Coherent phase shift keyed demodulator
First Claim
1. Apparatus for demodulating a phase modulated input carrier signal, comprising:
- means for sampling periodically an input carrier signal, converting each sample of the input carrier signal into a multi-bit input carrier signal representative of the input carrier signal at the moment of sampling, and generating instantaneous estimates of in-phase and quadrature-phase components of the current sample of the input carrier signal;
first control means for comparing the instantaneous estimates of the in-phase and quadrature-phase components of the current sample of the input carrier signal with prestored ideal components of an existing sample of the input carrier signal to determine phase angle deviation between the instantaneous estimates of the components and the ideal components; and
second control means for summing the phase angle deviation with a phase angle of the existing sample of the input carrier signal and a phase shift proportional to the differential phase shift between the baud period in which the current sample of the input carrier signal was taken and the baud period from which the existing sample of the input carrier signal was taken to effect a new phase angle for deriving a trigonometric function of the input carrier signal corresponding to the new phase angle for comparing with a next sample of the input carrier signal;
thereby incrementally effecting coherently demodulated and substantially ideal in-phase and quadrature-phase components of the input carrier signal.
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Accused Products
Abstract
A demodulator mechanism which uses estimates of the in-phase and quadrature-phase components of differential phase modulated carrier signals for performing a coherent demodulation of these signals is described. The instantaneous estimates, obtained from an estimator circuit, are fed into a differential carrier recovery circuit, which provides for a feedback of ideal sine and cosine components, and combined with the instantaneous estimates for incrementally decreasing a phase error signal generated in a computational circuit. By thus incrementally decreasing the phase error signal, an ideal phase angle is eventually obtained, thereby providing for coherent demodulated output components of the input carrier signals.
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Citations
22 Claims
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1. Apparatus for demodulating a phase modulated input carrier signal, comprising:
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means for sampling periodically an input carrier signal, converting each sample of the input carrier signal into a multi-bit input carrier signal representative of the input carrier signal at the moment of sampling, and generating instantaneous estimates of in-phase and quadrature-phase components of the current sample of the input carrier signal; first control means for comparing the instantaneous estimates of the in-phase and quadrature-phase components of the current sample of the input carrier signal with prestored ideal components of an existing sample of the input carrier signal to determine phase angle deviation between the instantaneous estimates of the components and the ideal components; and second control means for summing the phase angle deviation with a phase angle of the existing sample of the input carrier signal and a phase shift proportional to the differential phase shift between the baud period in which the current sample of the input carrier signal was taken and the baud period from which the existing sample of the input carrier signal was taken to effect a new phase angle for deriving a trigonometric function of the input carrier signal corresponding to the new phase angle for comparing with a next sample of the input carrier signal; thereby incrementally effecting coherently demodulated and substantially ideal in-phase and quadrature-phase components of the input carrier signal. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. Apparatus for demodulating a phase modulated carrier signal, comprising:
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means for periodically sampling an input carrier signal, converting each sample of the input carrier signal into a multi-bit input carrier signal representative of the amplitude values of the input carrier signal at the moment of sampling, and generating instantaneous estimates of in-phase and quadrature-phase components for a current sample of the input carrier signal; computational means for generating from the instantaneous estimates and cosine and sine components of an existing sample of the input carrier signal a phase error signal; delay means for outputting a current phase angle of the input carrier signal; summing means for adding to the phase error signal the phase angle of the current sample of the input carrier signal and a phase shift proportional to the differential phase shift between the baud period in which the current sample of the input carrier signal is taken and the baud period from which the existing sample of the input carrier signal was taken to effect a new phase angle; memory means for outputting a prestored trigonometric function representative of the current phase angle of the input carrier signal to the computational means as a feedback to incrementally eliminate the phase error signal; means for multiplying the trigonometric function from the memory means with the multi-bit input carrier signal and a corresponding phase shifted multi-bit input carrier signal, and adding results from the multiplying means to generate coherently demodulated in-phase and quadrature-phase components of the input carrier signal.
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9. Apparatus for demodulating a phase modulated carrier signal, comprising:
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sampling means for periodically sampling an input carrier signal and for converting each sample of the input carrier signal into a multi-bit input carrier signal representative of the amplitude values of the input carrier signal at the moment of sampling; filter means for filtering the multi-bit input carrier signal to generate a filtered carrier signal having the same amplitude values as the input carrier signal; filter and phase shift means for filtering and phase shifting the multi-bit input carrier signal to generate a filtered phase shifted carrier signal having the same amplitude values as the input carrier signal; estimator means for generating instantaneous estimates of components of the input carrier signal from the filtered carrier signals; computational means for generating from the instantaneous carrier signal estimates a phase error signal; delay means for outputting a current phase angle of the input carrier signal having a corresponding angular data binary number; summing means for adding to the phase error signal the current phase angle and a phase shift proportional to the differential phase shift between the baud period in which the sample of the input carrier signal is taken and the baud period from which an earlier sample of the input carrier signal was taken to effect a new phase angle to be fed to the delay means; and memory means for accepting the angular data binary number representative of the current phase angle from the delay means and for providing, in response thereto, cosine and sine components of the current phase angle, the components being fed back to the computational means for combining with the instantaneous carrier signal estimates to incrementally eliminate the phase error signal, thereby effecting coherent demodulation of the phase modulated carrier signal.
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10. Apparatus for demodulating a phase modulated carrier signal, comprising:
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means for periodically sampling an input carrier signal, converting each sample of the input carrier signal into a multi-bit input carrier signal representative of the amplitude of the input carrier signal at the moment of sampling, and generating instantaneous estimates of components of the input carrier signal; computational means for generating from the instantaneous carrier signal estimates a phase error signal; summing means for adding to the phase error signal a current phase angle and a phase shift proportional to the differential phase shift between the baud period in which the sample of the input carrier signal is taken and the baud period from which an earlier sample of the input carrier signal was taken to effect a new phase angle; memory means for accepting the current phase angle and for providing, in response thereto, a trigonometric function thereof, the components being fed back to the computational means for combining with the instantaneous carrier signal estimates to incrementally eliminate the phase error signal, thereby effecting coherent demodulation of the phase modulated carrier signal.
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11. Apparatus for demodulating a phase modulated carrier signal, comprising:
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phase shift means responsive to an input carrier signal for producing a phase shifted carrier signal; estimator means responsive to the input carrier signal and the phase shifted carrier signal for generating instantaneous estimates of in-phase and quadrature-phase components of the input carrier signal; computational means for comparing the instantaneous estimates of the in-phase and quadrature-phase components of the input carrier signal with predetermined ideal components of an existing input carrier signal to determine phase angle deviation therebetween; summing means for adding to the phase angle deviation a predetermined phase angle of the existing input carrier signal and a phase shift which is proportional to the differential phase shift between the input carrier signal and the existing input carrier signal to produce a new phase angle to be used as an input to update the predetermined ideal components; whereby the phase angle deviation between the instantaneous estimates of the in-phase and quadrature-phase components of the input carrier signal and the ideal components is incrementally eliminated as the phase angle deviation determined by the computational means incrementally decreases. - View Dependent Claims (12, 13, 14, 15)
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16. Apparatus for demodulating a phase modulated input carrier signal, comprising:
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means for sampling periodically the input carrier signal, converting each sample of the input carrier signal into a multi-bit input carrier signal representative of the input carrier signal at the moment of sampling, and generating instantaneous estimates of in-phase and quadrature-phase components of the current sample of the input carrier signal; first control means for comparing the instantaneous estimates of the in-phase and quadrature-phase components of the current sample of the input carrier signal with prestored ideal components of an existing sample of the input carrier signal to determine phase angle deviation between the instantaneous estimates of the components and the ideal components, the first control means including; at least two multiplier means each multiplying one of the instantaneous estimates with a corresponding one of the prestored ideal components of the existing input carrier signal sample; subtracter means for subtracting results from the multiplier means to effect the phase angle deviation; second control means for summing the phase angle deviation with a phase angle of the existing sample of the input carrier signal and a phase shift proportional to the differential phase shift between the baud period in which the current sample of the input carrier signal was taken and the baud period from which the existing sample of the input carrier signal was taken to effect a new phase angle for deriving a trigonometric function of the input carrier signal corresponding to the new phase angle for comparing with a next sample of the input carrier signal, the second control means including; an adder means for summing the phase angle deviation with the phase angle of the existing sample of the input carrier signal and the proportional differential phase shift, and for outputting the new phase angle; scaler means for multiplying the phase angle deviation with a fractional correction constant; a delay means for providing at its output the phase angle of the existing sample of the input carrier signal to the adder means and for receiving at its input the new phase angle output from the adder means, the delay means providing a delay of at least one baud period between the phase angle output therefrom and the new phase angle input thereto; thereby incrementally effecting coherently demodulated and substantially ideal in-phase and quadrature-phase components of the input carrier signal. - View Dependent Claims (17, 18, 19)
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20. A method of demodulating a phase modulated input carrier signal, comprising the steps of:
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sampling periodically the input carrier signal, converting each sample of the input carrier signal into a multi-bit input carrier signal representative of the input carrier signal at the moment of sampling, and generating instantaneous estimates of in-phase and quadrature-phase components of the current sample of the input carrier signal; comparing the instantaneous estimates of the in-phase and quadrature-phase components of the current sample of the input carrier signal with prestored ideal components of an existing sample of the input carrier signal to determine phase angle deviation between the instantaneous estimates of the components and the ideal components; summing the phase angle deviation with a phase angle of the existing sample of the input carrier signal and a phase shift proportional to the differential phase shift between the baud period in which the current sample of the input carrier signal was taken and the baud period from which the existing sample of the input carrier signal was taken to effect a new phase angle for deriving a trigonometric function of the input carrier signal corresponding to the new phase angle for comparing with a next sample of the input carrier signal; thereby incrementally effecting coherently demodulated and substantially ideal in-phase and quadrature-phase components of the input carrier signal. - View Dependent Claims (21, 22)
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Specification