Patent ID: 7043258

Claim:
A mobile telephony handset comprising a wireless communications transceiver for exchanging signals with a base station which has a base station reference time source, and a positioning receiver for receiving coded ranging signals from a satellite-based positioning system which has a positioning system reference time source, wherein the handset is configured such that the positioning receiver is activated only periodically to perform a position fix using the ranging signals and between such active periods is in a power-saving condition, the position fix including a respective time measurement in which a precision time indication referenced to the positioning system reference time source is recorded and saved, the handset including calibration means arranged, for each of a plurality of new such position fixes, to combine (a) an elapsed time indication derived from a repeated signal pattern which is received from the base station and is synchronised to the base station reference time source, the elapsed time indication being indicative of the time elapsed since a previous position fix, and (b) the precision time indication obtained with that previous position fix, thereby to generate a calibrated time reference for performing the new position fix.