Non-causal adaptive IIR filtering

A procedure to approximate non-causal adaptive IIR filtering is described. Such structures could be useful, for instance, in the equalization of non-minimum phase communication channels. The procedure is based on backward calculations within blocks of samples and we show that for adaptive filtering the overlap-save method is more suitable than the overlap-add method. Moreover, a temporary freeze of the adapted parameters at the beginning of the backward calculations for each block is also required. Finally, applying a previously presented method of convergence speed analysis, we show that in the inverse identification of a causal maximum-phase system with an anticausal adaptive filter, one of the conditions for faster convergence is always satisfied, regardless of the particular response of the system. A comparison with FIR adaptive filters is presented, showing that the proposed algorithm can achieve a better tradeoff bewtween convergence speed and computational complexity. Keywords— Non-causal filters, adaptive IIR filtering, convergence speed.