Processing GPS L2C signals under ionospheric scintillations

The objective of this study is to develop a software receiver to effectively process L2C GPS signals under ionosphere scintillations. Several L2C signal processing algorithms are implemented in a VC++ software receiver with efficient CM signal acquisition, rapid transferring from acquisition to tracking, and robust CL signal tracking. These algorithms are validated using live GPS signals and simulated RF signals. A conventional PLL and a Kalman Filter based PLL (KFPLL) tracking algorithm are implemented and their performances are evaluated using simulated digital IF signals under strong scintillation conditions. Our results show that the receiver estimated S4 index serves as a good indicator of scintillation intensity level even with frequent cycle slips during deep amplitude fading. Appropriate characterization of signal intensity spectrum is only possible with relatively high signal C/N0. The carrier phase scintillation is analyzed in terms of steady state tracking errors, cycle slips, standard deviation of detrended phase errors, as well as detrended carrier phase spectral analysis. Compared to the conventional PLL, the KFPLL has a slower but steadier transient response due to its incorporation of a priori information. Our test results show that the tracking threshold of our L2C software receiver reaches 22dB-Hz in the presence of moderate-level ionosphere scintillations.