LTE-M PSM Edge Cases and Questions

[jlangballeswift]

Hi,

I'm trying to set up a proof-of-concept asset tracker to be run for a few months, over large distances (cross-country), powered by battery, with no user inputs. I have some questions about PSM in LTE cat M1 because edge cases with connectivity and power consumption are very important for this application and I'd like to clear up as many unknowns as possible.

1. Is PSM part of LTE Cat M1? Does every MNO supporting LTE Cat M1 also support PSM? How much can the MNO dictate the PSM TAU and active time I’m allowed to use?
2. Is it possible to check from the device if the current carrier supports PSM?
3. If we request PSM but the MNO does not support it, how do we detect this?
4. How can we detect if we lose connection or start roaming? Is this handled in the modem firmware or will I need to write my own handlers?
5. Can we exit PSM if we start roaming? How do we detect this?
6. Can we exit PSM for any other reason? How do we detect this?

Thanks for the help and best regards.

[Hakon]

Hello,

 

Is PSM part of LTE Cat M1?

 No, it's also used in NB-IoT.

 

Does every MNO supporting LTE Cat M1 also support PSM?

 No, and the choosing of TAU and active time is often restricted.

 

How much can the MNO dictate the PSM TAU and active time I’m allowed to use?

 The MNO controls the TAU and active time at it's own discretion.

 

Is it possible to check from the device if the current carrier supports PSM?

 You can try to set PSM and see if it's rejected.

 

If we request PSM but the MNO does not support it, how do we detect this?

 Run

AT+CEREG=5

and read the last two parameters.

 

Can we exit PSM if we start roaming? How do we detect this?

 You can use the AT+CPSMS command.

 

Can we exit PSM for any other reason? How do we detect this?

  You can use the AT+CPSMS command for this too.