TABLE OF CONTENTS Network-assisted GPS methods grew out of a need to simultaneously reduce the time to produce a position solution and increase the sensitivity of the GPS receiver. One drawback of standard GPS is the long time to demodulate the satellite orbit parameters (ephemeris) and satellite clock correction parameters directly from the satellites. If a GPS receiver could acquire the satellites instantly, an additional 18 30 seconds of continuous tracking would be required to demodulate the 50-bps navigation data message for each satellite to extract the required orbital elements and satellite clock correction terms. In applications in which the GPS receiver is part of an emergency response system, waiting 30 seconds for data demodulation can seem like an eternity. As such, methods to eliminate the need to demodulate the satellite navigation data message directly and to decrease the acquisition time of the signals in weak signal environments has been the basis for all assisted GPS work.
There are two basic methods of assisted GPS employed in cellular handsets, mobile station (MS)-assisted and MS-based. In cellular telephone terminology, MS refers to a cellular phone. The two methods are quite different, but both require a complete or nearly complete GPS receiver to be integrated into the cellular handset.
In the MS-assisted method, the position solution is computed in the network. The MS-assisted handset shifts some of the functions of the traditional GPS receiver to a network-based processor or server. This method requires most of the hardware elements of a...
