Digital coherent phase demodulator
First Claim
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1. A process for demodulating a received, coherent phase-shift keyed signal comprising:
- (a) generating a local oscillator signal,(b) measuring the phase of the received signal relative to the local oscillator signal for each keying interval in successive preselected sets of keying intervals,(c) calculating an estimate of the unmodulated phase and rate of change of the unmodulated phase of the received signal relative to the local oscillator signal during each preselected set of keying intervals,(d) generating a phase reference for each preselected set of keying intervals from the estimate for each preselected set of keying intervals of the unmodulated phase and rate of change of unmodulated phase of the received signal relative to the local oscillator signal,(e) demodulating the received signal by comparing the phase of the received signal to the phase reference, and(f) outputting the demodulated received signal.
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Abstract
A digital system for demodulating coherent phase shift keyed signals. Maximum likelihood estimates of the unmodulated phase and rate of change of the unmodulated phase of the received signal relative to a local oscillator signal are used to improve the demodulation process. The maximum likelihood estimates are obtained from measurements of the phase of the received signal relative to the local oscillator signal over a predetermined set of keying intervals. The digital demodulation process permits rapid "lock-on" at low signal-to-noise ratios.
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4 Claims
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1. A process for demodulating a received, coherent phase-shift keyed signal comprising:
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(a) generating a local oscillator signal, (b) measuring the phase of the received signal relative to the local oscillator signal for each keying interval in successive preselected sets of keying intervals, (c) calculating an estimate of the unmodulated phase and rate of change of the unmodulated phase of the received signal relative to the local oscillator signal during each preselected set of keying intervals, (d) generating a phase reference for each preselected set of keying intervals from the estimate for each preselected set of keying intervals of the unmodulated phase and rate of change of unmodulated phase of the received signal relative to the local oscillator signal, (e) demodulating the received signal by comparing the phase of the received signal to the phase reference, and (f) outputting the demodulated received signal. - View Dependent Claims (2)
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3. A demodulator for demodulating a received, coherent phase-shift-keyed signal comprising:
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(a) means for generating a local oscillator signal, (b) means for measuring the phase of the received signal, relative to the local oscillator signal, for each keying interval in successive preselected sets of keying intervals, (c) means for calculating an estimate of the unmodulated phase and the rate of change of the unmodulated phase of the received signal, relative to the local oscillator signal, during each set of keying intervals, (d) means for generating a phase reference for each preselected set of keying intervals from the estimate of the unmodulated phase and the rate of change of the unmodulated phase of the received signal relative to the local oscillator signal, (e) means for demodulating the received signal by comparing the phase of the received signal to the phase reference and (f) means for outputting the demodulated received signal. - View Dependent Claims (4)
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Specification