METHOD AND DEVICE FOR DIGITAL ECHO CANCELLATION

摘要

Echo cancellation in signal transmission on four-wire telephone lines is effected digitally using an echo estimate and compensating for phase-roll between the echo and the signal originally transmitted. Digitized samples of sine and cosine functions of a pulsation corresponding to the phase-roll are generated. Digitized samples of a signal phase-shifted by 90.degree. are obtained from the echo. The same echo is delayed by a time equal to the time necessary for the phase-shifting operations. The samples of the phase-shifted and delayed signals are multiplied respectively by the samples of the sine and cosine functions, the resulting signals being added. The multiplication and addition operations give rise in the echo to a frequency-offset equal and opposite to the offset introduced by the line.