An adaptive time-discrete filter having an impulse response h(i) with i = 0,1,2,.... for forming a cancelling signal from synchronous data symbols (for example to cancel echoes or lagging intersymbol interference) comprises a transversal filter section (12) having adjustable coefficients Ci with i = 0,1,2,....,N-1 for realising the first N values h(i) of the impulse response as well as a recursive filter section (12') for realising the values h(i) with i = N,N+1,..... The recursive filter section (12') receives the input signal delayed over N-1 discrete time intervals from the adaptive filter as an input signal x(n) and forms an output signal y(n) according to the relationship: y(n) = CB[CAx(n-1) + y(n-1)] where CA is equal to the last adjustable coefficient CN-1 of the transversal filter section (12) and CB is a predetermined fixed coefficient.
ADAPTIVE TIME-DESCRETE FILTER FOR FORMING A CANCELLING SIGNAL FROM SYNCHRONOUS DATA SYMBOLS