Echo canceller having fir and iir filters for cancelling long tail echoes

Abstract From the Canadian patent

An echo canceller comprises a finite impulse response filter (6) connected to the incoming port of a hybrid (1) and a tail canceller (7), which includes an infinite impulse response filter (24; 40) having a multiplier (14; 33) for recursively multiplying an output digital symbol from the tapped-delay line (8) of the FIR filter with an attenuation coefficient R. A digital symbol from the IIR filter or one from the tappeddelay line (8) is multiplied with a tap-weight coefficient Ci and summed with the outputs of tap-weight multipliers of the FIR filter to produce a replica of an echo symbol, which is subtracted from a digital symbol yn from the outgoing port of the hybrid (1) producing a …