A frequency-domain approach to crosstalk identification in xDSL systems

Crosstalk between multiple services transmitting through the same telephone cable is the primary limitation to digital subscriber line services. From a spectrum management point of view, it is important to have an accurate map of all the services that generate crosstalk into a given pair. If crosstalk is measured via modem-based methods, i.e., while a digital subscriber line (DSL) system is running, what is measured is the crosstalk in the bandwidth of the considered DSL system. For this reason, DSL services running on adjacent pairs may not be detected if their bandwidth is not significantly overlapping with the bandwidth of the disturbed system. This is a major drawback of modem-based system identification techniques since, from a spectrum management point of view, it is important to be able to identify all crosstalkers. We address the important problem of crosstalk identification when the pair under test does not bear DSL services, i.e., via a non-modem-based approach. Crosstalk sources are identified in the frequency domain by finding the maximum correlation with a "basis set" of representative measured crosstalk couplings. The effectiveness of the proposed technique is also verified on the basis of real crosstalk measurements performed on actual cables. Finally, new techniques based on multiple regression and best basis selection are also discussed.