Hi,
I have a question about PSM mode of nRF9160.
As I know, PSM mode is supported after 3GPP release 12.
But I found out that some network operator doesn't support PSM mode.
In this case, if I use AT command related with PSM configuration, How nRF9160 operates?
nRF9160 maintains active state?
Or nRF9160 enters sleep and wake up every periodic TAU?
Thank you.
Best Regards
James Lee
Hi James,
So let's discuss the details about PSM mode and the eDRX interval which has a great impact on the avg. current consumption for the modem.
In the Figure above we see the three different states the cellular modem can be in.
The modem can be in either of these three modes:
In this mode, the radio is active (TX/RX) and the modem has to stay in sync. with the network, which needs the high accuracy timers to be enabled.
If the modem has nothing to send it will go in RRC IDLE mode automatically (or PSM mode if you have configured <active_time> to zero)
In this mode, you do not need to stay in sync. with the network. The transceiver is turned OFF and you utilize the eDRX intervals to sleep in between the paging time windows where you turn ON the receiver to check if there is some data from the network that you can receive. The device can request the eDRX interval, but the network decides if it will allow you this interval or not. What we usually see is that networks usually approve extending this interval compared to shortening it.
NOTE: When we discuss eDRX intervals we are actually talking about "idle eDRX" (iDRX), not "connected eDRX" (cDRX) since iDRX has a huge impact on avg. current consumption while cDRX has very little impact on the current consumption.
In this mode, you turn OFF the radio all together and the device is unreachable from the network side. The device can stay in PSM mode for ~6 minutes up to several weeks.
What should be noted is that the nRF91 device can itself wake up when it wants to from PSM mode and go to RRC Connected mode if it needs to send data, e.g. an alarm.
PSM floor current is 2,7µA for the nRF9160.
The GPS can only be used when the nrf9160 device is either in PSM mode or in the eDRX intervals in RRC IDLE mode. (GPS current consumption)
When it comes to testing if your network grants you PSM mode or not I recommend to e.g. run the AT Client sample and when you have turned ON the modem (AT+CFUN=1) you can request PSM mode and interval with command (AT+CPSMS)
AT+CPSMS=1,"","","00101010","00100001"
"Set Periodic-TAU timer to 10 hours and Active-Time to 1 minute."
Then you can read out if and what the network grants you with the command: (AT%XMONITOR)
AT%XMONITOR
So from the response you can see if the network grants you PSM mode an the intervals etc. but if the network for some reason does not grants you PSM mode,
(e.g. if the network does not support it, you are using a SIM card that the network will not give PSM mode to (e.g. roaming SIMs can be declined by some networks) or the PSM interval is too short or the parameter is invalid for the network) then it will only jump between RRC Connected and RRC IDLE.
Best regards,
Martin L.
