Joint Space-Time Interference Mitigation for Embedded Multi-Antenna GNSS Receivers

M.H. Castañeda, M. Stein, F. Antreich, E. Tasdemir, L. Kurz, T.G. Noll, J.A. Nossek

Abstract:	Accurate synchronization and positioning in space and time is a key enabler for a wide variety of technical applications ranging from remote farming, automatic docking and landing to network synchronization and location-based services. Today, radio-based positioning systems like Global Satellite Navigation Systems (GNSS) offer the possibility to perform precise positioning by means of range measurements to a set of satellites in line-of-sight of the receiver. While long spreading codes are employed in order to attain a high spreading gain against noise, as well as intra- and intersystem interference, GNSS is inherently vulnerable to terrestrial radio frequency interference (RFI) due to the low receive power of the desired signal. Such interference might arise from wide-band communication systems operating in neighboring frequency bands or from jamming devices which are intentionally perturbing the GNSS signal acquisition and tracking. Due to the large distances between the satellites and the GNSS receivers, the transmit signals of the satellites are strongly attenuated and hence, an interferer with relatively low transmit power suffices in order to drown the GNSS receivers in interference and effectively hinder its operation. Therefore, one of the major nuisances for precise positioning with conventional GNSS receivers is RFI . Typical approaches for RF interference mitigation exploit the signal structure of the interferer. For example Frequency Domain Adaptive Filtering (FDAF) methods are based on frequency-domain analysis for interference detection. FDAF can be applied effectively for narrow-band interference since this kind of interference signal can easily be identified by means of frequency spectrum analysis [1]. However, broad-band signals like strong, band-limited noise can hardly be identified since correlation in time-/frequency-domain is generally not evident. In order to counteract this kind of interference, filtering in spatial domain provides a powerful alternative. Using receivers with multiple contiguous antenna elements allows detection of spatially correlated signals. A single interference signal is always concentrated in the spatial domain and can be detected based on estimates of the spatial covariance matrix. In [2] an effective method has been demonstrated for suppression of strong, broad-band interference signals. However, this approach does not consider temporal correlation of the interference signal. This imperfect characterization of the received signals by using only the spatial covariance matrix in presence of temporally correlated interference theoretically leads to suboptimal filtering. Furthermore, the fact that spatial filtering with a reasonably small number of antenna elements also mitigates signals of interest in a wide spatial area motivates a joint estimation of spatial- and temporal-covariance matrix. Practically speaking, a narrow-band interferer should be mitigated in time-/frequency-domain whereas broad-band interferers should preferably be cancelled in spatial domain. Therefore, an efficient method will be presented to jointly estimate the space-time covariance matrix of interference and noise with a multiple antenna receiver under the justified assumption that the space-time covariance matrix follows a Kronecker structure. Aided by the fact that maximum likelihood estimation of the signal parameters, as the time delay and carrier phase, involves a spatial and temporal prewhitening, we show that optimum performance for signal parameter estimation is possible when space-time interference mitigation is based on correct estimates of the spatial and temporal covariance matrices of the interference and noise. In addition, we show the performance degradation for the case when mismatched filtering is performed based on the incorrect assumption of temporally white interference and noise by only taking into account the spatial covariance matrix. To this end, we will treat different types of interference sources including wideband, narrowband and sweeping interferers. [1] M. Cuntz et al., “Field Test: Jamming the DLR Adaptive Antenna Receiver”, ION GNSS 2011 [2] M. Sgammini et al., “Blind Adaptive Beamformer Based on Orthogonal Projections for GNSS”, ION GNSS 2012
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	3399 - 3408
Cite this article:	Castañeda, M.H., Stein, M., Antreich, F., Tasdemir, E., Kurz, L., Noll, T.G., Nossek, J.A., "Joint Space-Time Interference Mitigation for Embedded Multi-Antenna GNSS Receivers," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 3399-3408.
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