NRF9160 Modem Band Scan

[Thomas]

Hi,

Is there any way to tell when the modem has finished doing a band scan? I would like to know so I can swap between CAT-M1 and NB-IoT for globally deployed devices. 

Kind regards,

Thomas

[Hakon]

Hello,

you can use the +CEREG command to check the connection status. <stat> should be 0 if it is not searching, 2 if it is searching, and 1 or 5 if it is registered.

[Thomas]

Hi Hakon,

From what I see it just stays in mode 2, and does not transition to mode 0?

[Hakon]

It can usually take several minutes to get an LTE connection. You can reduce the time it takes by applying bandlock if you know which band to use. What operator/SIM are you using?

[Thomas]

Hi Hakon,

Sorry for the misunderstanding. We sell our products globally so we don’t know whether an end user will be requiring NB-IoT or CAT-M1 so we need to switch between the two if the device is not registering. So I was hoping to find a way to determine when the modem has finished doing a band scan on one technology so I can swap to the other. But it seems CEREG does not transition from mode 2 to mode 0 if a scan fails?

[Hakon]

Thomas said:

But it seems CEREG does not transition from mode 2 to mode 0 if a scan fails?

 What do you mean by "if a scan fails"? As far as I know the modem will keep searching until it finds a network. How do you know it is failing?

[Thomas]

Hi Hakon,

I am watching it on a power analyser. I can see it attempt scans on an exponential back off schedule dependant on XDATAPRFL. For example in ultra low power mode it attempts a scan, then retries in 20 seconds, 20 seconds, 40 seconds, 40 seconds, 5 minutes then retries every half an hour.

[Hakon]

If you have LTE_LINK_CONTROL=y enabled you can use LTE_NETWORK_USE_FALLBACK=y to change from CAT-M1 to NB-IoT after LTE_NETWORK_TIMEOUT seconds. If you know the time it usually takes to find a network then you can use that as a timeout.

[Thomas]

I am already doing something similar, is there no smarter/power efficient way to do it? Modems we have used in the past automatically switch between the two.

[Hakon]

I don't know, but I doubt it. I will ask R&D and see if they know something about this.

[Hakon]

They confirmed there is no other way than using +CEREG notification.