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高比特率数字用户环路技术是在光纤用户网普及之前，向用户提供宽带业务的一种过渡手段。DMT（离散多音频调制）是一种多载频调制，由于性能优越，被广泛应用于HDXSL和ADSL系统中。采取回波抵消的方法，可以提高系统传输速率、增加传输距离。本文着重介绍了基于DMT的HDSL和ADSL系统中的回被抵消技术─—TAFDEC（TimeandFrequencyDomainEchoCanceler）方法，即将频域的回波抵消器（EC）和时域的回波会成器（CES）结合起来，以达到减少运算量，降低复杂度的目的。并在此基础上，介绍一种改进结构，进一步降低复杂度。
High-bit-rate digital subscriber loop technology is a transitional means of providing broadband services to subscribers before the popularity of optical subscriber networks. DMT (Discrete Multi-tone Modulation) is a multi-carrier frequency modulation that is widely used in HDXSL and ADSL systems due to its superior performance. Take the echo cancellation method, you can increase the system transmission rate and increase the transmission distance. This article focuses on the time-frequency offset cancellation (TAFDEC) method in DMT-based HDSL and ADSL systems, combining the frequency domain echo canceller (EC) with the time domain echo renderer (CES) , In order to reduce the computational complexity and reduce the complexity of the purpose. Based on this, we introduce an improved structure to further reduce the complexity.