Interference canceller with feedforward transversal filter having switched tap-gain coefficients

An interference canceller comprising:

• means for detecting an interference signal transmitted from an undersired source for generating a gate control signal when the interference signal is detected;
• a feedforward equalizer for operating on a signal received by an antenna and producing an equalized feedforward output signal, said feedforward equalizer comprising (N-1) delay-line elements connected in series to define N delay-line taps for producing successively delayed versions of said received signal at said N delay-line taps, N multipliers for operating on the delayed signals at said delay-line taps, N correlators responsive to a first error control signal for modifying signals at said delay-line taps for respectively supplying tap-gain signals to said multipliers, summing means for combining outputs from said N multipliers into said equalized feedforward output signal, and means for nullifying the outputs of (N-1) ones of said N multipliers in response to said gate control signal;
• a decision circuit for deriving a decision output signal from an equalized desired signal;
• a first feedback equalizer for operating on decision output signals from said decision circuit in accordance with said first error control signal;
• a second feedback equalizer for nonlinearly filtering decision output signals from said decision circuit in accordance with a second error control signal for generating an estimate of a desired component of said equalized feedforward output signal;
• a first combiner for combining outputs from said second feedback equalizer and said feedforward equalizer and producing and supplying an estimate of an undesired component of said equalized feedforward output signal to said second feedback equalizer as said second error control signal;
• a second combiner for combining outputs from said first combiner, said feedforward equalizer and said first feedback equalizer and generating said equalized desired signal for said decision circuit;
• means responsive to a difference between the outputs of said second combiner and said decision circuit for generating said first error control signal for said feedforward equalizer and said first feedback equalizer;
• and
• gate means for establishing a connection between the output of said first combiner and an input of said second combiner in response to the presence of said gate control signal and clearing said connection in response to the absence of said gate control signal.