Question about #XSYSTEMMODE behavior

[Semin Ahn]

Hello,

My customer's project is Asset tracker.

Here is scenario.

1. set #XSYSTEMMODE=1,1,1,3 (enable LTE-M and NB-IOT to connect nRF Cloud, enable GNSS,  LTE preference 3)

2. Using global USIM(Telenor) and roaming.

3. Their device will be travel worldwide.

They ask 2 questions.

First, the meaning of sentence on LTE preference 3, "Network selection priorities override system priority, but if the same network or
equal priority networks are found, LTE-M is preferred".

What is the difference of "Network selection priority" and "system priority"?

Second, if there device turns on NB-IOT only counties(eq. China), what happens with LTE preference 3?

Thank you.

[Charlie]

Hi Semin,

I think sdk-nrf/lte_lc.h at v2.2.0 · nrfconnect/sdk-nrf (github.com) explained more details about your concerns.

Let me know if you need more help.

Best regards,

Charlie

[Semin Ahn]

Hi Charlie,

Thank you for the answer.

Almost clear, but I confuse just one sentence.

In the comment of LTE_LC_SYSTEM_MODE_PREFER_LTEM_PLMN_PRIO, it says "The modem will prioritize to stay on home network".

Is that mean the modem continuously try to connect to only one PLMN(set with AT+COPS)?

Best regards,

Semin

[Charlie]

Hi Semin,

I get more explanation about the system mode preference settings from our modem team.

In system mode 1 & 2 (i.e. one system preferred over the other regardless the networks available in the area) the preferred system will be always prioritized. For example, in system mode 1 LTE-M will always be used in case any suitable network is available. If there is no suitable network available, only then modem starts to search for network in NB-IoT. System modes 3 & 4 behave differently: PLMN selection is prioritized over the system. In this case, for example, when modem starts to search for PLMN A it will search it from both systems before searching PLMN B.

In summary: System modes 1 & 2 make sure that the device uses always the preferred system when possible, whereas system modes 3 & 4 make sure that device is always in the highest priority network.

Semin Ahn said:

Is that mean the modem continuously try to connect to only one PLMN(set with AT+COPS)?

Yes, if you manually select one network with AT+COPS. "The modem will prioritize to stay on the home network" meant for the default functionality (without +COPS). I think it is more accurate to say "The modem will stay on the highest priority network or manually selected network" when considering also doing AT+COPS configuration.

Best regards,

Charlie