: Radio Notification on connection events as a Central

This section clarifies the functionality of the Radio Notification feature when the SoftDevice operates as a Bluetooth® Low Energy Central. The behavior of the notification signals is shown under various combinations of active central links and scanning events.

See Radio Notification notation and terminology for the notations used in the text and the figures of this section. For a comprehensive understanding of role scheduling, see Scheduling.

For a central link, multiple packets may be exchanged within a single Radio (connection) Event. This is shown in the following figure.

Figure 1. Central link with multiple packet exchange per connection event

To ensure that the ACTIVE notification signal will be available to the application at the configured time when a single central link is established (Radio Notification signal in relation to a single active link), the following condition must hold:

t_ndist + t_event - t_prep < t_interval

Figure 2. Radio Notification signal in relation to a single active link

A SoftDevice operating as a Central may establish multiple central links and schedule them back-to-back in each connection interval. An example of a Central with three links is shown in Radio Notification signal with three active Central links. To ensure that the ACTIVE notification signal will be available to the application at the configured time when three links are established as a Central, the following condition must hold:

t_ndist + t_event,0 + t_event,1 + t_event,2 - t_prep < t_interval

Figure 3. Radio Notification signal with three active Central links

In case one or several central links are dropped, an idle time interval will exist between active central links. If the interval is sufficiently long, the application may unexpectedly receive the Radio Notification signal. In particular, the notification signal will be available to the application in the idle time interval, if this interval is longer than t_ndist. This can be expressed as:

Σ_i=m,...n t_event,i + t_prep > t_ndist

where Link-m, ..., Link-n are consecutive inactive central links.

For example, in the scenario shown in Radio Notification signal with two active Central links, Link-1 is not active and a gap of t_event,1 time units (e.g. ms) exists between Link-0 and Link-2. Consequently, the ACTIVE notification signal will be available to the application, if the following condition holds:

t_event,1 + t_prep > t_ndist

Figure 4. Radio Notification signal with two active Central links

A SoftDevice may additionally run a Scanner in parallel to the central links. This is shown in Radio Notification signals for three active central connections while scanning, where three central links and a Scanner have been established. To guarantee in this case that the ACTIVE notification signal will be available to the application at the configured time, the following condition must hold:

t_ndist + t_event,0 + t_event,1 + t_event,2 + Scan Window + t_ScanReserved < t_interval

Figure 5. Radio Notification signals for three active central connections while scanning