  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 vector delay/frequency-locked loop
(VDFLL) architecture for a dual constellation L1/E1 GPS/Galileo receiver is
proposed. In this implementation, the individual DLLs and FLLs of each tracked
satellite are replaced with an Extended Kalman filter (EKF), responsible for
both estimating the user's position, velocity and clock bias and closing the
code/carrier updates for each GPS L1 and Galileo E1 tracking channels. In this
work, a detailed performance comparison between the scalar tracking and VDFLL
configuration is assessed under signal outages and significant power drops
conditions that are simulated in different satellite channels. Contrary to the
conventional tracking, the L1/E1 VDFLL loop is able to recover the frequency
and code-delay estimation at the end of the simulated outages without the
requirement of signal reacquisition process.
