Adaptive frequency domain equalizer circuits, systems, and methods for discrete multitone based digital subscriber line modem

A method of modem communication between first and second modems over a communications facility, comprising the steps of:

• operating the first modem to perform the steps of:
• communicating a first set of communications to the second modem over the communications facility, wherein the first set of communications comprise a plurality of subchannel signals;
• and
• issuing a second set of communications to the second modem over the communications facility, wherein the second set of communications comprise a plurality of subchannel signals;
• and
• operating the second modem to perform the steps of:
• converting the first set of communications from time domain communications to frequency domain communications, wherein the frequency domain communications from the first set of communications comprise a plurality of subchannel signals, and wherein each of the plurality of subchannel signals from the first set of communications comprises an amplitude portion and a phase portion;
• equalizing the amplitude portion of each of the plurality of subchannel signals from the first set of communications using the fixed gain factors;
• equalizing the phase portion of each of the plurality of subchannel signals from the first set of communications using the adjustable phase factors to form a corresponding plurality of equalized subchannel signals;
• adjusting the adjustable phase factors in response to a relationship between a target plurality of subchannel signals and the plurality of equalized subchannel signals from the first set of communications;
• converting the second set of communications from time domain communications to frequency domain communications, wherein the frequency domain communications signals from the second set of communications comprise a plurality of subchannel signals, and wherein each of the plurality of subchannel signals from the second set of communications comprises an amplitude portion and a phase portion;
• equalizing the amplitude portion of each of the plurality of subchannel signals from the second set of communications to an approximately equal value using fixed gain factors corresponding to each of the plurality of subchannel signals from the second set of communications;
• and
• equalizing the phase portion of each of the plurality of subchannel signals from the second set of communications using adjustable phase factors corresponding to each of the plurality of subchannel signals from the second set of communications, wherein the adjustable phase factors are adjusted in response to the first set of communications from the first modem to the second modem.

A method of modem communication between first and second modems over a communications facility, comprising the steps of:

• operating the first modem to issue communications to the second modem over the communications facility, wherein the communications comprise a plurality of subchannel signals;
• and
• operating the second modem to perform the steps of:
• adjusting an oscillator for adjusting a rate of sampling the communications;
• converting the communications from time domain communications to frequency domain communications, wherein the frequency domain communications signals comprise a plurality of subchannel signals, and wherein each of the plurality of subchannel signals comprises an amplitude portion and a phase portion;
• equalizing the amplitude portion of each of the plurality of subchannel signals;
• equalizing the phase portion of each of the plurality of subchannel signals using adjustable phase factors corresponding to each of the plurality of subchannel signals;
• wherein the step of operating the second modem to adjust the oscillator introduces a jitter phase shift into the subchannel signals;
• and
• wherein the adjustable phase factors are adjusted in response to a corrective phase shift complementary to the jitter phase shift.

A first modem comprising:

• an interface for coupling to a communications facility, the communications facility coupled to communicate with a second modem;
• and
• processing circuitry responsive to communications received over the communications facility from the second modem, wherein the communications comprise a plurality of subchannel signals, and for performing the steps of:
• converting the communications from time domain communications to frequency domain communications, wherein the frequency domain communications signals comprise a plurality of subchannel signals, and wherein each of the plurality of subchannel signals comprises an amplitude portion and a phase portion;
• equalizing the amplitude portion of each of the plurality of subchannel signals using fixed gain factors corresponding to each of the plurality of subchannel signals;
• and
• equalizing the phase portion of each of the plurality of subchannel signals using adjustable phase factors corresponding to each of the plurality of subchannel signals, wherein the adjustable phase factors are adjusted in response to previous communications from the second modem to the first modem.

A first modem comprising:

• an interface for coupling to a communications facility, the communications facility coupled to receive communications from a second modem;
• an oscillator coupled to the interface and for establishing a rate of sampling the communications;
• and
• processing circuitry responsive to the communications, wherein the communications comprise a plurality of subchannel signals, and for performing the steps of:
• adjusting the oscillator for adjusting the rate of sampling the communications;
• converting the communications from time domain communications to frequency domain communications, wherein the frequency domain communications signals comprise a plurality of subchannel signals, and wherein each of the plurality of subchannel signals comprises an amplitude portion and a phase portion;
• equalizing the amplitude portion of each of the plurality of subchannel signals;
• equalizing the phase portion of each of the plurality of subchannel signals using adjustable phase factors corresponding to each of the plurality of subchannel signal;
• wherein the step of adjusting the oscillator introduces a jitter phase shift into the subchannel signals;
• and
• wherein the adjustable phase factors are adjusted in response to a corrective phase shift complementary to the jitter phase shift.