PLL bandwidth and noise in 100 Hz GPS measurements

Abstract

The impact of the phase-locked loop (PLL) bandwidth on the noise and correlations of GPS measurements sampled with a 100 Hz rate has been investigated using short and long baselines, and stationary or moving GPS rovers recording oscillations with known characteristics relative to "true" reference values. Data have been collected under various satellite constellations using various values of PLL bandwidth, particularly 25, 50, 100 Hz, and were processed in differential mode using different software packages. Analysis of standard deviations, spectra and autocorrelation functions of the differences between recorded and true displacements revealed that an increase in the PLL bandwidth leads to reduction in correlations and increase in low- and high-frequency noise of 100 Hz data. Optimal results can be obtained using either a pre-set 50 Hz PLL bandwidth or a 100 Hz PLL bandwidth combined with a posteriori band-pass filtering of the coordinates. Such optimal results permit accurate recording of high-frequency (>5 Hz), dynamic displacements of a few millimeters and indicate that 100 Hz data are useful for monitoring high-frequency structural vibrations, and also strong earthquake motions and high-frequency movements of vehicles.