IIR filtering for acoustic echo cancellation

Acoustic echo cancellation is based on the identification of an acoustic coupling channel by an adaptive filter. The response length of the channel induces a very high complexity, while its rapid variations require fast processing. The few attempts found in the literature, using infinite impulse response (IIR) filters to reduce the complexity, show poor performance as compared to those of the finite impulse response (FIR) filters. The fundamental question of whether the poor performance stems from a sub-optimality of the updating procedures or from an irrelevancy of the pole-zero structure itself is investigated. These two points are treated in terms of a wave equation in a closed space and Hankel-norm approximation theory