A method for checking an integrity of a localization obtained by determining a position of a mobile or fixed carrier by proximity to a set of predefined reference positions, for implementation on the mobile or fixed carrier, said method making it possible to check that a correlation function of received GNSS signals is consistent with a selected reference position said method comprising:
- (a) a step E1 for synchronizing a time base of the mobile or fixed carrier with a GNSS time calculated and transmitted by a GNSS positioning system;
- (b) a step E2 for calculating a code phase of GNSS signals predicted at reception for all said reference positions and for all satellites visible at said reference positions;
- (c) a step E3 for calculating a signal-to-noise ratio in an observation band after matched filtering of the received GNSS signals with said predicted GNSS signals;
- (d) a step E4 for jointly determining a minimum protection radius (PR0) and a processing integration time adapted to required risks of non-integrity and non-continuity, said minimum protection radius being determined as a function of a minimum delay (τ0) between a punctual correlation channel and early and late correlation channels, characteristic of a fault detection test applied to individual satellite signals, and a geometric dilution coefficient dependent on a spatial distribution of the received signals, defined according to the expression:
- PR
- 0
- =
- τ
- 0
- ×
- min
- (
- i
- ,
- j
- )
- ∈
- Ns
- ×
- Ns
- [
- (
- 1
- cos
-
- (
- E
-
- l
- i
- )
- ×
- 1
- cos
-
- (
- E
-
- l
- j
- )
- )
- ×
- 1
- s
-
- i
-
- I
-
- 1
-
- (
- A
-
- z
- i
- -
- A
-
- z
- j
- )
- ]
-
- where
- ,
- τ0 is the minimum spacing between the early, late and punctual correlation channels of a fault exclusion test applied to the individual satellite signals, to ensure the risks of non-integrity and non-continuity required for the integrity check and for the processing integration time;
- Ns represents the set of selected satellites;
- (i,j) is an index pair i and j among these satellites;
- Azi is the azimuth angle (relative to north) of the satellite signal i;
- Eli is the elevation angle (relative to the horizontal plane) of the satellite signal i;
- (e) a step E5, applied to each of said received GNSS signals and each of said reference positions, of calculating an effective level of the punctual correlation channel, obtained after adapted filtering of the signal by a local code expected for the predicted code phase, compensated for residual common biases of receiver group delay and GNSS time synchronization, after coherent and non-coherent integration;
- (f) a step E6, applied to each of said GNSS signals received and each of said reference positions, for calculating an effective level of the so-called early correlation and late correlation channels, obtained after adapted filtering of the signal by expected local codes shifted by a said fraction of code chip in advance and in delay with respect to said predicted code phase of a point channel, after coherent and non-coherent integration, said code chip fraction being determined so as to comply with a constraint of probability of non-detection of a code phase bias of the signal within a protection radius set by integrity loss risk objectives associated with a control process;
- (g) a step E7 for pre-selecting satellite signals suitable for taking part in a position integrity control test, based on a minimum signal-to-noise ratio criterion for the “point” channel, as calculated in step (E3), to ensure that the test is effective according to non-detection probability and false alarm probability objectives set for the integrity control;
- (h) a position integrity check step E8 to protect against an occurrence of faults in the signals selected for a position error protection radius PRk equal to or possibly a multiple of the minimum protection radius PR0, by excluding satellites whose code phases are not compatible with the predicted code phases for said reference positions tested, or which exhibit unexpected delay biases relative to the predicted code phases due to signal propagation or synchronization disturbances, the satellite exclusion method, being Maximum At Center (MAC), being characterized by the absence of a maximum at the center of a triplet (Tk) of 3 correlation channels, early-punctual-late, centered on the predicted code phase for the reference position and spaced by a delay deviation (tk) multiple of the value (τ0) of the minimum delay time offset of the early and late channels of a detection barrier;
- (i) a step E9 for calculating, for each of said reference positions, an effective power level obtained, called likelihood, by cumulating elementary powers of the various selected satellites, after coherent and non-coherent integration;
- and
- (j) a step E10 for determining the reference position closest to the actual reception position by identifying the reference position with the highest plausibility, within a protection radius compatible with the false alarm and non-detection probability constraints set for the position integrity control method.