Near-end distortion in over-sampled subband adaptive implementation of affine projection algorithm

The affine projection algorithm has been employed for echo cancellation using subband adaptive filters implemented with over-sampled filterbanks. We show that the near-end signal may be distorted or partially cancelled if proper regularization is not applied. We attribute these distortions to the nonlinear effects that appear mostly when narrow-band signals are involved in adaptive filtering. Supporting this assumption, it is shown that as the over-sampling rate increases and subband signals become more bandlimited, near-end cancellation also increases. The effect of adaptive filter length and the regularization parameter on near-end distortion is analyzed, leading to the result that near-end distortion can be avoided by proper regularization. As a result, a practical low-cost on-line regularization method is proposed for the affine projection algorithm, effectively eliminating near-end distortion.