Evaluation of near-end crosstalk noise affecting ADSL systems

One of the major concerns related to the introduction of asymmetric digital subscriber line (ADSL) systems is the compatibility between such systems and transmission systems already deployed in the access network. In particular, three main noise sources must be considered, namely, near-end crosstalk (NEXT), far-end crosstalk (FEXT) and impulsive noise. The problem of evaluating the amount of NEXT noise on ADSL receivers due to DSL, HDSL, E1 and POTS disturbers is considered. Firstly, mathematical expressions for the power spectral density (PSD) of the above disturbers are provided and an expression for evaluating NEXT noise PSD is presented. Finally, the results obtained considering different scenarios (i.e., low-noise, high-noise and worst case NEXT coupling), are reported and discussed with the aim of providing useful information and guidelines for the introduction of ASDL systems in the access network