Impact of Receiver Front-End Characteristics on High Order BOC Tracking

Abstract

Surface Acoustic Wave (SAW) or Bulk Acoustic Wave (BAW) filters are typically used in miniaturized GNSS receiver front-ends and antennas since they are relatively small, inexpensive and provide good frequency selectivity. However, SAW filters have large group delay variations which lead to distortions of the GNSS signal correlation function. With the multiple correlation peaks of higher-order binary offset carrier (BOC) signals, these distortions may lead to false locks on side-peaks, leading to systematic tracking errors and a consequently a corrupted PVT. A wideband commercial SAW filter has been inserted in the reception chain used for a pseudo-PRS tracking experiment, during which baseband samples have been recorded. These baseband samples have been processed with BOC tracking algorithms that exploit the BOC subcarrier for higher tracking accuracy, becoming heavily impacted by the distortions introduced by the SAW filter. These distortions are analyzed in greater detail, and an analytical signal model is derived which allows to systematically investigate the impact of these distortions on the side peak tracking detection capabilities of the Astrium Correlator high-order BOC tracking algorithm. It is shown that the impact of the SAW filter distortions can be countered by using an optimized early-minus-late spacing within the generation of the side peak detector signal, together with a shifting of corresponding thresholds for side peak detection.