Network echo canceller

Details Network echo canceller Network echo canceller

1994-02-28

1996-09-24

Hofsass, Jeffery

Telephonic communications

Subscriber line or transmission line interface

Network interface device

379406, 379390, 370 321, H04B 320

Patent

active

055598811

ABSTRACT:
An echo canceller and method for cancelling in a return channel signal an echoed receive channel signal where the echoed receive channel signal is combined by an echo channel with an input return channel signal. The echo canceller has a first filter which generates first filter coefficients, generates a first echo estimate signal with the first filter coefficients, and updates the first filter coefficients in response to a first filter control signal. A first summer subtracts the first echo estimate signal from a combined return channel and echo receive channel signal to generate a first echo residual signal. A second filter generates second filter coeffidents, generates a second echo estimate signal with the second filter coefficients, and updates the second filter coefficients in response to a second filter control signal. A second summer subtracts the second echo estimate signal from the combined signal to generate a second echo residual signal, and provides upon the return channel the second echo residual signal. A control unit determines from the receive channel signal, the combined signal, and the first and second echo residual signals, one of a plurality of control states wherein a first control state is indicative of a receive channel signal above a first predetermined energy level, wherein when the control unit is in the first control state it generates the first control signal and generates the second control signal when at least one of a first energy ratio of the first echo residual signal and the combined signal and a second energy ratio of the second echo residual signal and the combined signal exceed a predetermined level.

REFERENCES:
patent: 4697261 (1987-09-01), Wang et al.
patent: 4764955 (1988-08-01), Galand et al.
patent: 4782525 (1988-11-01), Sylvain et al.
"Echo Cancellation in Speech and Data Transmission" by David G. Messerschmitt, IEEE Journal on Selected Areas in Communication. vol. Sac-2, No. 2, Mar. 1984, pp. 283-297.
"A Double Talk Detection Method for an Echo Canceller" by S. Minami and T. Kawasaki, IEEE International Conference on Communications, 1985, pp. 1492-1497.
"A Fast Adaptive Echo Canceler with Delay Estimation for Time Variant Telephone Circuits" by R. Montagna, L. Nebbia, IEEE International Conference on Communications. 1984, pp. 1569-1574.
"Silencing Echoes on the Telephone Network" by Man Mohan Sondhi and David A. Berkey, Proceedings of the IEEE, vol. 68, No. 8, Aug. 1980, pp. 948-963 .

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