Methods and systems for handling outliers when using navigation satellite system observations

System comprising at least one of a navigation satellite system receiver, hereinafter abbreviated as “NSS receiver”, and a processing entity capable of receiving data from the NSS receiver, the system being for estimating parameters useful to determine a position, the NSS receiver being configured for observing at least one NSS signal from each of a plurality of NSS satellites over multiple epochs, and the system being configured for:

• receiving input data comprising at least one of:
• NSS signals observed by the NSS receiver, the NSS signals comprising at least one NSS signal from a first NSS satellite and at least one NSS signal from a second NSS satellite, and
• information derived from said observed NSS signals;
• operating an estimation process, hereinafter referred to as “estimator”, wherein the estimator uses state variables and computes the values of its state variables at least based on the received input data;
• and
• performing a procedure, hereinafter referred to as “outlier detection procedure”, comprising:
• computing a first statistic based on data outputted from the estimator, the data being associated with a set, hereinafter referred to as “current set”, of NSS observables;
• identifying, among the NSS observables of the current set, an NSS observable candidate for removal;
• computing a second statistic based on the data outputted from the estimator from which the data associated with the identified NSS observable has been removed;
• and
• determining whether the ratio of the first statistic to the second statistic exceeds a threshold, hereinafter referred to as “first threshold”, and, if so, removing the identified NSS observable from the current set, having the estimator recompute the values of its state variables without the removed NSS observable, and performing the outlier detection procedure again based on data newly outputted from the estimator.