nrf9160 Band Selection Algorithm

RE: nrf9160 Band Selection Algorithm

Hakon — Wed, 20 May 2020 10:27:21 GMT

Here's the answer I received;

"Device has selected the cell, which has worse RSSI at some point of time when it has been better, or network configuration for LTE idle mode mobility has directed device to it.

With current implementation modem will prefer the most recent cell/band where it has been in service and this means it will more likely select that same cell always again after boot. Device will stay there unless network's idle mode mobility configuration directs it to that cell on other band. Please note that network may apply an offset to idle mode mobility between cells, this offset may keep the device on current cell even though there would be stronger cell from the same network on other band."

RE: nrf9160 Band Selection Algorithm

Hakon — Thu, 14 May 2020 12:32:47 GMT

I have asked internally for details on the algorithm. I will let you know when I have more information.

RE: nrf9160 Band Selection Algorithm

Musa.A — Wed, 13 May 2020 11:32:28 GMT

mfw_nrf9160_1.2.0

RE: nrf9160 Band Selection Algorithm

Hakon — Wed, 13 May 2020 11:29:56 GMT

What modem firmware are you using?

RE: nrf9160 Band Selection Algorithm

Musa.A — Mon, 11 May 2020 08:27:12 GMT

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.

RE: nrf9160 Band Selection Algorithm

Martin — Fri, 01 May 2020 13:32:48 GMT

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.

RE: nrf9160 Band Selection Algorithm

Hakon — Thu, 30 Apr 2020 13:09:38 GMT

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.