標題: 以直接極/零點估計法用於適應性回音消除
Direct Pole/Zero Estimation for Adaptive Echo Cancellation
作者: 周昭政
Jou, Jau Jeng
謝世福
S. F. Hsieh
電信工程研究所
關鍵字: 回音;極點;零點;無限長脈衝響應;適應性濾波器;echo;pole;zero;IIR;adaptive filter
公開日期: 1997
摘要: 過長的濾波器長度對於適應性 FIR 濾波器不但會導致收斂速度變慢也會 讓我們所需付出的硬體成本增加。因此在針對回音消除上 IIR 濾波器似 乎是較為合適的,因為它可提供一個有無限長度的房間脈衝響應。但是到 目前為止仍有二個重大的缺點限制了 IIR 濾波器被廣泛的運用。一是濾 波器的穩定度,另外是參數可能會收斂到局部最佳值。 我們將以遞迴 估計錯誤(Recursive Prediction Error)的方法發展出以狀態(State)為 基礎直接極/零點估計法(SBDPZ)。SBDPZ有別於傳統估計係數方法,它可 直接觀測極點所在的位置,而不用像傳統估計係數的方法需要對分母的多 項式求根,再來判斷極點所在位置。然而矩陣運算卻是一項龐大的運算負 擔,因此我們將以減化誤差梯度計算的方法來降低系統運算複雜度。對於 非最小相位(Nonminimum phase)系統的估計,我們將用更多的運算以一級 一級的方法去求出誤差的梯度。最後在針對聲音的回音消除時我們採用傳 統 NLMS 和直接極點估計的合併方法 (NSBDP)。我們用 NLMS 來估計房間 響應零點的部分,只留下極點的部分是由直接估計法來完成。如此一來既 可保有容易觀察穩定度的特質又可大量減少運算的複雜度。 The problem of long filter length in adaptive FIR filters not onlyslows down the convergent speed but also increases the hardware cost.Adaptive IIR filters seem appropriate because they can provide infinitelylong response to approximatethe room impulse responses. But two disadvantages limitthe adaptive IIR filter to be widely used. One is the filter stability andthe other is local optimum in the error surface.Based on recursive prediction error algorithmwe will develop the state-based direct pole/zero (SBDPZ) estimation method.Unlike the traditional coefficients estimation method, SBDPZ canmonitor the poles' locations directly without finding the rootsof the denonimator polynomial.However, matrix operation is a serious computation load, so we deriveda simplified gradient method to reduce the computation complexity.Nonminimum phase system will also be investigated by further computationof the error gradient stage by stage.Finally, we use the combined method of the conventional NLMS and direct poleestimation to predict the zeros and poles, respectively, for acoustic echo cancellation.Therefore, we can not only keep the easier stability checkproperty but also reduce the computation complexity.
URI: http://140.113.39.130/cdrfb3/record/nctu/#NT860435032
http://hdl.handle.net/11536/63053
Appears in Collections:Thesis