant superposed signal be kept below a predetermined value
that causes distortion, i.e., that the output of the microphone
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