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

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

Achim Kraus — Tue, 02 Apr 2024 16:16:23 GMT

I guess, the first point will be to clarify, if your SIM card is really a multi IMSI card.

I developed a CoAP/DTLS 1.2 CID client in order to demonstrate the "power (saving)" of RFC 9146. That client is available at Zephyr - Coaps Demo Client with Eclipse/TinyDtls . The specific function is not isolated, so it will not help too much. I use a lot of API calls and a "hand full AT commands", especially to read more data from the SIM card.

You may start with implementing to read the IMSI "frequently" and see, if that is changing. If so, I usually stop a unsuccessful network search after 5 minutes and revert the preference of NB-IoT and LTE-M.

To be frank, I also replaced in the meantime this auto Multi-IMSI SIM cards by SIM cards with an IMSI select mode. That works in my experience just more smooth.

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

philrittenhouse — Tue, 02 Apr 2024 15:27:32 GMT

Thanks Achim!

Can you share your work-around for the problem? Have you written f/w for the nRF9160 that is able to detect the failure and switch modes automatically? Do you send your own AT commands or is there an API to do it?

Best regards

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

philrittenhouse — Tue, 02 Apr 2024 15:22:09 GMT

I think that's basically what we have already done. As I mentioned AT%XSYSTEMMODE=0,1,1,0 or AT%XSYSTEMMODE=1,0,1,0 does work if the corresponding region supports the selected mode (NB-IoT or LTE-M).

The problem is trying to have the modem automatically select between the two with AT%XSYSTEMMODE=1,1,1,0

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

RM — Mon, 01 Apr 2024 19:02:47 GMT

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

....

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

Achim Kraus — Sat, 30 Mar 2024 19:04:05 GMT

[quote userid="123982" url="~/f/nordic-q-a/109725/nrf9160-does-not-select-between-nb-iot-and-lte-m"]The problem is that it only works if we enable only one of LTE-M or NB-IoT at a time.[/quote]

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.

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

philrittenhouse — Thu, 28 Mar 2024 14:59:33 GMT

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

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

philrittenhouse — Thu, 28 Mar 2024 01:58:52 GMT

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

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

RM — Thu, 28 Mar 2024 00:19:59 GMT

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