Time-diversity interference canceler with add/subtract/select circuit responsive to decision error

Claim 2

An interference canceler comprising: a first time-diversity branch including a first complex multiplier for multiplying a signal recovered from a quadrature modulated carrier by a first correlation value; a second time-diversity branch including a delay element for producing a delayed version of the recovered signal and a second complex multiplier for multiplying the delayed version of the recovered signal by a second correlation value; an adder for additively combining output signals from the first and second complex multipliers; a subtractor for subtractively combining the output signals of said complex multipliers; amplifier means for producing a reference signal representative of an envelope of the output signal of the adder; a first correlator for detecting a correlation between the recovered signal and the reference signal and deriving therefrom said first correlation value; a second correlator for detecting a correlation between the delayed version of the recovered signal and the reference signal and deriving therefrom said second correlation value; a selector for selecting one of the outputs of the amplifier means and the subtractor; a decision feedback equalizer for operating on the output signal selected by the selector to produce a decision output and a decision error; and a comparator for comparing the decision error with a threshold value and controlling said selector depending on whether the decision error is higher or lower than the threshold value.

Claim 3

An interference canceler as claimed in claim 1, wherein said decision feedback equalizer comprises: a forward filter having a tapped delay line for receiving the output signal of the selector, a plurality of multipliers for weighting tap signals on the delay line by respective tap-weight coefficients, and an adder for summing the weighted tap signals to produce an output signal of the forward filter, said tapped delay line has a reference tap located at the center of the delay line; a backward filter having a tapped delay line for receiving the decision output, a plurality of multipliers for weighting tap signals on the delay line by respective tap-weight coefficients, and an adder for summing the weighted tap signals to produce an output signal of the backward filter; a combiner for combining the output signals of the forward and backward filters; a decision circuit connected to the output of the combiner for producing said decision output; an error detector connected to the input and output of the decision circuit for producing said decision error; and a plurality of first correlators for detecting correlations between the decision error and the tap signals of the forward filter and deriving therefrom the tap weight coefficients of the forward filter and a plurality of second correlators for detecting correlations between the decision error and the tap signals of the backward filter and deriving therefrom the tap weight coefficients of the backward filter.

Claim 4

An interference canceler comprising: first and second diversity branches, each of the diversity branches including: a first time-diversity branch inducting a first complex multiplier for multiplying a signal recovered from a quadrature modulated carrier by a first correlation value; a second time-diversity branch including a delay element for producing a delayed version of the recovered signal and a second complex multiplier for multiplying the delayed version of the recovered signal by a second correlation value; an adder for additively combining output signals from the first and second complex multipliers; a subtractor for subtractively combining the output signals of said complex multipliers; amplifier means for producing a first reference signal representative of an envelope of the output signal of the adder; a first correlator for detecting a correlation between the recovered signal and the first reference signal and deriving therefrom said first correlation value; a second correlator for detecting a correlation between the delayed version of the recovered signal and the first reference signal and deriving therefrom said second correlation value; and a selector for selecting one of the outputs of the amplifier means and the subtractor; first and second adaptive matched filters for respectively operating on the output signals of the selectors of the first and second diversity branches using a second reference signal and producing matched filter output signals which are matched in phase with each other; a combiner for combining the matched filter output signals to produce a combined output signal; a decision feedback equalizer for operating on the combined output signal to produce a decision output and a decision error and applying the decision output to the first and second adaptive matched filters as said second reference signal; and a comparator for comparing the decision error with a threshold value and controlling the selectors of the first and second diversity branches depending on whether the decision error is higher or lower than the threshold value.

Claim 5

An interference canceler comprising: first and second diversity branches, each of the diversity branches including: a first time-diversity branch inducting a first complex multiplier for multiplying a signal recovered from a quadrature modulated carrier by a first correlation value; a second time-diversity branch including a delay element for producing a delayed version of the recovered signal and a second complex multiplier for multiplying the delayed version of the recovered signal by a second correlation value; an adder for additively combining output signals from the first and second complex multipliers; a subtractor for subtractively combining the output signals of said complex multipliers; amplifier means for producing a first reference signal representative of an envelope of the output signal of the adder; a first correlator for detecting a correlation between the recovered signal and the first reference signal and deriving therefrom said first correlation value; a second correlator for detecting a correlation between the delayed version of the recovered signal and the first reference signal and deriving therefrom said second correlation value; and a selector for selecting one of the outputs of the amplifier means and the subtractor; first and second adaptive matched filters for respectively operating on the output signals of the selectors of the first and second diversity branches using a second reference signal and producing matched filter output signals which are matched in phase with each other; a combiner for combining the matched filter output signals to produce a combined output signal; a decision feedback equalizer for operating on the combined output signal to produce a decision output and a decision error and applying the decision output to the first and second adaptive matched filters as said second reference signal; and a comparator for comparing the decision error with a threshold value and controlling the selectors of the first and second diversity branches depending on whether the decision error is higher or lower than the threshold value.

Claim 6

An interference canceler as claimed in claim 3, wherein said decision feedback equalizer comprises: a forward filter having a tapped delay line for receiving the combined output signal of the combiner, a plurality of multipliers for weighting tap signals on the delay line by respective tap-weight coefficients, and an adder for summing the weighted tap signals to produce an output signal of the forward filter, said tapped delay line has a reference tap located at the center of the delay line; a backward filter having a tapped delay line for receiving the decision output, a plurality of multipliers for weighting tap signals on the delay line by respective tap-weight coefficients, and an adder for summing the weighted tap signals to produce an output signal of the backward filter; a combiner for combining the output signals of the forward and backward filters; a decision circuit connected to the output of the combiner for producing said decision output; an error detector connected to the input and output of the decision circuit for producing said decision error; and a plurality of first correlators for detecting correlations between the decision error and the tap signals of the forward filter and deriving therefrom the tap weight coefficients of the forward filter, and a plurality of second correlators for detecting correlations between the decision error and the tap signals of the backward filter and deriving therefrom the tap weight coefficients of the backward filter.