Cell ID and LAC are invalid values - but close

[DamoL]

Hi, 

I am using the nRF9160 in a datalogging product, logging environmental sensors and sending data via MQTT over a LPWAN network. Something that I have noticed for a while is that the Cell-ID and LAC codes seem to be wrong, and I assumed it was a parsing error on my side that I needed to fix. 

However it turns out that it isn't. the lte_lc library populates infomation about the cell tower it is connected to, but after cross referencing them on websites like cellmapper and opencellid it looks like they are slightly wrong. 

Cell-ID always has '1' added to it. For instance, their are 2 nearby cell towers that it has connected to before - 1357578, 1357588

However the values I always get are  - 1357579 1357589

Similarly, the LAC of both of these masts are 24715, but the LAC I always receive is 25715. 

With them being so close I feel like there must be an explanation for this, but I cant see it myself. 

I was planning to implement multicell location using HEREapi, which I have confirmed works with the corrected values using Postman. I need to find the root of the issue though, as I can't just expect that every cell it connects to will be off by 1.

Thanks, 

Damien

[dejans]

Hi,

Are you using nRF9160-DK or a custom board?

Which modem firmware version are you using?

Best regards,
Dejan

[DamoL]

Hi Dejan, 

It is a custom board with Modem FW 1.3.1 - I believe that is the latest.

Thanks, 

Damien 

[dejans]

Hi,

DamoL said:

Can you not verify that a Cell-ID that your DK connects to is a correct Cell-ID? You can use one of the two links to search for the Cell-ID you receive and see if they exist?

I am sorry, but we really need a trace because we need to check whether this is modem issue or not.. You can enable modem tracing by using CONFIG_NRF_MODEM_LIB_TRACE_ENABLED KConfig option which enables modem traces in the modem and forwards them to the Modem trace module.

Best regards,
Dejan

[DamoL]

Hi Dejan, 

Still haven't had time to do a trace. I will try and do that by the end of the week. 

However, I have noticed something odd. If I connect to an LTE-M Network it correct gives me the CellId and LAC, but on NB-IoT it does not. My code does not change depending on what network it's on so I can't see how this would be a parsing issue. Potentially an issue on the cell tower itself or in the modem firmware I would guess, but seems strange I am the only one who has noticed it. 

Thanks, 

Damien

[dejans]

Hi Damien,

In order to investigate the issue, please send us modem log when you have time.

Best regards,
Dejan

[dejans]

Hi Damien,

Are there any updates? Is the issue still present? Are you able to send the log to us? 

Best regards,
Dejan

[DamoL]

Hi Dejan, 

The issue is still there, but it seems its only in my location. I went to a Vodafone lab the other day and connected to different masts, and on both NB-IoT and LTE-M the values were the same and correct, so I guess there is an issue with my local masts and that's what is reporting the values incorrectly. I will try and get Vodafone to confirm this. 

Thanks, 

Damien

[dejans]

Hi Damien,

Thank you for this information.

Please let us know if there is anything else related to this issue that we can assist you with. 

Best regards,
Dejan