A method for estimating a position of a mobile device, said device being equipped with a GNSS receiver that is time-synchronized with a GNSS system time, the method comprising the steps of: a) providing a measurement of one or more GNSS satellite signals from respective GNSS satellites that were received, at a first time-instant, by the GNSS receiver; b) estimating a position and corresponding position accuracy measure of the mobile device for the first time-instant using: 1) obtained position and motion data for a second time-instant different from the first time-instant, 2) movement data concerning movement of the mobile device between the first and second time-instants and, optionally, 3) measurements of one or more of the received satellite signals which have not been determined to be invalid; characterized in that the method further comprises the steps of: c) for at least one of the received satellite signals: c1) determining a signal propagation characteristic pertaining to said at least one satellite signal using information contained in that satellite signal; c2) determining an expected range for said signal propagation characteristic based on orbital behavior of the GNSS satellite that transmitted said at least one satellite signal and the estimated position and position accuracy measure; c3) determining that said at least one satellite signal is a valid signal if the corresponding signal propagation characteristic falls in the determined expected range, and determining that said at least one satellite signal is an invalid signal if the corresponding signal propagation characteristic falls outside the determined expected range; and d) calculating the position, and preferably the position accuracy measure, of the mobile device at the first time-instant using the valid satellite signal(s). a) providing a measurement of one or more GNSS satellite signals from respective GNSS satellites that were received, at a first time-instant, by the GNSS receiver; b) estimating a position and corresponding position accuracy measure of the mobile device for the first time-instant using: 1) obtained position and motion data for a second time-instant different from the first time-instant, 2) movement data concerning movement of the mobile device between the first and second time-instants and, optionally, 3) measurements of one or more of the received satellite signals which have not been determined to be invalid; c) for at least one of the received satellite signals: c1) determining a signal propagation characteristic pertaining to said at least one satellite signal using information contained in that satellite signal; c2) determining an expected range for said signal propagation characteristic based on orbital behavior of the GNSS satellite that transmitted said at least one satellite signal and the estimated position and position accuracy measure; c3) determining that said at least one satellite signal is a valid signal if the corresponding signal propagation characteristic falls in the determined expected range, and determining that said at least one satellite signal is an invalid signal if the corresponding signal propagation characteristic falls outside the determined expected range; and c1) determining a signal propagation characteristic pertaining to said at least one satellite signal using information contained in that satellite signal; c2) determining an expected range for said signal propagation characteristic based on orbital behavior of the GNSS satellite that transmitted said at least one satellite signal and the estimated position and position accuracy measure; c3) determining that said at least one satellite signal is a valid signal if the corresponding signal propagation characteristic falls in the determined expected range, and determining that said at least one satellite signal is an invalid signal if the corresponding signal propagation characteristic falls outside the determined expected range; and d) calculating the position, and preferably the position accuracy measure, of the mobile device at the first time-instant using the valid satellite signal(s).