根據最佳收斂步伐與通道削減來提升非線性迴音消除的收斂性

Abstract

為了消除免持聽筒或者視訊會議上非線性的迴音，傳統上可以用Volterra 濾波器或Hammerstein 濾波器來追蹤非線性迴音的通道。然而這兩個濾波器最大的缺點就是收斂速度慢並需要付出高的計算量。 在此篇論文中，我們提出最佳的可調整式收斂步伐演算法並且應用在Volterra濾波器。其目的在於加快收斂速度，此收斂步伐是由估計濾波器與真實的最小閥係數誤差在均方誤差(MSE)。每一個閥，都隨著係數誤差改變而調整的收斂步伐，而由於此演算法需要知道真實的迴音通道，所以我們進一步提出模擬通道的實際的應用。 除了收斂步伐的控制，通道削減結構(channel shortening)也被用來解決Hammerstein濾波器收斂速度慢與高複雜度的問題。我們做了Least-square 和適應性演算法角的理論分析，並且提出多級更新係數的方法來更加快收斂速度。最後用電腦模擬來支持驗證之前的分析討論。

In order to cancel nonlinear acoustics echo in hands-free telephones or teleconferencing system. In general, adaptive Volterra filter and Hammerstein model are known to track nonlinear echo path. However, their major drawbacks are slow convergence rate and high computation complexity. In this thesis, we propose an optimum time–and tap– variant step-size for Volterra filter in order to speed up convergence rate. The step-size is based on the MMSE criterion of coefficients errors. As the optimum step-size needs to know the real echo path coefficient, we propose the exponential model for practical implementations. In addition to adaptive step-size control , the channel shortening structure was proposed to overcome slow convergence rate and high computation complexity in Hammerstein structure, we perform the least-square and adaptive algorithm theoretical analysis in channel shortening structure in case of a linear loudspeaker. From which a multiple stage update scheme is proposed in this structure to speed up convergence rate. Computer simulations justify our analysis and show the improved performance of the proposed nonlinear acoustic echo canceller.