Decision-feedback equalizer for cancelling CW interference

摘要

In an interference canceller, a feedforward filter receives an input signal to produce an equalized feedforward output signal in which CW interference is cancelled and a feedback filter receives the output of a decision circuit to produce an equalized feedback output signal. The equalized feedforward and feedback output signals are combined together to cancel intersymbol interference before being applied to the decision circuit. First tap-gain control circuits derive first tap-gain signals from a decision error and signals at the first delay-line taps and respectively apply these signals to the first tap-gain multipliers. Second tap-gain control circuits derive second tap-gain signals from the decision error and signals at the second delay-line taps and respectively apply these signals to the second tap-gain multipliers. A complex correlation is detected between signals at opposite ends of the first tapped delay line and compared with a threshold. At the instant the detected correlation becomes lower than the threshold, all tap-gain control circuits are caused to hold their outputs at the amplitude values which were attained at that instant. In a modified embodiment, correlations between the input signal received by the first tapped delay line and the delayed signals at the first delay-line taps are detected and normalized by a factor 1/N where N is equal to the number of delay taps. The normalized correlations are used as the tap-gain signals for all the tap-gain multipliers.