Echo canceller with means for determining filter coefficients from

Abstract

In a data transmission system where a first signal partially leaks as an echo from a first transmission line to a second transmission line through a hybrid circuit to form a mixed signal of the echo and a second signal on the second transmission line, an echo canceller is used for cancelling the echo by producing an echo replica at a transversal filter according to filter coefficients and subtracting the echo replica from the mixed signal. In order to reliably generate the filter coefficient for a reduced time duration, a series of autocorrelation coefficients of the first signal and a series of cross-correlation coefficients between the first and the mixed signals are calculated at calculators and the filter coefficients are determined from both of the autocorrelation and the cross-correlation coefficient series at a coefficient determining circuit. The coefficient determining circuit may be an arithmetic circuit for solving simultaneous linear equations. Another circuit for determining the filter coefficients may be a circuit where a first filter coefficient is determined by detecting the maximum value and the corresponding delay time from the series of cross-correlation coefficients, making a fresh series of cross-correlation coefficients with reference to the maximum values, the delay time and the first filter coefficient, then, determining a second filter coefficient from the fresh series. Then, filter coefficients are determined by repetition of the similar operation.