Article,
Multipath Mitigation in the Frequency Domain
Proc. of the IEEE Position Location and Navigation Symposium (PLANS), (2004)
Abstract
The GPS measurements can be modeled as true range plus other error
sources such as orbit and clock biases, ionosphere, troposphere,
multipath, and receiver noise. All of these errors have different
frequency spectrum components. Ionosphere and troposphere errors
are of low frequency, and the receiver noise has high frequency components.
Orbit errors are typically bias terms, and muttipath errors have
lowlmedium frequency components. Since these errors have different
frequency components, the methodology is presented whereby the multipath
error can be mitigated through frequency domain processing. In this
method, firstly, a validated multipath model provides the multipath
frequency spectrum analysis, which is used to bound the frequency
domain region for mitigation. Secondly, a code-minus-carrier (CmC)
analysis provides the major code multipath error and its frequency
spectrum; Thirdly, a code multipath correction is formed and applied
to mitigate the multipath error in the GPS pseudorange measurement.
Fourthly, a CmC analysis is performed on the multipath mitigated
measurements to illustrate a reduction in the multipath error. Lastly,
a compression ratio is defined which is used as a final metric to
assess the net improvement in the standard deviation of the multipath
mitigated CmC, as compared to the unmitigated CmC, on a percentage
basis. This technique does rely on an estimate of the peak frequency
component of the multipath to be mitigated. Additionally, real test
data shows the code multipath is mitigated without carrier phase
aiding. Therefore, both the multipath mitigated pseudorange measurement
and carrier phase measurement can be utilized for the user solution,
which improves both accuracy and integrity.
