| 摘要 |
A system to reduce the acquisition time necessary to access a GPS signal used to deterrffine the positional coordinates of a user associated with a wireless communications system. A wireless communications system can provide telephony and data service to mobile users throughout a large area. The wireless communications system provides transmissions and reception in a plurality of spotbeams or cells (17, 18, 19) comprising the large area. Each spotbeam or cell may be very large, up to 1500 km. in diameter for some satellite based systems, which precludes determining the subscribers precise location from his spotbeam ID or cell ID alone. With this invention, the wireless network broadcasts to user terminals within each spotbeam or cell, the GPS ID of all satellites that are visible within the zone along with Doppler and signal strength estimates for the visible GPS satellites. The user terminal (20) has a GPS receiver which is capable of receiving the C/A codes from the GPS satellites. The user terminal uses the broadcast GPS aiding data to quickly acquire the GPS C/A signals for all visible GPS satellites (14, 15, 16). The user terminal then returns the GPS C/A code measurements to the wireless network (24, 25, 11) which processes the measurements in conjunction with separate GPS data which it also receives to determine the users location. This precludes the user terminal from having to perform all the functions necessary to compute the geolocation. In this manner, the location of the user can be rapidly determined while reducing the cost of the user terminal. <IMAGE> |
