Method and apparatus for assisted GPS protocol

A method in a mobile radio communication device for determining a location of the mobile radio handset, the method comprising the steps of:

• receiving an ephemeris message, wherein said ephemeris message comprises Global Positioning System (GPS) ephemeris data for a plurality of GPS satellites and clock correction data;
• thereafter receiving a differential correction message comprising differential correction data;
• determining whether the GPS ephemeris data for one or more of the plurality of GPS satellites requires update;
• requesting an update message comprising updated GPS ephemeris data;
• receiving the update message;
• and
• determining the location of the mobile radio handset in response to the GPS ephemeris data, the clock correction data, the differential correction data, and the updated GPS ephemeris data, wherein the step of receiving an ephemeris message comprises the step of receiving a point-to-point ephemeris message particularly addressing the mobile radio handset, the step of receiving a differential correction message comprises the step of receiving a point-to-point differential correction message particularly addressing the mobile radio handset, and wherein the step of determining whether the GPS ephemeris data for one or more of the plurality of GPS satellites requires update comprises the steps of:
• calculating a computed location of the mobile radio handset;
• and
• determining a prediction of an accuracy of the computed location in response to the computed location, the GPS ephemeris data and a timing parameter.