Methods and apparatus for processing GNSS signals with selection of candidate sets

A method of estimating parameters derived from Global Navigation Satellite System (GNSS) signals useful for determining a position, comprising the steps of: Obtaining observations of a GNSS signal from each of a plurality of GNSS satellites; Inputting the observations into a filter having a state vector comprising at least one floating point ambiguity for each received frequency of the GNSS signals, each floating point ambiguity forming a real number estimate associated with an integer number of wavelengths of the GNSS signal between a receiver of the GNSS signal and the GNSS satellite from which it is received, and wherein the filter is arranged to estimate a floating point value for each floating point ambiguity of the state vector; Assigning integer values to at least a subset of the estimated floating-point values to define a plurality of integer ambiguity candidate sets; Selecting a first number of candidate sets that have a quality measure that is better than a first threshold, the first threshold being based on a ...