How to remove modem's memory of previously connected to tower/technology used?

[leo_nam]

Hello,

The nrf9160 took over 3 minutes to connect to a cell tower after moving from one country (Singapore, NBIOT) to another (Canada, LTE-M). 

After moving, the nrf9160 first attempted to connect to towers using NB-IOT but these connections were rejected by the tower. This was expected because all the nrf9160 devices that remained in Canada are using LTEM.

XCOUNTRYMODE was used with the setting "4,302,12,0" but the device continued to attempt NB-IOT connections until it gave up and started using LTE-M after which it connected. 

First connect time was shortened by using XBANDLOCK. The problem is that the device will be moved from country to country by it's users so it's unknown what bands to lock it to.

First connect time was also shortened by using XFACTORYRESET which seemed to make the modem "forget" the previous NBIOT tower that it was connected to in Singapore (this is just a guess). XSYSTEMMODE was also changed to 1,1,1,0 after doing the XFACTORYRESET. 

Related settings were

AT%XSYSTEMMODE = 1,1,1,0 (preference is set to 0 because device can be used in any country)

AT%XBANDLOCK="",""

Modem FW version 1.3.5

Is there a way to make the modem "forget" or "override" the tower/technology it used for its previous successfull connection without doing an XFACTORYRESET? 

EDIT: Also changed SIMs in the move from Singapore(Onomondo) to Canada (1nce).

[Simon D-M]

Hi,

The best command to use here is the %XCOUNTRYDATA AT-command (link). It should allow the device to accelerate the search quite significantly if configured correctly. It is quite strange that in your case it still tried to search for NB-IoT networks, can you maybe take a modem trace of this happening?

You can also try to perform a forced PLMN search with the %COPS=? AT-command (link) or a normal one with +COPS=? (link). However, it is a bit hard for me to test the actual search time improvement but from what I can read in the documentation it seems like it will perform a fresh search.

Best regards,

Simon

[Achim Kraus]

Maybe start with a simple question:

How does the device knows the country?

I would guess, it requires to find a mobile network to read the MCC. After that, it may be faster to register at the right network with XCOUNTRYMODE. But until a first mobile network is found, it can't help.

If your device is in NB-IoT, but the country offers only LTE-M, that search for a first network may take longer. If you "remove" NB-IoT from the "modem's memory", what should the modem use to start with? Not knowing the country without a first mobile network. And with countries only offer NB-IoT and others only offer LTE-M?

So, accept the 3 minutes :-). 

[leo_nam]

Sometimes it is what it is.

Thank you for your replies, 

I will try to approach this problem differently.