QAM receiver with improved immunity to crosstalk noise

An equalization system for producing an output data signal from an input signal corrupted by channel distortion and crosstalk noise, the crosstalk noise having a frequency characteristic, the channel distortion causing inter-symbol interference, the equalization system comprising:

• an adaptive linear equalizer for filtering the input signal and producing an intermediate signal having reduced crosstalk noise and reduced inter-symbol interference, wherein the adaptive linear equalizer has a frequency response controllable by a first error signal;
• a decision-feedback equalizer connected to the adaptive linear equalizer, for filtering the intermediate signal and further reducing the inter-symbol interference contained therein, thereby to produce the output data signal;
• an offset filter connected to the adaptive linear equalizer, for filtering the intermediate signal in accordance with a selectable offset frequency response and producing an offset-filtered signal, wherein the offset frequency response is selected to resemble the crosstalk frequency characteristic;
• and
• an error calculation block connected to the decision-feedback equalizer, to the offset filter and to the adaptive linear equalizer, for measuring a characteristic of the difference between the offset-filtered signal and a delayed version of the output data signal, thereby to produce the first error signal.

A receiver used for producing a plurality of streams of digital data from a received analog input signal containing an analog message signal carrying the digital data, the message signal being centered about a carrier frequency and corrupted by channel distortion and crosstalk noise having respective frequency characteristics, the channel distortion causing inter-symbol interference, the receiver comprising:

• a bandpass filter for receiving the analog input signal and extracting the analog message signal therefrom;
• an analog-to-digital converter connected to the bandpass filter for converting the analog message signal to an intermediate digital signal;
• a demodulator connected to the analog-to-digital converter for creating a plurality of digital output signals from the intermediate digital signal;
• at least one decision-feedback equalizer connected to the demodulator for filtering the digital output signals and creating the digital data streams therefrom;
• and
• an adaptive equalization means placed at one or more points between the bandpass filter and the at least one decision-feedback equalizer, the adaptive equalization means having a selectable overall frequency response;
• wherein the overall frequency response of the adaptive equalization means is selected to resemble a difference between the inverse of the frequency characteristic of the channel distortion and the frequency characteristic of the crosstalk noise.