Variable-delay, sine-cosine non-coherent demodulator
First Claim
1. A demodulator for recovering information angle-modulated onto a radio-frequency (RF) carrier signal, comprising:
- means for converting the frequency of the RF carrier signal to an IF signal at a frequency close to a desired demodulation frequency;
means for providing a digital sampling signal at a sample frequency which is a selected integer H multiple of the demodulation frequency;
means for converting the IF signal into a pair of time-current baseband quadrature-phased I and Q digital data words responsive to alternate cycles of said sampling signal;
first means for delaying each of the respective I and Q data words by a first selected time interval T1 to provide respective first-delayed I1 and Q1 data words;
second means for delaying each of the respective I1 and Q1 data words by a second selected time interval T2 to provide second-delayed respective I2 and Q2 data words;
detector means for providing a first detector data word and a second detector data word respectively responsive to the sine and cosine of the instantaneous difference between the IF signal frequency and the sampling signal frequency;
means for selecting one of the first and second detector data words as a demodulator output data signal;
means for controlling both the first delay time interval T1, responsive to an offset data signal proportional to the average frequency separation between the IF and sampling frequencies, and the second delay time interval T2, as the difference between the present first delay time interval and a total delay time inversely proportional to the sampling frequency; and
AFC means, receiving at least the first detector data word and controlling the carrier signal converting means, for minimizing the separation between the actual IF signal frequency and a submultiple, set by division, by the same integer H, of the sampling frequency.
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Abstract
A variable-delay, sine-cosine non-coherent demodulator recovers digital data angle-modulated upon a radio-frequency (RF) carrier signal, by frequency conversion of the carrier signal to a selected IF frequency, which is ideally equal to one-fourth of a sample frequency supplied to the demodulator. The IF signal is sampled at the sample frequency, and the samples are then sorted to provide a pair of baseband quadrature-phased I and Q signals. Each of the I and Q signals is delayed by a variable first delay T1 to provide first-delayed in-phase I1 and first-delayed quadrature-phased Q1 signals. These signals are then delayed by a second delay T2 to provide twice-delayed in-phase I2 and twice-delay quadrature-phase Q2 signals. The sum of the two delays is a constant related to the sample frequency, which itself is related to the data bit rate, but the first delay T1 is variably dependent upon the frequency offset between the IF signal and the sample signal. The various signals are applied to a sine (discriminator) detector and to a cosine (differential) detector, with the output of a selected detector being filtered and processed to provide the recovered data. The detected data output is also utilized to control the first and second delays and to provide, in coordination with the discriminator detector output, automatic frequency control of an oscillator, in the frequency converter means, to minimize the difference between the IF signal frequency and the desired submultiple of the sample frequency.
21 Citations
20 Claims
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1. A demodulator for recovering information angle-modulated onto a radio-frequency (RF) carrier signal, comprising:
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means for converting the frequency of the RF carrier signal to an IF signal at a frequency close to a desired demodulation frequency; means for providing a digital sampling signal at a sample frequency which is a selected integer H multiple of the demodulation frequency; means for converting the IF signal into a pair of time-current baseband quadrature-phased I and Q digital data words responsive to alternate cycles of said sampling signal; first means for delaying each of the respective I and Q data words by a first selected time interval T1 to provide respective first-delayed I1 and Q1 data words; second means for delaying each of the respective I1 and Q1 data words by a second selected time interval T2 to provide second-delayed respective I2 and Q2 data words; detector means for providing a first detector data word and a second detector data word respectively responsive to the sine and cosine of the instantaneous difference between the IF signal frequency and the sampling signal frequency; means for selecting one of the first and second detector data words as a demodulator output data signal; means for controlling both the first delay time interval T1, responsive to an offset data signal proportional to the average frequency separation between the IF and sampling frequencies, and the second delay time interval T2, as the difference between the present first delay time interval and a total delay time inversely proportional to the sampling frequency; and AFC means, receiving at least the first detector data word and controlling the carrier signal converting means, for minimizing the separation between the actual IF signal frequency and a submultiple, set by division, by the same integer H, of the sampling frequency. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification