Abstract: A blind convergence process for an adaptive decision feedback equalizer that includes an quadrature amplitude modulation (QAM) slicer having a index n, a forward filter defined by a plurality of forward tap coefficients and a feedback filter defined by a plurality of feedback tap coefficients. The blind convergence process includes initializing the forward tap coefficients of the forward filter and the feedback tap coefficients of the feedback filters with predetermined values. The slicer operates in two modes: a clustering mode and a decision directed mode. In the clustering mode the following steps are performed: (1) update the forward tap coefficients of the forward filter using an error estimate (e.g. Sato error), and (2) update the feedback tap coefficients of the feedback filter using an error estimate (e.g. Sato error).

Abstract: A system of energy detection for detecting a valid signal in a modem to enable power savings in receiver and transmitter circuits. The method of energy detection includes the steps of: (a) processing a prescribed number of signal samples (e.g. typically between 512 and 2048); (b) determining an average energy level for the prescribed number of signal samples; (c) determining a gain of an amplifier based on the processed signal samples; (d) comparing the average energy level with a prescribed energy level threshold; and (e) comparing the gain of the amplifier with a prescribed amplifier gain threshold. If the average energy level is greater than the prescribed energy level threshold and if the gain of the amplifier is less than the prescribed amplifier gain threshold then a valid signal is declared and the transmitter of the modem is activated.

Abstract: A method of detecting misconvergence in an equalizer having a quadrature amplitude modulation (QAM) slicer having an index n. The method includes the steps of initializing a plurality of signal counters then processing random symbols (for example between 500 and 20000 symbols) through the equalizer where the symbols are quantized into an appropriate constellation point in an n-QAM constellation map, where each signal counter corresponds to a respective one of the constellation points in the constellation map. The signal counters are incremented when one of the symbols is quantized to the corresponding constellation point. After the signals have been processed into the constellation map the number of non-zero counters are detected. If the number of non-zero counters is less than a prescribed number (for example between approximately 0.5n and approximately 0.

Abstract: A method of estimating signal-to-noise ratio at an output of an adaptive decision feedback equalizer receiving an input signal. The method of SNR estimation includes (a) calculating an average output error of the equalizer; and (b) estimating the signal-to-noise ratio (SNRest=kn−20 log10(Eavg)) where kn is a constant based on a QAM index n and Eavg is the average output error of the equalizer. The estimated SNR can be used to detect proper equalizer convergence by comparing the estimated SNR to an SNR threshold (e.g. lowest SNR for a 4QAM signal), wherein the equalizer is not properly converged when the estimated SNR is lower than the SNR threshold. The estimated SNR can also be used to adjust the operating QAM index of the equalizer by comparing the estimated SNR to an ideal SNR based on an objective bit error rate for a prescribed QAM index, and reconverging the equalizer at a QAM index lower than the prescribed QAM index when the estimated SNR is lower than the ideal SNR.

Abstract: A blind convergence process for an adaptive decision feedback equalizer having an quadrature amplitude modulation (QAM) slicer, a forward filter defined by a plurality of forward tap coefficients and a feedback filter defined by a plurality of feedback tap coefficients. The blind convergence process includes the step of initializing the forward tap coefficients of the forward filter and the feedback tap coefficients of the feedback filters with predetermined values. The QAM slicer operates in two modes: a clustering mode and a decision directed mode. The clustering mode includes the step of updating only the forward tap coefficients of the forward filter for a prescribed start-up QAM index (such a 4 QAM). The decision directed mode is predefined for set of QAM indexes having values n1, n2, . . .

Abstract: A method of reducing leakage noise introduced to an equalizer in a modem during steady state operation. The equalizer includes forward and feedback filters represented by tap coefficients. The tap coefficients of the filters are updated using least mean squares adaptation equations at a symbol rate during steady state operation. The method of the invention includes the steps of: (a) reducing the absolute value of the updated tap coefficients of the filters at a prescribed rate that is less than the symbol rate. Long term convergence stability is improved and leakage noise is reduced by leaking the filter coefficients less frequently than the symbol rate.