RE: nRF9160 NB-IoT Cell Selection

Charlie — Wed, 15 Dec 2021 14:38:50 GMT

Hi,

[quote user=""]The nRF9160 is powered up once an hour to transmit some data over HTTPS. It also logs the RSRP and RSRQ measurements (via AT+CESQ), as well as the ID of the connected cell (via AT+CEREG). After completing (or aborting) the data transmission and telemetry logging, the nRF9160 is completely powered off (power-gated using a MOSFET switch).[/quote]

I doubt if this is a good design. The power-off does save power, but keep in mind the process of power-on will also consume more power than the normal running period, especially when you enable PSM for your application. Searching and connecting with cellular stations are power-hungry. A one-hour interval is quite short for a cellular IoT application, I do not think the power-off period can compensate for the power-on process power consumption. I suggest you do some experiments to compare their difference. I expect only when the interval is serval days or longer then it is worth trying your power-off method, otherwise you should keep the power on and use PSM for your application.

[quote user=""]I am curious whether RSRQ is taken into account in the cell selection process?[/quote][quote user=""]would the nRF9160 just pick the first detected cell, or is there any mechanism to pick the "best" cell to camp on?[/quote]

According to our cellular modem expert, cell selection is based on the S criteria following 3GPP TS 36.304 specification, so RSRQ should be used as

[quote user=""]When I analyzed such telemetry data, I noticed that quite a number of devices (all fixed in the same location over time) tend to jump between different cells in each time the nRF9160 is powered on.[/quote][quote user=""] I am wondering if this is the expected behavior?[/quote]

I am not sure why this happens, maybe you are on the edge of several cells. It would be better to get some information about the neighbor cells for further analysis, you can refer to the discussion on this ticket: nrf9160 AT%NCELLMEAS reports only 1 cell and send back one modem trace with AT+NCELLMEAS experiments. By the way,10 to 60 seconds of searching time sounds like a normal result.

Best regards,

Charlie

RE: nRF9160 NB-IoT Cell Selection

Charlie — Tue, 14 Dec 2021 13:23:54 GMT

Hi Macro and Matthias,

Sorry for the late reply. My colleague has a sick leave and I will provide you with a reply soon.

Best regards,

Charlie

RE: nRF9160 NB-IoT Cell Selection

Chraebs — Fri, 03 Dec 2021 13:38:59 GMT

helsing did you get some information about this. It is an interesting topic.

RE: nRF9160 NB-IoT Cell Selection

helsing — Mon, 25 Oct 2021 12:17:24 GMT

Hi Marco,

Thank you for your questions. I will check with the team an get back to you later this week.

Best regards,

Håkon