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This letter addresses echo cancellation for digital subscriber line (DSL) communications with discrete multitone (DMT) modulation. The described adaptive echo canceller operates entirely in the frequency domain. The method allows estimation and subtraction of an echo signal impaired by intercarrier and intersymbol interference present when the impulse response of the echo channel is longer than the cyclic prefix. Implementation aspects for symmetric and asymmetric DMT-based systems are described together with ways to lower the computational complexity. Finally, computer simulation results are presented that validates the proposed method.Index Terms-Adaptive signal processing, DSL, echo cancellers, intersymbol interference.

This work proposes a new method for automatically identifying topologies of lines with one or more sections in a telephone network. The method is based on the examination of both impulse response and time-domain reflectometry trace of a line under test. They are analyzed using a method based on the wavelet transform that identifies and extracts features that contain information about the line topology. Those features are interpreted by an expert system composed of three sequential modules that estimate, respectively, the type of line makeup (serial or bridge tap), the lengths of the line sections, and the corresponding cable type, which are the parameters that completely identify the topology according to the assumed model. A thorough comparison with two state-of-the-art methods is also presented using several twisted-pair copper cables. The results show that the proposed method provides good accuracy with respect to topology identification at low computational cost.