Local oscillator phase noise effects on phase angle component of GNSS code correlation

This paper demonstrates the effect of radio frequency (RF) front-end (FE) free-running local oscillator (FRO) phase noise (PN) on the phase component of the Global Navigation Satellite System (GNSS) code correlation product. It is observed that as FE PN increases, it adversely affects the stability of the phase component of the code correlation. The tracking loops in baseband processing of a GNSS receiver attempt to lock on to the frequency, delay and phase of the correlation product. Until these parameters are varying within acceptable bounds, set by the dynamics handling capability of the tracking loops, the tracking loops are able to successfully track the satellite signal. However, PN increases the variation in phase of the correlation product calculated over consecutive epochs and may also cause loss of tracking lock if these variations go beyond phase locked loop (PLL) pull-in range thresholds. This paper studies the relation between FRO PN and phase component of correlation through numerical analysis, and software simulations by artificially contaminating GNSS signal stream with PN of increasing variance and checking the result on the standard deviation (SD) of the phase component of correlation product. Based on these results, this paper recommends certain maximum limits on the FE PN in order to keep the SD of phase component below the one-sigma phase error limits of the PLL used in typical GNSS tracking loops.