Enhancing time keeping accuracy for low power GPS receivers

[0017]Embodiments of the present invention will now be described in the context of a GPS positioning device incorporated in to a mobile phone. It will however be apparent that the present invention is applicable to any positioning system in a mobile device where accurate time data is required for position fixing, or high clock accuracy is required. Furthermore, embodiments of the present invention are described in the context of a mobile device operating the Global System for Mobile Communications GSM standard, however the present invention could equally be incorporated in a mobile device using different cellular air interfaces such as Time Division Multiple Access TDMA in a TDMA network, Code Division Multiple Access CDMA in a CDMA network, or Personal Digital Cellular PDC in a PDC network.

[0018]FIG. 1 illustrates an overview of a global position system wherein a mobile device MS has a built in GPS receiver which is able to determine its position based on CDMA signals received from fo