Use of a vector delay lock loop receiver for GNSS signal power analysis in bad signal conditions

The paper describes a vector delay/frequency lock loop (VDLL and VFLL) GPS receiver following the software defined radio approach and the use of this receiver to analyze signal power of GPS C/A code signals in a selection of experiments including indoor signals, car navigation and satellites at negative elevation angles. In vector mode, the navigation processor controls the code and carrier numerically controls oscillators (NCOs) replacing the tracking loops. A major advantage of this method is that after once a good position, velocity and time (PVT) solution is available, all GPS signals are continuously tracked even under weak (or no) signal conditions. Two different C/N-0 estimators (squaring and differential) are introduced and discussed. They allow signal power estimation even below 10 dBHz for GPS C/A code signals. Altogether the presented method allows characterizing the highly variable C/N-0 values in bad signal conditions. Variations with amplitudes of up to 20 dBHz occur with a timescale of less than 1 s.