PSM sleep

Power Saving Mode (PSM) sleep is typically a longer sleep that ranges from minutes to hours. The PSM period starts after radio connection has ended when the negotiated activity time has elapsed.

The network knows when the User Equipment (UE) is in PSM. During that period, the network does not try to contact the UE, and the UE does not monitor the serving cell. PSM ends when timer T3412 expires and the UE performs a periodic Tracking Area Update (TAU). The application can interrupt PSM at any time with uplink data or other activity that triggers the establishing of a radio connection.

The application can synchronize uplink data with the PSM period by using modem sleep notifications. If uplink data is sent before the PSM sleep ends, there is no need to perform a periodic TAU, and the amount of signaling is reduced. The prewarning notification can be used as a trigger to send uplink data.

The application can save power by deactivating hardware components during PSM sleep and allocating resources used by the modem for other purposes.

With modem firmware versions 2.0.x≥0, a proprietary PSM feature can be used in addition to normal PSM. In %XMODEMSLEEP, the proprietary PSM feature uses a similar mechanism and notifications as normal PSM. For more information, see nRF91x1 Cellular AT Commands.

The following notification example indicates the activation of PSM sleep with a 200000 ms period:
%XMODEMSLEEP: 1,200000

The following notification example is a prewarning of the end of the PSM sleep 1500 ms before the sleep ends:


The following notification example indicates that the PSM sleep has ended as <warning_time> is 0: