用於主動消噪系統之新可變長度與步階大小的FXLMS 演算法

Abstract

FxLMS 演算法已廣泛的使用於主動消噪系統(ANC)，之前一 些不同版本的FxLMS 演算法已研究過如何減少計算複雜度或增進 收斂速度。在一般的應用上，傳統的FxLMS 演算法雖其結構可能 容易實現，但因使用的濾波器長度較長，故其收斂速度十分緩慢。 在本篇論文中，提出新的可變長度及步階大小之FxLMS 演算法用 於消噪系統。有鑑於低通濾波器在消噪系統第二路徑的影響，控制 濾波器的脈衝響應之包跡以非對稱指數衰減函數來模擬，用以發 展我們的演算法。模擬結果顯示，相較於固定長度的FxLMS 演算 法與先前提出的可變步階大小的FxLMS 演算法，此一演算法確實 能夠顯著的改進收斂速度及訊噪比。

The filtered-X least mean square (FxLMS) algorithm is widely used for active noise cancellation (ANC). Some variants of FxLMS algorithms have been studied to reduce computational complexity or to improve convergence rate. In general applications, a long tap length is usually required for the conventional FxLMS method which convergence rate is very slow though its structure is possibly very easy to implement. In this paper, a new ANC system is proposed with a variable tap length and step size FxLMS algorithm. Taking into account the effect of the lowpass filter in the secondary path of an ANC system, the impulse response of the control filter is modeled with an unsymmetric and exponential decaying envelope to develop our algorithm. Simulation results show that the proposed algorithm does provide a significant performance improvement on convergence rate and noise reduction ratio compared to the fixed tap FxLMS and previously proposed variable step size FxLMS algorithms.