Pre-equalization technique for upstream communication between cable modem and headend

A cable modem termination system (CMTS) that can receive a signal transmitted in a cable modem system on an upstream channel, the CMTS comprising:

• a demodulator;
• a notch filter connected to the demodulator, the notch filter having coefficients that are adjustable to cancel noise applied to the demodulator;
• a media access controller (MAC) that processes binary data and generates for downstream transmission MAP messages that assign time slots in which cable modems may transmit signal bursts on the upstream channel;
• and
• a decision feedback equalizer coupled to the demodulator, the decision feedback equalizer including a feedforward filter for establishing pre-equalization coefficients.

A method for compensating for conditions on an upstream channel from a plurality of cable modems to a cable modem termination system (CMTS), the method comprising the steps of:

• transmitting on a downstream channel from the CMTS to a plurality of cable modems MAP messages that assign time slots in which cable modems may transmit signal bursts on the upstream channel, the MAP messages including idle slots that are assigned to no cable modems;
• monitoring conditions on the upstream channel during the idle slots;
• compensating for the monitored conditions on the upstream channel;
• and
• receiving at the CMTS signal bursts on the upstream channel after such compensation.

A method for compensating for conditions on an upstream channel from a plurality of cable modems to a cable modem termination system (CMTS), the method comprising the steps of:

• compensating for noise on an upstream channel;
• receiving on the compensated upstream channel a ranging signal from one of the cable modems;
• adjusting filter coefficients to compensate for intersymbol interference on the upstream channel responsive to the received ranging signal;
• and
• transmitting the adjusted coefficients on a downstream channel to the cable modem for the purpose of pre-equalization of the upstream channel.