nrf9160 unable to connect when all bands are enabled.

[Umer Mahmood]

nrf9160 fails to form a connection when all bands are enabled, and the available band is higher up in the list. Following was the exact test scenerio:

Connection attempt:

Modem Firmware Version: 1.3.0

Config: AT%%XSYSTEMMODE=1,1,0,1 #ltm and nbiot enabled, gnss disabled, ltm prefered.

LTM is available at : Band 12 (Here nrf91 fails to form a connection, CEREG response: +CEREG 4)

Previous Successful Connection:

Was connected to LTM at Band 8, until band 8 was not available anymore.

Other observations:

Interesting is if I now apply a band lock, with only following bands enabled, nrf91 is able to form a connection successfully:

enabled bands: 8,12,13,18,19,20,25,26,28

After a restart now, nrf91 is able to form a connection on bands 12,13,18,19,20 but will fail again to connect to band 25 until I change the band lock to enable following bands:

enabled bands: 20,25,26,28,66

Is it required to always have a band lock? Does modem always start searching for available network starting from the first enabled band and going up? Is there a configurable timeout or something which could be disrupting the connection attempt?

[Håkon Alseth]

Hi,

 

Could you share a log from the LTE Link Monitor showing the behavior?

Issue:

at+cereg=5
at+cfun=1
at+cfun?

When using the LTE LM, it will automatically enable other AT commands, such as ESM/EMM return codes.

 

Kind regards,

Håkon

[Umer Mahmood]

Hello,
The situation mention above was observed during percertification testing in the lab. I have tried to some what simulate the same situation as follows:
At the location where I am testing, bands 3 and 20 are available.

1. I only enabled band 3
2. Enabled nbiot and ltm with ltm prefered: AT%XSYSTEMMODE=1,1,0,1
3. Enable using CFUN=1
4. I see that I get a positive CEREG
5. I disbable using CFUN=0
6. Now enable all bands except band 3. (I expect the device to go through bands and connect to band 20)
7. Enable again using CFUN=1
8. Again I get positive CEREG 

This works. But clearly it is slightly different from the pre certification testing in the lab. Where all bands are enabled, and CFUN=0 is never done after CFUN=1. Following was the setup in the lab:

1. Enable all bands
2. Enabled nbiot and ltm with ltm prefered: AT%XSYSTEMMODE=1,1,0,1
3. Enable using CFUN=1
4. Enable ltm base station with bands 1
5. Wait and Observe for 3 to 5 minutes
6. Turn off base station with band  1
7. Wait for negative CEREG response
8. Enable ltm base station with band 2
9. And so on ...
10. After band 12 modem seems to respond continuously with +CEREG: 4

[Håkon Alseth]

Hi,

 

Umer Mahmood said:

This works. But clearly it is slightly different from the pre certification testing in the lab. Where all bands are enabled, and CFUN=0 is never done after CFUN=1. Following was the setup in the lab:

The modem will, based on historical data, try to connect to the formerly connected tower (if available), and when you're changing the band this tester is operating on, it will cause the nRF9160 to use longer time to connect.

A log from LTE Link Monitor showing the behavior would be good. If there is some mismatch in the configuration or similar, this should be highlighted by checking the EMM/ESM cause code.

  

Please note that it is expected that it can take up to several minutes to search all bands, especially when you have Cat M and NB1 enabled on the nRF side.

 

Kind regards,

Håkon

[Umer Mahmood]

This makes sense. What I understand from your feedback that historical data is considered:

• If we test modem on band 1
• Then make band 1 unavailable in the test envoirnment and instead make band 2 available
• Modem will first try to find band 1 and afterwards will try to look at band 2
• .....
• .....
• Moving on, after testing connection to band 8.
• When we try to test band 12.
• The modem must be trying to first look for 1,2,3,4,5,8 since it was able to connect to them previously, and finally it should start looking for band 12. After a long time, but eventually it should be able to connect to band 12.

This does make sense, but  if this was the case, shouldn't modem have only responded with CEREG 2 (connection in progress/searching) until it finally is able to connect? (maybe we didn't wait long enough.). But from the limited logs I have modem only responded with CEREG 4 (unknown). 

What I also want to know, is there anyway to reset this historical data for testing purpose? There is a factory reset command (AT%XFACTORYRESET=0), does this reset the historical data?

I will try to get those logs in the next testing session.

[Håkon Alseth]

Hi,

 

Are you resetting the nRF9160 between each test? If so, you can get into this reset loop restriction:

https://infocenter.nordicsemi.com/topic/nwp_042/WP/nwp_042/intro.html?cp=2_0_6_0

  

Umer Mahmood said:

There is a factory reset command (AT%XFACTORYRESET=0), does this reset the historical data?

This will place the nRF9160 into a factory mode, clearing such data.

Umer Mahmood said:

I will try to get those logs in the next testing session.

This would be very helpful, especially with these AT commands enabled (AT+CMEE=1 + AT+CNEC=24):

https://infocenter.nordicsemi.com/topic/ref_at_commands/REF/at_commands/mobile_termination_errors/mob_termination_errors.html?cp=2_1_8

 

Kind regards,

Håkon