A Graph Optimization Method for GNSS Signal Tracking Loop

Abstract

Global Navigation Satellite System (GNSS) constructed based satellites in space has been extended in almost everywhere in our daily life for providing precise position, velocity and time (PVT) information. GNSS receivers process the signals and generate measurements for calculating the PVT information. Signal tracking in a GNSS receiver is composed of carrier and code tracking, and pseudo-range and pseudo range rates are generated individually from the two tracking loops. A Frequency Lock Loop (FLL) and Phase Lock Loop (PLL) are common methods for carrier tracking and code tracking respectively. Kalman Filter was employed to mitigate the carrier tracking errors with the carrier phase dynamic model. Therefore, the PLL could work with a wider bandwidth to tolerate higher dynamics or weak signals. In this paper, we proposed a Graph Optimization (GO) method based carrier tracking errors mitigation method, GO method utilized the inherent relationship between the tracking errors in time domain. With a GPS L1 dataset collected in real environment, the KF and GO were compared, and the phase tracking errors decreased by xx, which supported the conclusion that GO was superior than KF in mitigating the carrier tracking errors.