Dual-constellation Vector Tracking algorithm in Ionosphere and Multipath conditions

In urban environments, standalone GNSS receivers can be strongly affected to the point of not being able to provide a position accuracy suitable for use in vehicular applications. In this paper, a dual constellation GPS + Galileo single frequency L1/E1 Vector Delay Frequency Lock Loop (VDFLL) architecture for the automotive usage in urban environment is presented. In the proposed architecture, the usual scalar tracking loops are abolished and instead an EKF-estimated navigation solution drives the code delay (VDLL part) and carrier frequency (VFLL part) Numerical Control Oscillators (NCOs) in the feedback loop for each tracking channel. However, the use of single frequency L1 band signals implies the necessity of taking into account the ionospheric error effect. This paper focuses on the implementation of the dual-constellation single-frequency VDFLL architecture, capable of estimating the ionosphere residual error present in the received observations. This work investigates the VDFLL superiority w.r.t the scalar tracking receiver in terms of positioning performance and tracking robustness in urban area in the presence of multipath and ionosphere residual errors. Contrary to the conventional tracking, the L1/E1 VDFLL loop is able to accurately pursue the frequency and code-delay estimation without the requirement of signal reacquisition process and within limited positioning error.