nRF9160 and eDRX mode on LTE-M connection

[bjornolav]

We are using eDRX to save power, but it seems like eDRX is not active always. 

We currently use LTE_LC_EVT_EDRX_UPDATE callback to determine if eDRX is active. Is this a safe way to determine if the cell has eDRX activated? Quite often we do not receive the callback. Quite often we do not receive this callback when connecting. Does that indicate no eDRX?

nRF Connect SDK v2.3.0

Modem fw 1.3.4

Best regards

Bjørn Olav Steihaug

Datek Next

[Kazi Afroza Sultana]

Helo Bjørn,

I have talked to our team. I got some feedback.

You can either check via CEDRXS at command (which is the one you also get with LTE_LC_EVT_EDRX_UPDATE), or via XMODEMSLEEP as described here:https://devzone.nordicsemi.com/support-private/support/283529#permalink=750997 

[bjornolav]

Thank you Kazi

Does CEDRXS give the the current eDRX value or just the value we have requested. The documentation say:

"The command is used to read the requested eDRX parameters."

The XMODEMSLEEP seems to be promising. 

[Achim Kraus]

AFAIK, eDRX applies in RRC idle and supports larger receiver intervals there.

Once the modem enters "deep sleep mode" eDRX is not longer applied.

GSMA - Improving Energy Efficiency for Mobile IoT, March 2022

And yes, the eDRX status notifications may be mixing up, e.g. if you request to disable it, you don't get a "finally disabled" notification.

I haven't tested, what happens, if a device moves from a eDRX supporting network to a not supporting network. Nor if there is a eDRX notification after the +CEREG.

Lot's of good question.

But XMODEMSLEEP will be the wrong path ...

[Achim Kraus]

My inquiry sum-up:

The eDRX values are split into "requested", "provided by network", and "provided by cell".

The first two do have read functions and XMONITOR will also report the network value.

The cell values are only reported with change events/notifications. If the modem is restarted (CFUN=0, CFUN=1), then you need to reregister for the eDRX events and reset the eDRX call values as well.

[Achim Kraus]

I also tried to test, if "%XMODEMSLEEP:" reports something related to eDRX as the docu mentions with

"2 RF inactivity. Modem sleeps due to RF inactivity, including eDRX.".

I used a nRF9160-DK (mfw 1.3.6) and a nRF9161-DK (mfw 2.0.0).

I've tested with 655.36s and 61.44s. 

I get the events, that eDRX is active in the cell, my PPK II shows the longer intervals. With that eDRX is active.

But "%XMODEMSLEEP: 2" is not reported.

Maybe, someone from Nordic helps with the details about the preconditions here. Not that in the end it takes a SIM card, which switches off for eDRx.

(If I enable PSM, "%XMODEMSLEEP: 1" gets reported, e.g. eDRX 61.44s, PSM act time 120s => "%XMODEMSLEEP: 1".)

[Achim Kraus]

I found the missing trick:

LTE_LC_MODEM_SLEEP_NOTIFICATIONS_THRESHOLD_MS is set to 20 minutes per default.

If a notification is wanted for eDRX 61.44s, it's required to adjust that value as well.