Method for operating a plurality of gnss receivers for detecting satellite signal deformation

A method for operating a plurality of GNSS (Global Navigation Satellite System) receivers, wherein for position determination, the GNSS receivers receive GNSS code signals belonging to signals sent from a multitude of satellites, and wherein each received GNSS code signal is correlated with a reference code signal generated by the receiving GNSS receiver to obtain an autocorrelation function (ACFobs), wherein a multitude of function values of the autocorrelation function (ACFobs) at different discrete chip spacings are analyzed and used in obtaining a test metric, wherein using the test metric, a decision is made whether the received GNSS code signals are suitable for position determination or unsuitable for position determination due to satellite signal deformation, and wherein the GNSS code signals found unsuitable for position determination are excluded from position determination, wherein for each satellite i, with i being a satellite index, using the test metric includes the following steps:

• a) for each time epoch tk in which the GNSS receivers receive GNSS code signals belonging to the signal of the same carrier frequency sent from the satellite i, forming a vector {right arrow over (X)}i,k of measurement values Xm,i,k, with m being a chip spacing index, and k being a measurement time epoch index, and the respective measurement value Xm,i,k being derived from normalized and bias-removed function values of the autocorrelation functions (ACFobs) of the GNSS code signals received at the GNSS receivers, combined for a multitude of the GNSS receivers;
• b) obtaining the correlation matrix Ri,n at time epoch tn from the epoch-wise measurement value vectors {right arrow over (X)}i,k obtained over a plurality of n time epochs tk with k=1, . . . , n, with n being a monitoring time epoch index, which results in matrix in Xi,n=
• X
• i
• ,
• n
• =
• [
• X
• ->
• i
• ,
• 1
• ⋮
• X
• ->
• i
• ,
• n
• ]
• ,
• in particular with Ri,n˜XTi,n Xi,n with XTi,n being the transpose matrix of Xi,n;
• c) doing a principal component analysis on correlation matrix Ri,n, thus obtaining an eigendecomposition of matrix Ri,n into a multitude of eigenpairs, being pairs of eigenvector and eigenvalue;
• d) calculating for time epoch tn a signal quality monitor test metric SQMi,n by transforming vector {right arrow over (X)}i,n to vector {right arrow over (T)}i,n via multiplication with principal component matrix PCi,n (160) and forming the square sum of vector {right arrow over (T)}i,n's entries, wherein PCi,n contains at least two eigenvectors of Ri,n, with the eigenvectors chosen having the largest eigenvalues of all eigenpairs;
• e) comparing SQMi,n to a predefined threshold value THR, and if SQMi,n exceeds THR, the entirety of GNSS code signals received at all GNSS receivers belonging to the signal of the same carrier frequency sent by satellite i in time epoch tn are considered unsuitable for position determination due to satellite signal deformation;
• wherein for subsequent time epochs having passed, the signal quality monitor test metric SQMi,n is determined again, with n increasing by 1 for each time epoch having passed.