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Title: Improved FLL-assisted PLL with in-phase pre-filtering to mitigate amplitude scintillation effects
Authors: Xu, R
Liu, Z 
Chen, W 
Keywords: FLL-assisted PLL
In-phase pre-filtering
Ionospheric amplitude scintillation
Issue Date: 2015
Publisher: Springer
Source: GPS Solutions, 2015, v. 19, no. 2, p. 263-276 How to cite?
Journal: GPS solutions 
Abstract: Ionospheric scintillation can increase carrier tracking error of the Global Positioning System (GPS) receiver and may lead to loss of lock under serious conditions. It is a threat to reliable and accurate GPS applications. Kalman filter-based phase lock loop, frequency lock loop-assisted phase lock loop (FAP) and vector-based tracking algorithms are considered as solutions to improve the robustness of carrier tracking. However, their performances are sensitive to loop parameters: noise bandwidth and integration period. We analyze the effects of amplitude scintillation on inputs signals, in-phases and quadra-phases, of carrier tracking loop. Analysis result shows amplitude scintillations affect in-phase much more seriously than quadra-phase. Based on the results, the FAP with in-phase pre-filtering (FAP_IPF) method is proposed to mitigate the amplitude scintillation effect on in-phase. IPF is placed before discriminators of FAP to restrict the in-phase variation within a reasonable range. The tracking loop FAP_IPF is tested using both simulated and real-world GPS intermediate frequency (IF) data with amplitude scintillation and compared to the traditional third-order PLL and FAP without IPF. The tracking results show that FAP_IPF is more robust than FAP and traditional PLL. In 10 simulation scintillation cases (S4?=?0.6¡V1.0 and C/N0?=?40?dB¡VHz), FAP_IPF can maintain tracking in 6¡V9 cases even if its bandwidth Bn varies in a large range 7.5¡V15?Hz. FAP has the best performance at bandwidth Bn?=?10?Hz, but its performance is degraded dramatically at other bandwidths. PLL shows the worst performance among the three algorithms. In real-world GPS IF data with real-world scintillation S4?=?1.11 and £m??=?1.49?rad, FAP_IPF can successfully maintain signal tracking within bandwidth Bn?=?7.5¡V12.5?Hz, while both FAP and traditional PLL lose signal trackings.
ISSN: 1080-5370
EISSN: 1521-1886
DOI: 10.1007/s10291-014-0385-5
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