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.