Questions about signal quality polling in nRF9160

[Fredrik]

Hi,

I am mapping NB-IoT and LTE-M1 indoors coverage using the nRF9160, mostly just to familiarize myself with the nRF91 DK. I have a basic application which toggles between NB and M1 mode and records the RSRP for each of them, and I have a few questions about the CEREG and CESQ commands.

Below is the log output when connecting to NB-IoT and polling CEREG and CESQ every 10 seconds. In the log, '--->' denotes commands sent to the modem, and '<---' denotes the modem response.

[00:00:01.866,394] ---> AT+CFUN=4
[00:00:01.887,420] ---> AT%XSYSTEMMODE=0,1,0,0
[00:00:01.911,285] ---> AT+CFUN=1

[00:00:01.962,219] ---> AT+CESQ
[00:00:01.976,470] <--- +CESQ: 99,99,255,255,255,255
[00:00:01.985,198] ---> AT+CEREG?
[00:00:01.999,664] <--- +CEREG: 0,4,"FFFE","FFFFFFFF",9

[00:00:12.015,777] ---> AT+CESQ
[00:00:12.030,120] <--- +CESQ: 99,99,255,255,255,255
[00:00:12.038,879] ---> AT+CEREG?
[00:00:12.053,253] <--- +CEREG: 0,4,"FFFE","FFFFFFFF",9

// some time passes

[00:01:02.250,152] ---> AT+CESQ
[00:01:02.264,495] <--- +CESQ: 99,99,255,255,255,255
[00:01:02.273,223] ---> AT+CEREG?
[00:01:02.287,628] <--- +CEREG: 0,4,"FFFE","FFFFFFFF",9

[00:01:12.297,027] ---> AT+CESQ
[00:01:12.311,370] <--- +CESQ: 99,99,255,255,19,46
[00:01:12.319,915] ---> AT+CEREG?
[00:01:12.334,320] <--- +CEREG: 0,2,"9FC5","0103A167",9

[00:01:22.343,902] ---> AT+CESQ
[00:01:22.364,318] <--- +CESQ: 99,99,255,255,19,46
[00:01:22.372,802] ---> AT+CEREG?
[00:01:22.393,463] <--- +CEREG: 0,2,"9FC5","0103A167",9

Initially, the modem status reported by the CEREG command is 4 (unknown), and then it flips to 2 (not registered, searching). At the same time I receive valid RSRP values from the CESQ command. The modem status never changes after this. Is this expected? Can I have valid RSRP, <tac> and <ci> on NB-IoT without having modem status equal to 1 or 5? Repeating the same procedure for LTE-M1 always gives initial modem status 4, then 5.

I'm on nRF Connect SDK v1.0.0, modem FW mfw_nrf9160_1.1.0. The SIM card is an iBasis SIM which was provided with the nRF9160 DK.

[Fredrik]

Hi,

I tried with a Telenor SIM, and I got the exact same results: valid RSRP with modem status 2 on NB, no issues on LTE-M1. I called Telenor to make sure both LTE-M1 and NB-IoT is included in the subscription, and that there is coverage on both in my area.

Could this be an issue with my DK? It's an early model PCA10090 v0.8.2.

[Håkon Alseth]

Fredrik said:

I tried with a Telenor SIM, and I got the exact same results: valid RSRP with modem status 2 on NB, no issues on LTE-M1. I called Telenor to make sure both LTE-M1 and NB-IoT is included in the subscription, and that there is coverage on both in my area.

Could this be an issue with my DK? It's an early model PCA10090 v0.8.2.

This shouldn't be a problem with the DK.

Could you try programming your kit with "at_client", input the following:

AT%XSYSTEMMODE=0,1,0,0

AT+CEREG=5

AT+CFUN=1

 

Then wait 10 minutes, and upload the output log here?

 

Kind regards,

Håkon

[Fredrik]

Sure, here is the log:

2019-11-23T13:44:40.183Z INFO Application data folder: /home/fredrik/.config/nrfconnect/pc-nrfconnect-linkmonitor
2019-11-23T13:44:40.306Z DEBUG App pc-nrfconnect-linkmonitor v1.1.1 official
2019-11-23T13:44:40.306Z DEBUG App path: /home/fredrik/.nrfconnect-apps/node_modules/pc-nrfconnect-linkmonitor
2019-11-23T13:44:40.306Z DEBUG nRFConnect 3.3.0 is supported by the app (^3.2.0)
2019-11-23T13:44:40.306Z DEBUG nRFConnect path: /tmp/.mount_nrfconjpLbRj/resources/app.asar
2019-11-23T13:44:40.306Z DEBUG HomeDir: /home/fredrik
2019-11-23T13:44:40.306Z DEBUG TmpDir: /tmp
2019-11-23T13:44:41.916Z INFO Modem port is opened
2019-11-23T13:44:47.696Z DEBUG modem >> AT\x0D\x0A
2019-11-23T13:44:47.767Z DEBUG modem << OK\x0D\x0A
2019-11-23T13:44:50.943Z DEBUG modem >> AT%XSYSTEMMODE=0,1,0,0\x0D\x0A
2019-11-23T13:44:50.963Z DEBUG modem << OK\x0D\x0A
2019-11-23T13:44:55.215Z DEBUG modem >> AT+CEREG=5\x0D\x0A
2019-11-23T13:44:55.231Z DEBUG modem << OK\x0D\x0A
2019-11-23T13:44:59.417Z DEBUG modem >> AT+CFUN=1\x0D\x0A
2019-11-23T13:44:59.465Z DEBUG modem << OK\x0D\x0A
2019-11-23T13:45:22.777Z DEBUG modem << +CEREG: 2,"9FC5","0103A167",9,0,0,"11100000","11100000"\x0D
2019-11-23T13:49:04.906Z DEBUG modem << +CEREG: 2,"FFFE","FFFFFFFF",9,0,0,"11100000","11100000"\x0D
2019-11-23T13:49:13.175Z DEBUG modem << +CEREG: 2,"9FC5","0103A167",9,0,0,"11100000","11100000"\x0D\x0A
2019-11-23T13:52:56.828Z DEBUG modem << +CEREG: 2,"FFFE","FFFFFFFF",9,0,0,"11100000","11100000"\x0D\x0A
2019-11-23T13:53:03.576Z DEBUG modem << +CEREG: 2,"9FC5","0103A167",9,0,0,"11100000","11100000"\x0D\x0A

I used the Telenor SIM for this test.

[Håkon Alseth]

This is similar to the behavior that I see on my older telenor SIMs (and the iBasis one for that matter), where the network doesn't allow NB1 on the specific SIM:

+CEREG: 2,"9DD1","0145B864",9,0,0,"11100000","11100000"
+CEREG: 2,"FFFE","FFFFFFFF",9

 

Have you contacted telenor, supplying them with the IMSI (the numbers physically printed on your SIM), and asked them to verify that NB1 is enabled for that specific SIM card? If your SIM is old, it might be that you need a new one.

 

Kind regards,

Håkon

[Fredrik]

I called telenor again, and the customer rep said he didn't know but he'd open an internal case and get back to me in a few days. I'll put this on hold until i hear back from them.

Thanks for your help.