Abstract
This paper addresses the signal acquisition problem in the presence of interferences using antenna arrays in the general framework of Global Navigation Satellite Systems receivers. We describe and compare two different approaches: the first one is based on the generalized likelihood ratio test (GLRT) detector directly applied on the array snapshots, and the second one uses a digital beamformer as a spatial filter to mitigate the interferences and acquire the signal using the beamformer output. We show that the array-based GLRT acquisition is equivalent to a conventional acquisition based on the output of a time reference beamformer. The test statistics of the techniques are analyzed in terms of the probability of detection and false alarm. Monte Carlo simulations using the Galileo E1 signal structure support the theoretical results, even when the array is moderately uncalibrated.
Highlights
The fact that current and planned accurate positioning and timing services rely on Global Navigation Satellite Systems (GNSS) has raised the concern about possible denial of service situations, as reported in [1] among others
We considered three different designs: the time reference beamformer (TRB), which relies on a priori knowledge of a reference waveform; the minimum variance distortionless response (MVDR), which relies on a priori knowledge of the spatial signature of the signal using direction-ofarrival (DOA) estimation; and the blind null-steering, which is known as power minimization beamformer in the GNSS literature
We prove that the proposed multi-antenna generalized likelihood ratio test (GLRT) acquisition algorithm is equivalent to a TRB beamformer followed by a single-antenna acquisition
Summary
The fact that current and planned accurate positioning and timing services rely on Global Navigation Satellite Systems (GNSS) has raised the concern about possible denial of service situations, as reported in [1] among others. It is possible to filter out the interferences using a blind null-steering beamformer (see, e.g., [15]) This approach presupposes that the GNSS signals are well below the noise floor, and their contribution to the array covariance matrix is negligible. The algorithm minimizes the beamformer output power by nulling the directions where interfering signals are present This beamformer is a particular case of the MVDR beamformer, where the steering vector is defined as h0 = href = [ 1 0 . Where xi is the received signal vector for the ith antenna element In this particular case, the beamformer only activates the reference antenna and the resulting acquisition does not benefit from the available array gain.
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