Process and device for adaptive digital cancellation of the echo generated in time-varying telephone connections

An echo canceller for cancelling an echo generated in telephone connections with electrical characteristics that vary rapidly in time, comprising:

• means for estimating a propagation delay INDX between a voice signal x(t) generated by a far-end talker and an echo signal d(t) produced by reflection of said voice signal toward the far-end talker along an echo path, t being a temporal variable discretized at a sampling frequency of the voice and echo signals x(t) and d(t);
• means for generating an input vector X.sub.N (t') having a number N of voice samples x(t') of the far-end talker, t' being equal to t-INDX;
• means for generating an adaptive coefficient vector C.sub.N (t.sub.) having coefficients (c.sub.i), N being the number of said coefficients (c.sub.i), and means for iteratively updating said coefficient vector by adding algebraically, upon each iteration, to a value which said coefficient vector had for a previous iteration an appropriate correction term proportional to a value of the echo residual signal calculated for a present iteration;
• non-recursive digital filtering means for producing a sequence of samples of an estimated signal d(t) calculated by multiplying a transposition of the coefficient vector C.sub.N (t) by said input vector X.sub.N (t');
• subtraction means for subtracting the samples of said estimated signal d(t) from samples of the echo signal d(t) to obtain samples of a echo residual signal e(t) sent to the far-end talker without the effects due to the echo signal d(t);
• and
• timing means for generating a timing signal having a frequency which is a multiple M of the sampling frequency, said timing signal controlling updating iterations of said coefficient vector C.sub.N (t).

A process for adaptive digital cancellation of an echo generated in telephone connections with electrical characteristics that vary rapidly in time, comprising the steps of:

• estimating a pure propagation delay INDX between a voice signal x(t) of a far-end talker and an echo signal d(t) produced by reflection of said voice signal toward the far-end talker along an echo path, t being a temporal variable discretized at a sampling frequency of the voice and echo signals x(t) and d(t);
• non-recursive digital filtering with adaptive coefficients (c.sub.i) by multiplying a transposition of a vector C.sub.N (t) having a number N of adaptive coefficients (c.sub.i) by an input vector X.sub.N (t') having an identical number N of voice samples x(t') of the far-end talker delayed by said propagation delay INDX of the echo path, where t'=t-INDX, for generation of samples of an estimated signal d(t) of the echo signal d(t);
• subtraction of said estimated signal d(t) from the echo signal d(t) to obtain an echo residual signal e(t) sent to the far-end talker without effects due to the echo signal d(t);
• iteratively updating said adaptive coefficients (c.sub.i) by adding algebraically upon each iteration, to a value of said adaptive coefficients in an immediately preceding iteration;
• calculating a correction term proportional to a value of the echo residual signal for a present iteration;
• and
• providing a frequency of the updating iterations of said adaptive coefficients (c.sub.i) that has a value which is a multiple M of said sampling frequency.