DSL transmission system with means for ensuring local echo orthogonality

A digital subscriber line transmission system comprising an IFFT circuit (14) generating successive outgoing time domain symbols (S) on a subscriber line from respective groups of digital frequency domain coefficients; an FFT circuit (18) generating groups of digital frequency domain coefficients from respective incoming time domain symbols (S') received on the subscriber line, a current incoming symbol being delayed with respect to a current outgoing symbol by a predetermined time interval ( delta ); and means (82) for, during an end portion of a current incoming symbol, subtracting from the signal (IN) received on the subscriber line an estimated echo obtained by a filter (84) from a signal portion (Xn+1) following the end of the current outgoing symbol, and adding thereto, through said filter, a beginning portion (Xn) of the current outgoing symbol, wherein said portions have a duration at least equal to said predetermined time interval.