Method for protecting a radio navigation receiver user against aberrant pseudo-range measurements

1. A method of processing radionavigation receiver signals, the method comprising:

providing, at an equipment with a Receiver Autonomous Integrity Monitoring (RAIM) functionality, measurements of pseudo-ranges between a plurality of satellites and a primary radionavigation receiver;

providing, at the equipment, a geographical position and a clock shift of the primary radionavigation receiver;

calculating, at the equipment, residuals of measurements of pseudo-ranqes obtained on the basis of the geographical position and the clock shift provided by said primary radionavigation receiver and on the basis of measurements of pseudo-ranges provided by said primary radionavigation receiver, said residuals being denoted by Yi, where i is an index of a satellite i in the plurality of satellites;

forming, at the equipment, subsets of the residuals of a cardinal denoted by h=N−1 and/or N−2, N being the number of said residuals;

calculating, at the equipment, a standard deviation of each subset with σ min being a smallest standard deviation and used as reference to weight said residuals;

determining, at the equipment, a minimum value h min of the cardinal for which said σ min was calculated, a value of Y min , a vector of corresponding cardinal h min , and a value of m min , m min being a mean value of Y min ;

for each satellite i, calculating, at the equipment, a first vector of residuals defined by:

r

vec

,

1

=

(

Yi

-

m

min

)

2

σ

min

for the plurality of satellites, sorting, at the equipment, elements of the first vector r vec,1 in ascending order to obtain a sorted vector r vec,1 sorted ;

calculating, at the equipment, a factor f defined by:

f

=

(

χ

2

)

-

1

⁢

(

h

min

N

,

1

)

,

 where (χ 2 ) −1 (.,1) is an inverse of a Chi-squared x 2 statistic distribution with one degree of freedom;

weighting at the equipment, said σ min in the following manner:

σ

min

,

2

=

r

vec

,

1

sorted

⁡

(

h

min

)

f

*

σ

min

for each said satellite, calculating, at the equipment, a new vector of residuals defined by:

r

vec

,

2

=

(

Yi

-

m

min

)

2

σ

min

,

2

;

defining, at the equipment, a threshold T such that: T=(χ 2 ) − 1 (P,1), where P is a probability whose optimal value is determined by a probabilistic simulation; and

comparing, at the equipment, each element of the new vector of residuals r vec,2 with the threshold T and if r vec,2 (i)>T, a fault is declared to have been detected, and said satellite i is excluded.

2. The method of claim 1 , wherein the probabilistic simulation used for the definition of the threshold T is a scheme of the Monte-Carlo type.

3. The method of claim 1 , wherein, the measurements provided by the primary radionavigation receiver are preprocessed to remove propagation and measurement errors.

4. The method of claim 1 , wherein a corrected position is calculated when an error in the measurements is detected.

5. The method of claim 1 , wherein a corrected clock value is calculated when an error in the measurements is detected.

6. The method of claim 1 , wherein protection radii relating to the measurements are calculated in a customary manner.

7. The method of claim 1 , wherein an alarm is emitted when an error in the measurements is detected.

8. The method of claim 1 , wherein the the primary radionavigation receiver does not posses a source of robust protection against measurement errors.