Digital modulation signal receiver with adaptive channel equalization employing discrete fourier transforms
First Claim
1. A receiver apparatus for digital signals of a prescribed baud rate transmitted by respective amplitude-modulated radio-frequency carriers through a medium subject to multipath distortion, said receiver apparatus comprising:
- a receiver front-end connected for responding to any selected one of said digital signals transmitted by respective amplitude-modulated radio-frequency carriers through said medium subject to multipath distortion, to generate an amplitude-modulated intermediate-frequency carrier that is amplitude modulated in accordance with said selected one of said digital signals and any multipath distortion thereof;
demodulator and oversampling analog-to-digital conversion circuitry connected to receive said amplitude-modulated intermediate-frequency carrier from said receiver front-end and to supply a digital baseband signal at an oversampling rate higher than said prescribed baud rate;
an analyzer filter for generating the discrete Fourier transforms of successive portions of said digital baseband signal, said analyzer filter connected to receive said digital baseband signal from said demodulator and oversampling analog-to-digital conversion circuitry;
a bank of multipliers for multiplying the terms of each said discrete Fourier transform of said digital baseband signal, term by term, by respective ones of a set of adaptive weighting coefficients to generate a set of products describing the discrete Fourier transform of an equalizer response to said digital baseband signal;
apparatus for generating, in response to the discrete Fourier transforms of successive portions of said digital baseband signal that provide a sampling window moving through a succession of different positions in each of successive data fields, said set of adaptive weighting coefficients for use by said bank of multipliers;
a synthesizer filter connected for receiving said set of products from said bank of multipliers and for generating therefrom said equalizer response as the inverse discrete Fourier transform of said discrete Fourier transform of said equalizer response described by said set of products;
a decimation filter connected for re-sampling said equalizer response supplied from said synthesizer filter to generate as a decimation filter response an equalized digital baseband signal re-sampled at said prescribed baud rate; and
decoding apparatus connected for decoding said decimation filter response to recover a data stream.
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Abstract
Techniques for calculating the system characteristic of the adaptive filtering used for equalization and echo-suppression in a digital communications receiver, such as one used for receiving over-the-air broadcast digital television signal, are described. In these techniques, the system characteristic of the adaptive filtering is calculated from the discrete Fourier transform of successive portions of the input signal supplied to the adaptive filtering and from the discrete Fourier transform of corresponding portions of the transmitted signal, as estimated in the receiver. Receivers for implementing these techniques in various ways are also disclosed.
197 Citations
31 Claims
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1. A receiver apparatus for digital signals of a prescribed baud rate transmitted by respective amplitude-modulated radio-frequency carriers through a medium subject to multipath distortion, said receiver apparatus comprising:
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a receiver front-end connected for responding to any selected one of said digital signals transmitted by respective amplitude-modulated radio-frequency carriers through said medium subject to multipath distortion, to generate an amplitude-modulated intermediate-frequency carrier that is amplitude modulated in accordance with said selected one of said digital signals and any multipath distortion thereof; demodulator and oversampling analog-to-digital conversion circuitry connected to receive said amplitude-modulated intermediate-frequency carrier from said receiver front-end and to supply a digital baseband signal at an oversampling rate higher than said prescribed baud rate; an analyzer filter for generating the discrete Fourier transforms of successive portions of said digital baseband signal, said analyzer filter connected to receive said digital baseband signal from said demodulator and oversampling analog-to-digital conversion circuitry; a bank of multipliers for multiplying the terms of each said discrete Fourier transform of said digital baseband signal, term by term, by respective ones of a set of adaptive weighting coefficients to generate a set of products describing the discrete Fourier transform of an equalizer response to said digital baseband signal; apparatus for generating, in response to the discrete Fourier transforms of successive portions of said digital baseband signal that provide a sampling window moving through a succession of different positions in each of successive data fields, said set of adaptive weighting coefficients for use by said bank of multipliers; a synthesizer filter connected for receiving said set of products from said bank of multipliers and for generating therefrom said equalizer response as the inverse discrete Fourier transform of said discrete Fourier transform of said equalizer response described by said set of products; a decimation filter connected for re-sampling said equalizer response supplied from said synthesizer filter to generate as a decimation filter response an equalized digital baseband signal re-sampled at said prescribed baud rate; and decoding apparatus connected for decoding said decimation filter response to recover a data stream. - View Dependent Claims (2, 3)
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4. A receiver apparatus for digital signals of a prescribed baud rate transmitted by respective amplitude-modulated radio-frequency carriers through a medium subject to multipath distortion, said receiver apparatus comprising:
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a receiver front end connected for responding to any selected one of said digital signals transmitted by respective amplitude-modulated radio-frequency carriers through said medium subject to multipath distortion, to generate an amplitude-modulated intermediate-frequency carrier that is amplitude-modulated in accordance with said selected one of said digital signals and any multipath distortion thereof; analog-to-digital conversion circuitry connected to receive as its respective input signal said amplitude-modulated intermediate-frequency carrier from said receiver front-end and to supply, at an oversampling rate higher than said prescribed baud rate, a digitized amplitude-modulated intermediate-frequency carrier; an analyzer filter for generating the discrete Fourier transforms of successive portions of said digitized amplitude-modulated intermediate-frequency carrier, said analyzer filter connected to receive said amplitude-modulated intermediate-frequency carrier from said receiver front-end; a bank of multipliers for multiplying the terms of each said discrete Fourier transform of said amplitude-modulated intermediate-frequency carrier, term by term, by respective ones of a set of adaptive weighting coefficients to generate a set of products describing the discrete Fourier transform of an equalizer response to said amplitude-modulated intermediate-frequency carrier; apparatus for generating, in response to the discrete Fourier transforms of successive portions of said amplitude-modulated intermediate-frequency carrier that provide a sampling window moving through a succession of different positions in each of successive data fields, said successive sets of adaptive weighting coefficients for use by said bank of multipliers; a synthesizer filter connected for receiving said set of products from said bank of multipliers and for generating therefrom said equalizer response as the inverse discrete Fourier transform of said discrete Fourier transform of said equalizer response described by said set of products; digital synchrodyne circuitry connected to receive said equalizer response from said synthesizer filter and to supply a digital baseband signal at said oversampling rate higher than said prescribed baud rate; a decimation filter connected for re-sampling said digital baseband signal supplied from said digital syncrodyne circuitry, to generate as a decimation filter response an equalized digital baseband signal re-sampled at said prescribed baud rate; and decoding apparatus connected for decoding said decimation filter response to recover a data stream. - View Dependent Claims (5)
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6. A receiver apparatus for digital signals of a prescribed baud rate transmitted by respective amplitude-modulated radio-frequency carriers through a medium subject to multipath distortion, said receiver apparatus comprising:
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a receiver front-end connected for responding to any selected one of said digital signals transmitted by respective amplitude-modulated radio-frequency carriers through said medium subject to multipath distortion, to generate an amplitude-modulated intermediate-frequency carrier that is amplitude-modulated in accordance with said selected one of said digital signals and any multipath distortion thereof; a first adaptive digital filter having a kernel composed of weighting coefficients that can be adjusted, said first adaptive digital filter connected for supplying a first adaptive digital filter response to said amplitude-modulated intermediate-frequency carrier generated by said receiver front-end; apparatus for computing respective discrete Fourier transforms responsive to successive portions of said amplitude-modulated intermediate-frequency carrier that is amplitude-modulated in accordance with said selected one of said digital signals and any multipath distortion thereof, said successive portions of said amplitude-modulated intermediate-frequency carrier providing a sampling window moving through a succession of different positions in each of successive data fields; and apparatus for computing the weighting coefficients of said first adaptive digital filter so as to suppress an unwanted portion of said first adaptive digital filter response arising from the amplitude of said amplitude-modulated intermediate-frequency carrier being modulated in accordance with multipath distortion of said selected one of said digital signals, with the computation of said weighting coefficients being based on said discrete Fourier transforms of said successive portions of said amplitude-modulated intermediate-frequency carrier providing said sampling window moving through said succession of different positions in each of said successive data fields. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A receiver apparatus for single-carrier digital modulation signals of a prescribed baud rate transmitted by respective amplitude-modulated radio-frequency carriers through a medium subject to multipath distortion, said receiver apparatus comprising:
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a receiver front-end connected for responding to any selected one of said single-carrier digital modulation signals transmitted at radio frequencies, thereby to supply a converted digital modulation signal at intermediate frequencies; synchrodyning circuitry connected for responding to said converted digital modulation signal to supply a first digital baseband signal and a second digital baseband signal, said first digital baseband signal resulting from synchrodyning said converted digital modulation signal with an intermediate-frequency carrier of a leading first phasing, said second digital baseband signal resulting from synchrodyning said converted digital modulation signal with an intermediate-frequency carrier of a lagging second phasing in quadrature with said leading first phasing, the relative lead of said first phasing of said intermediate-frequency carrier and the relative lag of said second phasing of said intermediate-frequency carrier being adjustable in response to an automatic frequency and phase control signal; first and second adaptive digital filters, each having a respective kernel composed of weighting coefficients that can be adjusted, said first adaptive digital filter connected to receive as its respective input signal said first digital baseband signal supplied by said synchrodyning circuitry, said first adaptive digital filter connected to supply a first adaptive digital filter response to its respective input signal, said second adaptive digital filter connected to receive as its said respective input signal said second digital baseband signal supplied by said synchrodyning circuitry, and said second adaptive digital filter connected to supply a second adaptive digital filter response to its respective input signal; a first adaptive-filter-kernel computer for computing the weighting coefficients in the kernel of said first adaptive digital filter, said first adaptive-filter-kernel computer connected to receive said first adaptive digital filter response and to receive said first digital baseband signal supplied by said synchrodyning circuitry; a second adaptive-filter-kernel computer for computing the weighting coefficients in the kernel of said second adaptive digital filter, said second adaptive-filter-kernel computer connected to receive said second adaptive digital filter response and to receive said second digital baseband signal supplied by said synchrodyning circuitry; apparatus for recovering a data stream from an equalized in-phase digital modulation signal that is formed by combining said first adaptive digital filter response and said second adaptive digital filter response in a first way; and apparatus for recovering said automatic frequency and phase control signal from an equalized quadrature-phase digital modulation signal that is formed by combining said first adaptive digital filter response and said second adaptive digital filter response in a second way, one of said first and second ways of combining said first adaptive digital filter response and said second adaptive digital filter response being additive in nature and the other being subtractive in nature. - View Dependent Claims (24, 25)
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26. A receiver apparatus for single-carrier digital modulation signals of a prescribed baud rate transmitted by respective amplitude-modulated radio-frequency carriers through a medium subject to multipath distortion, said receiver apparatus comprising:
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apparatus for converting a selected one of said single-carrier digital modulation signals transmitted at radio frequencies to an amplitude-modulated intermediate-frequency carrier, an analog-to-digital converter connected to receive as its respective input signal said amplitude-modulated intermediate-frequency carrier from said apparatus for converting said selected one of said single-carrier digital modulation signals and to supply, at an oversampling rate higher than said prescribed baud rate, a digitized amplitude-modulated intermediate-frequency carrier, a phase-splitter connected to receive as its respective input signal said digitized amplitude-modulated intermediate-frequency carrier supplied from said analog-to-digital converter, said phase-splitter operable to supply orthogonal first and second phase-splitter responses; first and second adaptive digital filter, each having a respective kernel composed of weighting coefficients that can be adjusted, said first adaptive digital filter connected to receive as its respective input signal said first phase-splitter response supplied by said phase-splitter, said first adaptive digital filter connected to supply a first adaptive digital filter response to its respective input signal, said second adaptive digital filter connected to receive as its said respective input signal said second phase-splitter response supplied by said phase-splitter, and said second adaptive digital filter connected to supply a second adaptive digital filter response to its respective input signal; digital synchrodyne circuitry connected for generating at said oversampling rate a first digital baseband signal by synchrodyning said first adaptive digital filter response with an intermediate-frequency carrier of a leading first phasing and for generating at said oversampling rate a second digital baseband signal by synchrodyning said second adaptive digital filter response with an intermediate-frequency carrier of a lagging second phasing, the relative lead of said first phasing of said intermediate-frequency carrier and the relative lag of said second phasing of said intermediate-frequency carrier being adjustable in response to an automatic frequency and phase control signal; a first decimation filter connected for supplying a first decimation filter response generated by re-sampling to said prescribed baud rate said first digital baseband signal generated by said digital synchrodyne circuitry; a second decimation filter connected for supplying a second decimation filter response generated by re-sampling to said prescribed baud rate said second digital baseband signal generated by said digital synchrodyne circuitry; a first adaptive-filter-kernel computer for computing the weighting coefficients in the kernel of said first adaptive digital filter, said first adaptive-filter-kernel computer connected to receive said first decimation filter response and to receive said first phase-splitter response supplied by said phase-splitter; a second adaptive-filter-kernel computer for computing the weighting coefficients in the kernel of said second adaptive digital filter, said second adaptive-filter-kernel computer connected to receive said second decimation filter response and to receive said second phase-splitter response supplied by said phase-splitter; apparatus for recovering a data stream from an equalized in-phase digital modulation signal that is formed by combining said first decimation filter response and said second decimation filter response in a first way; and apparatus for recovering said automatic frequency and phase control signal from an equalized quadrature-phase digital modulation signal that is formed by combining said first decimation filter response and said second decimation filter response in a second way, one of said first and second ways of combining said first decimation filter response and said second decimation filter response being additive in nature and the other being subtractive in nature. - View Dependent Claims (27, 28)
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29. A method for adapting weighting coefficients for channel equalization filtering in a receiver for a digital signal of a prescribed baud rate transmitted by respective amplitude-modulated radio-frequency carriers through a channel apt to include more than transmission path for said digital signal, which digital signal is in substantial part randomized and is disposed in successive data fields, said method comprising the steps of:
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estimating from an actual input signal with accompanying multipath distortion thereof that is supplied to said channel equalization filtering what an ideal input signal supplied to said channel equalization filtering would be in the absence of said accompanying multipath distortion thereof; computing respective discrete Fourier transforms for successive portions of said actual input signal supplied to said channel equalization filtering and corresponding successive portions of said ideal input signal estimated from said actual input signal, said successive portions of said actual input signal providing a sampling window moving through a succession of different positions in each of said successive data fields including said substantial parts that are randomized; generating discrete Fourier transform specifications of said channel equalization filtering, through term-by-corresponding-term division of each of the discrete Fourier transforms of successive portions of said ideal input signal by the discrete Fourier transform of the corresponding portion of said actual input signal supplied to said channel equalization filtering; computing tentative sets of weighting coefficients for said channel equalization filtering from said discrete Fourier transform specifications of said channel equalization filtering; low-pass filtering successive said tentative sets of weighting coefficients for said channel equalization filtering to generate discrete Fourier transform descriptions of final sets of weighting coefficients for said channel equalization filtering; and utilizing said final sets of weighting coefficients for said channel equalization filtering. - View Dependent Claims (30, 31)
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Specification