nRF9160 with NB-IoT in Switzerland

[Chraebs]

Hi

I'd like to use NB-IoT in Switzerland.

According to https://www.gsma.com/iot/mobile-iot-commercial-launches/ there is support for both LTE-M and NB-IoT in Switzerland.

Also, when looking at the AT+CEREG notifications I get on my devkit running the at_client example, it indicates <AcT> 9 which means "E-UTRAN NB-S1".

However, the modem (v1.3.0) fails to complete registering at the network cell.

2021-07-19T14:38:54.033Z DEBUG modem << +CEREG: 2,"EBF0","0114A96A",9,0,0,"11100000","11100000"
2021-07-19T14:39:00.143Z DEBUG modem << %CESQ: 24,1,2,0
2021-07-19T14:39:02.968Z DEBUG modem << %CESQ: 19,0,0,0
2021-07-19T14:39:06.927Z DEBUG modem << %CESQ: 14,0,0,0
2021-07-19T14:39:13.187Z DEBUG modem << %CESQ: 24,1,4,0
2021-07-19T14:39:13.265Z DEBUG modem << +CEREG: 2,"EBF0","0112A06B",9,0,0,"11100000","11100000"
2021-07-19T14:39:15.983Z DEBUG modem << %CESQ: 25,1,9,1
2021-07-19T14:39:18.535Z DEBUG modem << %CESQ: 14,0,0,0
2021-07-19T14:39:19.247Z DEBUG modem << %CESQ: 21,1,0,0
2021-07-19T14:39:22.468Z DEBUG modem << %CESQ: 27,1,7,1
2021-07-19T14:39:22.575Z DEBUG modem << +CEREG: 2,"ECB8","00772B69",9,0,0,"11100000","11100000"
2021-07-19T14:39:23.662Z DEBUG modem << %CESQ: 28,1,13,1
2021-07-19T14:39:25.264Z DEBUG modem << %CESQ: 25,1,6,0
2021-07-19T14:39:25.464Z DEBUG modem << %CESQ: 21,1,0,0
2021-07-19T14:39:26.287Z DEBUG modem << %CESQ: 25,1,6,0
2021-07-19T14:39:26.687Z DEBUG modem << %CESQ: 28,1,11,1
2021-07-19T14:39:27.280Z DEBUG modem << +CNEC_EMM: 15
2021-07-19T14:39:27.337Z DEBUG modem << +CEREG: 4,"ECB8","00772B69",9,0,15,"11100000","11100000"

I tested this both with a "roaming" SIM (IMSI 20408...) and a "native" SIM (IMSI 22802).

I also found that iBasis SIM (IMSI 20408) notes a "N/A" for Switzerland https://www.nordicsemi.com/-/media/Software-and-other-downloads/3rd-party/iBasis-simplified-coverage-map-for-web.pdf?la=en&hash=CA7DBF400243D8A7A7BDA94873B50E73C26B4FAC.

Questions:

* Has anyone ever used NB-IoT in Switzerland

* Is my interpretation right, that <AcT> 9 means that the cell supports both LTE-M and NB-IoT, and <AcT> 7 means only LTE-M is supported. Or what is the exact meaning of it?

[Hakon]

Hello,

there is no coverage for NB-IoT for iBasis in Switzerland yet. You will need to contact iBasis or the local carrier if you need more details.

[Chraebs]

Can you point me to some explanation of the <AcT> field in the AT+CEREG response (EUTRAN vs EUTRAN NB-S1)?

[Hakon]

You can check the 3GPP spec, I believe you can find a detailed explanation about the AT command response there. There is also this document, but I'm not sure how helpful it is. You can read more about the EUTRAN definition here.

[Chraebs]

Yes I know I can check the general 3GPP spec (especially 3GPP TS 27.007 section 10.1.22). But appologize my ignorance: From a logical point of view I'd expect at least 3 different variants:

1. Only LTE Cat M1 available
2. Only LTE Cat NB1 available
3. Both variants available
The 4th case "No variant available" is not necessary, as we wouldn't register to a cell then.

But according to Nordic and 3GPP spec, only two options are applicable:

<AcT>

7 – E-UTRAN

9 – E-UTRAN NB-S1

are listed in https://infocenter.nordicsemi.com/topic/ref_at_commands/REF/at_commands/nw_service/cereg_read.html?cp=2_1_7_7_1. I know this might not be a Nordic issue, but I'm not sure how I would safely know that my device is in a region with only NB-IoT available (and no M1). ... ...

Thus I don't see a meaningful way to check which variants are available..

[Hakon]

Chraebs said:

I know this might not be a Nordic issue, but I'm not sure how I would safely know that my device is in a region with only NB-IoT available (and no M1).

 From reading the 3GPP spec, my interpretation is that E-UTRAN in nb-s1 mode is equivalent with NB-IoT.

"NB-IoT is a non-backward compatible variant of E-UTRAN supporting a
reduced set of functionality."

So if it says "9 – E-UTRAN NB-S1", it should mean that NB-IoT is available exclusively. And because it is non-backward compatible, 7 – E-UTRAN should be exclusively for Cat M1.

I have no way of confirming this at the moment, since the modem team is unavailable for the moment.