Echo canceller

Details Echo canceller Echo canceller

1994-02-24

1996-06-18

Hofsass, Jeffery

Telephonic communications

Echo cancellation or suppression

379410, 379411, 370 321, H04B 320

Patent

active

055286879

ABSTRACT:
An echo canceller provided with an expected echo generating unit which generates an expected echo of a transmission signal and a frequency offset correction unit which detects a phase error between an echo in a received signal and an expected echo from the expected echo generating unit and corrects the frequency offset for the expected echo by an offset frequency estimated based on the phase error, wherein use is made of the expected echo after offset correction by the frequency offset correction unit so as to suppress the echo in the received signal, the frequency offset correction unit using the phase error obtained after normalizing the phase error by the magnitude of the echo in the received signal. By this, it is possible to perform frequency offset correction adaptive to the far-end echo characteristics. Further, it is desirable to perform the frequency offset correction after it is confirmed that the rate of change of the output from a subtractor for cancellation of the near-end echo has become almost zero.

REFERENCES:
patent: 4574166 (1986-03-01), Gritton
patent: 4621173 (1986-11-01), Guidoux
patent: 4742510 (1988-05-01), Quantieri et al.
Macchi et al., "An Echo Canceller with Controlled Power for Frequency Offset Correction," IEEE Transactions on Communications, vol. COM-34, No. 4, Apr. 1986, New York, N.Y., pp. 408-411.
Quantieri et al., "Decision-Directed Echo Cancellation for Full-Duplex Data Transmission at 4800 BPS," ICASSP 86, Tokyo, JP, 1988, pp. 1337-1340.
Park et al., "A Phase-Adaptive Echo Canceller with Reduced Sensitivity to Power Variations," IEEE Transactions on Communications, vol. COM-35, No. 8, Aug. 1987, New York, N.Y., pp. 865-867.
Harman et al., "Frequency Offset Compensation Techniques for Echo-Cancellation-Based Modems," IEEE/IEICE Global Telecommunications Conference '87, Nov. 15-18, 1987, Tokyo, JP, pp. 1945-1949.
J. M. Cioffi, "Chapter 4--A Memory-Efficient Adaptive Algorithm for Steady-State Adjustment of the Echo Canceller," Information Systems Laboratory, Stanford, CA, Jan. 4, 1988, pp. 1-11.
J. M. Cioffi, "Chapter 5--Frequency Offset Tracking in the Far-End Canceller," Information Systems Laboratory, Stanford, CA, Jan. 4, 1988, pp. 1-19 and Figures.

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