Wideband digital subscriber access with multidimensional block modulation and decision-feedback equalization

The potential transmission performance of pair-wire subscriber lines at the rate of 800 kb/s is investigated. Block modulation schemes of one to four dimensions, at 2 bits/dimension, are considered. The multiple dimensions are multiplexed together using time division multiplexing. The environmental noise is assumed to be dominated by near-end crosstalk. Computer simulation shows that the coding gain of a multidimensional modulation scheme is fully preserved after transmission if the equalizer is long. However, the gain can be much lower, or none at all, if the equalizer is short and hence unable to whiten the decision-point noise sufficiently