Adaptive echo canceller with multi-increment gain coefficient corrections

Claim 1

A digital transversal adaptive echo canceller of the type having means for storing a fixed number of most recent samples of a received signal, means for storing a corresponding fixed number of estimated impulse response coefficients, digital convolution means responsive to said stored samples and said stored coefficients for generating an approximate echo signal, means for subtracting said approximate echo signal from a real echo signal thereby producing a residual echo, and adaptive control loop means responsive to said residual echo and said stored samples for adding incremental values to said stored coefficients respectively, the improvement being in said adaptive control loop means and comprising, a. multi-level threshold detector means responsive to the magnitude of said residual echo for generating output signals indicating the signal of said residual echo and the number of predetermined discrete threshold levels equalled or exceeded by said residual echo, b. sign product detector means responsive to each said last mentioned sign indicating output signal and to the sign of each of said stored samples, respectively, for generating a sign product output signal which is the product of the sign of said residual echo and the sign of said stored sample, respectively, c. incremental adder means, responsive to each said sign product output signal and to each said output signal representing threshold levels equalled or exceeded, for adding to each said stored coefficient an incremental value having a sign which is the same as said respective sign product output signal and a magnitude dependent on the number of predetermined discrete threshold levels equalled or exceeded by said residual echo.