Multipath mitigation in the frequency domain

摘要

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 multipath errors have low/medium 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 un-mitigated 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.