Selective block update of NLMS type algorithms

Adaptive filters for the cancellation of acoustic echoes, as applied in hands-free telephone sets, require about a thousand coefficients and more to get a significant echo reduction. This leads to a very high computational effort and cannot be realized on most low-cost DSPs. One common proposition to decrease the computational load is to update only a portion of the coefficients at a time. This decreases not only the computational load but also the convergence speed. To reduce this drawback, it has been suggested that only the most significant coefficients be updated. This improves the convergence speed considerably. Unfortunately, it requires additional memory of twice the filter length. In our proposal, we present a modified version of the mentioned algorithm which has almost the same adaptation speed but consumes significantly less memory