Process for starting up a modem containing a variable-phase echo

Details Process for starting up a modem containing a variable-phase echo Process for starting up a modem containing a variable-phase echo

1994-09-08

1996-11-05

Chin, Stephen

Pulse or digital communications

Transceivers

Modems

379411, 370 321, H04B 323

Patent

active

055725457

ABSTRACT:
A start-up method for a data modem having an echo cancelling loop between the send port and receive port, the loop including a transversal filter having adjustable coefficients, adjustable phase-shifter and a subtractor for subtracting send port data symbols which have been filtered and phase shifted from data symbols received at the receive port. During start-up, in response to a series of data symbols supplied at the send port, a microprocessor iteratively adjusts the filter coefficients and the phase shift to cancel any echo at the output of the subtractor. In order to reduce the convergence time, the start-up method includes estimating the power of the echo over a time period corresponding to a predetermined number of data symbols at the send port, quantizing the estimated power, and adjusting the filter coefficients and the phase shift on the basis of the quantized echo power level.

REFERENCES:
patent: 5351291 (1994-09-01), Menez et al.
Park, K. H., and Macchi, O., "A Phase-Adaptive Echo Canceller with Reduced Sensitivity to Power Variations," IEEE Trans. on Communications, vol. COM-35, No. 8, Aug. 1987, pp. 865-867.
Richard D. Gitlin et al, "A Phase Adaptive Structure for Echo Cancellation", IEEE Trans. on Communication, vol. COM-26, No. 8, Aug. 1978, pp. 1121-1220.
Edward A. Lee et al, "Digital Communication", Kluwer Academic Publishers, Boston, 1988, pp. 642-668.

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