Measured scanning procedure a few minutes after connection establishment

[Christian22]

Hello,

I'm doing a few power consumption tests on the nrf9160 DK with NB-IoT for a battery powered application. PSM mode works as expected but I measured a current drain of about 35mA a few minutes after the nrf9160 has connected to the cellular network (see screenshots below). The procedure that leads to the 35mA is as follows:

1. Powered the nrf9160 DK
2. Application on the nrf9160 establishes a connection to the NB-IoT network
3. Application on the nrf9160 exchanges data with a cloud application every 60s (works as expected)
4. About 2 minutes after the connection establishment procedure the nrf9160 modem consumes 35mA for about 1 to 2 minutes while the data exchange with the cloud still works as expected. 

In the case I linked below it turned out that the current drain of about 35mA is due to the network scanning procedure. I assume this also applies to my case. But in the linked case they only talk about a scanning procedure during the connection establishment process and not if the system is already connected.

https://devzone.nordicsemi.com/f/nordic-q-a/68411/9160-continuous-current-drain-during-cell-tower-connection----is-this-expected

Now I wanted to know if it is normal that the modem performs a scanning procedure while it is already connected?

If yes, can I disable the scanning procedure that is executed while in connection? Because it consumes a lot of energy and the nrf9160 is already connected anyway.

Start of the scanning procedure after a packet exchange

Packet exchange during the scanning procedure

How the scanning procedure looks like when zoomed in

End of the scanning procedure

I use the following setup:

• nrf9160 DK revision 1.1.0
• ncs v2.0.0
• modem firmware is mfw_nrf9160_1.3.2
• MNO is Deutsche Telekom

Thanks in advance.

Best regards,

Christian

[Michal]

Hello again Christian,

Sorry for the long delay, I had an unexpected event I had to attend to.

I have consulted my colleagues about it and using the +COPS command is not recommended for that at all.

The issue is that when using a SIM card in roaming mode, the card has to do those searches as it is something required by the 3GPP specification.

The only true workaround would be to use only home network instead of roaming as in home network there are no HPPLMN searches.

Best regards,

Michal

[Achim Kraus]

I'm not really wondering, that the answer in this other ticket is slightly different. Maybe, an other expert has a different view on it. Using +COPS is exactly the opposite, the HPPLMN is good for. So I'm really not wondering, that the expert involved here doesn't recommend it.

> "The only true workaround would be to use only home network instead of roaming as in home network there are no HPPLMN searches."

At that point I' struggling. I use several SIM card providers in several countries. Exactly 0 of them are reporting to be in the "home network", all are reporting "roaming". If you read the other ticket, the question there was, how someone knows, that device spends energy in such HPPLMS searchs. I use the time from RRC idle to sleep and that indicates, that it doesn't depend on "home network" or "roaming", it's more the question, if your modem connects already to a "highest priority network".

With an explicit event for such HPPLMNS search (that's requested in the other ticket), Nordic would make this transparent to users and the users may be able to chose the proper SIM card for the region. That saves a lot of energy.

[Christian22]

Hi all,

Sorry for the delay, I was in vacation and I'm also very busy this week so I will come back to the question next week.