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Multipath mitigation of GPS carrier phase measurement using unscented Kalman filter

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Abstract

This paper describes the development of a method of multipath mitigation of GPS (Global Positioning System) carrier phase measurement. Multipath is a major source of error in high precision GPS static and kinematic differential positioning. Multipath accounts for most of the total error budget in carrier phase measurements in an attitude determination system. In order to estimate and remove carrier phase measurement multipath, an array GPS antenna system has been used. The known geometry between the antennas is the useful information to estimate multipath parameters. The extended Kalman filter (EKF) is a popular estimator, which uses a combination of the available information from an array antenna system to estimate various multipath parameters. The unscented Kalman filter (UKF) is newly focused from many areas to overcome some of the limitations of the extended Kalman filter. The UKF is applied for estimating multipath parameters in this paper.

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... a is the distance delay of a reflected signal [11]. ...
... When the single frequency carrier phase measurements are used, at least four antennas are needed to estimate the multipath error parameters [11]. When the dual frequency carrier phase measurements are used the number of antennas can be reduced. ...
... For multipath mitigation, the EKF has been a popular estimator, which uses a combination of the available information from an array antenna system to estimate various multipath parameters [11]. Although the EKF inherits the fancy feature of a linear Kalman filter under process and measurement noises, the EKF has several drawbacks due to its linearization scheme. ...
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This paper describes a multipath estimation method for Global Positioning System (GPS) dual frequency carrier phase measurements. Multipath is a major error source in high precision GPS applications, i.e., carrier phase measurements for precise positioning and attitude determinations. In order to estimate and remove multipath at carrier phase measurements, an array GPS antenna system has been used. The known geometry between the antennas is used to estimate multipath parameters. Dual frequency carrier phase measurements increase the redundancy of measurements, so it can reduce the number of antennas. The unscented Kalman filter (UKF) is recently applied to many areas to overcome some of the limitations of the extended Kalman filter (EKF) such as weakness to severe nonlinearity. This paper uses the UKF for estimating multipath parameters. A series of simulations were performed with GPS antenna arrays located on a straight line with one reflector. The geometry information of the antenna array reduces the number of estimated multipath parameters from four to three. Both the EKF and the UKF are used as estimation algorithms and the results of the EKF and the UKF are compared. When the initial parameters are far from true parameters, the UKF shows better performance than the EKF.
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