Echo cancellation

Details Echo cancellation Echo cancellation

1987-07-02

1989-03-14

LaRoche, Eugene R.

Telephonic communications

Subscriber line or transmission line interface

Network interface device

379411, 370 321, H04L 514

Patent

active

048130737

ABSTRACT:
Echo cancellation to remove, from a locally received data communication signal, an echo signal component having a changing phase difference relative to the phase of a locally transmitted data communication signal, said locally transmitted communication signal are generated by modulating a carrier based on sequences of complex data signal points, is accomplished by correcting the phase of an input sequence of complex samples of the modulated carrier based on the changing phase difference to generate complex phase corrected samples, and generating a real-valued simulation of the echo signal based on the complex, phase corrected samples. Another aspect is estimating the phase difference between two signals based on samples of the real signal component of one of the signals, and the real component of the difference between the signals; successive estimates of the phase difference are generated based on successive applications of an approximate Hilbert transform to samples of each of the real signal component of one of the signals, and to the samples of the real component of the difference between the signals, each application of the Hilbert transform being limited to two of the samples. Another aspect is averaging a succession of sample values and scaling the result of the averaging in accordance with a variable scaling factor; the succession of sample values is accumulated as a cumulative sample value, and an output indicative of the result is provided by comparing the cumulative sample value with a threshold that is based on the variable scaling factor.

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Gitlin et al, "A Phase Adaptive Structure for Echo Cancellation", IEEE Transactions on Communications, vol. com-26, No. 8, Aug. 1978.
Weinstein, "A Passband Data-Driven Echo Canceller for Full-Duplex Transmission on Two-Wire Circuits", IEEE Transactions On Communications, vol. Com-25, No. 7, Jul. 1977.
Wang et al, "Performance Analysis of An Echo-Cancellation Arrangement That Compensates For Frequency Offset in the Far Echo".
Wittke et al., "Measurements of Echo Parameters Pertinent to High-Speed Full-Duplex Data Transmission on Telephone Circuits", IEEE Journal on Selected Areas In Communication, vol. Sac-2, No. 2, Sep. 1984.
Werner, "Effects of Channel Impairments on the Performance of an In-band Data-Driven Echo Canceler", AT&T Technical Journal, vol. 6, No. 1, Jan., 1985.

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