AT%PERIODICSEARCHCONF=0,0,0,0,"1,20,600" - but with pretty low signals, I don't see more than one search

[Achim Kraus]

nRF9160, mfw 1.3.7, NCS 2.9.2

Case:

The modem first connects to LTE-M (Germany, band 3), pretty well.

Then the modem is moved into a building basement (band 8 or 20), with that the modem get's unregistered with the next sent message and starts one network search. That's not successful, maybe because of very low signals (-125 dBm and less), so also somehow OK. But then I don't detect any network search for 1h (instead of my configuration, which in my interpretation of the documentation should trigger new searchs after 10 minutes sleeps). After that hour, the device gives up and reboots ... and then after a couple of minutes (2-5) finds a network.

So, why does the modem not start the configured follow up network searches? Is there something as an optimization "no networks => no new search"?

(Unfortunately, I'm not able to provide modem-traces, at least that will be very, very complicated.)   

[Hakon]

Is it possible that the reboot is caused by the application, like for instance after a crash? Modem team mentioned "the “reboot” is a bit disturbing as we don’t have such functionality for the case where not being able to find cell."

Does modem start searching if triggered with %PERIODICSEARCHCONF=3 ?

Without modem trace it is hard to suggest anything more.

[Achim Kraus]

> Is it possible that the reboot is caused by the application, like for instance after a crash?

The restart is caused by a intended reboot, if the device is not able to register in a network for longer (e.g. 1-6h).

> Does modem start searching if triggered with %PERIODICSEARCHCONF=3 ?

I tried that, but that seems to have no effect. Also CFUN=0, CFUN=1 seems to have no effect. 

> Without modem trace it is hard to suggest anything more.

May question was  

"So, why does the modem not start the configured follow up network searches? Is there something as an optimization "no networks => no new search"?

I would assume, that if there is something implemented, which prevents such a network search on pretty low radio signals, then Nordic should know that. Regardless of a modemtrace.

[Hakon]

No, there is not that kind of “no search” feature.

If CFUN=0, CFUN=1 does not help either, it sounds like there is some kind of permanent prevention. Could it be Reset loop restriction? Have you subscribed %MDMEV?

[Achim Kraus]

> No, there is not that kind of “no search” feature.

OK. Thanks for clarifying. 

> Could it be Reset loop restriction?

No, not in my tests. 

> Have you subscribed %MDMEV?

It's unfortunately a custom board. There it's neither easy to get logs nor modem traces. I just kept some counters in "__noinit" to see, what was reported before the modem reboots.

I guess, it will take some more tests to see, if reboot helps or just my tests (2 devices, about 20 tests in all) pretends, that it requires a reboot. We will see, even if that will take some time to come back with more experience.