How long should nRF9160 stay in CEREG mode 4 on startup?

[Jonathan]

When I start my nRF9160 modem (AT+CFUN=1) it can sit in CEREG mode 4 (unknown) for a couple of minutes, before it switches to 2 (searching) then 1 (registered).

Is that normal? Is there any way to speed it up?

It is running modem firmware 1.0.1.

[MJD093]

This is normal, the modem has to listen first to sync itself to the LTE network before beginning the attachment process. The whole process will take a while in poor signal conditions or it can be very rapid. The device will attempt to connect as quickly as possible but it always has enviromental factors that increase attachment time.

The important thing is that the connection occurs. From my examinations, I have seen the connection take anywhere from less than a minute to over 10 minutes in poor signal areas.

[Sigurd]

Jonathan said:

Is there any way to speed it up?

If you know what band you want to connect on, you can set it with AT command %XBANDLOCK. After you have done that, save the modem settings to persistent storage with AT+CFUN=0. You will then only search on the bands specified, and it should reduce the time spent searching/connecting to the network.

[jbrzozoski]

One thing we stumbled on was that our application was re-forcing a bunch of modem settings on every power up, but some of them would cause the modem to lose warm-start info it had saved previously.  Specifically, we found that sending "AT+COPS=0" on every power-up before going online would trigger a full sweep and auto-select which could take minutes.  If we skipped that, the modem would retain warm-start info under some conditions (not entirely clear to me when) and would often be able to get online in less than 5 seconds.

If we query the COPS setting it still shows 0 and the modem will still jump between operators if it loses connection, but it can remember who it connected to previously and re-use that as a first attempt on the next power cycle.  The first connect in a new location will still take minutes, but for our product that is less likely to happen.

As a matter of curiosity, can anyone from Nordic comment on when the modem will save information like this for use after reboot?  Our application doesn't normally go to CFUN=0, so I'm pretty sure that's not triggering it. Yet, our devices connect very quickly and appear to have saved sometime.