應用DMT技術於非對稱數位用戶迴路之回音消除器研究

Abstract

回音(Echo)在用戶迴路(Subscriber Loop)的雙向傳輸(Full- duplex Transmission)中是一個很嚴重的問題。岔路器(Hybrid Circuit)並不能 有效解決此一問題，所以回音消除器通常是必需的。在非對稱數位用戶迴 路中(ADSL)，因相當高的傳輸速使得傳統的回音消除器非常複雜而不適用 。本文描述一種由資料驅動(Data-driven) 的回音消除器並模擬觀察其效 果。它結合頻率域及時序域捲積(Time-domain Convolution)的信號處理 技術而降低了複雜度且適用於利用DMT (Dis- crete Multitone)技術之非 對稱數位用戶迴路。本文並用 "回音量測" (Echo Measurement)的方法來 達到快速收斂的目的。此外，採用簡單的 1-D 濾波器或(1-D)^2 濾波器 於回音消除器中可省去時序域捲積的一部分，進一步降低了複雜度及運算 量。 Echo is a very serious problem for the full-duplex transmission over subscriber loop. Hybrid circuit can not solve this problem because of its imperfect. Thus the echo canceller is usuallly necessary in the transceiver. Because of the high transmitting rate of ADSL(asymmetric digital subscriber loop), echo canceller becomes too complex. A lowcomplexity data- driven echo canceller is described and simulated. It combines frequency-domain LMS filter and time- domain convolution, and suits the ADSL with DMT. A method of "echo measurement" is proposed to make it converge quickly. A simple 1-D filter or (1-D)^2 filter is included in the echo canceller to reduce the complexity and computation by saving some part of time-domain convolution.