In a cellular communications network, additional control signals comprising virtual base station identification data are distributed in the radio system from well defined locations by e.g. transmitters. Since there is a connection between each virtual base station identification data and the location from where it is transmitted, a mobile terminal can use the information for improving its position estimation according to conventional procedures. No modifications of the mobile terminals are therefore necessary. The mobile terminal is not able to connect to the communications system using the virtual base station identification data, since this data only is intended for position estimating purposes. In such a way, the devices for providing the additional information necessary for the improved position estimation can be made very simple and inexpensive.