Anchor base stations are arranged around an area in which positions for radio transmitter tags are to be determined. The anchor base stations have known locations, and the location of an intermediate base station added to the system is determined by: arranging the intermediate base station between first and second anchor base stations; determining, based on propagation-delay measurements of a signal emitted by the intermediate base station and using the global time reference a first calculated distance between the first anchor base station and the intermediate base station, and a second calculated distance between the second anchor base station and the intermediate base station (BSI5); obtaining an elevation indicator specifying whether the intermediate base station is located in level with, above or below the common plane; and determining the location of the intermediate base station based on the first and second calculated distances and the elevation indicator.