Echo cancelling system for multiplex telephone circuits

Details Echo cancelling system for multiplex telephone circuits Echo cancelling system for multiplex telephone circuits

1976-05-28

1977-12-20

Claffy, Kathleen H.

H04B 320

Patent

active

040643786

ABSTRACT:
An echo cancelling system for multiplex circuits, in which an impulse response of an echo-path is obtained from signals at respective ends of the transmission path and the receiving path connected to the echo-path to produce an echo-path model, and in which a pseudo echo signal is then provided to subtract it from an echo signal of the echo-path thereby to cancel the echo signal. In accordance with this invention, adaptive echo-path models each for corresponding channel of the multiplex circuits are provided for storing impulse response signals within a holding time of an impulse response in the long distance multiplex telephone circuits, and an adaptive echo-path model for the common use of multiplex circuits is provided for storing, in a time-divisional manner according to the known queue control, (a) information within a flat delay time of the impulse response, (b) impulse response signals within the holding time of the impulse response and (c) information within a certain constant time after the impulse response. The adaptive echo-path model for the common use is activated if the level of a residual echo signal is higher than a predetermined value, and the adaptive echo-path model for each channel is activated if the level of a residual echo signal is smaller than the predetermined value.

REFERENCES:
patent: 3787645 (1974-01-01), Ochiai et al.
patent: 3828147 (1974-08-01), Ochiai et al.

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