At a current position, a measurement packet is determined by a mobile terminal device at a measurement time. The measurement packet includes transmitter identifications of radio transmitters receivable at the current position of the mobile terminal device at the measurement time. By means of reference measurement packets provided to the mobile terminal device, the mobile terminal device itself can determine its current position. Additionally, a deviation of the determined transmitter identifications of the measurement packet from reference transmitter identifications of the reference measurement packets is determined. If a deviation of the reference transmitter identifications from the transmitter identifications determined at the current position is detected, experience messages can be generated that can again result in an update measure as, for example, updating the reference database by adding new transmitter identifications to the reference database and/or removing obsolete reference transmitter identifications from the reference database.