A new efficient implementation of the AIFIR echo tail canceller for ISDN applications

An efficient echo tail canceller is proposed for use with the 2B1Q receiver for ISDN (integrated services digital network) applications. The overall echo cancellor is composed of a direct form FIR (finite impulse response) main canceller to cancel the main part of the echo followed by an adaptive interpolative FIR section (AIFIR) for tail cancellation. The AIFIR is a cascade of an adaptive sparse filter and a fixed interpolator filter. Preliminary results show that, by implementing the interpolator as a cascade of combinations of comb filters, one can achieve echo attenuation close to that obtainable by min-max interpolators while reducing the number of multipliers required