Echo cancellation apparatus

Details Echo cancellation apparatus Echo cancellation apparatus

1994-02-01

1995-12-05

Hofsass, Jeffery A.

Telephonic communications

Subscriber line or transmission line interface

Network interface device

379402, 379411, 379406, 379412, 381 91, 381 94, 381101, 381103, H04M 900

Patent

active

054736862

ABSTRACT:
The length (or the number of taps) of an adaptive finite impulse response (AFIR) filter is continuously modified to produce optimal echo cancellation. In accordance with one illustrative embodiment, this modification is performed by increasing or decreasing the number of delayed samples which are used to generate an echo estimate. More specifically, the number of samples used to generate the echo estimate is determined by selecting a trial number of samples and operating the filter for a sufficient length of time to allow the tap weights in the filter to stabilize. The tap weights are then examined to determine whether the taps at the end on the filter contribute at least a first threshold amount to the echo estimate. If not, the number of samples used in the filter is reduced and the process repeated. If the taps at the end of the filter contribute more than a second threshold amount, the number of samples is increased and the process is repeated.

REFERENCES:
patent: 4866779 (1989-09-01), Kennedy et al.
patent: 4922530 (1990-05-01), Kenney et al.
patent: 4965834 (1990-10-01), Miller
patent: 5084865 (1992-01-01), Koike
patent: 5351291 (1994-09-01), Menez et al.
patent: 5371789 (1994-12-01), Hirano
Digital Signal Processing Applications With The TMS320 Family, vol. 1, Edited by Kun-Shan Lin, Ph.D., Digital Signal Processing Semiconductor Group Texas Instruments, pp. 417-454, 1986.
Adaptive Signal Processing, Prentice-Hall Signal Series, B. Widrow and S. D, Stearns, 1985, pp. 302-367.

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