<FONT face=Verdana>Proportionate adaptive algorithms exploit structure characteristic of sparse impulse response to considerably improve the convergence speed. However

the requirements of fast convergence and low steady-state misalignment are conflict for constant step-size adaptive algorithms

whose step size parameter has to be selected by compromising these two conflict requirements. In this article

a novel variable step-size method is proposed for proportionate adaptive algorithm to solve this problem. By using principle of minimal disturbance to proportionate adaptive algorithm

we first provide a derivation of proportionate NLMS. Then by taking into account the disturbance signal

forcing the a posterior error to cancel negative effect of disturbance signal

we obtain a new optimization criterion. At last

using this criterion

we propose a step size control approach for proportionate NLMS algorithm. Simulation results verify the effectiveness of the proposed algorithm.