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DSL Advances by Peter J. Silverman, John M. Cioffi, Massimo Sorbara, Thomas Starr

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10.5. Foundation for Determining Acceptable Levels for Spectral Compatibility

As discussed in the previous chapter on spectral compatibility, near-end crosstalk (NEXT) is a much stronger disturber than far-end crosstalk (FEXT) because the crosstalk coupling between the wire pairs in the cable is much greater. Signals in the cable that have overlapping upstream and downstream frequency components will experience near-end crosstalk with each other. A special case of overlapping frequency spectra occurs with systems that use echo-cancellation for upstream and downstream duplexing. When the upstream and downstream signals use the same spectrum, there is full overlap of the frequency components, and the echo canceler removes the disturbance from the ...

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