Method Of Processing Positioning Signals, In Particular For Indoor Applications

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 positioning signal over a predetermined time span, sampling the received positioning signal 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 modulating code, said trial carrier frequency shifts and said 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 (c1) and trial carrier frequency shift:
• (c1) determining a main correlation peak of greatest magnitude (Xi(τ*f0, f0)) as a function of the trial code delay (1);
• (c2) determining if said main correlation peak (Xi(τ*f0, f0) is possibly representative of an individual signal generated by an emitter using said modulating code (ci), by comparing its magnitude to a threshold (2);
• and
• (c3) if said main correlation peak (Xi(τ*f0, f0)) is determined to be possibly representative of an individual signal, determining if it is affected by interferences from individual signals generated by other emitters by comparing its magnitude to that of a secondary correlation peak of smaller magnitude (Xi(τ′f0, f0)) corresponding to a different code delay for the same trial carrier frequency shift (3);
• (d) for each known modulating code selecting, among the correlation peaks which have been determined to be possibly 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.