nrf9160 multiple cell location - how to perform neigbour cell detection?

Hello,

I know this topic has been discussed yet and I have read all the relevant posts.

What we have to do is multiple cell geolocation with nrf9160. The "multiple" here is the keyword, because in my tests, it was impossible to get more than the connected cell. Although I checked the coverage MAP and I know for sure multiple nearby cells are available.

We tried, as everybody else, the %NCELLMEAS and %NBRGRSRP commands, but we only manage to get the serving cell.

I also know that this is due to a specification on the 3GPP standard:

"Neighboring cell measurements are valid and available only when neighbors are being monitored, which means that the strength and quality of the current cell signal do not meet the network configured level. For more information, see the requirements in 3GPP TS 36.304."

However, it seems strange to me that:

  • a specific example is given "multicell_location" that will almost never work for me
  • other modules (such as QUECTEL BG95/96) do have a method to perform nearby cell scanning (and thus clearly overcome the limit of the standard)

So what I wanted to understand is:

  • is there any news on the topic? This is really important for non-GNSS location applications and could make a big difference
  • if not, is there any plan to implement a deeper call search function?
  • are the %XDEEPSEARCH or %PERIODICSEARCHCONF somewhat related to this?

Thanks to everybody that will help me. I am puzzled by the fact that this point seems not properly addressed yet.

  • Hi,

    Neighbour cell meassurements while in RRC Connected mode is decided by the network. However, if you run %NCELLMEAS while in RRC Idle, you will have a better chance of finding neighbour cells.

    However, even when used while in RRC Idle we depend on network support. If the network does not brodcast SIB3 (and ideally also SIB4 and SIB5)

    %NBRGRSRP is limited to only search when configured by the network, and will not trigger a new search when used.

    are the %XDEEPSEARCH or %PERIODICSEARCHCONF somewhat related to this?

    No, those commands does not affect the neighbour cell meassurements, as far as I know.

    Best regards,

    Didrik

  • Thank you Didrik!!

    I will add some more questions.

    • what are SIB3? Can you help me find some literature on this?
    • how can I check if I am getting them? What should I look for into the trace?
    • can you suggest me a procedure to perform this command %NCELLMEAS in the best possible configuration?

    Finally, what I can find (up to now) is that:

    • nrf9160 module does not find any neighbour cell
    • other modules find one or two neighbours

    I would love to get to obtain the same results with nrf9160 because I love the architecture and SDK that Nordic built.

    Thanks,

    Marco

  • barbiz said:
    what are SIB3? Can you help me find some literature on this?

    SIB3 is short for System Information Block 3. I am not really well versed in this part of the LTE spec, and my sources are mostly internal conversations with the developers, so I unfortunately don't have any literature to point you to.

    barbiz said:
    how can I check if I am getting them? What should I look for into the trace?

    This is what it looks like for me, in a modem trace taken from the Trace Collector V2 Preview:

    Note that in this case, the SIB3 is in the same packet as the SIB2. I do not know if this always will be the case.

    barbiz said:
    can you suggest me a procedure to perform this command %NCELLMEAS in the best possible configuration?

    Wait until you are in RRC Idle (you can use the +CSCON command to keep track of which RRC state you are in).

    Other than that, I don't know of any tricks for making it work.

  • Dear Didrik,

    I captured some trace. Please see it attached. I attached a screen of the SIB3 packet as well.

    What do you think?

    Marco

     trace.pcap

  • In the trace, the first %NCELLMEAS is done while in an RRC connection. So only one cell in that response is not surprising.

    However, the second %NCELLMEAS is done while in RRC idle, so the device should have been able to do a more thorough search. Are you sure the other cells in your area are NB-IoT cells?

    Also, since you don't get any SIB5s, the neighbour cells must be on the same frequency as the cell you are camped on.

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