Annex F (informative):

Alternative Frequency and announcement signalling

F.0 Introduction

The DRM system can signal alternative frequencies for the whole DRM multiplex or some DRM services of the tuned DRM multiplex to allow the receiver to counter reception problems by automatically and quickly switching to an alternative frequency providing better reception conditions.

It is also possible to signal service linking information which allows the service provider to establish one or more sets of identifiers that carry identical, in the case of a hard link, or related, in the case of a soft link, content. The set of identifiers is called a linkage set. There may be several linkage sets that are valid at different times of day. Each linkage set is identified by the Linkage Set Number together with a set of flags, and by use of the Linkage Actuator, linkage sets can be activated and deactivated. The receiver uses these linkage sets during service selection and service following to determine a set of candidate services, potentially on different bearers, that are equivalent or related to the selected service. The receiver selects an appropriate service from these candidates based on criteria such as service availability and quality.

In addition, the DRM system can signal announcements (e.g. traffic or news announcements), so that the receiver can automatically switch to another DRM service or even to another broadcast system for the duration of an active announcement.

These features are signalled using a combination of SDC data entities. This annex describes the general capabilities of the alternative frequency signalling, linking and announcement features. It also explains how the different SDC entities work together to enable this kind of signalling.

F.1 Possibilities of the Alternative Frequency Signalling

feature

Using the Alternative Frequency feature, the broadcaster can signal to the receiver alternative frequencies for the following items:

•the whole DRM multiplex, being broadcast identically and synchronously on other frequencies; the receiver can check whether it receives the identical DRM multiplex on the indicated frequencies and also their reception quality; if required the receiver can instantly switch to another frequency without service interruption;

•the whole DRM multiplex (all services with the same Service identifiers), but with different channel parameters and/or multiplex timing (non-synchronous); frequency switching causes a service interruption;

•single services of the tuned DRM multiplex; frequency switching causes a service interruption; single services can be available:

-in other DRM multiplexes using the same Service identifiers;

-in other broadcast systems (e.g. AM, FM, FM-RDS, DAB) or other DRM multiplexes using a different Service identifier;

•the frequency of the enhancement layer from the base layer, or vice versa.

The validity of alternative frequency lists can be restricted to certain times (schedule definition feature) and/or to certain geographic areas (region definition feature). The schedule definition feature is based on a weekly schedule. The region definition feature allows the definition of geographic areas by longitude/latitude plus extent as well as by internationally standardized CIRAF zones.

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If the list of alternative frequencies links to a service carried using another broadcast system, or to a service with a different service identifier, it can be indicated whether the other service carries the identical audio programme or a similar one. The receiver will try to switch to the "same service" before trying to switch to an alternative service. If it is necessary to signal changes to these equivalent or related services dynamically and/or for short durations then service linking may be used additionally to alternate frequencies in order to build up linkage sets and then rapidly switch between them.

DRM receivers should store the complete alternative frequency information (all five data entity types 3, 4, 7, 11 and 13) when assigning a DRM service to a station button (see clause G.2). Therefore it is sensible for the broadcaster to signal his complete frequency schedule to the receiver. The frequency schedule should provide the full week's changes rather than only provide a subset, for example only indicating daytime frequencies during daytime transmissions and nighttimes frequencies during night time transmissions. This permits faster start-up of a service if the frequency of the DRM multiplex is different from the last time the service was selected.

It is essential that all frequencies used in a synchronous multi-frequency network are signalled because the bitstream from all transmitters in the network are identical. This is also highly recommended even if the network is not synchronous because receivers can then store all the possible frequencies when defining a station button including the principle tuned frequency of the multiplex. This frequency information is necessary if the receiver has to tune away and then wants to get back again. It is also required to help a receiver to identify its current region (see clause F.3).

It is recommended that broadcasters specify all alternative sources of each service and include all frequencies. Receivers will sequentially test all given frequencies. If no frequency information is provided, then receivers have to scan for the service identifier if they are to find the service, and that may take so long as to provide an unacceptable user experience.

Broadcasters should note that links to completely analogue broadcast systems have unpredictable results for the receiver, because receivers are unable to check that the correct service is received on the given frequency.

If the broadcaster uses scheduled frequency information he will provide SDC data entity "Time and date information data entity - type 8" as the time reference for the schedules in "Alternative frequency signalling: Schedule definition data entity - type 4".

F.2 Possibilities of the announcement feature

The announcement feature can be used to interrupt the currently presented audio programme by another providing short clips of information.

Using the announcement feature, the broadcaster can signal to a receiver:

•which types of announcements are provided;

•which type of announcement is currently active;

•whether the announcement content is carried by a DRM service within the current DRM multiplex or by a service on another frequency or from a different broadcast system like FM or DAB.

This information can be specified for each DRM service or for any combination of DRM services within the tuned DRM multiplex.

If the announcement signalling directs the receiver away from the tuned multiplex to another service carrying the announcement content (e.g. on a different type of broadcast system) then the other service will provide the mechanism to indicate the end of the announcement such that the original listening can be restored. The service identifiers for the other services carrying the announcement content (and optionally their frequencies) are signalled in the SDC by the "Alternative frequency signalling: Other services data entity - type 11" with the "Short Id/Announcement Id flag" set to 1.

EXAMPLE 1: Within the tuned DRM multiplex the broadcaster provides four DRM services named A, B, C and D. A and B provide English programmes while C and D carry German versions of the programmes.

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EXAMPLE 2: The broadcaster may use the announcement feature to signal to the receiver that in case of a traffic announcement service A should switch to service B, while service C should switch to service D. Alarm information may only be available in English, so services A, C and D should switch to service B in case of available warning information. The news channel is not broadcast in the tuned DRM multiplex, so service A switches to a DAB service (specifying the other service identifier along with an optional list of frequencies) while service C switches to an FM-RDS service.

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F.3 SDC data entities overview for Alternative Frequency and announcement signalling

Figure F.1: Alternative Frequency and Announcement Signalling -

Involved SDC data entities

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