Time (and What You Need to Know About It)Time
Time plays an essential role in electronic systems, and certainly in the operation of DAB+. A basic understanding of the various time scales is necessary to fully grasp synchronization within a Single Frequency Network (SFN).
DAB+ employs various mechanisms to enable this synchronization. Which ones are used depends on the manufacturer’s implementation and the network configuration.
In this chapter, we discuss the key concepts needed to understand the time references within DAB+.
The SI-second
The SI second is the official unit of time in the International System of Units (SI). It forms the basis of virtually all modern time systems and is essential for applications in which accuracy and synchronization are of great importance.
The SI second is defined as 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine energy levels of the ground state of the cesium-133 atom. This extremely stable reference is realized using atomic clocks.
Atomic Time (TAI)
TAI (Temps Atomique International) is the international atomic time and is based entirely on the SI second. Unlike UTC, TAI does not include leap seconds, and time passes completely continuously.
PLEASE NOTE:
There is an important distinction between TAI and the “TAI-based” time used in the EDI interface. For example, TAI starts counting from January 1, 1958! The EDI standard for DAB+ makes an important adjustment here and starts on January 1, 2000!
Within the EDI standard, time is represented as the number of SI seconds that have elapsed since January 1, 2000, at 00:00:00 TAI. This is therefore not a complete TAI time scale, but a TAI-based time measurement with a fixed reference date.
This continuous time scale forms the basis for the synchronization of DAB+ stations within an SFN network.
TAI is a fully continuous time scale based exclusively on atomic clocks.
UTC time
UTC (Coordinated Universal Time) is the international standard time displayed on our clocks worldwide. As the Earth’s rotational speed is not entirely constant, UTC is adjusted by adding (or, in theory, removing) leap seconds. In this way, UTC remains closely aligned with the Earth’s rotation.
Because of these leap seconds, UTC is less suitable as a time reference for precise synchronisation applications such as a DAB+ SFN. For this reason, a continuous atomic time reference is used for synchronisation.
However, UTC remains essential for applications where a human-readable date and time format is required, such as log files, error messages and event logging.
UTC also attempts to keep pace with the Earth’s rotation. When the Earth’s rotation slows slightly, a positive leap second is added to UTC. As a result, UTC always lags slightly behind TAI.
UTCO (UTC Offset)
In order to derive UTC from the TAI-based time, the UTCO (UTC Offset) field is included in EDI messages. This field consists of 8 bits and contains the number of leap seconds that have been introduced since 1 January 2000.
Using this offset, the UTC time can be easily calculated:
UTC = TAI-based time − UTCO
The combination of a continuous atomic time and the UTC offset makes it possible, on the one hand, to achieve extremely accurate SFN synchronisation and, on the other hand, to display log files and events in the familiar UTC time.
The leap second is being phased out: what does this mean for DAB+?
The 28th General Conference on Weights and Measures (CGPM), which took place in Versailles from 13 to 15 October 2026, took an important decision regarding the future of the leap second. From 20 May 2027, UTC will become a continuous time scale, with no further periodic leap seconds being inserted.
What impact does this have on DAB+?
With DAB+, time information is distributed via the EDI (Encapsulated DAB Interface), which, amongst other things, allows the time to be derived in UTC. The synchronisation of transmitters within a Single Frequency Network (SFN) is based on a continuous, atomic-clock-based time reference and does not depend on the insertion of leap seconds.
The EDI time information also contains the UTCO (UTC Offset) field, which allows the time scale used to be linked to UTC. An important distinction must be made here: the value of this field is not simply the total number of leap seconds since 1972.
Once no further leap seconds are inserted from 20 May 2027 onwards, the existing relationship between the EDI time reference and UTC will continue to be maintained. For DAB+ networks that process this time information correctly, this means that the transition itself does not require any change to SFN synchronisation. However, EDI implementations and the associated logging systems must take the new international time regulation into account.
For the values to be entered in the UTCO field in EDI (UTC Offset), we recommend consulting the EDI implementation manuals and the manufacturer’s implementation documentation. Normally, this should currently be 5 leap seconds.
The date 20 May 2027 and the transition to continuous UTC are set out in Resolution 5 of the 28th CGPM.