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 ma p of all the services that generate crosstalk into a given pair. If crossta lk is measured via modem-based methods, i.e., while a digital subscriber li ne (DSL) system is running, what is measured is the crosstalk in the bandwi dth 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 dra wback of modem-based system identification techniques since, from a spectru m management point of view, it is important to be able to identify all cros stalkers. In the present paper, we address the important problem of crossta lk 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 f requency domain by finding the maximum correlation with a "basis set" of re presentative measured crosstalk couplings. The effectiveness of the propose d technique is also verified on the basis of real crosstalk measurements pe rformed on actual cables. Finally, new techniques based on multiple regress ion and best basis selection are also discussed.