NRF9160 NB-IOT disconnecting (+CEREG registration = 0) after period of stable connection.

[narrowerband]

Hello,

I'm currently developing on the NRF9160, a sensor implementation that sends a few 100 bytes every 24hrs.

However, for demo purposes we need to send the payload every minute or so. To do so, I changed the firmware to not disable the modem (PSM not yet implemented), but to keep the modem on. During the demo power usage is not a factor.

After connection is setup, all works well for about 10 to 15 minutes, until out of the blue, the network registration status is set to 0.

[00:37:47.185,607] <dbg> lte_lc.at_handler: +CSCON notification
[00:37:47.185,729] <inf>   lte.lte_handler: RRC mode : Connected
[00:37:47.185,974] <dbg> lte_lc.at_handler: +CEREG notification: +CEREG: 0,"051D","04A6FA67",9,0,0,"11100000","11100000"
 
[00:37:47.186,279] <dbg> lte_lc_helpers.parse_cereg: Network registration status: 0
[00:37:47.186,340] <dbg> lte_lc_helpers.parse_cereg: LTE mode: 9
[00:37:47.335,052] <dbg> lte_lc.at_handler: +CSCON notification
[00:37:47.335,174] <inf>   lte.lte_handler: RRC mode : Idle

The device doesn't seem to automatically reconnect, so when this happens, I put the modem into flight mode CFUN=4, and back to CFUN=1, reconnecting.

<dbg> lte_lc.at_handler: +CEREG notification: +CEREG: 5,"051D","04A6FA67",9,,,"11100000","01011111"

This works, but the CEREG=0 notification now seem to happen every minute.

<dbg> lte_lc.at_handler: +CEREG notification: +CEREG: 0,"051D","04A6FA67",9,0,0,"11100000","01011111"

A known error is that the PSM parameters I set do not get returned by the CEREG notification, the network seem to override the parameters I try to set. I have verified with my operator that the parameters I set should be allowed, but this issue seems to me unrelated to random network kicks.

Can anyone point me in the direction of where my error lies?

[Didrik Rokhaug]

Hi,

What modem firmware version are you using?

If you are using 1.3.0 or newer, could you subscribe to modem events (AT%MDMEV=1), and see if that reports anything?

Best regards,

Didrik

[narrowerband]

Hi Didrik,

I am using modem firmware 1.2.7 (because our devices are the NRF9160 SiP revision 1 (B0)) which is to our understanding the highest modem firmware that the B0 can safely run.

I will update a development kit to 1.3.0 to see what comes from the modem events.

[narrowerband]

Hi Didrik,

It seems that I've fixed my issue. It was related to a hardware issue where the power supply was not able to deliver the current needed for the modem, so the voltage dipped to a point that it did not trigger a brownout, but did trigger a network disconnect.

[Didrik Rokhaug]

Great to hear that you found the cause!

In modem fw version 1.2.x, you can use the %XVBAT, %XVBATLVL, %XVBATLOWLVL and %XPOFWARN to monitor the voltage level. You can also use +CGEREP to subscribe to +CGEV events (which can give you much of the same information as %MDMEV).

Best regards,

Didrik