Crosstalk identification in xDSL systems

Crosstalk among telephone lines in the same or neighboring bundles is a maj or impairment in current xDSL systems. This paper proposes a novel idea of an impartial third party that identifies the crosstalk coupling functions a mong the twisted pairs in these xDSL systems. The crosstalk identification technique includes the following four major procedures: 1) the transmitted and received signals from each DSL modem for a predefined time period are c ollected and sent to the third party; 2) the signals are resampled accordin g to the clock rate of the receiver of interest; 3) the signals' timing dif ferences are estimated by cross correlation; and 4) the crosstalk coupling functions are estimated using the least-squares method. The performance of the cross correlation and least-squares methods is analyzed to determine th e amount of data needed for identification. Simulation results show that th e proposed methods can identify the crosstalk functions accurately and are consistent with theoretical analysis. These identified crosstalk functions can be used to significantly improve the data rate (e.g., multiuser detecti on) and to facilitate provisioning, maintenance, and diagnosis of the xDSL systems.