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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.

  • 0 in reply to Håkon Alseth

    It turns out regular consumer SIM cards from Telenor do not support the IoT bands. I ordered a dedicated IoT SIM card from them instead, and NB-IoT works fine with that.

    Thanks for your help!

    EDIT: NB-IoT does not seem to work with the new SIM either.

    I ran the original test again with the new SIM (which I am sure supports NB-IoT) outside in an open area. This is the log:

    [00:00:00.431,793] ---> AT+CPSMS=0
[00:00:00.454,589] ---> AT+CEREG=4
[00:00:00.475,494] ---> AT%CESQ=1
[00:00:00.496,215] ---> AT+CFUN=4
[00:00:00.516,937] ---> AT%XSYSTEMMODE=0,1,0,0
[00:00:00.540,435] ---> AT+CFUN=1
[00:00:27.303,375] <--- %CESQ: 94,4,18,2
[00:00:27.311,584] <--- +CEREG: 2,"9FC5","0114CF67",9,,,"11100000","11100000"
[00:00:32.353,790] <--- +CEREG: 4,"9FC5","0114CF67",9,,,"11100000","11100000"
[00:00:32.393,127] <--- %CESQ: 255,0,255,0
[00:00:32.401,489] <--- +CEREG: 4,"FFFE","FFFFFFFF",9,,,"11100000","11100000"
[00:00:42.296,203] <--- %CESQ: 97,4,23,3
[00:00:42.304,412] <--- +CEREG: 2,"0EDB","020D8112",9,,,"11100000","11100000"
[00:00:43.590,759] <--- +CEREG: 2,"0EDB","020D8112",9,,,"11100000","11100000"
[00:00:43.725,555] <--- %CESQ: 255,0,255,0
[00:00:43.733,947] <--- +CEREG: 2,"FFFE","FFFFFFFF",9,,,"11100000","11100000"
[00:00:51.500,823] <--- %CESQ: 94,4,20,2
[00:00:51.509,002] <--- +CEREG: 4,"9FC5","0103A167",9,,,"11100000","11100000"
[00:00:58.853,546] <--- %CESQ: 89,4,20,2
[00:01:03.973,602] <--- %CESQ: 89,4,15,2
[00:01:06.533,630] <--- %CESQ: 89,4,20,2
[00:01:14.213,745] <--- %CESQ: 89,4,10,1
[00:01:16.773,773] <--- %CESQ: 94,4,18,2
[00:01:21.893,829] <--- %CESQ: 88,4,18,2
[00:01:34.694,000] <--- %CESQ: 88,4,13,1
[00:01:39.814,056] <--- %CESQ: 88,4,18,2
[00:01:44.934,112] <--- %CESQ: 93,4,18,2
[00:01:50.054,138] <--- %CESQ: 93,4,12,1
[00:01:52.614,227] <--- %CESQ: 93,4,19,2
[00:01:55.174,224] <--- %CESQ: 88,4,12,1
[00:01:57.734,222] <--- %CESQ: 88,4,17,2
[00:02:00.294,250] <--- %CESQ: 88,4,23,3
[00:02:07.974,334] <--- %CESQ: 88,4,18,2

    Around 51.500 seconds I receive modem status 4 ("unknown") with valid tac etc. However, I also receive very strong RSRP values. I can't make sense of this. As usual, LTE-M1 works fine.

  • 0 in reply to Håkon Alseth

    Hi Håkon,

    Any update? I edited my previous reply and rejected the "verified answer", but I'm worried you were not notified.

  • 0 in reply to Fredrik

    Hi,

     

    My apologies for the delay.

    Could you take a modem trace so we can look at what happens?

    Here's a howto on enabling modem traces: https://devzone.nordicsemi.com/nordic/nordic-blog/b/blog/posts/how-to-get-modem-trace-using-trace-collector-in-nrf-connect

     

    Kind regards,

    Håkon

  • 0 in reply to Håkon Alseth

    Sure. Here is the modem trace:

    trace-2019-12-12T12-47-42.604Z.bin

    Pseudo-log of AT commands sent/received:

    [00:00:06.754,486] ---> AT%XMODEMTRACE=1,2
[00:00:06.778,350] ---> AT+CEREG=5
[00:00:06.800,872] ---> AT%CESQ=1
[00:00:06.823,181] ---> AT+CFUN=4
[00:00:06.848,907] ---> AT%XSYSTEMMODE=0,1,0,0
[00:00:06.875,885] ---> AT+CFUN=1
[00:00:30.485,015] <--- %CESQ: 54,2,23,3
[00:00:30.500,701] <--- +CEREG: 2,"9FC5","0103A167",9,0,0,"11100000","11100000"
[00:00:38.578,460] <--- +CEREG: 4,"9FC5","0103A167",9,0,15,"11100000","11100000"
[00:00:38.631,622] <--- %CESQ: 255,0,255,0
[00:00:38.644,073] <--- +CEREG: 4,"FFFE","FFFFFFFF",9,0,15,"11100000","11100000"
[00:00:49.760,467] <--- %CESQ: 72,3,22,3
[00:00:49.805,938] <--- +CEREG: 2,"0EDB","020D8126",9,0,15,"11100000","11100000"
[00:00:51.073,577] <--- +CEREG: 2,"0EDB","020D8126",9,0,14,"11100000","11100000"
[00:00:51.231,048] <--- %CESQ: 255,0,255,0
[00:00:51.239,105] <--- +CEREG: 2,"FFFE","FFFFFFFF",9,0,14,"11100000","11100000"
[00:00:56.075,988] <--- %CESQ: 54,2,22,3
[00:00:56.083,831] <--- +CEREG: 4,"9FC5","0103A167",9,0,14,"11100000","11100000"
[00:01:00.846,466] <--- %CESQ: 54,2,27,3
[00:01:49.487,640] <--- %CESQ: 47,2,27,3
[00:01:54.607,757] <--- %CESQ: 54,2,27,3

  • 0 in reply to Fredrik

    Hi,

     

    Thank you for the trace logs.

    I can see that the eNB (the cell tower) releases the connection very quickly. This is very similar behavior with one of my SIM cards that does not support NB1.

    I will ask R&D to look at the modem trace as well, in case I have missed something.

     

    Kind regards,

    Håkon

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