The capacity of NEXT-impaired subscriber loops

The capacities of near-end crosstalk (NEXT) coupled channels when the power spectral densities of the signals in the two directions of transmission are permitted to be unequal are determined. It is assumed that each of the channels is equipped with a different front-end receiving filter. The transmitted signal spectrum is chosen to maximize the channel capacity subject to a constraint on the crosstalk power at the output of the front-end filter on the disturbed channel. The front-end filter characteristics are optimized to maximize the capacity thus obtained. Calculations show that the improvement introduced is small unless the signals transmitted in the two directions of transmission are allowed to occupy different frequency bands