Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Patent
1997-09-15
1999-03-16
Tarcza, Thomas
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
701213, 375350, G01S 502, H04B 7185
Patent
active
058835954
ABSTRACT:
A method of smoothing Kalman Filter position states forming a "groundtrack" in a receiver used in a satellite based positioning system (e.g. GPS). In such systems, data pairs including an incoming value and a "raw" reliability estimate (e.g. a standard deviation) are normally fed directly to the Kalman Filter. The Kalman Filter computes the resultant and an overall uncertainty estimate by applying a "weight" to each successive incoming value based on its reliability. The Kalman Filter also estimates incoming values based on past values.
The method involves the unique steps of replacing the raw reliability with a "modified" reliability if the incoming value is too far from the estimate in view of an adjustable limit envelope defined by the current uncertainty estimate and reliability value. If the difference between what we get and what we expect is small, then the reliability value is passed without modification. If the difference is large, however, then we decrease the reliability value to tell the Kalman Filter that the value is less reliable. In other words, we "de-weight" implausible values. The modified reliability value is preferably scaled or decreased in proportion to the amount by which the square of the incoming value is outside of the limit envelope. This even minimizes the effect of values that are very strong (have high "reliability"), but still very wrong, and thereby smoothes the resultants produced by the Kalman Filter.
REFERENCES:
patent: 5416712 (1995-05-01), Geier et al.
patent: 5590043 (1996-12-01), McBurney
patent: 5615232 (1997-03-01), Van Nee
Cray William C.
O'Shaughnessy James P.
Oh Susie H.
Phan Dao L.
Rockwell International Corporation
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