Feedback nonlinear equalization of modulated data signals
First Claim
1. An arrangement for .[.equalizing.]. .Iadd.processing .Iaddend.samples of a received modulated data signal having a predetermined carrier frequency, said arrangement including means operative in response to said samples for forming decisions as to the values of data symbols represented thereby, each of said decisions being represented by a complex number,characterized in that said arrangement further includes means (51-55, 61-65) for forming a plurality of signal products associated with an individual one of said samples, each multiplicand of each product being derived from a respective one of said decisions, each said respective one of said decisions bearing a predetermined temporal relationship to said one of said samples, at least one multiplicand of individual ones of said signal products being the complex conjugate of the decision from which said one multiplicand is derived, and means (71-75) for multiplying each of .Iadd.at least ones of .Iaddend.said products by an associated coefficient and by a predetermined harmonic of said carrier frequency to form a plurality of modulated weighted products, .Iadd.and further characterized in that .Iaddend.said decision forming means .[.including.]. .Iadd.includes .Iaddend.data recovery means (14, 17) for forming a decision as to the value of the data symbol represented by said one of said samples in response to said modulated weighted products.
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Accused Products
Abstract
A receiver for a quadrature amplitude modulated data signal impaired by linear and nonlinear distortion, phase jitter and additive noise includes circuitry which compensates for these impairments. In particular, the receiver includes a processor (FIG. 1 44; FIG. 2, 44'"'"') which subtracts a feedback nonlinear signal (FIG. 1, D(n); FIG. 2, D'"'"'(n)) from each sample of the received signal, either prior or subsequent to demodulation, providing compensation for nonlinear intersymbol interference. The feedback nonlinear signal subtracted from each sample is comprised of a weighted sum of products of individual data decisions and/or the complex conjugates of data decisions, each such product, in turn, being multiplied by a predetermined harmonic of the carrier frequency. In an illustrative embodiment, compensation for second- and third-order intersymbol interference is provided by including two- and three-multiplicand weighted products in the feedback nonlinear signal. Weighting coefficients for each product are adaptively updated in a decision-directed manner.
175 Citations
31 Claims
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1. An arrangement for .[.equalizing.]. .Iadd.processing .Iaddend.samples of a received modulated data signal having a predetermined carrier frequency, said arrangement including means operative in response to said samples for forming decisions as to the values of data symbols represented thereby, each of said decisions being represented by a complex number,
characterized in that said arrangement further includes means (51-55, 61-65) for forming a plurality of signal products associated with an individual one of said samples, each multiplicand of each product being derived from a respective one of said decisions, each said respective one of said decisions bearing a predetermined temporal relationship to said one of said samples, at least one multiplicand of individual ones of said signal products being the complex conjugate of the decision from which said one multiplicand is derived, and means (71-75) for multiplying each of .Iadd.at least ones of .Iaddend.said products by an associated coefficient and by a predetermined harmonic of said carrier frequency to form a plurality of modulated weighted products, .Iadd.and further characterized in that .Iaddend.said decision forming means .[.including.]. .Iadd.includes .Iaddend.data recovery means (14, 17) for forming a decision as to the value of the data symbol represented by said one of said samples in response to said modulated weighted products.
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8. An arrangement operative during each one of a plurality of successive sampling periods for .[.equalizing.]. .Iadd.processing .Iaddend.a respective one of a succession of .Iadd.linearly equalized .Iaddend.samples of a received modulated data signal having a predetermined carrier frequency, said arrangement including feedback means (FIG. 1, 44;
- FIG. 2, 44'"'"') for generating an individual feedback signal associated with said one sample, and decision forming means (FIG. 1-12, 14, 17, 46;
FIG. 2-12, 14, 17, 46'"'"') jointly responsive to said one sample and its associated feedback signal for forming a decision as to the value of .[.the.]. .Iadd.a .Iaddend.data symbol represented by said one sample, said one sample and said decision being represented by respective complex numbers,characterized in that said feedback signal includes a plurality of signal products .[.each.]. .Iadd.at least ones of which are .Iaddend.multiplied by an associated coefficient and by a predetermined harmonic of said carrier frequency, each multiplicand of each signal product being derived from a respective decision formed by said decision forming means during a previous one of said sampling periods, each said respective decision bearing a predetermined temporal relationship to said one sample, at least one multiplicand of individual ones of said signal products being the complex conjugate of the decision from which said one multiplicand is derived. - View Dependent Claims (9, 10, 11, 12, 13, 14)
- FIG. 2, 44'"'"') for generating an individual feedback signal associated with said one sample, and decision forming means (FIG. 1-12, 14, 17, 46;
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15. A method operative during each one of a plurality of successive sampling periods for .[.equalizing.]. .Iadd.processing .Iaddend.a respective one of a succession of complex samples of a received modulated data signal having a predetermined carrier frequency, said method including the steps of generating an individual feedback signal associated with said one sample, and forming a complex decision as to the value of the data symbol represented by said one sample in response to said one sample and its associated feedback signal,
characterized in that said feedback signal includes a plurality of signal products .[.each.]. .Iadd.at least ones of which are .Iaddend.multiplied by an associated coefficient and by a predetermined harmonic of said carrier frequency, each multiplicand of each signal product being derived from a respective decision formed during a previous one of said sampling periods, each said respective decision bearing a predetermined temporal relationship to said one sample and at least one multiplicand of individual ones of said signal products being the complex conjugate of the decision from which said one multiplicand is derived.
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22. A method for use in a receiver of the type in which a decision is formed during the nth one of a plurality of successive periods of duration T, said decision being formed by quantizing a respective demodulated sample of a received complex modulated data signal having a carrier frequency fc, both the carrier amplitude and phase of said signal being information bearing, said decision being represented by a complex number A(n), said method including the steps of
combining a feedback signal V(n) with said sample to form a signal Y(n) and forming said decision in response to said signal Y(n), said method characterized in that said signal V(n) includes the terms ##EQU22## where * indicates complex conjugate and Φ -
2,0 and Φ
1,1 are selected phase angles, the coefficients ##EQU23## having respective values associated with said decision A(n), and the index pairs (j1,j2) and (j3,j4) having respective sets of predetermined values. - View Dependent Claims (23, 24, 25, 26)
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2,0 and Φ
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27. A method for use in a receiver of the type in which a decision is formed during the nth one of a plurality of successive periods of duration T, said decision being as to the value of a respective demodulated complex sample of a received data signal modulated at a carrier frequency fc, both the carrier amplitude and phase of said signal being information bearing, said decision being represented by a complex number A(n), said method including the steps of
combining a feedback signal V(n) with said sample to form a signal Y(n) and forming said decision in response to said signal Y(n), said method characterized in that said signal V(n) includes the terms ##EQU34## where * indicates complex conjugate and Φ -
2,0 and Φ
1,1 are selected phase angles, the coefficients ##EQU35## having respective values associated with said decision A(n), and the index pairs (j1,j2) and (j3,j4) having respective sets of predetermined values. - View Dependent Claims (28, 29, 30, 31)
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2,0 and Φ
Specification