Abstract: A radio beacon (105(5)) is for use in location determination inside a building (103) or other enclosure. The beacon transmits a RF signal equivalent to a partially coded GPS (Global Positioning System) signal which includes an identity code identifying the beacon but null data in at least one GPS data field. A mobile station (101) includes a GPS receiver (208) for receiving GPS signals and a processor (202) for processing data extracted from signals received by the GPS receiver. The GPS receiver is operable to receive a signal from a transmitting beacon (105(5)). The processor is operable to recognise a beacon identity code from the data extracted from the received signal and thereby detect that the signal is from a radio beacon rather than a GPS satellite and thereby to apply a further procedure to calculate the location of the mobile station based upon a known location of the identified beacon.

Abstract: A subscriber unit (103) for a cellular communication system (100) comprises a first location processor (117) which determines a location estimate from signals transmitted from satellites (105) and from satellite information related to the satellites (105). The satellites (105) may be Global Positioning System (GPS) satellites. The subscriber unit (103) also comprises a receiver (115) which receives the satellite information, and further comprises a second location processor (111) which determines location estimates based on uplink or downlink transmissions in the cellular communication system (100). An update controller (121) determines an update time for the satellite information in response to the location estimates of the second location processor (111). Accordingly, the update operation may be optimised for the specific movement of the subscriber unit (103) without requiring satellite based location estimates.