GNSS Vulnerabilities Atomic Clock Network Processing Receiver Network GNSS Rx Atomic Clock Monitoring and Characterization GNSS Satellite TF Array Processing GNSS Rx Multiantenna Spatial Processing GNSS Rx RF Interference Front-end Front-end Front End Front End y [n ] TF Interference Detection and Mitigation Ionosphere GNSSSignal Signal GNSS GNSS Signal Processing Processing Processing GNSS Signal Acquisition/Tracking Processing Acquisition/Tracking Acquisition/Tracking Acquisition/ Tracking GNSS Observations TF Filtering and Smoothing (a) GNSS Satellites Spatial Decorrelation Ionospheric Scintillation Electron Density Irregularities Ionosphere GBAS Antenna Time Nominal Case Time Scintillation Case Signal Intensity Signal Intensity Ionospheric Delay Spatial Decorrelation Time (b) CDMA CDMA 400 m LTE LTE CDMA Uncertainty Ellipsoids GPS Only Ettus E312 USRPs Ellipsoid Volume GPS Only (Seven Satellites) Volume: VGPS GPS + Five BTSs (Three CDMA and Two LTE) Volume: 0.16·VGPS GPS + Five BTSs (c) Although GNSS is the positioning technology of choice when it is available, it has some known vulnerabilities that can be addressed: (a) jamming interferences, monitoring of satellites clock, and scintillation characterization (see the article "Time-Frequency Analysis for GNSSs" by Amin et al.), (b) monitoring and mitigation of ionospheric gradients and scintillation perturbations (see the article "Monitoring and Mitigation of Ionospheric Anomalies for GNSS-Based Safety Critical Systems" by Lee et al.), and (c) use of signals of opportunity as a complement to GNSS signals (see the article "I Hear, Therefore I Know Where I Am" by Kassas et al.) 14 IEEE SIGNAL PROCESSING MAGAZINE | September 2017 |