nRF9160 stuck in CEREG reject cause 15

[MJD093]

Hi,

I have an issue with the nRF9160 getting stuck in CEREG response 4 (Unknown). When I look into the full CEREG status, I can see that the EMM reject cause is 15 (Cause #15 – No suitable cells in tracking area). This will continue forever as the device seems to have no method of finding a different cell to connect to.

I know that there are cells in my area that I can in fact connect to as a power on reset will find a connectable network in under 30 seconds with a CESQ RSRP of around 20-26. I would like to know is there a method of purging the known cell tower from the modem so that it will not attempt to reconnect with the tower that is sending the rejection? My application swaps between LTE and GPS so the modem characteristics (CFUN, XSYSTEMMODE, MAGPIO, CGDCONT) are being reset between each swap but the previously connected cell is what the device locks onto once LTE is active again.

[2020-02-24 16:59:26] Socket status: 5:11, No more processes
[2020-02-24 16:59:26] Sending AT command: AT+CEREG?
[2020-02-24 16:59:26] Modem response: +CEREG: 1,4
[2020-02-24 16:59:26] OK
[2020-02-24 16:59:26] 
[2020-02-24 16:59:26] Socket status: 18:11, No more processes
[2020-02-24 16:59:26] Failed to receive "+CEREG: 1,5" from modem
[2020-02-24 16:59:26] Requesting Advanced CEREG
[2020-02-24 16:59:26] Radio Scheduler had error with task: 3:-3
[2020-02-24 16:59:27] Sending AT command: AT+CEREG=5
[2020-02-24 16:59:27] Modem response: OK
[2020-02-24 16:59:27] 
[2020-02-24 16:59:27] Socket status: 5:11, No more processes
[2020-02-24 16:59:27] Sending AT command: AT+CEREG?
[2020-02-24 16:59:27] Modem response: +CEREG: 5,4,"A45D","07CBF70B",9,0,15,"11100000","11100000"
[2020-02-24 16:59:27] OK
[2020-02-24 16:59:27] 
[2020-02-24 16:59:27] Socket status: 65:11, No more processes
[2020-02-24 16:59:36] Sending AT command: AT+CEREG=1
[2020-02-24 16:59:36] Modem response: OK
[2020-02-24 16:59:36] 
[2020-02-24 16:59:36] Socket status: 5:11, No more processes
[2020-02-24 16:59:36] Sending AT command: AT+CEREG?
[2020-02-24 16:59:36] Modem response: +CEREG: 1,4
[2020-02-24 16:59:36] OK
[2020-02-24 16:59:36] 
[2020-02-24 16:59:36] Socket status: 18:11, No more processes
[2020-02-24 16:59:36] Failed to receive "+CEREG: 1,5" from modem
[2020-02-24 16:59:36] Requesting Advanced CEREG
[2020-02-24 16:59:36] Radio Scheduler had error with task: 3:-3
[2020-02-24 16:59:37] Sending AT command: AT+CEREG=5
[2020-02-24 16:59:37] Modem response: OK
[2020-02-24 16:59:37] 
[2020-02-24 16:59:37] Socket status: 5:11, No more processes
[2020-02-24 16:59:37] Sending AT command: AT+CEREG?
[2020-02-24 16:59:37] Modem response: +CEREG: 5,4,"A45D","07CBF70B",9,0,15,"11100000","11100000"
[2020-02-24 16:59:37] OK
[2020-02-24 16:59:37] 
[2020-02-24 16:59:37] Socket status: 65:11, No more processes
[2020-02-24 16:59:44] Sending AT command: AT%XVBAT
[2020-02-24 16:59:44] Modem response: %XVBAT: 4395
[2020-02-24 16:59:44] OK
[2020-02-24 16:59:44] 
[2020-02-24 16:59:44] Socket status: 19:11, No more processes
[2020-02-24 16:59:44] iVBatt: 4395
[2020-02-24 16:59:46] Sending AT command: AT+CEREG=1
[2020-02-24 16:59:46] Modem response: OK
[2020-02-24 16:59:46] 
[2020-02-24 16:59:46] Socket status: 5:11, No more processes
[2020-02-24 16:59:46] Sending AT command: AT+CEREG?
[2020-02-24 16:59:46] Modem response: +CEREG: 1,4
[2020-02-24 16:59:46] OK
[2020-02-24 16:59:46] 
[2020-02-24 16:59:46] Socket status: 18:11, No more processes
[2020-02-24 16:59:46] Failed to receive "+CEREG: 1,5" from modem
[2020-02-24 16:59:46] Requesting Advanced CEREG
[2020-02-24 16:59:46] Radio Scheduler had error with task: 3:-3
[2020-02-24 16:59:47] Sending AT command: AT+CEREG=5
[2020-02-24 16:59:47] Modem response: OK
[2020-02-24 16:59:47] 
[2020-02-24 16:59:47] Socket status: 5:11, No more processes
[2020-02-24 16:59:47] Sending AT command: AT+CEREG?
[2020-02-24 16:59:47] Modem response: +CEREG: 5,4,"A45D","07CBF70B",9,0,15,"11100000","11100000"
[2020-02-24 16:59:47] OK
[2020-02-24 16:59:47] 
[2020-02-24 16:59:47] Socket status: 65:11, No more processes
[2020-02-24 16:59:56] Sending AT command: AT+CEREG=1
[2020-02-24 16:59:56] Modem response: OK
[2020-02-24 16:59:56] 
[2020-02-24 16:59:56] Socket status: 5:11, No more processes
[2020-02-24 16:59:56] Sending AT command: AT+CEREG?
[2020-02-24 16:59:56] Modem response: +CEREG: 1,4
[2020-02-24 16:59:56] OK
[2020-02-24 16:59:56] 
[2020-02-24 16:59:56] Socket status: 18:11, No more processes
[2020-02-24 16:59:56] Failed to receive "+CEREG: 1,5" from modem
[2020-02-24 16:59:56] Requesting Advanced CEREG
[2020-02-24 16:59:56] Radio Scheduler had error with task: 3:-3
[2020-02-24 16:59:57] Sending AT command: AT+CEREG=5
[2020-02-24 16:59:57] Modem response: OK
[2020-02-24 16:59:57] 
[2020-02-24 16:59:57] Socket status: 5:11, No more processes
[2020-02-24 16:59:57] Sending AT command: AT+CEREG?
[2020-02-24 16:59:57] Modem response: +CEREG: 5,4,"A45D","07CBF70B",9,0,15,"11100000","11100000"
[2020-02-24 16:59:57] OK
[2020-02-24 16:59:57] 
[2020-02-24 16:59:57] Socket status: 65:11, No more processes
[2020-02-24 17:00:01] Reset variables
[2020-02-24 17:00:01] Changing uControl_Word state
[2020-02-24 17:00:01] IDLE state
[2020-02-24 17:00:01] Event NBIOT_COMPLETE Triggered!
[2020-02-24 17:00:01] Changing uControl_Word state
[2020-02-24 17:00:01] GPS state
[2020-02-24 17:00:01] Sending AT command: AT+CFUN=4
[2020-02-24 17:00:01] Modem response: OK
[2020-02-24 17:00:01] 
[2020-02-24 17:00:01] Socket status: 5:11, No more processes
[2020-02-24 17:00:01] Sending AT command: AT%XSYSTEMMODE=0,0,1,0
[2020-02-24 17:00:01] Modem response: OK
[2020-02-24 17:00:01] 
[2020-02-24 17:00:01] Socket status: 5:11, No more processes
[2020-02-24 17:00:01] Sending AT command: AT%XMAGPIO=1,1,1,1,7,1574,1577
[2020-02-24 17:00:01] Modem response: OK
[2020-02-24 17:00:01] 
[2020-02-24 17:00:01] Socket status: 5:11, No more processes
[2020-02-24 17:00:01] Sending AT command: AT+CFUN=1
[2020-02-24 17:00:01] Modem response: OK
[2020-02-24 17:00:01] 
[2020-02-24 17:00:01] Socket status: 5:11, No more processes
[2020-02-24 17:00:01] Socket created
[2020-02-24 17:00:01] Socket ID 1232491587
[2020-02-24 17:00:01] Fix retry err: 0:11 No more processes
[2020-02-24 17:00:01] Fix interval err: 0:11 No more processes
[2020-02-24 17:00:01] nmea mask err: 0:11 No more processes
[2020-02-24 17:00:01] GPS start err: 0:11 No more processes
[2020-02-24 17:00:01] Changing uControl_Word state
[2020-02-24 17:00:01] GPS state
[2020-02-24 17:00:01] Tracking: 2 Using: 0 Unhealthy: 0
[2020-02-24 17:00:01] Scanning [|]
[2020-02-24 17:00:01] Seconds Since GPS Search Start 0
[2020-02-24 17:00:01] 
[2020-02-24 17:00:02] Tracking: 0 Using: 0 Unhealthy: 0
[2020-02-24 17:00:02] Scanning [/]
[2020-02-24 17:00:02] Seconds Since GPS Search Start 1
[2020-02-24 17:00:02] 
[2020-02-24 17:00:03] Tracking: 0 Using: 0 Unhealthy: 0
[2020-02-24 17:00:03] Scanning [-]
[2020-02-24 17:00:03] Seconds Since GPS Search Start 2
[2020-02-24 17:00:03] 

...................

[2020-02-24 17:01:53] 
[2020-02-24 17:01:54] Tracking: 0 Using: 0 Unhealthy: 0
[2020-02-24 17:01:54] Scanning [|]
[2020-02-24 17:01:54] Seconds Since GPS Search Start 112
[2020-02-24 17:01:54] 
[2020-02-24 17:01:55] Tracking: 0 Using: 0 Unhealthy: 0
[2020-02-24 17:01:55] Scanning [/]
[2020-02-24 17:01:55] Seconds Since GPS Search Start 113
[2020-02-24 17:01:55] 
[2020-02-24 17:01:56] Interrupt tripped!
[2020-02-24 17:01:56] Tracking: 0 Using: 0 Unhealthy: 0
[2020-02-24 17:01:56] Scanning [-]
[2020-02-24 17:01:56] Reading Status Register
[2020-02-24 17:01:56] SPI Interrupt: 0x21
[2020-02-24 17:01:56] Deactivate
[2020-02-24 17:01:56] Disabling UART
[2020-02-24 17:01:56] Disabling SPI
[2020-02-24 17:01:56] Seconds Since GPS Search Start 114
[2020-02-24 17:01:56] 
[2020-02-24 17:01:57] Event DEACTIVATE Triggered!
[2020-02-24 17:01:57] Changing uControl_Word state
[2020-02-24 17:01:57] PRESLEEP state
[2020-02-24 17:01:57] Halting GPS Scan, INT1 shutdown
[2020-02-24 17:01:57] Shutting down GPS
[2020-02-24 17:01:57] Enabling Sleep mode, switching to NB-IoT
[2020-02-24 17:01:57] Sending AT command: AT+CFUN=4
[2020-02-24 17:01:57] Modem response: OK
[2020-02-24 17:01:57] 
[2020-02-24 17:01:57] Socket status: 5:11, No more processes
[2020-02-24 17:01:57] Sending AT command: AT%XSYSTEMMODE=0,1,0,0
[2020-02-24 17:01:57] Modem response: OK
[2020-02-24 17:01:57] 
[2020-02-24 17:01:57] Socket status: 5:11, No more processes
[2020-02-24 17:01:57] Sending AT command: AT%XMAGPIO=1,1,1,1,5,791,849
[2020-02-24 17:01:57] Modem response: OK
[2020-02-24 17:01:57] 
[2020-02-24 17:01:57] Socket status: 5:11, No more processes
[2020-02-24 17:01:57] Sending AT command: AT+CGDCONT=0,"IP","ep.inetd.gdsp"
[2020-02-24 17:01:58] Modem response: OK
[2020-02-24 17:01:58] 
[2020-02-24 17:01:58] Socket status: 5:11, No more processes
[2020-02-24 17:01:58] Sending AT command: AT+CFUN=1
[2020-02-24 17:01:58] Modem response: OK
[2020-02-24 17:01:58] 
[2020-02-24 17:01:58] Socket status: 5:11, No more processes
[2020-02-24 17:01:58] Enabling Sleep mode
[2020-02-24 17:01:58] Changing uControl_Word state
[2020-02-24 17:01:58] IDLE state
[2020-02-24 17:01:59] Sending AT command: AT+CEREG=1
[2020-02-24 17:01:59] Modem response: OK
[2020-02-24 17:01:59] 
[2020-02-24 17:01:59] Socket status: 5:11, No more processes
[2020-02-24 17:01:59] Sending AT command: AT+CEREG?
[2020-02-24 17:01:59] Modem response: +CEREG: 1,4
[2020-02-24 17:01:59] OK
[2020-02-24 17:01:59] 
[2020-02-24 17:01:59] Socket status: 18:11, No more processes
[2020-02-24 17:01:59] Failed to receive "+CEREG: 1,5" from modem
[2020-02-24 17:01:59] Requesting Advanced CEREG
[2020-02-24 17:01:59] Radio Scheduler had error with task: 3:-3
[2020-02-24 17:01:59] Sending AT command: AT+CEREG=5
[2020-02-24 17:01:59] Modem response: OK
[2020-02-24 17:01:59] 
[2020-02-24 17:01:59] Socket status: 5:11, No more processes
[2020-02-24 17:01:59] Sending AT command: AT+CEREG?
[2020-02-24 17:01:59] Modem response: +CEREG: 5,4,"A45D","07CBF70B",9,0,15,"11100000","11100000"
[2020-02-24 17:01:59] OK
[2020-02-24 17:01:59] 
[2020-02-24 17:01:59] Socket status: 65:11, No more processes
[2020-02-24 17:02:09] Sending AT command: AT+CEREG=1
[2020-02-24 17:02:09] Modem response: OK
[2020-02-24 17:02:09] 
[2020-02-24 17:02:09] Socket status: 5:11, No more processes
[2020-02-24 17:02:09] Sending AT command: AT+CEREG?
[2020-02-24 17:02:09] Modem response: +CEREG: 1,4
[2020-02-24 17:02:09] OK
[2020-02-24 17:02:09] 
[2020-02-24 17:02:09] Socket status: 18:11, No more processes
[2020-02-24 17:02:09] Failed to receive "+CEREG: 1,5" from modem
[2020-02-24 17:02:09] Requesting Advanced CEREG
[2020-02-24 17:02:09] Radio Scheduler had error with task: 3:-3
[2020-02-24 17:02:09] Sending AT command: AT+CEREG=5
[2020-02-24 17:02:09] Modem response: OK
[2020-02-24 17:02:09] 
[2020-02-24 17:02:09] Socket status: 5:11, No more processes
[2020-02-24 17:02:09] Sending AT command: AT+CEREG?
[2020-02-24 17:02:09] Modem response: +CEREG: 5,4,"A45D","07CBF70B",9,0,15,"11100000","11100000"
[2020-02-24 17:02:09] OK
[2020-02-24 17:02:09] 
[2020-02-24 17:02:09] Socket status: 65:11, No more processes
[2020-02-24 17:02:19] Sending AT command: AT+CEREG=1
[2020-02-24 17:02:19] Modem response: OK
[2020-02-24 17:02:19] 
[2020-02-24 17:02:19] Socket status: 5:11, No more processes
[2020-02-24 17:02:19] Sending AT command: AT+CEREG?
[2020-02-24 17:02:19] Modem response: +CEREG: 1,4
[2020-02-24 17:02:19] OK
[2020-02-24 17:02:19] 
[2020-02-24 17:02:19] Socket status: 18:11, No more processes
[2020-02-24 17:02:19] Failed to receive "+CEREG: 1,5" from modem
[2020-02-24 17:02:19] Requesting Advanced CEREG
[2020-02-24 17:02:19] Radio Scheduler had error with task: 3:-3
[2020-02-24 17:02:19] Sending AT command: AT+CEREG=5
[2020-02-24 17:02:19] Modem response: OK
[2020-02-24 17:02:19] 
[2020-02-24 17:02:19] Socket status: 5:11, No more processes
[2020-02-24 17:02:19] Sending AT command: AT+CEREG?
[2020-02-24 17:02:19] Modem response: +CEREG: 5,4,"A45D","07CBF70B",9,0,15,"11100000","11100000"
[2020-02-24 17:02:19] OK
[2020-02-24 17:02:19] 

[Martin Lesund]

HI mjd093,

Which modem firmware version are you running?
It would be interesting to get the results from %NBRGRSRP command also the CESQ info from the eNB.

Could you try to set the AT+COPS command to select the network and xbandlock to restrict the modem to connect to the wanted network?

[MJD093]

Hi Martin Lesund

I am using mfw v1.1.0 as I have a few deployed devices that I can update the application but not the modem firmware one. I can't update my mfw until I get those devices back as to ensure any fixes I make are compatible.

I had been meaning to add bandlock to my application, so I added that shortly after making this question and haven't seen it go to 1,4 recently. It sometimes gets stuck for a while in 1,2 but that would explain why 1,4 is difficult to clear if the network is hard to acquire at times.

I have added a bit of debug code for the 1,4 return case, utilising CEREG lvl 5 and XMONITOR, I will add the neighbouring cell command as well to this.

I'm hesistant to use COPS to directly select a network as my devices could be connected to different networks (have been used in 3 different regions so far) as I don't know if that would be a one-command-fits-all on the Vodafone networks.

I will monitor this for a few days and respond here. If I don't see it anymore then the XBANDLOCK command has done the trick.

[Martin Lesund]

Awesome, keep me updated if the issue appears again.

[MJD093]

Hi Martin Lesund

The issue has popped up again and I have some additional AT information.

Socket status: 15:11, No more processes
Sending AT command: AT+CEREG=1
Modem response: OK

Socket status: 5:11, No more processes
Sending AT command: AT+CEREG?
Modem response: +CEREG: 1,4
OK

Socket status: 18:11, No more processes
Failed to receive "+CEREG: 1,5" from modem
*Debug* Requesting Advanced CEREG
Radio Scheduler had error with task: 3:-3
Sending AT command: AT%XMONITOR
Modem response: %XMONITOR: 4
OK

Socket status: 19:11, No more processes
Sending AT command: AT%NBRGRSRP
Modem response: %NBRGRSRP: 14,6254,33,276,6254,31,209,6254,30,393,6254,25,207,63
OK

Socket status: 88:11, No more processes
Sending AT command: AT+CEREG=5
Modem response: OK

Socket status: 5:11, No more processes
Sending AT command: AT+CEREG?
Modem response: +CEREG: 5,4,"A45D","07CBF70B",9,0,15,"11100000","11100000"
OK

Socket status: 65:11, No more processes
Sending AT command: AT+CGDCONT?
Modem response: +CGDCONT: 0,"IP","ep.inetd.gdsp","",0,0
OK

Socket status: 46:11, No more processes
Sending AT command: AT+CGACT?
Modem response: +CGACT: 0,0
OK

Socket status: 18:11, No more processes
Sending AT command: AT+COPS=3,2
Modem response: OK

Socket status: 5:11, No more processes
Sending AT command: AT+COPS?
Modem response: +COPS: 0
OK

EDIT:
I took this same device for a drive as well later in the day. Hours after this log was taken, the device showed visual signs of being unable to reach the network until I had travelled around 5-6 miles. Note, the entire area is within NB-IoT coverage and as mentioned previously, a device reset can yield a very fast network connection even if 5,4 was detected before the reboot.

[Martin Lesund]

Hi mjd093,
Sorry for the delay.

I cannot confirm this without a modem trace, but I think this could be that you are actually traveling in some areas that actually have bad NB-IoT coverage, OR (most likely not) that you have enabled some bandlocks that prevents the modem from finding the bands of the subscribed network cells.

What you could do is to run at+cops=? (manual PLMN search) in that area to see what NB-IoT networks are available. (I guess the result is that there are only "visitor PLMNs" i.e. all except the subscribed network)

You could try to perform the same test with modem trace enabled so we could look at the logs to analyze further what is happening. 

Note: The bandlock can potentially make things worse. Based on experiences testing in Finland we have found that in urban areas cells are mostly on band 3 whereas in rural areas band 20 is used more (fewer clients, lower frequency = bigger cells).

Now if you have locked for example only "band 3", the service on "carrier A" may be obtained very fast in the urban area, but it is completely lost when the device moves out of the city -> the modem may find a cell of "carrier B" in the rural area, determines that "this is really the only available cell, we will need to try this" -> attempt that leads to #15 reject "no suitable cells in tracking area".

Best regards,
Martin L.