NRF9160 PSM

[chapman]

I am now using SDK1.3.0-rc1 with NRF9160. I use the serial_lte_modem project and using nrf52 to send at command for controlling nrf9160.

I can connect to the network, but I have a problem on using PSM. 

I send the AT command to turn set the TAU period to be 1 minute and Active time to be 30 sec.  

AT+CPSMS=1,,,"10100001","00001111"

After it connect to the network, I got the following CEREG response. 

+CEREG: 1,"C3B5","0186E6CA",9,,,"00001111","11100000"

I have checked that once it goes into low power , it never wake up again. 

 

I see that the TAU timer  in the response is invalid and I also try longer time for 1 hour  , 2 hour or more but the results always show invalid timer. 

so I ask the service provider and they told me that it should be correct and tell me asking for module provider.  

The commands that I used is simply as follow: (nbiot with legacy pco)

AT+CPSMS=1,,,"10100001","00001111"

AT%XSYSTEMMODE=0,1,0,0

AT%XEPCO=0

AT+CFUN=1

Does that mean I should add a timer to trigger the nrf9160 for turning on after some times? 

Or do you have any suggestion?

Are there any more setting that I need to operate in PSM? Thank you

[Martin Lesund]

Hi Chapman,
Could you please provide a full serial output log from LTE Link Monitor where you try to request PSM mode (with higher intervals)?

[chapman]

The following is the uart log and the attached file is the modem trace log. Thanks.

The AT host sample started

AT%XSYSTEMMODE=0,1,0,0

OK

AT%XEPCO=0

OK

AT+CEREG=5

OK

AT+CPSMS=1,"","","00100100","00001010"

OK

AT+CFUN=1

OK

+CEREG: 2,"C3B5","0186E6CA",9,0,0,"11100000","11100000"

+CEREG: 1,"C3B5","0186E6CA",9,,,"00001010","11100000"

AT+CEREG?

+CEREG: 5,1,"C3B5","0186E6CA",9,,,"00001010","11100000"

OK

AT%XMONITOR

%XMONITOR: 1,"","","45412","C3B5",9,3,"0186E6CA",,,,,"","00001010","11100000","01001001"

OK



trace-2020-06-15T02-44-07.684Z.bin

[Martin Lesund]

Hi Chapman,
We have been able to reproduce what you are seeing and we have also analyzed the modem trace you shared. (thank you for that)

The negotiated parameters are:

• T3412 = 54 minutes          ("Periodic TAU timer")
• T3412 extended = OFF
• T3324 = 20 seconds        ( "Active-Timer" which is RCC IDLE mode)

This means that the nRF9160 will enter Power Save Mode (PSM) 20 seconds after the RRC Connection Release, and will wake up from PSM after T3412(not extended) timer. 

[note: 'T3412' and 'T3412 extended' are two different parameters]

The timer T3412 is also known as the "Periodic TAU", which is the Periodic Tracking Area Update used to notify the availability of the User Equipment (UE) (nRF9160 in this case) to the network. A longer periodic TAU timer is possible using T3412 extended timer. (The value of timer T3412 is sent by the network to the UE in the ATTACH ACCEPT message and can be sent in the TRACKING AREA UPDATE ACCEPT message)

(The explanation can be found here).

---

If you want to wake up every 4 hours, you would need to contact China Mobile when opening a new SIM card, so you can dedicate an APN which supports 4 hours of 'T3412 extended timer'.


Best regards,

Martin L.

[chapman]

Thank you. 

Does that mean we can get the T3412 value by using this command XMONITOR?

it seems that the T3412 is  54 minutes even though I request with other values.?

 
I also try set the Periodic Ta 2 mintues for Periodic TAU timer, but the result are same even I set
AT+CPSMS=1,,,"10100010","00001111"
It keeps at the idle state and it won't wake up after 2 minutes.

Does that mean my service provider doesn't allow me to change the Periodic TAU timer?

Can I use a timer to change the UE state to connected state? Which AT command should I use?


In addition, I found that  after successfully connected to network (CEREG == 1), the current consumption keep high (around 30mA ) for 30 seconds.

Then it will goes to the IDLE state for what I set in the active timer. In this case, this is 20 seconds. 

After that, it will go into lower power IDLE state.

Can I shorten the time that keep the current high from 30 seconds to a lower period? 

If I use the "serial_lte_modem" example and enable LTE_AUTO_INIT_AND_CONNECT which allows it to auto connect to the network, this high current state is in in a shorter time. Is there any AT command that can turn the UE into IDLE state?

 

[Martin Lesund]

Hi Chapman,

The Periodic TAU timer gathered from %XMONITOR is the same as for +CEREG.
You need to contact China Mobile with regards to get access to other intervals, there is nothing we can do about that. If the network only grants you one specific interval, then there is not much you can do without contacting them and maybe getting a dedicated APN with support for other intervals.

Remember there are three states the modem can be in:

• RRC Connected
• RRC Idle 
• PSM

When using Serial LTE Modem I would assume that you instead would use AT commands to get connected to the network. The modem will automatically go into RRC IDLE if there is nothing the modem needs to transmit. most likely the application you are running is sending stuff or the networks have extra long time before it releases the RRC Connected mode for some reason.
Hard to say without modem trace, current measurements, or logs in general.