1. A method for transmitting data over an intersymbol interference channel using a predetermined signal-space code, the method comprising the steps of: receiving a sequence of input signal points (408) selected from a predetermined constellation of signal points; and adding a dither signal to each of the input signal points, the dither signal (406) applied to a present signal point being selected as a function of previous signal points in the sequence and the current state of a finite-state machine (400) used to generate the signal-space code.