Abstract
Measurements from Global Positioning System (GPS) satellites are subject
to corruption by signal interference and induced offsets. This paper.presents
two independent algorithms to ensure the navigation system remains
uncorrupted by these possible GPS failures. The first is parameter
estimation algorithm that estimates the measurement noise variance
of each satellite. A redundant measurement differencing (RMD) technique
provides direct observability of the differenced white measurement
noise samples. The variance of the noise process is estimated and
provided to the second algorithm, a parallel Kalman filter, which
then adapts to changes in the real-world measurement noise strength.
The parallel Kalman filter structure detects and isolates signal
offsets in individual GPS satellites. The offset detection algorithm
calculates test statistics on each of the filters and decides which
satellites to use in the solution based on these statistics. The
two algorithms contain several user-definedparameters thathave significant
effects when adjusted. The various effects of parameter variation
are described and a parameter set is chosen at which to evaluate
the algorithms. The combined algorithm performs quite well in computer
simulations.
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