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

[dejans]

Hi,

marsal said:

Thanks, here is the idea - this means a rework of the current setup, of course:

10 to 20 trackers in one race  + 1 gateway. Distance between trackers and gateway can be up to 1km, direct line of sight. If not enough for the data transfer, an "intermediate" node is expected to be positioned somewhere in the middle between the gateway and the more distant place of the race.

The key here is good hardware radiated performance. Otherwise, NR+ 1.9 GHz should be able to handle distances relatively easy.

marsal said:

Trackers (using our current hardware, btw ;-),  ):
a) Sending to the gateway each 200ms data about position/speed/direction (approx 100 bytes each)
b) Receiving from gateway each 1 second GNSS correction RTK data (up to 1KB each second, same for each tracker)
Idea: trackers typically communicate with gateway, if the gateway is not reachable for a tracker and vice versa, they send/receive via another tracker (mesh).

NR+ should be able to handle such traffic per tracker node, NR+ sink node connected to Cellular/LTE gateway would be the focus point performance wise.

marsal said:

Gateway (our current hardware + LTE modem rework):
a) receiving position/speed/direction data from trackers, sending it to an MQTT server via LTE (I guess not via LTE-M for this case)
b) receiving RTK corrective data from another server and sending them to trackers via DECT NR+
c) Some other communication (AGNSS, some controls)

RTK correction data would be more of a broadcast type than point-to-point per each tracker node.

marsal said:

one question regarding the current setup: are you please aware of an implementation with LTE-M NRF9161 where the handover goes smoothly? Which carrier provider?

Yes, any cellular provider which supports handover for LTE-M1 which would for example be just about every network in US or Nordics. This feature has been enabled for several years already, and it should not be a big task for any carrier to enable it.

marsal said:

So, any hints and DECT NR+ firmware to test this warmly welcomed.

I recommend that you contact your regional sales manager to discuss the possibilities of going forward with NR+.

Best regards,
Dejan

[marsal]

Thanks again, dejans, we hope our O2 negotiations will be fruitful. But as our project lasts 9 months already without usable outcome, even a quick "smoke" mesh test could heal the business position for us.