GNSS timing synchronisation in critical infrastructures: dependency and resilience
Mobile telecommunications networks, electrical distribution systems and financial settlement platforms share a structural dependency on the time reference provided by GNSS systems. The frequency and phase synchronisation required by these infrastructures is not an auxiliary parameter but a first-order operational condition. In the latest-generation mobile networks, coordination between radio access nodes demands synchronisation precisions in the order of one microsecond or below to guarantee transmission coherence and avoid inter-cell interference. In electrical distribution systems, synchronised phasor measurement by PMU units likewise depends on a common and stable time reference to enable real-time monitoring of network status. The GNSS timing signal, derived from the atomic clocks on board the satellites and corrected by the ground control segments, reaches receivers with a precision that, under nominal conditions, satisfies the requirements of the majority of these applications. However, this dependency introduces a systemic vulnerability: any degradation in signal availability, whether due to adverse propagation conditions, unintentional radio-frequency interference or constellation anomalies, may result in a loss of time reference with cascading effects on the systems that depend upon it. In response to this situation, critical infrastructure operators apply continuity strategies based on several complementary layers. The first is the use of high-stability clocks with holdover capability, which maintain the time reference for a defined period once the GNSS signal has been lost, with a controlled and predictable drift according to the oscillator specifications. The second consists of incorporating redundant time sources, including the simultaneous reception of multiple GNSS constellations, which reduces the probability of total reference loss in the event of failure of a single constellation. The third strategy involves the distribution of time over the network by means of standardised synchronisation protocols, which allow the time reference to be propagated from nodes with direct GNSS access to network elements operating in environments with limited sky visibility. From the European regulatory perspective, the resilience of timing synchronisation in critical infrastructures has acquired growing relevance within the framework of network and information systems security policies. Administrations and operators with essential service obligations must evaluate their timing architectures against operational continuity criteria, document the maximum admissible holdover periods for each service and periodically verify the behaviour of their systems in the absence of an external reference. Temporal resilience planning cannot be limited to the statistical availability of the GNSS signal, but must encompass scenarios of sustained degradation and define verifiable recovery procedures.
NASSAT - Network Satellite Systems