Decision-directed, automatic frequency control technique for non-coherently demodulated M-ARY frequency shift keying
First Claim
1. For use in a demodulator for detecting information symbols which are encoded in the form of a frequency shift keying carrier signal, said demodulator containing means for generating a local carrier signal, an arrangement for controlling said local carrier signal for tracking frequency changes therein comprising:
- first means for combining said local carrier signal and an incoming frequency shift keying signal to be demodulated and producing therefrom signals representative of the modulation information contained in said incoming signals;
second means, coupled to said first means, for deriving output signals representative of the information symbols by which said carrier signal was modulated to form said frequency shift keying signals;
third means, responsive to signals produced by said first and second means, for deriving error signals representative of the frequency error in said local carrier signal; and
linear discriminator means, responsive to said error signals, for controlling said local carrier signal generating means so as to track frequency changes in said incoming frequency shift keying signal to be demodulated.
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Accused Products
Abstract
A data receiver apparatus for recovering digital data signals from an M-ARY FSK modulated signal incorporates a dedicated linear discriminator, downstream of the data recovery process, in the carrier tracking loop. Because the signal modulation components are removed prior to tracking, only frequency error remains, which is employed by the linear discriminator for steering a VCO in the frequency tracking loop. This results in a closed loop step response that rapidly converges to a stable level, and a linear frequency estimation characteristic.
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Citations
14 Claims
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1. For use in a demodulator for detecting information symbols which are encoded in the form of a frequency shift keying carrier signal, said demodulator containing means for generating a local carrier signal, an arrangement for controlling said local carrier signal for tracking frequency changes therein comprising:
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first means for combining said local carrier signal and an incoming frequency shift keying signal to be demodulated and producing therefrom signals representative of the modulation information contained in said incoming signals; second means, coupled to said first means, for deriving output signals representative of the information symbols by which said carrier signal was modulated to form said frequency shift keying signals; third means, responsive to signals produced by said first and second means, for deriving error signals representative of the frequency error in said local carrier signal; and linear discriminator means, responsive to said error signals, for controlling said local carrier signal generating means so as to track frequency changes in said incoming frequency shift keying signal to be demodulated. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A demodulator for extracting information signals that have been encoded in the form of an FSK-modulated carrier signal comprising:
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a controlled carrier oscillator; first means coupled to receive an FSK-modulated carrier signal and combining said FSK-modulated carrier signal with the output of said carrier oscillator and producing therefrom signals representative of modulation information contained in said modulated signal; second means, coupled to said first means, for deriving output signals representative of information symbols by which said carrier signal was modulated to produce said FSK-modulated carrier signal; third means for combining the signals produced by said first and second means to obtain error signals representative of the frequency error in the output of said controlled carrier oscillator; and linear discriminator means for producing a control signal in accordance with the frequency error signal produced by said third means and coupling said control signal to said controlled carrier oscillator, so as to track frequency changes in said FSK-modulated carrier signal. - View Dependent Claims (9, 10, 11, 12, 13)
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14. For use in a non-coherent demodulator wherein information symbols from a received FSK-modulated carrier signal are extracted by a decision-directed signal process network, a method of controlling the frequency of a local carrier generator so as to track the variations in frequency in said received signal comprising the steps of:
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combining said received FSK-modulated carrier signal with the local carrier signal from said local carrier generator and deriving therefrom a signal representative of the frequency error in said local carrier signal; and applying said frequency error representative signal to a linear discriminator exclusive of said decision-directed signal processing network, to produce a frequency estimate control signal that is applied to said local carrier generator to control the frequency of the local carrier generator.
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Specification