Integration of GPS with Other Sensors and Network Assistance - Understanding GPS: Principles and Applications - page 523

Reference
DR filtered
GPS solution

3rd Ave

9th Ave

0 250 500 m

Figure 9.34 GPS and ABS integration filter results.

Table 9.4 Summary Comparison, Gyro
Odometry, and ABS Integrations

Maximum
Error

RMS
Error DR

ABS 115m 17m

Gyro/odometry 69m 13m

Source: [29].

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 naviga-
tion data message for each satellite to extract the required orbital elements and sat-
ellite 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 stand-alone GPS receiver (an antenna, RF section, and digital proces-