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  • Case ID: 289603
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Automatic dual mode scan

user116293

We are trying to achieve automatic scan and join in both LTE-M and NB-IoT network modes. We are using SICA B1 -SiP with modem FW 1.3.1, and %XSYSTEMMODE=1,1,0,0 setting.

In our understanding, this (XSYSTEMMODE-setting) would suggest that the modem supports both LTE-M- and NB-IoT-mode. We would also assume that the scan should automatically happen in both modes.

In our experience, if the previous connection has been in LTE-M-mode, and changing to NB-IoT-only SIM, the modem persists to scan in LTE-M-mode only.

It can, however, randomly scan and join in NB-IoT-mode after from >30 minutes to tens of hours, but sometimes totally fail after days of scanning.
If the scan and join has been established, the modem can randomly drop out from the network in NB-IoT-mode and scan only in LTE-M-mode for several hours or days, while set to %XSYSTEMMODE=1,1,0,0.


Using the preferred mode or priority mode settings does not improve the behavior in the expected automatic mode change in network scan.

Our questions:

Is it safe to assume that the network scan is automatic, covering both modes?
Is there anything to consider when assuming this automation to the modem?

  • 0

    Hi Sami,

    Thanks for inquiring us and it is very interesting to learn about this issue you encountered. I barely tested with NB-IoT before and need to contract with our modem development team for further analysis, so I need your help to provide more evidence for the next step.

    Could you do experiments with AT commands(using nRF9160: Serial LTE modem) and enable modem trace(need to run "AT%xmodemtrace=1,2" to active predefined trace set manually) to get modem trace recordings? According to your feedback, we need the following mode trace recordings:

    1) the previous connection has been in LTE-M-mode and changing to NB-IoT-only SIM for a new connection. Expect to see if the scan and join has been established, the modem can randomly drop out from the network in NB-IoT-mode and scan only in LTE-M-mode for several hours or days, while set to %XSYSTEMMODE=1,1,0,0.

    2) similar experiment with preferred mode enabled.

    Feel free to add more if you have other observations.

    Best regards,

    Charlie

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