Ionospheric scintillation is a phenomenon caused by varying concentrations of charged particles in the upper atmosphere that induces deep fades and rapid phase rotations in satellite signals, including GPS. During periods of scintillation, carrier tracking loops often lose lock on the signal because the rapid phase rotations generate cycle slips in the PLL. One solution to mitigating this problem is by employing decision-directed carrier recovery algorithms that achieve data wipe-off using differential bit detection techniques. Other techniques involve PLLs with variable bandwidth and variable integration times. Since nearly 60% of the GPS signal repeats between frames, this thesis explores PLLs utilizing variable integration times and decision-directed algorithms that exploit the repeating data as a training sequence to aid in phase error estimation. Experiments conducted using a GPS signal generator, software radio, and MATLAB scintillation testbed compare the bit error rate of each of the receiver models. Training-based methods utilizing variable integration times show significant reductions in the likelihood of total loss of lock.
Worcester Polytechnic Institute
Electrical & Computer Engineering
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Olivarez, Nathan, "Mitigating the Effects of Ionospheric Scintillation on GPS Carrier Recovery" (2013). Masters Theses (All Theses, All Years). 245.
Matlab, phase locked loop, pll, costas, training, tracking, carrier recovery, ionospheric scintillation, gps, integration time, step size, differential, bit detection, decision directed, software radio, sdr