StoriesSystem: Timing and PNT

Time as infrastructure

A 5G cell must hold its phase within 3 µs of its neighbours, ±1.5 µs of a common reference¹; a synchrophasor’s one per cent vector error leaves room for only tens of microseconds of timing error². Most of that time comes from satellites, which can be jammed or spoofed. A national order in 2020 named the problem³.

Systems: GNSS, Precision time protocol, Holdover clocks
Toward 2030: Authenticated satellite navigation, Resilient PNT
Figures: 4, systems diagram, simulator, data story, timeline to 2030

Go to the references

01Systems diagram

Where the time comes from.

A primary reference time clock disciplined by satellite navigation feeds a grandmaster; the precision time protocol carries time through boundary clocks to the radio and the substation⁴. An enhanced reference clock adds an atomic standard that can hold time for days when the satellites are lost⁵. Jam the receiver and see what still has time.

Scenario

Figure as text: A time distribution chain with an enhanced reference

A four-tier diagram: satellite navigation and an atomic clock, reference clocks, boundary clocks, and the radio sites and substations that need time.

Sources: GNSS, Atomic clock
Reference clocks: PRTC, ePRTC
Transport: Boundary clock, Boundary clock
End applications: Radio site, Substation

9 links. Scenarios: Satellites available; Satellite signal jammed; Jammed, no atomic reference.

02Simulator

How long a clock can coast.

Without a reference, a clock drifts by its frequency offset every second. The time it can coast within a budget is the budget divided by the offset: at one part per billion, ±1.5 µs lasts 25 minutes. Reference clocks are specified to their accuracy against UTC⁶; the network budget is shared between them and the transport⁷.

Figure as text: Holdover time against a time error budget

A line chart of time error growing with holdover time, crossing the dashed budget line at the point marked in red.

Holdover time against a time error budget, at the starting values
Frequency offset	1 ppb
Time error budget	1.5 µs
Holdover within the budget	25 min
Error after one hour	3.60 µs
Error after one day	86.4 µs

03Data story

Holdover by oscillator stability.

The same arithmetic for five frequency offsets, from a hundredth of a part per billion to fifty. Each tenfold improvement in stability buys ten times the holdover; this is why atomic references sit at the top of the chain.

Figure as text: Holdover within ±1.5 µs by frequency offset

A bar chart of holdover hours for five frequency offsets, from about 42 hours at 0.01 ppb to about half a minute at 50 ppb.

Holdover within ±1.5 µs by frequency offset (h)
Frequency offset	Hours
0.01 ppb	41.67
0.1 ppb	4.17
1 ppb	0.42
10 ppb	0.04
50 ppb	0.01

04Timeline to 2030

Toward resilient positioning, navigation and timing.

Authentication of navigation messages lets a receiver reject forged signals; Galileo declared its open-service authentication operational in 2025⁸. With enhanced reference clocks and terrestrial distribution, it is part of making time a resilient public good³.

Figure as text: Timing standards and resilient PNT policy

A timeline from 2016 to 2030 with the enhanced reference clock recommendation, the time and phase budget, the precision time protocol revision, the PNT executive order and authenticated Galileo signals.

2016-11 Enhanced reference clocks specified (ITU-T G.8272.1). Atomic-backed reference clocks with long holdover.⁵
2020 Network time and phase budget (ITU-T G.8271). Time error limits for telecom networks.⁷
2020-02 PNT resilience order. Responsible use of positioning, navigation and timing services in critical infrastructure.³
2020-06 Precision time protocol revised (IEEE 1588-2019). The 2019 edition of the protocol published.⁴
2025-07 Authenticated Galileo signals. Navigation message authentication declared operational.⁸

Figure 1

Systems diagram

Sources reaching the end clocks: 2 of 2
Longest route: 3 hops
State: Satellites available

Figure 1. A time distribution chain with an enhanced reference. A four-tier diagram: satellite navigation and an atomic clock, reference clocks, boundary clocks, and the radio sites and substations that need time.

References

3GPP TS 38.133: NR requirements for support of radio resource management (cell phase synchronisation accuracy). 3rd Generation Partnership Project, 2024.
IEEE C37.118.1-2011: Standard for synchrophasor measurements for power systems. IEEE Standards Association, 2011.
Executive Order 13905: Strengthening national resilience through responsible use of positioning, navigation, and timing services. Executive Office of the President of the United States, Federal Register 85 FR 9359, 2020.
IEEE 1588-2019: Standard for a precision clock synchronization protocol for networked measurement and control systems. IEEE Standards Association, 2020.
Recommendation ITU-T G.8272.1: Timing characteristics of enhanced primary reference time clocks. International Telecommunication Union, Telecommunication Standardization Sector, 2016.
Recommendation ITU-T G.8272: Timing characteristics of primary reference time clocks. International Telecommunication Union, Telecommunication Standardization Sector, 2018.
Recommendation ITU-T G.8271: Time and phase synchronization aspects of telecommunication networks. International Telecommunication Union, Telecommunication Standardization Sector, 2020.
Galileo Open Service Navigation Message Authentication (OSNMA): service declaration. European Union Agency for the Space Programme, 2025.

Where this applies

Positioning, navigation and timing Connectivity Security and trust Protocol & Grid Test and qualification Telecom Energy Transport Government Field tour: ground station