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nrf9160 Band Selection Algorithm

Musa.A


We are wondering how nrf9160 modem decides which band to use when there are multiple bands available (LTE CAT NB) and there isn't any apllied band lock from the software side. In our use case, although there are 2 bands available for the device, it selects mostly the one which has worse RSSI. Is it possible to make one band preferable without locking the other band?

Best Regards,
Musa

  • 0

    Hello,

    there is no way to manually set priority on bands, if that's what you're asking. However, the modem will prioritize bands automatically based on previous connection attempts. I would guess it prioritizes based on signal strength, that would make the most sense. So it is a bit strange that in your case it chooses the band with the lowest RSSI. It is important that you turn the modem off with AT+CFUN=0 before rebooting, otherwise the modem will not store information from the network search, and thus it won't be able to prioritize correctly.

  • 0

    Hello

    I think the selection of the network can be influenced also by the SIM.

    At the moment I experience various implementation issues with network operators: some implementing PSM, others not, some taking 60s to idle the connection, always doping first packet, etc etc
    This has been an issue traditionally even with 2G and 3G networks (especially roaming).

    This is why you could scan the available networks first with AT%COPS and then have a table with priorities that take into account past experiences with the network. Especially in roaming this can save you a lot of connection attempts with exponential back-off ...

    If you know the continent you are in (GPS) or country (MCC) then you might also restrict the available bands. This can speed up network scanning and connection performance.

  • 0

    Right now the problem we have is even if we put the 2 device at the same location( with 5cm distance in between) they are connecting to the different cells with NBIoT (both are in band 20). And while the one cell provides -80dbm signal, the other one can only provide around -110 dbm. So we are wondering why it choose the worst one while there are 2 available cells and the other one is far better. We had this problem more than one area with different devices.

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