Abstract: There is provided a system for carrying out a height calibration process in a wireless indoor location tracking network, comprising: a plurality of fixed location tracking nodes disposed indoors to cover an indoor area, wherein the plurality of fixed location tracking nodes is configured to carry out location tracking in the indoor area; a mobile tag configured to communicate with at least one location tracking node at a given time at least for the purposes of determining the location of the mobile tag, wherein that the mobile tag comprises a height sensor configured estimate the height of the mobile tag; and at least one location tracking node of the plurality of fixed location tracking nodes is a calibration node configured to co-operate in carrying out a height calibration process during operation of the location tracking network, wherein the height of each calibration node is known.