ADAPTIVE FORECAST TYPE DIGITAL ECHO CANCELLER

摘要

PURPOSE:To decrease the circuit scale of an echo canceller by constituting an adaptive forecast digital filter with an FIR filter and an IIR filter to reduce remarkably number of taps of the adaptive forecast digital filter. CONSTITUTION:A signal from a sending remote caller is supplied in a form of a transfer function in equation I. Further, Hz(z) in the equation I is a transfer function of a transversal filter 3-5 and given by equation II. Moreover, Hp(z) in the equation I is a transfer function of an IIR filter 3-6 and given respectively in prescribed equations with respect to even and odd number orders. An output 3-14 of the filter 3-5 and an output 3-15 of the IIR filter 3-6 are added by an adder 3-9 to generate a forecast output y3-16. An echo signal from an echo path is converted into a digital signal 3-17 by an A/D converter 3-3 and added to the forecast output y3-16 by the adder 3-10. Its output (e) is a residual signal without an echo signal and it is sent to a reception side remote end caller after D/A conversion.