Radio Notification on connection events as a Central

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

See Table 1 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 Figure 1.

Figure 1. A Bluetooth low energy central link with multiple packet exchange per connection event

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

To ensure that the ACTIVE notification signal will be available to the application at the configured time when a single central link is established (Figure 2), the following condition must hold:

tndist + tevent -tprep < tinterval

Figure 3. Bluetooth low energy Radio Notification signal in relation to three active links

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 Figure 3. 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:

tndist +tevent,0 +tevent,1 +tevent,2 -tprep < tinterval

Figure 4. Bluetooth low energy Radio Notification signal when the number of active links as a Central is 2

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 tndist. This can be expressed as:

Σi=m,...n tevent,i + tprep > tndist

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

For example, in the scenario shown in Figure 4, Link-1 is not active and a gap of tevent,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:

tevent,1 + tprep > tndist

Figure 5. Bluetooth low energy Radio Notification signal in relation to three active connections as a Central while scanning

A SoftDevice may additionally run a Scanner in parallel to the central links. This is shown in Figure 5, 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:

tndist + tevent,0 + tevent,1 + tevent,2 + Scan Window + tScanReserved < tinterval