Maritime GNSS Threats and Resilience: A Layered Review of Vulnerabilities and Defences

Global Navigation Satellite Systems (GNSS) underpin maritime Positioning, Navigation, and Timing (PNT), supporting bridge functions such as the Automatic Identification System (AIS), the Electronic Chart Display and Information System (ECDIS), radar overlays, and track-control systems. This dependence exposes vessels to non-malicious degradation, unintentional interference, jamming, spoofing, and replay-based (meaconing-type) deception. Using a structured scoping review with narrative synthesis, this paper synthesises evidence on maritime GNSS threats and resilience across the receiver-to-bridge chain. The review develops a maritime-oriented taxonomy and maps disruption across the radio-frequency (RF) front-end, acquisition and tracking, navigation-estimation, and integrated-bridge layers. It examines suppression-oriented resilience, including front-end mitigation, spatial anti-jamming, and multi-sensor fusion, alongside deception-oriented detection, integrity monitoring, and authentication, including correlator-domain monitoring, navigation-engine integrity monitoring, Galileo Open Service Navigation Message Authentication (OSNMA), and bridge-level cross-checks. The analytical novelty lies in integrating disruption mechanism, security objective, evidence type, layer of action, and residual protection gap within a maritime cross-layer decision framework spanning the receiver-to-bridge chain. This framework enables resilience measures to be interpreted and compared according to what they protect and what remains unprotected, supporting complementary rather than interchangeable defences. The synthesis shows that maritime GNSS resilience extends beyond the RF receiver to navigation-solution trust and integrated-bridge safety.