nRF9160 does not select between NB-IoT and LTE-M

[philrittenhouse]

Hi,

We are testing in two cellular service regions, one with LTE-M support and one with NB-IoT support. Following the instructions from this ticket devzone.nordicsemi.com/.../nrf9160-confirming-support-of-both-nb-iot-and-lte-m-in-same-firmwares-without-reflashing we are able to connect to the local cellular network in each region.   The problem is that it only works if we enable only one of LTE-M or NB-IoT at a time.

That is  AT%XSYSTEMMODE=1,1,1,0 does not work (can't get LTE connection status green in the LTE Link Monitor) in either region but AT%XSYSTEMMODE=0,1,1,0 or AT%XSYSTEMMODE=1,0,1,0 does work (in the corresponding region)

Since we need to support both networks and we would prefer not to have two different products with different firmware, this is a problem.  Has anyone else run into this?   Is there something we are doing wrong?

We are running modem f/w version 1.3.3

So far we have only verified this issue using the AT commands.   I assume we would have the same problem with the CONFIG_LTE_NETWORK_MODE_LTE_M_NBIOT_GPS option.   Is it possible to switch between LTE-M only and NB-IoT only options at run time instead of compile time?

Thanks,
Phil

[RM]

Hi Phil,

You can switch between the two modes in runtime by placing the modem in CFUN=0 mode and then re-configuring to required mode.

Would suggest you post your AT commands and responses for further support, along with the board (nrf9160 rev2 ?) you're using, also would recommend updating to modem fw 1.3.5

Thanks,

Reuven

[philrittenhouse]

Thanks Reuven,

Here are the AT commands we use to change the mode:

AT+CFUN=0 
AT%XSYSTEMMODE=1,1,1,0
AT+CFUN=4 
AT+CFUN=1
AT+CFUN?

The board we are using is our own custom design.

I will try the latest f/w to see if it helps.

> You can switch between the two modes in runtime by placing the modem in CFUN=0 mode and then re-configuring
Can you tell me what the API commands are to do that?   So far I have only found the settings in the prj.conf.

Best regards,
Phil

[philrittenhouse]

Just a quick update:   I get the same results with version 1.3.5 of the modem f/w

[Achim Kraus]

philrittenhouse said:

The problem is that it only works if we enable only one of LTE-M or NB-IoT at a time.

In my experience, that may be caused by multi-IMSI cards with short auto-switching timeout. Here in south Germany it takes a little more than about 2 minute to search for a network in NB-IoT or LTE-M. If both are enabled, the modem switches after that 2 minutes to the other technology and search for a network again. If now a auto Multi-IMSI is used, that may interfere with that. The SIM card may switch the IMSI after 2 minutes and cause the modem to restart the network search. It never switches to the other technology or didn't search long enough with that. The timeouts of these Multi-IMSI cards differs, in my experience from 2 to 10 minutes. And some SIM card provider also start to provide multi IMSI cards with and additional "imsi select" mode.

[RM]

First would suggest trying with bare bone modem at application:

 for LTE-M1:

AT+CFUN=0

AT%XSYSTEMMODE=1,0,1,0

....

AT+CFUN=1

...

switch NB-IoT:

AT+CFUN=0

AT%XSYSTEMMODE=0,1,1,2

....

AT+CFUN=1

....