PERFORMANCE IMPROVEMENT OF VARIABLE STEPSIZE NLMS

Improvement of the convergence characteristics of the NLMS algorithm h as received attention in the area of adaptive filtering. A new variabl e stepsize NLMS method, in which the stepsize is updated optimally by using variances of the measured error signal and the estimated noise, is proposed. The optimal control equation of the stepsize has been der ived from a convergence characteristic approximation. A new condition to judge convergence is introduced in this paper to ensure the fastest initial convergence speed by providing precise timing to start estima ting noise level. And further, some adaptive smoothing devices have be en added into the ADF to overcome the saturation problem of the identi fication error caused by some random deviations. By the simulation, th e initial convergence speed and the identification error in precise id entification mode is improved significantly by more precise adjustment of stepsize without increasing in computational cost. The results are the best ever reported performances. This variable stepsize NLMS-ADF also shows good effectiveness even in severe conditions, such as noisy or fast changing circumstances.