On the NEXT and impulse noise properties of subscriber loops

The transmission range of subscriber loops carrying ISDN (integrated services digital network) signals with a net bit rate of 144 kb/s is limited mainly by the near-end crosstalk (NEXT) between cable pairs and by impulse noise transformed into these loops owing to their imperfect symmetry. In order to be able to predict this transmission range, a considerable amount of experimental and theoretical work was required prior to the introduction of ISDN for a better understanding of the cross-talk and noise phenomena in these loops. The author summarizes NEXT measurement results and modeling methods and reports on impulse noise measurements and the statistical models derived from them. Detailed results of swept-frequency measurements in different cables are considered. Measurement results indicate considerable variation in the density of impulse noises within 24 h, a hyperbolic distribution, interval distribution according to the sum of exponential functions, and steadily increasing amplitude density below 40 kHz