System for setting coarse GPS time in a mobile station within an asynchronous wireless network

A mobile station for determining position utilizing periodically transmitted navigation bits from a plurality of SVs synchronized with GPS time, the periodically transmitted navigation bits including a time indicator field, the mobile station also communicating with one or more base stations and a position determining entity (PDE) comprising:

• a two-way communication system for communicating with the base stations and the PDE;
• a position location system that includes a GPS clock;
• means for requesting an assistance message from the PDE, the assistance message including a sequence of predicted navigation bits sent from the base station approximately synchronized in time with GPS time;
• means for saving a time of receipt of the assistance message;
• means for locating the predicted time indicator field within the predicted navigation bits;
• means, responsive to the located time indicator field, for determining a predicted Time of Week;
• and
• means for setting coarse GPS time within the GPS receiver responsive to the predicted Time of Week and the time of receipt.

A method for synchronizing a GPS receiver with coarse GPS time in a mobile station (MS) communicating with a base station and a position determining entity (PDE) using the IS-801 standard, the GPS receiver configured to receive periodically transmitted navigation bits from a plurality of SVs synchronized with GPS time, the transmitted navigation bits having a format including a plurality of frames, each frame organized into a plurality of subframes, each subframe having a SUB-FRAME COUNT message, comprising:

• by the MS, requesting a Sensitivity Assistance (SA) message from the PDE, the SA message including
• a Predicted Navigation Bits field that includes a sequence of predicted navigation bits including at least one subframe,
• a Data Record Size field that specifies the length of the Predicted Navigation Bits field, and
• a Reference Bit Number field that designates a bit within a frame of the actual navigation bits, thereby associating the predicted navigation bits with a group of navigation bits;
• responsive to the request from the MS, sending the SA message from the base station approximately in time with GPS time;
• receiving the SA message in the MS, and saving a time of receipt of the SA message;
• responsive to the Reference Bit Number field and the Data Record Size field, determining a first bit of the sequence of predicted navigation bits that corresponds to the position of the first bit of the sequence within a frame of actual navigation bits;
• responsive to the position of the first bit of the sequence of predicted navigation bits, locating the SUB-FRAME COUNT field within the predicted navigation bits;
• decoding the located SUB-FRAME COUNT field to provide a predicted SUB-FRAME COUNT value;
• responsive to the predicted SUB-FRAME COUNT value, determining the Time of Week at the first bit of the sequence of predicted navigation bits;
• and
• coincident with the first bit of the sequence of predicted navigation bits, setting coarse GPS time within the GPS receiver responsive to the predicted SUB-FRAME COUNT and the time of receipt.