The performance of positioning and timing services provided by Global Navigation Satellite Systems (GNSSs) for instance by GPS or Galileo largely depends on the ranging accuracy, i.e. the accuracy of estimating the propagation delays of individual line-of-sight signals from the navigation satellites. This estimation process is affected by many sources of errors like satellite clock error, varying signal propagation delays in ionosphere and troposphere etc. Modern high-end GNSS receivers are capable of removing most of the errors by utilizing sophisticated signal models and applying differential corrections. However differential techniques are not able to remove the effect of the local errors specific to a given receiver, which leaves multipath echoes and radio frequency interference as the dominant remaining error sources affecting the GNSS performance. These phenomena become an especially serious threat in case of GNSS application with safety aspects. In the worst case scenario, a GNSS receiver encountering strong interference or multipath is not able to track a sufficient number of satellite signals to obtain a navigation solution. However, even if the navigation solution is available, the accuracy of the pseudorange and/or carrier-phase measurements provided by the tracking loops of the receiver accuracy may be severely degraded, raising continuity and integrity issues. In view of this, array processing techniques allowing for spatial filtering of the incoming signals have attracted substantial interest in recent years because of their ability to increase the signal-to-noise ratio (SNR) of the signals of interest and reject interference and/or multipath signals.
The group of User Algorithms of the Department of Navigation is developing robust spatial filtering techniques (digital beamforming algorithms) as well as advanced array processing techniques (e.g. high resolution estimation methods), especially for safety critical GNSS applications. The developed algorithms are implemented and tested in an in-house software multi-antenna GNSS receiver, a MATLAB post-processing tool, while using realistic signal data collected during measurements campaigns. The well-proven algorithms are then used in real time experimental systems, e.g. in a resilient array GNSS receiver GALANT, for demonstration purposes and enabling the next step towards the technology transfer to industrial players.