Method of processing positioning signals, in particular for indoor applications
First Claim
1. A method of processing a set of code-modulated positioning signals constituted by a superposition of individual signals generated by a plurality of emitters, the individual signal generated by each emitter being defined by a known modulation code, by an unknown code delay and by an unknown carrier frequency shift, the method comprising the steps of:
- (a) receiving and down-converting said set of code-modulated positioning signals over a predetermined time span, sampling it at a predetermined sampling period and converting it to digital form;
(b) for each known modulating code, determining first sets of trial carrier frequency shifts and of code delays, locally generating code modulated signals defined by said known modulating code and said first sets of trial carrier frequency shifts and of trial code delays, and computing correlations of said digitized signal with said locally generated code-modulated signals;
characterized in that it further comprises the steps of;
(c) for each known modulating code and for each trial carrier frequency shift of said first set of trial carrier frequency shifts;
(c1) determining a primary correlation peak of greatest magnitude as a function of the trial code delay;
(c2) determining if said primary correlation peak is representative of an individual signal generated by one of the plurality of emitters using said modulating code, by comparing its magnitude to a threshold; and
(c3) if said main correlation peak is determined to be representative of an individual signal, determining if it is affected by interferences from individual signals generated by another of the plurality of emitters by comparing its magnitude to that of a secondary correlation peak of smaller magnitude corresponding to a different code delay for a same trial carrier frequency shift;
(d) for each known modulating code selecting, among the primary correlation peaks which have been determined to be representative of an individual signal and not to be affected by interferences from individual signals generated by another of the plurality of emitters, if any, the one having the greatest magnitude, and taking the corresponding trial carrier frequency shift and code delay as estimates of the unknown carrier frequency shift and code delay of said individual signal.
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Accused Products
Abstract
A method of processing positioning signal constituted by a superposition of individual signals generated by a plurality of emitters, in particular satellite emitters, comprising:—a first step of coarse acquisition of said individual signals, comprising correlation of the received positioning signal with locally generated replicas of said individual signals;—a step of identifying spurious correlation peaks induced by interferences; and—a step of estimating the code delays and the carrier frequency shifts of the acquired individual signals which are not affected by said interferences. According to preferred embodiments of the invention, the method can also comprise:—a refining step of determining more accurate estimates of said code delays and carrier frequency shifts; and—a step of interference cancellation. The method of the invention is particularly suitable to indoor positioning applications.
43 Citations
29 Claims
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1. A method of processing a set of code-modulated positioning signals constituted by a superposition of individual signals generated by a plurality of emitters, the individual signal generated by each emitter being defined by a known modulation code, by an unknown code delay and by an unknown carrier frequency shift, the method comprising the steps of:
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(a) receiving and down-converting said set of code-modulated positioning signals over a predetermined time span, sampling it at a predetermined sampling period and converting it to digital form; (b) for each known modulating code, determining first sets of trial carrier frequency shifts and of code delays, locally generating code modulated signals defined by said known modulating code and said first sets of trial carrier frequency shifts and of trial code delays, and computing correlations of said digitized signal with said locally generated code-modulated signals; characterized in that it further comprises the steps of; (c) for each known modulating code and for each trial carrier frequency shift of said first set of trial carrier frequency shifts; (c1) determining a primary correlation peak of greatest magnitude as a function of the trial code delay; (c2) determining if said primary correlation peak is representative of an individual signal generated by one of the plurality of emitters using said modulating code, by comparing its magnitude to a threshold; and (c3) if said main correlation peak is determined to be representative of an individual signal, determining if it is affected by interferences from individual signals generated by another of the plurality of emitters by comparing its magnitude to that of a secondary correlation peak of smaller magnitude corresponding to a different code delay for a same trial carrier frequency shift; (d) for each known modulating code selecting, among the primary correlation peaks which have been determined to be representative of an individual signal and not to be affected by interferences from individual signals generated by another of the plurality of emitters, if any, the one having the greatest magnitude, and taking the corresponding trial carrier frequency shift and code delay as estimates of the unknown carrier frequency shift and code delay of said individual signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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26. A method of processing a set of spread-spectrum positioning signals constituted by a superposition of individual signals generated by a plurality of emitters, the individual signal generated by each emitter being defined by a known modulating code, by an unknown code delay and by an unknown carrier frequency shift, the method comprising the steps of:
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acquiring from a terrestrial assistance emitter a set of modulating codes corresponding to satellite emitters from which individual signals are received; performing a second method until a first emitter is determined to be free from interferences, the second method comprising the steps of; (a) receiving and down-converting said set of code-modulated positioning signals over a predetermined time span, sampling it at a predetermined sampling period and converting it to digital form; (b) for each known modulating code, determining first sets of trial carrier frequency shifts and of code delays, locally generating code modulated signals defined by said known modulating code and said first sets of trial carrier frequency shifts and of trial code delays, and computing correlations of said digitized signal with said locally generated code-modulated signals; characterized in that it further comprises the steps of; (c) for each known modulating code and for each trial carrier frequency shift of said first set of trial carrier frequency shifts; (c1) determining a primary correlation peak of greatest magnitude as a function of the trial code delay (1); (c2) determining if said primary correlation peak is representative of an individual signal generated by one of the plurality of emitters using said modulating code, by comparing its magnitude to a threshold; and (c3) if said main correlation peak is determined to be representative of an individual signal, determining if it is affected by interferences from individual signals generated by another of the plurality of emitters by comparing its magnitude to that of a secondary correlation peak of smaller magnitude corresponding to a different code delay for a same trial carrier frequency shift; (d) for each known modulating code selecting, among the primary correlation peaks which have been determined to be representative of an individual signal and not to be affected by interferences from individual signals generated by another of the plurality of emitters, if any, the one having the greatest magnitude, and taking the corresponding trial carrier frequency shift and code delay as estimates of the unknown carrier frequency shift and code delay of said individual signal; and (e) determining that one of the plurality of emitters is affected by interferences from individual signals generated by others of the plurality of emitters if, for the modulating code corresponding to said emitter, all the correlation peaks which have been determined to be representative of an individual signal have also been determined to be affected by interferences;
otherwise determining that said emitter is free from interferences;obtaining from said terrestrial assistance emitter, whose position is known, a set of code delays relative to said terrestrial assistance emitter, corresponding to satellite emitters from which individual signals are received; for each remaining modulating codes corresponding to said satellite emitters from which individual signals are received; determining first sets of trial carrier frequency shifts and of code delays, said first set of trial code delays being a reduced set determined on the basis of said set of code delays relative to said known-position terrestrial assistance emitter and on the basis of the code delay of said first acquired emitter; locally generating code modulated signals defined by said modulating code, said trial carrier frequency shifts and said trial code delays, and computing correlations of said received, sampled and digitized signal with said locally generated code-modulated signals; computing linear correlations of the received, sampled and digitized signal with said locally generated code-modulated signals; for each of said modulating codes and trial carrier frequency shifts; determining a correlation peak as a function of the trial code delay; determining if said correlation peak is representative of an individual signal generated by an emitter using said modulating code, by comparing its magnitude to a first threshold; for each modulating code for which at least a correlation peak has been determined to be possibly representative of an individual signal generated by the emitter using said modulating code; estimating a carrier-to-noise spectral density ratio for the corresponding individual signal; if said carrier-to-noise spectral density ratio is greater than a second threshold, determining that said individual signal is not affected by interferences from individual signals generated by other emitters; for each said modulating code selecting, among the correlation peaks which have been determined to be representative of an individual signal and not to be affected by interferences from individual signals generated by other emitters, if any, the one having the greatest magnitude, and taking the corresponding trial carrier frequency shift and code delay as estimates of the unknown carrier frequency shift and code delay of said individual signal. - View Dependent Claims (27, 28, 29)
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Specification