Method and device for the demodulation of signals with constant envelope and continuous phase angle modulation by a train of binary symbols tolerating frequency drifts
First Claim
1. A method for the demodulation of constant envelope and continuous phase signals having a bit period Tb, consisting in the performing of a digital processing operation for successive groups of nb bits, of a received signal brought into baseband, the phase of which is over-sampled with respect to the bit period Tb, consisting:
- in a first stage, in measuring q subsets of nb differential phases at the bit period, using starting instants, staggered with respect to one another by fractions Tb /q of this period to form staggered sampling combs at the bit period;
in a second stage, in making d a priori corrections of each of said q subsets of differential phases by phase deviations associated with a set of d pre-defined frequency drifts, to generate d times q subsets of nb corrected differential phases, and deducing therefrom d times q sets of nb associated demodulated bits, each corresponding to a measured subset of differential phases associated with one of said d pre-defined drifts;
in a third stage, reconstructing the differential phases supposed to have been emitted from each of the sets of nb demodulated bits, and in computing, for each of the d times q sets of demodulated bits, a noise criterion taking into account the subset of reconstructed differential phases and the associated subset of corrected differential phases measured and corrected as a function of a predefined drift;
in a fourth stage, selecting the set of nb bits that minimizes the noise criterion, the predefined frequency drift that is associated with said selected set of nb bits corresponding to a rough estimation of the real drift;
in a penultimate stage, computing, on the basis of the selected set of demodulated bits, a fine estimation of the real drift by calculating mean of differences between the measured differential phases and the reconstructed differential phases associated with this set of nb bits, and then a final phase deviation associated with said fine estimation of the real drift;
and, in a last stage, performing a demodulation of the q subsets of measured differential phases, after having corrected them by the final phase deviation associated with the fine estimate of the real drift, in computing, for each, the noise criterion and in selecting, among the sets of resulting bits, that set which minimizes the noise criterion, the sampling comb associated with it forming the synchronization bit.
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Abstract
The continuous phase angular demodulation method disclosed digitally processes the signal in baseband after having over-sampled it with reference to the bit period. The processing consists in routinely demodulating sub-sets of differential phases at the bit period Tb shifted with respect to one another by fractions Tb /q of this period, in correcting them, a priori, by the phase deviations associated with a set of pre-defined d frequency drifts and in computing, for the d.q sets thus obtained, a noise criterion. The set of demodulated bits chosen is the one that reduces this noise criterion to the minimum. The set of bits then enables computation of the phase variation emitted and, using this variation and the measured variation, the real frequency drift. Another demodulation taking this drift into account is done for the q sets of initial differential stages and the set minimizing the noise criterion is then chosen and fixes the synchronization bit by the sampling instants associated with it.
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Citations
8 Claims
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1. A method for the demodulation of constant envelope and continuous phase signals having a bit period Tb, consisting in the performing of a digital processing operation for successive groups of nb bits, of a received signal brought into baseband, the phase of which is over-sampled with respect to the bit period Tb, consisting:
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in a first stage, in measuring q subsets of nb differential phases at the bit period, using starting instants, staggered with respect to one another by fractions Tb /q of this period to form staggered sampling combs at the bit period; in a second stage, in making d a priori corrections of each of said q subsets of differential phases by phase deviations associated with a set of d pre-defined frequency drifts, to generate d times q subsets of nb corrected differential phases, and deducing therefrom d times q sets of nb associated demodulated bits, each corresponding to a measured subset of differential phases associated with one of said d pre-defined drifts; in a third stage, reconstructing the differential phases supposed to have been emitted from each of the sets of nb demodulated bits, and in computing, for each of the d times q sets of demodulated bits, a noise criterion taking into account the subset of reconstructed differential phases and the associated subset of corrected differential phases measured and corrected as a function of a predefined drift; in a fourth stage, selecting the set of nb bits that minimizes the noise criterion, the predefined frequency drift that is associated with said selected set of nb bits corresponding to a rough estimation of the real drift; in a penultimate stage, computing, on the basis of the selected set of demodulated bits, a fine estimation of the real drift by calculating mean of differences between the measured differential phases and the reconstructed differential phases associated with this set of nb bits, and then a final phase deviation associated with said fine estimation of the real drift; and, in a last stage, performing a demodulation of the q subsets of measured differential phases, after having corrected them by the final phase deviation associated with the fine estimate of the real drift, in computing, for each, the noise criterion and in selecting, among the sets of resulting bits, that set which minimizes the noise criterion, the sampling comb associated with it forming the synchronization bit. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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Specification