Abstract: Symbols which are representative of customer data are transmitted in bursts. In the idle mode, i.e., the time intervals between bursts, symbol sequences which are a priori known to the receiver are transmitted. Such idle mode symbols maintain adaptive apparatus, such as NEXT cancellers and equalizers, in their properly converged state. To reduce crosstalk and spectral emissions, the idle mode symbols are selected to be the innermost symbols in the signal constellation encompassing the ensemble of all symbols.

Abstract: A technique for use in communications systems utilizing busy and idle modes. In the busy mode, symbols representative of data are transmitted to system end users. In the idle mode, during which no data is communicated to end users, idle mode symbols are transmitted. Such idle mode symbols are not used to represent data and are only transmitted during the idle mode. Advantageously, such idle mode symbols maintain adaptive apparatus, such as AGC circuits, NEXT cancellers and equalizers, in their properly converged state. In the disclosed embodiment, the idle mode symbols are the innermost symbols in a signal constellation and transition from the idle to busy mode is represented by the transmission of a predetermined number of outermost symbols in the signal constellation. Use of such symbols for idle-to-busy mode transitions advantageously provides ready detection of such transitions. In addition, use of the innermost symbols for the idle mode reduces spectral emission and crosstalk.