Title: Multi-Channel Extended Kalman Filter for Tracking BOC modulated signals in the presence of multipath
Author(s): Mariana Spangenberg, Vincent Heiries, Audrey Giremus and Vincent Calmettes
Published in: Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005)
September 13 - 16, 2005
Long Beach Convention Center
Long Beach, CA
Pages: 2155 - 2165
Cite this article: Spangenberg, Mariana, Heiries, Vincent, Giremus, Audrey, Calmettes, Vincent, "Multi-Channel Extended Kalman Filter for Tracking BOC modulated signals in the presence of multipath," Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005), Long Beach, CA, September 2005, pp. 2155-2165.
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Abstract: Multipath is one of the main error sources when tracking signals in the GNSS systems. The presence of reflected signals gives place to a bias when estimating the propagation delay of the direct signal. There are several ways for mitigating this multipath problem. Several solutions have already been discussed for different techniques [1] such as Narrow Correlator, Double delta or Early1/Early2 where the key factor concerns the discriminator curve shape to be used in a conventional DLL(delay lock loop). For INS/GPS solution with ultra tightly coupled GPS, multiple correlation channels are used and the performance depends on the correlators positioning. In this paper the proposed methodology is based on the Extended Kalman filter (EKF) with multiple correlators. This model allows not only working with sub-chip delayed components but it has been shown [2] that it can optimally combine multiple correlation channels to better estimate the desire parameters, such as delay and phase. However, it will be no longer possible to use non correlated measurements due to this sub-chip difference between correlators outputs. In contrast with most models proposed when using the EKF [3], where the parameters taken into account in the state model include not only those of the direct signal but also those due to multipath (reflected signal), in this paper the state vector just includes the parameters of the direct signal lowering the calculations’ complexity. On the other hand, an optimal distribution for the multi correlators scheme is pursued. The idea is to find a disposition for which the estimation error introduced by multipath can be reduced and so the error envelope area. The study is done using Binary Offset Carrier modulation (BOC) which is seen as a serious candidate for many radio navigation signals, including several GALILEO signals as well as GPS M-code. BOC autocorrelation function (ACF) presents multiple positive and negative peaks, which greatly improve positioning accuracy and enhance multipath rejection. So an important part of this work consists of studying the interest of correlators distributed on the secondary peaks, mainly for a BOC(10, 5) modulation. In this paper, a theoretical introduction to some key concepts is proposed and the utilized filter model is presented. The filter characterization in the presence of noise and multipath is studied. Considering a BOC signal, different alternatives for the multicorrelators scheme are studied.