PAM radio signal receiver with phase-tracker succeeding adaptive FIR filtering and preceding adaptive IIR filtering
First Claim
1. In combination:
- a receiver for supplying digital samples of a baseband demodulation response to the pulse amplitude modulation of said selected radio-frequency carrier, which pulse amplitude modulation provides symbol coding of digital data;
first adaptive digital filtering with adjustable weighting coefficients, connected for receiving said baseband demodulation response as its input signal and for supplying its response to said baseband demodulation response;
second adaptive digital filtering with adjustable weighting coefficients, connected for receiving a feedback signal as its input signal and for supplying its response to said feedback signal;
apparatus for adjusting the sampling of the response of said first adaptive digital filtering to generate an adjusted first adaptive digital filtering response providing for minimal intersymbol interference in an equalizer response to said baseband demodulation response;
apparatus for combining the adjusted first adaptive digital filtering response with the second adaptive digital filtering response to generate said equalizer response to said baseband demodulation response;
apparatus for adapting the adjustable weighting coefficients of said first adaptive digital filtering and said second adaptive digital filtering to equalize symbol coding in said equalizer response; and
circuitry for deriving said feedback signal from said equalizer response.
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Abstract
A PAM receiver for reproducing a baseband signal that symbol codes digital data is combined with an decision-feedback equalizer (DFE) incorporating first adaptive digital filtering as a feed-forward element and second adaptive digital filtering as a feedback element. The DFE response is supplied to symbol decoding circuitry for reproducing the digital data. A de-rotator re-samples the first adaptive digital filtering response before it is combined with the second adaptive digital filtering response to generate an equalizer response. The resulting baud-rate equalizer response is sampled at baud rate and quantized to generate baud-rate decisions that applied to the second adaptive digital filtering as input signal, for completing the decision-feedback loop. The re-sampling of the first adaptive digital filtering response by the de-rotator is controlled, so as to provide a phase-tracker that reduces phase noise and intersymbol interference, prior to the making of decisions for decision feedback.
52 Citations
17 Claims
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1. In combination:
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a receiver for supplying digital samples of a baseband demodulation response to the pulse amplitude modulation of said selected radio-frequency carrier, which pulse amplitude modulation provides symbol coding of digital data;
first adaptive digital filtering with adjustable weighting coefficients, connected for receiving said baseband demodulation response as its input signal and for supplying its response to said baseband demodulation response;
second adaptive digital filtering with adjustable weighting coefficients, connected for receiving a feedback signal as its input signal and for supplying its response to said feedback signal;
apparatus for adjusting the sampling of the response of said first adaptive digital filtering to generate an adjusted first adaptive digital filtering response providing for minimal intersymbol interference in an equalizer response to said baseband demodulation response;
apparatus for combining the adjusted first adaptive digital filtering response with the second adaptive digital filtering response to generate said equalizer response to said baseband demodulation response;
apparatus for adapting the adjustable weighting coefficients of said first adaptive digital filtering and said second adaptive digital filtering to equalize symbol coding in said equalizer response; and
circuitry for deriving said feedback signal from said equalizer response. - View Dependent Claims (2, 3, 4, 5)
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6. In combination:
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a receiver for supplying digital samples of a first baseband signal descriptive of the pulse amplitude modulation of a selected radio-frequency carrier, which pulse amplitude modulation provides symbol coding of digital data;
first adaptive digital filtering with adjustable weighting coefficients, connected for receiving said digital samples of said first baseband signal as its input signal, and connected for supplying digital samples of a second baseband signal as its response to said first baseband signal;
a first digital adder for combining digital samples of a third baseband signal with digital samples of a fourth baseband signal, to generate digital samples of a fifth baseband signal;
a data-slicer for quantizing baud-rate digital samples of said fifth baseband signal to generate a sixth baseband signal;
second adaptive digital filtering with adjustable weighting coefficients, connected for receiving as its input signal digital samples of said fifth baseband signal, and connected for supplying the digital samples of said third baseband signal as its response to said sixth baseband signal;
apparatus for adapting the adjustable weighting coefficients of said first adaptive digital filtering and said second adaptive digital filtering to equalize symbol coding of said fifth baseband signal;
circuitry for reproducing said digital data from said fifth baseband-signal; and
a first phase-tracker, connected for receiving as is input signal said second baseband signal supplied as the response of said first adaptive digital filtering, and connected for supplying digital samples of said fourth baseband signal as re-sampled response of said second baseband signal, the phasing of the re-sampling of said second baseband signal by said first phase-tracker being controlled so as to reduce intersymbol interference in the symbol coding of said fifth baseband signal. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13, 14)
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15. In combination:
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a receiver for supplying digital samples of a baseband demodulation response to the pulse amplitude modulation of said selected radio-frequency carrier, which pulse amplitude modulation provides symbol coding of digital data, said digital samples of said baseband demodulation response being supplied at a double baud rate that is twice the baud rate of said pulse amplitude modulation;
first adaptive digital filtering with adjustable weighting coefficients, connected for receiving said baseband demodulation response as its input signal, and connected for supplying at said double baud rate digital samples of its response to said baseband demodulation response;
apparatus for re-sampling the response of said first adaptive digital filtering with a plurality P of different sampling phases to generate P respective re-sampled first adaptive digital filtering responses each sampled at said double baud rate, P-being a positive integer greater than one;
circuitry for re-sampling a to said double baud rate a decision-feedback signal generated at the baud rate of said pulse amplitude modulation, thereby to generate a re-sampled decision-feedback signal;
second adaptive digital filtering with adjustable weighting coefficients, connected for receiving a re-sampled decision-feedback signal as its input signal, and connected for supplying at said double baud rate digital samples of its response to said re-sampled decision-feedback signal;
a plurality P in number of digital adders originally numbered first through Pth, each connected for receiving said second adaptive digital filtering response as one of its summand input signals, each connected for receiving a respective one of said P re-sampled first adaptive digital filtering responses as another of its summand input signals, and each connected for supplying at said double baud rate digital samples of a respective sum output signal;
a plurality P in number of 2;
1 decimation filters originally numbered first through Pth, each connected for receiving the sum output signal of the digital adder with corresponding ordinal number and for supplying a respective decimation response to that sum output signal;
a plurality P in number of data-slicers ordinary numbered first through Pth, each data-slicer connected for receiving as its respective input signal the decimation response of said 2;
1 decimation filter with corresponding ordinal number and for quantizing that decimation response to generate a respective output signal for that said data-slicer;
a plurality P in number of error detectors ordinary numbered first through Pth, each error detector connected for measuring how much the input and output signals of said data-slicer with corresponding ordinal number depart from each other and for supplying the absolute value of the resulting measurement as a respective output signal for that said error detector;
a plurality P in number of accumulators ordinally numbered first through Pth, each connected for accumulating over a prescribed period of time the respective output signal of said error detector with corresponding ordinal number and for supplying the accumulation result;
apparatus for adapting the adjustable weighting coefficients of said first adaptive digital filtering and said second adaptive digital filtering to equalize symbol coding of an equalizer output signal selected from the respective sum output signals of said plurality of digital adders ordinally numbered first through Pth;
comparison circuitry for determining by comparison which of the accumulators ordinally numbered first through Pth supplies the smallest accumulation result;
first selection circuitry for reproducing the respective sum output signal of a selected one of said digital adders ordinally numbered first through Pth, the selected one of said digital adders ordinally numbered first through Pth having the same ordinal number as said accumulator determined by said comparison circuitry to supply the smallest accumulation result, the sum output signal reproduced by said first selection circuitry providing said equalizer output signal as sampled at said double baud rate;
apparatus for generating a decision-feedback signal as its response to said equalizer output signal;
circuitry for re-sampling said decision-feedback signal to said double baud rate to generate said re-sampled decision-feedback signal supplied to said second adaptive digital filtering as the input signal thereof. - View Dependent Claims (16, 17)
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Specification