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

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 σmin being a smallest standard deviation and used as reference to weight said residuals;
• determining, at the equipment, a minimum value hmin of the cardinal for which said σmin was calculated, a value of Ymin, a vector of corresponding cardinal hmin, and a value of mmin, mmin being a mean value of Ymin;
• 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 rvec,1 in ascending order to obtain a sorted vector rvec,1sorted;
• calculating, at the equipment, a factor f defined by:
• f
• =
• (
• χ
• 2
• )
• -
• 1
• ⁢
• (
• h
• min
• N
• ,
• 1
• )
• ,
• where (χ2)−1(.,1) is an inverse of a Chi-squared x2 statistic distribution with one degree of freedom;
• weighting at the equipment, said σmin 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=(χ2)−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 rvec,2 with the threshold T and if rvec,2(i)>T, a fault is declared to have been detected, and said satellite i is excluded.