A Noise-Insensitive Compromise Gradient Method for the Adjustment of Adaptive Echo Cancellers

The time-optimum gradient method for the coefficient adjustment of adaptive echo cancellers allows a fast adjustment and a high echo return loss enhancement (ERLE) in the noise-free case. If noise occurs on the echo path, a compromise is necessary between the relatively large step size needed for rapid convergence and the relatively small step size needed for noise insensitivity. In this paper a noise-insensitive compromise method is proposed, which guarantees an acceptable ERLE in the noise-free case, as well as under line noise conditions. The method has, furthermore, the advantage of being easily instrumented. The efficiency of the proposed algorithm is determined by computer simulations under realistic conditions with two algorithms frequently used in previous publications: with the time-optimum gradient method and with a method with constant step-size factor. The simulations were carried out with floating-point arithmetic and with fixed-point arithmetic with 16 and 12 bit resolution to determine the maximum performance and necessary implementation expense of the different adjustment methods.