Modems, methods, and computer program products for identifying a signaling alphabet in variance with an ideal alphabet due to digital impairments

A modem having a signaling alphabet identification capability for decoding transmitted symbols, comprising:

• means for establishing a plurality of alphabet thresholds corresponding to valid transmitted symbols;
• means for receiving the transmitted symbols in an equalizer and generating output symbols in response thereto;
• means for computing an average value for each of the output symbols corresponding to the plurality of alphabet thresholds;
• and
• means for updating the alphabet thresholds with their corresponding average values.

A computer program product for identifying a signaling alphabet used by a modem receiver to decode transmitted symbols, comprising:

• a computer readable storage medium having computer readable program code means embodied therein, the computer readable code means comprising:
• logic configured to establish a plurality of alphabet thresholds corresponding to valid transmitted symbols;
• logic configured to receive the transmitted symbols in an equalizer and generate output symbols in response thereto;
• logic configured to compute an average value for each of the output symbols corresponding to the plurality of alphabet thresholds;
• and
• logic configured to update the alphabet thresholds with their corresponding average values.