Critical government and industry sectors (such as law enforcement, transportation, communication, and finance) are growing increasingly dependent on Global Navigation Satellite Systems (GNSS) for positioning, navigation, and timing. At the same time, the availability of low-cost GNSS jamming devices are presenting a serious threat to GNSS and increasing the likelihood of outages to infrastructures relying on GNSS. The attacks range from malicious parties intentionally jamming GNSS signals within a targeted geographical region to uninformed users causing accidental interference. This paper is an overview of different approaches adopted to date to mitigate GNSS disruption caused by intentional and unintentional jamming. The first approach outlined in this paper is the use of inertial systems to aid GNSS. The second and third approaches are the filtering of jamming/interference in the spatial and time-frequency domains, respectively. The fourth approach is vector tracking of GNSS signals in the receiver.

This paper presents the performance analysis of signals from the Galileo satellites in the E1 and E5a frequency bands and GPS L5 signals as measured by DLR's experimental ground‐based augmentation system. The results show that the raw noise and multipath level of Galileo signals and of the GPS L5 signals are smaller than that of GPS L1. The new signals are also less sensitive to the choice of carrier‐smoothing time constant. Furthermore, the inter‐frequency biases that affect dual‐frequency processing are investigated. These biases differ between satellites and depend on satellite and receiver hardware, but they can be determined a priori. With known receiver and antenna configurations, it is possible to correct for these biases. A residual uncertainty associated with the bias correction has to be taken into account. This can be modeled as part of the ground and airborne bounding standard deviations (σ_{pr_gnd} and σ_{pr_air}) used in GBAS processing. Copyright © 2017 Institute of Navigation.

This paper presents an architecture for an embedded multi-antenna digital GNSS receiver. A two-stage adaptive beamformer for interference suppression and Line-of-Sight (LoS) signal amplification is presented and analyzed w.r.t. to an efficient implementation on embedded receivers. Jammer signals are mitigated at pre-correlation stage whereas the LoS signals are amplified at post-correlation stage. The method is based on a subspace-based approach where filter coefficients are derived from the eigenvalues and -vectors of the covariance matrix. In the first stage, the covariance matrix is determined immediately from the digital antenna signals for interference mitigation and in the second stage, the matrix is computed based on the correlator outputs of each satellite in LoS. Dedicated buildingblocks for covariance matrix estimation and filtering are required for interference mitigation since this operation is computed on sampling rate. A fixed-point VHDL implementation and related costs in terms of logic-cell requirements on an FPGA are provided for both blocks. Eigendecomposition is computed on an embedded processor. The implementation of two decomposition algorithms (one for interference mitigation and the other one for LoS-signal amplification) are presented. Optimizations and costs in terms of processing-cycles on an embedded processor are provided.

Modeling of both nominal distortions and signal anomalies (i.e., evil waveforms) is crucial for an accurate user error budget for satellite based augmentation systems (SBAS) and multi-frequency multi-constellation ground based augmentation systems (GBAS). Such analysis is of particular interest for the ongoing standardization work of L1-L5 SBAS services. In this paper we propose a method to jointly estimate analog and digital distortion of a satellite navigation signal based on high gain antenna measurements. Joint estimation of analog and digital distortion is needed in case the estimates of these two satellite signal imperfections are interdependent. This is the case when the time-bandwidth product of the satellite signal is small. The impact of both satellite imperfections on the ranging performance of a GNSS receiver is assessed by means of analytical formulations which make use of the cross-power spectral density (CPS) between the distorted and the ideal signal and of the power spectral density (PSD) of the nominal (ideal) signal. Copyright © 2016 Institute of Navigation