RE: Clarifications on PSM functions

Achim Kraus — Fri, 13 Jan 2023 17:49:02 GMT

If you enable PSM, the modem enters the sleep mode after a quiet period, which is defined by an RRC (in)activity timer and the PSM activity timer (see GSMA Energy Efficiency for Mobile IoT the names of the timers seems to be changing slightly from document to document).

The quiet period refers to "radio data messages", which may differ from application messages depending on the used protocol. e.g. "keep alive" messages usually keeps also the modem alive.

Once you enable PSM with lte_lc_psm_req(true) the only thing your device needs to do is not the sent data. After the timers expires, the modem goes to sleep (with the exception of executing an HPPLMN search, if pending). No need for lte_lc_func_mode_set(LTE_LC_FUNC_MODE_OFFLINE) or something else. To wake up the modem, just send data.

Using RAI may then also "short cut" these times, if it's possible to be used for the communication logic an supported by the network.

> Is there a way to know if PSM is supported during runtime ?

AFAIK, the reported "active time" of -1 (<0) when PSM is enabled indicates, that PSM is not supported.