DISTRIBUTED KALMAN FILTER ARCHITECTURE FOR CARRIER RANGE AMBIGUITY ESTIMATION

Methods and apparatus for determining navigation data (124) using carrier range measurements obtained by a GNSS receiver for a plurality of GNSS satellites, the apparatus comprising: a first Kalman filter (100) configured to determine an a posteriori estimate of a first state vector based at least in part on a first set of GNSS measurements (104) obtained by the, and/or a further, GNSS receiver and an a priori estimate of the first state vector, the first state vector comprising carrier range ambiguity values relating to the plurality of GNSS satellites and a position of the, and/or the further, GNSS receiver; and a second Kalman filter (102) configured to determine an a posteriori estimate of a second state vector, which comprises the navigation data (124), based at least in part on a second set of GNSS measurements (106) obtained by the, and/or a further, GNSS receiver, an a priori estimate of the second state vector, and carrier range ambiguity data (126) based on the carrier range ambiguity values determined in the a posteriori estimate of the first state vector.