Integration of GPS with Other Sensors and Network Assistance - Understanding GPS: Principles and Applications - page 554

handset is a periodic fix mode, in which the handset accepts the ephemeris assist
data and then computes position at some periodic rate (e.g., once per minute). The
handset only needs to get current ephemeris for each satellite at the start, as its useful
life is 2 hours around the TOE time. In an assisted mode, the handset may never

observe the satellite-broadcast real-time integrity data that is available in the 50-bps
satellite navigation data message. Thus, if a particular satellite fails between the time
the handset accepts ephemeris and the time it wants to use it for a position solution,
the handset will not have knowledge of the failed state and could produce erroneous
position data.
To combat this potential problem, a short real-time integrity message was added
to the RRLP protocol to inform the handset when a particular satellite has failed.
The real-time-integrity message is requested at the start of each location attempt and
consumes only a few bits of the available bandwidth. The network-generated
real-time-integrity message is then sent to the handset. For the case of no failed satel-
lites, this message returns one zero bit. For the case of a failed satellite or group of
failed satellites, the satellite IDs of the failed satellite(s) are returned to the handset;
the handset excludes those failed satellites from any subsequent position solution.
As such, the MS-based handset needs to request real-time integrity information at
the start of each location attempt to ensure solution integrity.

±

References

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[4] Lawrence, A., Modern Inertial Technology: Navigation, Guidance, and Control , New

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[5] Gelb, A., et al., Applied Optimal Estimation , Cambridge, MA: MIT Press, 1992.

[6] Kalman, R. E., “A New Approach to Linear Filtering and Prediction Problems,” Journal of

Basic Engineering (ASME) , Vol. 82D, March 1960, pp. 35-37.

[7] Frazer, D. E., et al., “T-33 Aircraft Demonstration of GPS Aided Inertial Navigation,” Proc.

of The Institute of Navigation Satellite Division Technical Meeting , Colorado Springs, CO,
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Thornton, C. L., and G. J. Bierman, UDU T Covariance Factorization for Kalman Filtering ,
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[8]

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[11] Carroll, R. W., et al., “Velocity Aiding of Non-Coherent GPS Receiver,” Proc. of 1977

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[12] Widnall, W. S., “Alternate Approaches for Stable Rate Aiding of Jamming Resistant GPS

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[13] Copps, E. M., et al., “Optimal Processing of GPS Signals,” NAVIGATION: Journal of The

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