nRF9160 - Improve slow cellular registration

RE: nRF9160 - Improve slow cellular registration

Achim Kraus — Wed, 20 Mar 2024 12:37:23 GMT

My experience:

If the modem searches for a network, that may take a while.

The modem keeps the last network successfully registered.

If the modem is restarted (cfun=0/cfun=1), the modem persist that last successful network and uses that for the first try. If the network is still there, the registration is quite fast. If not, it again takes a while to search a network.

If the modem isn't switched off (cfun=0) before the SoC restarts/reboots, then it depends on how long the modem was on. According the doc:

"The command configuration is stored to NVM approximately every 48 hours and when
the modem is set to minimum functionality mode with the +CFUN=0 command."

So, if you reboot the SoC, then you may either use a CFUN=0 before, or you may depend on how long the modem is running after it successfully registers to a network. If none is true, then the found network may be not persisted and that may end in longer search for a network after the modem restarts with the SoC.

My app measure the time to register and if that's more than 60s, then I do a CFUN=0/CFUN=1 in order to ensure, the found network is persisted.

RE: nRF9160 - Improve slow cellular registration

Achim Kraus — Wed, 20 Mar 2024 07:19:49 GMT

Other tickets about the "periodicsearchconf" already turned out, that on missing networks the modem stay in idle (for emergency calls, even if it's unclear, how that applies to the nRF9160) instead of sleeping. And that the modems sticks to network rejection, which then requires either to wait longer or switching the modem off/on.

RE: nRF9160 - Improve slow cellular registration

Håkon Alseth — Tue, 19 Mar 2024 14:07:44 GMT

Hi,

Is there a bad reception where you are testing?

Can you share the output of AT%XMONITOR ?

[quote user=""]It works great. However, when uploading a new firmware, the duration to re-connect to the network is very inconsistent : sometimes it connects within less than 30 sec, and sometimes it is still not connected after 3 minutes. In both cases, the device it at the same location, on my desk.[/quote]

When you say new firmware, do you mean new modem firmware or application based firmware? If it is new modem fw, it will clear information related to the cell towers that you've successfully connected to in the past.

[quote user=""]Because my device might be placed in a location where network is not reachable, I have implemented a timer that will switch off the device in case it takes too long to connect. This will prevent draining too much battery. The question is : how long is too long ? Is there a way to improve that ? For example, being able to detect that there are no cells around, so there is not point waiting for too long ?[/quote]

This highly depends on your application and what you deem to be "too long". I can state that the modem itself will duty cycle its searching over time, to avoid excessive current consumption.

You can have a look at this AT command: https://infocenter.nordicsemi.com/topic/ref_at_commands/REF/at_commands/mob_termination_ctrl_status/xdataprfl_set.html?cp=2_2_0_4_13_0

Which also sets how the periodic search behaves:

https://infocenter.nordicsemi.com/topic/ref_at_commands/REF/at_commands/nw_service/periodicsearchconf_set.html

Kind regards,

Håkon