PSM + eDRX

[Joao Dullius]

Hello,

I'm trying to understand if it makes sense to use PSM and eDRX at the same time.

On my NB-IoT carrier (Vivo), I can get both PSM and eDRX, but not on the same time, as follows:

TAU Request with PSM only - PSM Granted on TAU Accept
TAU Request with eDRX only - eDRX Granted on TAU Accept
TAU Request with both PSM and eDRX - PSM Granted, but eDRX not Granted  on TAU Accept

Looking at Modem Shell notifications, when using eDRX only, I see the following when configuring eDRX: 163.839996, PTW: 5.120000:

[1970-01-01 00:48:59.372] Modem sleep exit pre-warning: time: 5.00 seconds, type: RF inactivity
[1970-01-01 00:49:04.374] Modem sleep exit: time: 0.00 seconds, type: RF inactivity
[1970-01-01 00:49:12.012] Modem sleep enter: time: 156.00 seconds, type: RF inactivity
[1970-01-01 00:51:43.218] Modem sleep exit pre-warning: time: 5.00 seconds, type: RF inactivity
[1970-01-01 00:51:48.219] Modem sleep exit: time: 0.00 seconds, type: RF inactivity
[1970-01-01 00:51:55.856] Modem sleep enter: time: 156.00 seconds, type: RF inactivity
[1970-01-01 00:54:27.062] Modem sleep exit pre-warning: time: 5.00 seconds, type: RF inactivity
[1970-01-01 00:54:32.064] Modem sleep exit: time: 0.00 seconds, type: RF inactivity
[1970-01-01 00:54:39.701] Modem sleep enter: time: 156.00 seconds, type: RF inactivity

On my understanding the modem is getting into sleep for 156 seconds after the 5.12 PTW.

How does this RF inactivity sleep differs from a PSM sleep as bellow?

Modem sleep enter: time: 3179.00 seconds, type: PSM

Are both sleeps expected to have the same 2.7uA floor level? If not, what would be the floor level for the RF inactivity sleep from eDRX?

Would enabling (if possible) both PSM + eDRX would make the modem sleep on a lower floor level during the 156 seconds of the eDRX interval?

[Håkon Alseth]

Hi,

 

TAU Request with both PSM and eDRX - PSM Granted, but eDRX not Granted  on TAU Accept

You can only be in one sleep mode at the same time.

 

On my understanding the modem is getting into sleep for 156 seconds after the 5.12 PTW.

How does this RF inactivity sleep differs from a PSM sleep as bellow?

There's two different modes of sleep. PSM is normally used for longer periods than eDRX.

Are both sleeps expected to have the same 2.7uA floor level? If not, what would be the floor level for the RF inactivity sleep from eDRX?

Both yes and no. The modem can turn off the clock to the SIM if the SIM supports lower power modes (see here for more info https://infocenter.nordicsemi.com/topic/ps_nrf9160/ip/radio_lte/doc/simif_lte_m/frontpage.html?cp=2_0_0_6_0).

There's a tradeoff between SIM-wear wrt. going into lower power mode, so you usually need to check how many read/write cycles your SIM can handle to ensure that it stays operational for the duration period of the product. Please see this AT command for more info:

https://infocenter.nordicsemi.com/topic/ref_at_commands/REF/at_commands/mob_termination_ctrl_status/xdataprfl_set.html?cp=2_1_4_13_0

 

If the SIM is powered on, you'll normally see a idle current of ~20-60 uA from the SIM itself (depends on the type of SIM).

Would enabling (if possible) both PSM + eDRX would make the modem sleep on a lower floor level during the 156 seconds of the eDRX interval?

No, not possible. You're either in eDRX or PSM, not both.

 

Kind regards,

Håkon