Patent Document ID: 5418849
Application ID: 07870179
Patent Flag: 1

Claim One:
1. Procedure for adaptive digital cancellation of echo generated in a telephone connection by signals transmitted between a far-end talker and a near-end talker over a communications channel having characteristics varying rapidly in time, comprising the following steps: (a) estimating an initial propagation delay (INDX) between a sequence of digital samples of an input signal x(t) coming from a far-end talker and a sequence of digital samples of an echo signal d(t) produced by reflection of said signal x(t), wherein t is a discrete time variable, including the substep of computing a maximum correlation point between the two sequences of digital samples; (b) recursively digitally filtering with adaptive coefficients (C.sub.k) the samples of the input signal x(t) and the echo signal d(t), wherein the samples of the input signal x(t) are delayed by the value of the estimated propogation delay INDX, said filtering producing samples d(t) of an estimation of the echo signal d(t) by multiplying a vector C.sub.N (t) which includes the adaptive filter coefficients C.sub.k, the subscript N indicating the number of coefficients of the vector, and an input vector X.sub.N (t) which includes a first number N.sub.1 of delayed input signal samples x(t'), where t'=t-INDX, and a second number N.sub.2 of samples of the echo signal d(t); (c) subtracting the estimation signal d(t) from an output signal which contains the echo signal d(t) and obtaining a residual echo signal e(t); (d) calculating a present value of a gain vector K.sub.N (t) which has coefficients determined based upon minimization of the power of the residual echo signal e(t); and (e) iteratively updating the vector of coefficients C.sub.N (t) by adding, at each iteration, to the values the vector had at a previous iteration a product of the residual echo signal e(t) and the present value of the gain vector K.sub.N (t), wherein each iterative updating of the coefficient vector C.sub.N (t) is accomplished in a predetermined number M&gt;1 of sample periods corresponding to the sampling of the signals x(t) and d(t).