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

[Achim Kraus]

Seems to be a topic, which irritates more people. Here is an link with some additional background information:

nRF9160-DK - sometimes busy for 1 minute before entering PSM

It's a little long to read all the comments, but after passing the questions the issue was answered by the modem team:

"The log shows that there is Higher Priority PLMN (HPPLMN) search initiated after one of the RRC connection releases and that caused the delay."

In the case, you operate the device more statically, you may try to use a PLMN lock, which suppresses such HPPLMN searches (see the comments after the answer).

[Michal]

Thank you for the link Achim.

Christian, please let me know if that answer satisfies you, or if we should look more into it.

Best regards,

Michal

[Christian22]

Thanks for your answers.

The +COPS command did the job in the first test. But how can I handle it if I sell the product almost world wide? How flexibile is the +COPS command if it is used in semi mobile devices?

Would it be possible to start the nrf9160 in automatic network search mode and change the network search to manual mode after the connection has been established for the first time in case the device is used in the same location for a longer time?

Would it also be possible switch back to automatic mode at any time in case the device is moved to another location? 

[Michal]

Hello Christian,

I will look more into it.

Best regards,

Michal

[Susheel Nuguru]

Sorry for delays in the response, Michal is currently OoO  and will return in few days. I need to seek some help from the colleagues on your last query as I am not an expert in this.