nRF9160 modem: AT+COPS=? does not work with SIM inserted

[Bjorn191023]

When I run "AT+COPS=?" WITHOUT a SIM the modem always responds properly.

When I run "AT+COPS=?" WITH a SIM the modem does not respond as expected. I get error after approx a minute. I lock to one band to narrow down the scan. I use the following procedure:

1) Cold start the modem

2) AT%XBANDLOCK=2,"10000000000000000000" (lock to band 20)

3) AT+CFUN=1 (enter normal mode)

4) AT+COPS=? => ERROR after a minute

If I repeat step 4 the modem often starts responding after three attempts. If I change operator manually it also starts responding. The conclusion is that the command is instable!

I use the following software versions:

Modem: mfw_nrf9160_1.0.1

Firmware in app MCU: thingy91_at_client_v0.2.3

LTE Link Monitor: v1.1.1

Tested on Thingy91

[Håkon Alseth]

Hi,

 

The AT+COPS=? command will take several minutes, especially on NB1, to return with the carriers in your area.

Even if the LTE Link Monitor times out, the command is executed and you'll have to wait for 2-to-10 minutes (depending on M1 or NB1), before it returns with the discovered list.

Could you try submitting the command only once, and wait for ~10 minutes to see if you get a response?

 

Kind regards,

Håkon

[Bjorn191023]

Hi Håkon,

Thanks for your prompt response. 

Yes, I have noticed that LTE Link Monitor times out very fast and that the command continues. It is not that timeout I am refering to. I get an actual "ERROR" response from the modem after ~ 1 minute.

We have narrowed scan to one band (20) to reduce the scan time. Without a SIM it takes around 5 seconds to get a proper response. 

We are using LTE-M mode.

So I have already tested what you request.

[Håkon Alseth]

Hi,

 

I was able to successfully discover on both M1:

AT+COPS=?
+COPS: (2,"","","24201",7)
OK

And NB1:

AT+COPS=?
+COPS: (1,"","","24201",9),(3,"","","24202",9)
OK

 

I also locked the band to 20, and repeated with and without SIM card, and got the same responses.

I was able to get the "ERROR" response once (which can come if there's network disruptions), and running COPS=? again provided a list. You can try waiting till the link is up, and see if this has an impact. Is this behavior consistent on your side? ie: do you always get "ERROR" back?

[Bjorn191023]

Hi,

Yes, it is consistent after cold start. The cold start (restart) of Thingy91 is important, otherwise the modem state is retained. 

As I stated I can get it to work with SIM after a number of attempts (often three attempts) without cold start in between. Also selecting another operator manually (e.g. Tele2 instead of Telia) makes the command work. When it starts working it continues to work.

[Håkon Alseth]

Its likely interrupted because you are, mid-process of COPS=?, attaching to your network, which will give an incomplete list back, as per the documentation:

https://infocenter.nordicsemi.com/topic/ref_at_commands/REF/at_commands/nw_service/cops_test.html?cp=2_1_6_0_2

As mentioned, I also got an error once while continuously resetting in between tests.

[Bjorn191023]

Hi Håkon,

Thanks for your response.

How can I find out when the network attachment is done and it is safe to scan for operators without being interrupted? The required state is not clear from the documentation.

Another question: the link you sent states the following: "The command fails if the device has an active radio connection. It returns ERROR or +CME ERROR: 516"

What is meant by "an active radio connection"? 

BR / Björn

[Håkon Alseth]

Hi Björn,

 

Bjorn191023 said:

What is meant by "an active radio connection"? 

 If you start the search, then get an ATTACH to the network mid-COPS=?, that would be an active radio connection, or the application starts connecting to a mqtt broker for instance (ie: high throughput on IP). If you wait until the connection is attached (watch AT+CEREG? to see status, if application is connecting to a server, wait until that if finished as well), then issue COPS=?, you should be able to successfully discover other networks.

 

Kind regards,

Håkon

[Bjorn191023]

Thanks a lot Håkon, I will try to implement something like this

BR / Björn