nRF9160 not connecting to LTE-M network

[AlinP]

Hi,

Last week we received Nordic's Thingy:91 development kit and prototyping platform for nRF9160.

The kit also included 1x iBasis SIM card. According to iBasis, LTE-M is the local cellular standard in Bucharest, Romania.

We've went trough registering the device on the nrfcloud and failed with the following error:

---

There was an error adding your device: No device found with id 'nrf-352656100830366'. Verify you are passing a valid device id and not a device name. Also ensure that your device is powered on and its LED(s) indicate that it is connected to nRFCloud. If the LED(s) do not indicate a connection, there may be a problem with your device certificate. In that case, search Nordic DevZone for "certificate update" for a possible solution.

---

So, we've then went troguht the certificate update process described over here. Since LTE-M cellular connectivity is not available with the pre-compiled thingy91_at_client and, since that is the only up-to-date binary file that supports long AT commands (3kB or higher), we had no choice but to go trough the hassle of installing all the necessary (God knows how many) tools for compiling our own binaries from the up-to-date releases.

As described in the Thingy:91 Firmware Update using MCUboot tutorial we've pre-compiled the v1.1.0 nRF Connect SDK with the following 2 modifications made to the source code:

1.  the CONFIG_AT_CMD_RESPONSE_MAX_LEN was modified from a default value of 2700 to a value of 3074
2.  the AT_HOST_STACK_SIZE was modified from a value of 512 to a value of 1024. This was done because the modem (Zephyr RTOS) was crashing with a stack overflow error with only the first modification made (CONFIG_AT_CMD_RESPONSE_MAX_LEN set to 3074)

From the obtained build directory, we've uploaded the app_update.bin via mcumgr app and then succesfully updated the certificates via LTE Link Monitor.

After all this steps, the board still refuses to connect to the LTE-M network. I'll attach some of the terminal monitor printscreens bellow.

Any help regarding the issue would be greatly appreciated!

[AlinP]

Øyvind said:

Yes, this is correct, however with limited coverage. I would ask iBasis what limited coverage means. 

 We sent a request to iBasis having them confirming the LTE-M coverage at our location, in Bucharest.

Øyvind said:

There is currently a bug in nRF Cloud that we are working with. Your issue seems to be related to this issue. I will forward your IMEI information

That's good to know, but still, the modem should be able to connect and register with the LTE-M network, independent of the nrf cloud bug.

Øyvind said:

LTE-M or NB-IoT is irrelevant for the AT Client. You can configure both using AT client and the %XSYSTEMMODE command. Make sure to issue AT+CFUN=4 first, to turn off modem.

That's really great news! We've now flashed the thingy91_at_client_v0.2.3.bin (as it is a good, thrust-worthy binary compared to the one we've obtained via compiling the v1.1.0 SDK with the 2 mentioned modifications) via mcumgr.

1. We've went trough succesfully uploading the new certificates. 
2. We've put the modem in offline mode (AT+CFUN=4)
3. We've then enabled the modem with LTE-M network active (AT%XSYSTEMMODE=1,0,1,0)

The modem still does not connect to the network 

 

Øyvind said:

Can you please provide full output from the LTE Link Monitor? Please issue the command AT%XMONITOR (as the example in the bottom of page) as well.

 Sure, here's the output:

AT+CFUN?
+CFUN: 1
OK
AT+CGSN=1
+CGSN: "352656100830366"
OK
AT+CGMI
Nordic Semiconductor ASA
OK
AT+CGMM
nRF9160-SICA
OK
AT+CGMR
mfw_nrf9160_1.0.1
OK
AT+CEMODE?
+CEMODE: 2
OK
AT%XCBAND=?
%XCBAND: (1,2,3,4,5,8,12,13,14,17,18,19,20,25,26,28,66)
OKAT+CMEE?
+CMEE: 1
OK
AT+CNEC?
+CNEC: 24
OK
AT+CGEREP?
+CGEREP: 1,0
OK
AT+CIND=1,1,1
OK
AT+CEREG=2
OK
AT+CEREG?
+CEREG: 2,4,"FFFE","FFFFFFFF",7
OK
AT%CESQ=1
OK
AT+CESQ
+CESQ: 99,99,255,255,255,255
OK
AT%XSIM=1
OK
AT%XSIM?
%XSIM: 1
OKAT+CPIN?
+CPIN: READY
OK
AT+CPINR="SIM PIN"
+CPINR: "SIM PIN",3
OK
AT+CIMI
204080813516240
OK
AT+CESQ
+CESQ: 99,99,255,255,255,255
OK

AT%XMONITOR
%XMONITOR: 2
OK

Later edit: Something that concerns me is that the AT+CPIN? command returns the following:

AT+CPINR="SIM PIN"
+CPINR: "SIM PIN",3

However, the GUI of the LTE Link Monitor cleary says in the top right info panel: Pin: no PIN required

Trying to set the PIN number via AT+CPIN="0000" results in ERROR being displayed. Could you please offer a clarification regarding this?