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

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

Didrik Rokhaug — Thu, 21 Apr 2022 13:25:13 GMT

The current neighbour cell measurement algorithm is heavily biased towards low power consumption, which means that it will try to not search for new cells as much as possible, just measure the ones it already knows about (if it has previously searched for neighbours on instruction from the network).

However, if you start the search with AT%NCELLMEAS=2, you can tell the modem to prioritise finding neighbours higher. However, it is still not a guarantee that it will actually find anything. Another limitation is that it will only search for NB-IoT (or LTE-M), and not "normal" LTE cells.

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

barbiz — Fri, 08 Apr 2022 11:20:36 GMT

You are right. This means it happens sometime. I attach here a new trace, where, according to the serial log, the radio find 0 neighbours. This was tried 10 times in a row with the same result before taking the trace.

[00:04:50.873,413] <inf> multicell_location_sample: Button 1 pressed, starting cell measurements
%NCELLMEAS: 0,"0097A56F","22210","69D9",96,6354,319,66,22,301198,270183
[00:05:01.810,821] <inf> multicell_location_sample: Neighbor cell measurements received
[00:05:01.820,159] <inf> multicell_location_sample: Neighbor cells found: 0
[00:05:01.828,491] <inf> multicell_location_sample: Current cell:
[00:05:01.835,693] <inf> multicell_location_sample: MCC: 222
[00:05:01.842,590] <inf> multicell_location_sample: MNC: 010
[00:05:01.849,456] <inf> multicell_location_sample: Cell ID: 9938287
[00:05:01.857,147] <inf> multicell_location_sample: TAC: 27097
[00:05:01.864,227] <inf> multicell_location_sample: EARFCN: 6354
[00:05:01.871,490] <inf> multicell_location_sample: Timing advance: 96
[00:05:01.879,364] <inf> multicell_location_sample: Measurement time: 301198
[00:05:01.887,817] <inf> multicell_location_sample: Physical cell ID: 319
[00:05:01.895,965] <inf> multicell_location_sample: RSRP: 66
[00:05:01.902,832] <inf> multicell_location_sample: RSRQ: 22
[00:05:01.909,729] <inf> multicell_location_sample: *** No neighbor cells found ***devzone.nordicsemi.com/.../trace_2D00_2022_2D00_04_2D00_08T11_2D00_16_2D00_52.159Z.bin

Marco

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

Didrik Rokhaug — Fri, 08 Apr 2022 11:05:39 GMT

Thanks for the trace. But I see that in this trace, you actually got a neighbour:

AT_STRING <= %NCELLMEAS: 0,"0097A56F","22210","69D9",80,6354,319,67,32,192580, 6354,329,54,6,0, 77807\r\n

I've added some extra spaces to the above response to show the neighbour more clearly.

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

barbiz — Thu, 07 Apr 2022 14:42:55 GMT

Hello! Perfect, please see the attached RAW dump.

Thanks :)

devzone.nordicsemi.com/.../trace_2D00_2022_2D00_04_2D00_07T14_2D00_37_2D00_52.404Z.binMarco

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

Didrik Rokhaug — Thu, 07 Apr 2022 12:05:33 GMT

[quote user="barbiz"]Sure, how can I take a raw modem trace?[/quote]

Same way you took the live trace (i.e. the Wireshark screenshot you shared previously), just enable "RAW" as well (you don't actually need to have LIVE enabled at the same time, but it will lte you see what happens):

After you start tracing, it is nice if you reset the device, so that the trace includes the modem startup.

[quote user="barbiz"]I will send you a PM for getting the RSM contact, thanks much![/quote]

I have replied with the contact details.

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

barbiz — Wed, 06 Apr 2022 16:04:45 GMT

Sure, how can I take a raw modem trace?

I will send you a PM for getting the RSM contact, thanks much!

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

Didrik Rokhaug — Wed, 06 Apr 2022 15:45:04 GMT

If you take a raw modem trace, I can give it to our modem team for analysis. They should be able to give a better answer of why you don't find any neighbours.

[quote user="barbiz"]So my question is: is there any plan to implement "cell survey" function?[/quote]

Questions about future plans should be directed to your Regional Sales Manager. If you don't know how to contact your RSM, you can send me a private message with your location, and I will give you the contact details.

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

barbiz — Wed, 06 Apr 2022 08:50:49 GMT

Hi Didrik,

For the second measurement: yes, I am sure since other modules capable of scanning detect at least one more cell, anc in some cases I've been able to connect to that.

About the SIB5... what does it mean? It's ok to me to find "intra neighbours".

What I am spotting out is that there seems to be a gap between the nrf9160 and other chipsets that are capable of scanning (apart from the technical points, I am just noticing the external behavior)

So my question is: is there any plan to implement "cell survey" function?

Marco

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

Didrik Rokhaug — Tue, 05 Apr 2022 13:56:46 GMT

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.

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

barbiz — Thu, 31 Mar 2022 17:27:40 GMT

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

devzone.nordicsemi.com/.../trace.pcap

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

Didrik Rokhaug — Thu, 31 Mar 2022 16:31:54 GMT

[quote user="barbiz"]what are SIB3? Can you help me find some literature on this?[/quote]

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.

[quote user="barbiz"]how can I check if I am getting them? What should I look for into the trace?[/quote]

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.

[quote user="barbiz"]can you suggest me a procedure to perform this command %NCELLMEAS in the best possible configuration?[/quote]

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.

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

barbiz — Thu, 31 Mar 2022 14:43:19 GMT

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

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

Didrik Rokhaug — Thu, 31 Mar 2022 13:44:15 GMT

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.

[quote user=""]are the %XDEEPSEARCH or %PERIODICSEARCHCONF somewhat related to this?[/quote]

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

Best regards,

Didrik