nrf9160 %NCELLMEAS requirements

[amessner]

Hello,

When using the NCELLMEAS (search_type = 3) command I get inconsistent results. Generally, I don't see more than 1 neighbor. If my device (nRF9160, mfw 1.3.2) is in my basement I do get 1 neighbor in 2 out of 3 measurements, in my backyard I get none.

What requirements do need to be met so that NCELLMEAS returns all neighboring cells?

After going through some posts (specifically this one with a similar issue:  RE: nrf9160 AT%NCELLMEAS reports only 1 cell ) I understand that there are multiple variables that affect the output:

1. Only LTE-M/NB-IoT cells are detected
2. Results depend on the network configuration:
   1. SIB3 is minimum requirement for neighbor cell measurements. SIB4 includes additional information about intra neighbor but not mandatory for intra measurements. SIB5 (in addition to SIB3) is required for inter measurements. Otherwise results are available only from own cell.
   2. NCELLMEAS issued while UE is in RRC connected mode is not (always?) configured. Results are available only from own cell if not configured.

Is this correct?

I couldn't find much of a documentation on this. If someone can point me to a source where I can read up on this that would be much appreciated.

Thanks

[Albrecht Markus Schellenberger]

Hello, 

Is this correct?

Yes, that is correct.

I couldn't find much of a documentation on this. If someone can point me to a source where I can read up on this that would be much appreciated.

You can find some documentation on the %NCELLMEAS AT command itself.

Cheers, 

Markus 

[amessner]

We've been comparing cell measurements in RRC idle vs RRC connected, but we don't really see much of a difference.

We use PoLTE for our location service and there seem to be slightly less outliers when performing the cell measurements in RRC idle, however the number of neighbors we are seeing are still the same (0 to 1 neighbor usually).

I attached a modem trace of a cell measurement in RRC idle. In this trace I see 1 single neighbor:

{"earfcn":5070,"time_diff":0,"phys_cell_id":271,"rsrp":53,"rsrq":14}

Could a support engineer please help me analyze this trace to answer the following questions:

1) I parsed the modem trace into a PCAP file - I can see SIB1, SIB2 and SIB3 packages. Does this mean that I can only detect intra-band and NOT inter-band neighbors?

2) Is something of the network configuration preventing me from finding more neighbor cells?

3) Any suggestions on how to detect more neighbor cells?

4) Is there a way to force the modem into RRC idle?

trace-2022-08-18T14-42-37.438Z.bin

Thanks

[Didrik Rokhaug]

Hi,

amessner said:

1) I parsed the modem trace into a PCAP file - I can see SIB1, SIB2 and SIB3 packages. Does this mean that I can only detect intra-band and NOT inter-band neighbors?

Yes.

amessner said:

2) Is something of the network configuration preventing me from finding more neighbor cells?

3) Any suggestions on how to detect more neighbor cells?

As far as I can see, everything works as it should. What makes you think that you don't see all neighbour cells?

amessner said:

4) Is there a way to force the modem into RRC idle?

No, there are no practical way to make the modem enter RRC Idle other than not using the LTE link and let the inactivity timer (in the network) time out.

Best regards,

Didrik

[amessner]

Didrik Rokhaug said:

As far as I can see, everything works as it should. What makes you think that you don't see all neighbour cells?

Thanks Didrik. I understand that I can only see LTE-M/NB-IoT cell towers, and (due to missing SIB4/SIB5) only those that use the same band as the one I am connected to. 

However I'm in the middle of a city (Edmonton, Canada - population > 1M)  so I expected to see more neighbor cells. 

Is there a resource/map I can use to see which towers are nearby my location and support LTE-M/NB-IoT? All websites I found do not let me filter for LTE-M/NB-IoT capable cells.