Patent ID: 8059700

Claim:
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.