Patent Document ID: 8131463
Application ID: 12393665
Patent Flag: 1

Claim One:
1. A method for providing a Global Navigation Satellite System (GNSS) navigation position solution with guaranteed integrity in non-controlled environments, the method comprises the steps of: A) processing a Global Navigation Satellite System (GNSS) signal including a plurality of satellites generating at least one signal to obtain carrier phase and pseudorange measurements; B) pre-processing said measurements to detect and characterize local errors in said measurements, wherein said local errors cannot be ascertained a priori, said characterization including providing error bounds estimated by measuring said carrier phase and pseudoranges measurements, thereby providing a set of measurements rejections when said characterization is not possible; C) using said estimated error bounds, together with error bounds provided by the GNSS signal itself concerning satellite and ionospheric errors, to build in each measurement an estimated noise level in said measurements as input to a weighted Receiver Autonomous Integrity Monitoring (RAIM) algorithm in order to compute position coordinates and associated protection levels in the non-controlled environments, wherein said step of pre-processing said measurements further includes using traditional carrier phase step detectors and cycle slip detectors together with a carrier phase RAIM algorithm, for the detection and rejection of reflected signal errors, wherein said carrier phase RAIM algorithm excludes multipath reflected measurements based on inconsistencies between observed Doppler effect and velocity vectors, in order to ensure detection and exclusion of multipath reflected measurements and to compute velocity and associated protection levels, wherein ionospheric errors are compensated based on at least two frequency measurements, wherein smoothed pseudoranges are computed using a real-time filter, and wherein it uses an algorithm that, based on the time correlation of the multipath errors, characterizes local pseudorange errors—multipath and receiver noise—in terms of associated variance, wherein measurements with excessive multipath errors are excluded for later computations and multipath is mitigated in valid measurements, said algorithm comprises the following steps: computing snapshot carrier phase non-integer ambiguity N i (t k ) for each of said satellites, comparing iono-free pseudorange ρ i,iono-free (t k ) and carrier phase measurements Φ i,iono-free (t k ) for the current epoch: N i (t k )=ρ i,iono-free (t k )−Φ i,iono-free (t k ); resetting a cycle slip detector filter when there is a cycle slip; updating a buffer of ambiguities by removing the oldest one if the buffer is full, and adding the previously computed ambiguity, and if the number of ambiguities is above a certain minimum number (N min ), computing the average for short-term and long-term filters, N i,average,short (t k ) and N i,average,long (t k ) respectively, together with the associated residual covariance, S 2 i,short (t k ) and S 2 i,long (t k ), as follows: N i , average , short ⁡ ( t k ) = 1 M 1 ⁢ ∑ l = 0 M 1 - 1 ⁢ N i ⁡ ( t k - l ) S i , short 2 ⁡ ( t k ) = 1 M 1 - 1 ⁢ ∑ l = 0 M 1 - 1 ⁢ ( N i ⁡ ( t k - l ) - N i , average , short ⁡ ( t k ) ) N i , average , long ⁡ ( t k ) = 1 M 2 ⁢ ∑ l = 0 M 2 - 1 ⁢ N i ⁡ ( t k - l ) S i , long 2 ⁡ ( t k ) = 1 M 2 - 1 ⁢ ∑ l = 0 M 2 - 1 ⁢ ( N i ⁡ ( t k - l ) - N i , average , long ⁡ ( t k ) ) with M 1 and M 2 being in the order of 100 and 600 seconds, respectively; for each filter and for each snapshot ambiguity, if the difference between said snapshot ambiguity and the average is greater than three times the corresponding standard deviation, then the snapshot ambiguity is rejected and averages and covariance are computed again; if the user velocity becomes greater than a certain minimum value (V user,min ) for at least a certain minimum time greater than M 2 , then the smoothed pseudorange {tilde over (ρ)} i,iono-free (t k ) and the associated residual noise σ 2 i,noise (t k ) are as follows: ρ ~ i , iono ⁢ - ⁢ free ⁡ ( t k ) = N i , average , long ⁡ ( t k ) + Φ i , iono ⁢ - ⁢ free ⁡ ( t k ) σ i , noise 2 ⁡ ( t k ) = 1 M 2 · ( S i , noise ⁡ ( t k ) · t P - 1 , md K N , md ) 2 where: t P-1,md is the point of a t-Student distribution with P−1 degrees of freedom that leaves in the tails a probability equal to the missed detection (md) probability assigned to the whole RAIM algorithm; the number of independent samples being calculated by means of computing the autocorrelation function of residuals with respect to averaged ambiguity; K N,md is the point of a Gaussian distribution with zero mean and variance equal to 1 that leaves in the tails a probability equal to the missed detection probability assigned to the whole RAIM algorithm; if the user velocity becomes lower than a certain minimum value, then the output of the short-term filter is used to build a smoothed pseudorange correcting it with the difference between the output of both filters when the velocity is equal tot the minimum; and in the transition time between both situations, a smoothed variation scheme is used.