Array Processing

Concept of Spatial Filtering or Digital Beamforming

The quality of the data provided by a Global Navigation Satellite System (GNSS) receiver depends largely on the synchronization error with the signal transmitted by the GNSS satellite (navigation signal), that is, on the accuracy in the propagation delay estimation of the direct signal (line-of-sight signal, LOSS). The precision provided by current generation GNSS receivers together with the use of sophisticated processing methods, such as differential and kinematic techniques, to remove certain errors (e.g. ionospheric error), leaves multipath and interference as the dominant remaining error sources affecting GNSS performance, distorting the received signal in a way that may cause a bias in delay and carrier-phase estimations. In the worst case, a GNSS receiver encountering strong interference or multipath might not be able to track a sufficient number of satellite signals to obtain a navigation solution. However, even if the navigation solution is available, the pseudorange and/or carrier-phase accuracy may be degraded, raising continuity and integrity issues especially for safety-critical applications. Thus, a receiver that is not prepared to detect and mitigate undesired in-band signals will either loose lock of valuable satellites or will let the navigation solution be degraded without notification of the user. Array processing techniques and other spatial and temporal filtering techniques have attracted substantial interest in recent years for their ability to increase incoming signal-to-noise ratio (SNR), as well as to reject interference and/or multipath.
In order to effectively mitigate interference and multipath in a GNSS receiver the group of algorithms and user terminals is developing and testing robust spatial filtering techniques (digital beamforming algorithms) and advanced array processing techniques (e.g. high resolution estimation methods), especially for safety critical applications. The algorithms are implemented and tested in a software GNSS receiver and in experimental systems.