PSM Application Note r2

80471NT11483A Rev. 2 Page 10 of 24 2017-06-06
3. PSM DESCRIPTION
The Power Saving Mode (PSM) in 3GPP Rel12 allows the Module to skip idle mode tasks
for a longer time period while still maintaining the NAS context.
This feature permits to reduce the overall power consumption when there is no required
data activity with the network for a long time.
This saves the power also related to the Paging activity.
The PSM reduces the signaling load between the LE866 and the network on NAS level
(24.301 Rel.12 chapter 5.3.11) compared to a standard attach/detach procedure.
Within the attach/RAU/TAU procedure the UE indicates that it supports PSM.
The network confirms PSM usage by sending a value for a timer (T3324) in the confirmation
message.
The timer T3324 specifies an active period after the RAU/TAU procedure the UE has to
follow the normal idle mode procedures (paging reception, measurements,..).
After timer T3324 elapses the Module enters PSM state, i.e. it disables all AS/NAS activities
until the next periodic RAU/TAU update.
A second Timer (T3412) is defining the duration of the PSM.
During this period the Module is NOT reachable by the network, i.e. it cannot be paged and
stops access stratum activities.
Before the inactivity period the complete NAS context needs to be stored and reused when
accessing the network again.
The Module can leave the PSM mode at any point in time when there is MO data or when
periodic TAU timer expires.
The PSM is only intended for those Modules that can tolerate a high MT Call latency.
The 3GPP standard does not imply whether or to which extend the PSM does reduce the
power of the Module. Only the signaling reduction (i.e. Not doing a reattach but just a
RAU/TAU procedure) is defined.