Nonlinear Filtering in GNSS Pseudorange Dynamics Estimation Combining Code Delay and Carrier Phase

Abstract

In Global Navigation Satellite System (GNSS) receivers, code delay measurements yield unambiguous but noisy pseudorange estimates. On the other hand, the pseudorange obtained with carrier phase measurements is almost noiseless, but is affected by an ambiguity term multiple of the carrier wavelength. In this paper, we propose a structure for code and carrier phase estimation and a novel technique to merge those estimates. The overall architecture consists of 1) a bank of correlators, each one feeding an extended Kalman filter, 2) an interpolation algorithm to produce the best code delay and carrier phase estimates, and 3) a nonlinear filter that combines these estimates to reduce progressively the phase ambiguity, yielding precise pseudorange estimates in high dynamics scenarios and in the presence of weak signals. The proposed approach is able to accommodate the majority of the new GNSS signals (modernized GPS and Galileo), produces smaller mean square errors than the conventional code/phase merge technique (Hatch filter), is robust to transients that may affect the phase estimation during the reception of weak signals, and is free from false code-locks.