NRF9161 based LTE-M tracker data drops while moving – can it be optimized?

[marsal]

Hi everyone,

I’m using a custom board (a tracker) that can travel at speeds up to 65 km/h and transmits data regularly every 200 ms. I expect, therefore, that the inactivity timer should not be activated. While the device is in motion, I’m seeing intermittent data gaps ranging up to several seconds, which is unacceptable for our application.

Could this be caused by non-optimal cell-handover settings? I’ve attached a few logs below for reference.

Any suggestions would be greatly appreciated.

Thanks,
Martin

 

Three log fragments examples, related to data send drops:

 

17:31:57.179 +CSCON: 0

17:31:57.230 <inf> main: RRC mode: Idle

17:31:57.276 +CEREG: 1,"04D3","0DBC2351",7,,,"11100000","11100000"

17:31:57.298 <inf> main: Cell update, cell tac: 1235, cell id: 230433617

17:31:57.371 +CSCON: 1

17:31:57.429 <inf> main: RRC mode: Connected

17:31:57.539 +CSCON: 0

17:31:57.568 <inf> main: RRC mode: Idle

17:31:57.907 +CSCON: 1

17:31:57.926 <inf> main: RRC mode: Connected

***

17:37:54.095 +CEREG: 1,"04D3","0DC18750",7,,,"11100000","11100000"

17:37:54.154 [00:54:10.770,263] <inf> main: Cell update, cell tac: 1235, cell id: 230786896

***

17:38:05.373 +CEREG: 1,"04D3","0DDD4350",7,,,"11100000","11100000"

17:38:05.434 <inf> main: Cell update, cell tac: 1235, cell id: 232604496

***

 

Modem firmware: mfw_nrf91x1_2.0.2

 

Current 9161 modem initiation sequence is:

 

AT+CFUN=0

AT%XSYSTEMMODE=1,0,0,0

AT+CPSMS=0

AT+CEDRXS=0

AT%RAI=0

AT+CSCON=1

AT+CEREG=5

AT+CFUN=1

[Achim Kraus]

marsal said:

I’m seeing intermittent data gaps ranging up to several seconds, which is unacceptable for our application.

marsal said:

5 Hz to an MQTT broker

You chose MQTT. That usually queues the messages and transmit them, when transmission is possible. So, there may be a short gap in the time-stream, but not the data-stream, that's just delayed. If you add the "sensor-time" to the data, you will also be able to have the time-stream available with delays.

I guess, you need to adapt your application to that common practice.

[marsal]

Thanks, well, my interval_between_two_subsequent_successful_mqtt_sends is between 210ms and 300ms in case that there are no cell updates, which is OK for me. When cell update comes, it raises to e.g. 1.5 sec. So the cell update seems really be the case.

Er, I am struggling just now to catch the modem trace... Not sure if UART or RTT approach is better for me. 2.6.3.

[dejans]

Hi,

Have you started data logging?
You can capture modem trace from JLink Viewer by clicking on Logging -> Start Data Logging and saving data log to .bin file.

Best regards,
Dejan

[marsal]

Oh, thank you for your patience, dejans...

Please download the trace from here: https://e.pcloud.link/publink/show?code=XZ0rTqZdiRVUEHQm9hG8n3zxMfHOHDJ2bRy

The trace is from a short car ride, observing cells switching. Thank you very much!

Below is what I did meanwhile (lock for band 20 for Czechia as O2 operator is used who has no other bands for LTE-M. full .config is FYI here: https://e.pcloud.link/publink/show?code=XZmrTqZUNoHFDGILALna6f7gRDrRzMaOtFk):

### LTE
CONFIG_LTE_NETWORK_MODE_LTE_M=y
CONFIG_LTE_LINK_CONTROL=y
CONFIG_LTE_PSM_REQ=n
CONFIG_LTE_EDRX_REQ=n
CONFIG_LTE_RAI_REQ=n
CONFIG_LTE_NETWORK_TIMEOUT=60
CONFIG_LTE_LC_TAU_PRE_WARNING_NOTIFICATIONS=n
CONFIG_LTE_LOCK_BANDS=y
CONFIG_LTE_LOCK_BAND_MASK="10000000000000000000"

And in runtime (possibly duplicate to config), I am sending:
"AT+CFUN=0";
"AT%%XSYSTEMMODE=1,0,0,0";
"AT+CPSMS=0";
"AT+CEDRXS=0";
"AT%%RAI=0";
"AT%%XBANDLOCK=2,\"10000000000000000000\"";
"AT+CSCON=1";
"AT+CEREG=5";
"AT+CFUN=1";

[dejans]

Hi,

Thank you for the trace and additional information.

There seems to be only one cell change in your log. Increased delay which you observed might be normal, but we will check this further. I will get back to you during next week.

Best regards,
Dejan

[marsal]

Thanks, dejans, a lot!

Well, the best case could be that the descibed changes could have improved the behavior described in the very first email.

I have made the changes described in the previous email with trace link and only then I was recording the trace. Before the change, at the same path, I had observed number of cell switch changes with 1-2 secs data transfer breaks. In general, my question would be if the described settings are OK and/or what could be done more. Big thanks again.

[dejans]

Hi Martin,

marsal said:

In general, my question would be if the described settings are OK and/or what could be done more.

Connection re-establishment is triggered due to sync loss to serving cell (T310 expiry). This is normal operation for moving UE. Data paths are suspended for time of connection re-establishment. Parameters which control re-establishment are given by the network. There is nothing which could be done from UE side to avoid this interruption. You could contact the carrier regarding network support for LTE-M handover.

Best regards,
Dejan