GPS Tracking Loop Designs Using the Unscented Particle Filter

• Main Authors: Chia-Sheng Hsu, 許家盛
• Other Authors: Dah-Jing Jwo
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/64535693564700614434

碩士 === 國立臺灣海洋大學 === 通訊與導航工程學系 === 101 === This thesis investigates the GPS tracking loop designs using the unscented particle filter (UPF). The research work covers two parts: (1) the UPF-based tracking loop design with multipath parameter estimation; and (2) the vector tracking loop design based on the UPF. Multipath error is the code tracking loop error caused by the direct signals of satellite and the reflected signals in the vicinity of the receiver. In the first part, the UPF-based GPS tracking loop with multipath parameter estimation and mitigation capability is proposed, in which the multipath interference is one of the dominant sources of errors. The I (in-phase) and Q (quadrature) accumulator outputs from the GPS correlators are used as the observational measurements of nonlinear filters to estimate the multipath parameters such as amplitude, code delay, phase, and carrier Doppler. Since the measurement of (I and Q) for the filter and the system states are highly nonlinearly related, the nonlinear filters are potentially useful. For certain problems, a Gaussian assumption cannot be applied with confidence. One of the adequate methods is to use the Bayesian filter/particle filter (PF) to improve the estimation. The PF possesses superior performance as compared to extended Kalman filter (EKF) and unscented Kalman filter (UKF) as an alternative estimator for dealing with the nonlinear, non-Gaussian system. The degeneracy of particles and accumulation of estimation errors in the PF are difficult to overcome. To handle the problem of heavy-tailed probability distribution, one of the strategies is to incorporate the UKF into the PF as the proposal distribution, leading to the UPF. Performance evaluation for the UPF as compared to the conventional approaches is presented. The second part of the thesis deals with the vector tracking loop design based on the UPF .The vector tracking loop better than the scalar tracking loop .The scalar tracking loop uses the independent parallel tracking loop approach, and the vector based tracking loop technique uses the correlation of each satellite signal and user dynamics. In second part, the vector tracking loop design based on pre-filter is selected, and the navigation filter used includes the UPF and the UKF. The results show that the tracking loop based on the UPF can effectively estimate multipath parameters. Furthermore, the vector tracking loop design based on the UPF demonstrates better performance than the UKF-based vector tracking loop design, especially for the non-Gaussian noise.