| 摘要 |
An extended impulse response characteristic is obtained by connecting a plurality of adaptive echo cancelers in a tandem connection (FIG. 1 or FIG. 2). Delay units (102) are associated with receive inputs (X) of the adaptive echo cancelers (101, FIG. 1, or 201 FIG. 2) so that each canceler models a predetermined fixed portion of the extended impulse response characteristic. The relative positions of the cancelers in the tandem connection are controllably switched (via 103-0 through 103-(N-1) and (104) at a predetermined rate (via 105) to insure so-called "good" adaptation of the individual adaptive echo cancelers. In one embodiment, the adaptive echo canceler in a preferred position in the tandem connection is allowed to adapt at its normal rate while the other cancelers are inhibited (via &upbar& I) from adapting. In another embodiment, the adaptive echo canceler in the preferred position is allowed to adapt at the normal rate while the other cancelers are allowed to adapt at slower rates (via GAIN) determined in accordance with their relative positions in the tandem connection.
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