SARA-R42 - Application note
UBX-20050829 - R02
PSM, eDRX and deep-sleep mode
Page 30 of 58
C1-Public
the many retransmissions related to the Coverage Extension (CE) mode currently assigned to the UE.
This can be checked via the
+CEINFO
AT command and the
+CSCON
URC.
IP based applications (e.g., MQTT, USOCK, UDNS, UFTP, HTTP) instead have no control on deep-sleep.
They might be negatively impacted by the UE entering in deep-sleep state during the data sessions
(such as UDP, TCP or secure sockets). This may happen in case the RRC connection is released and,
in case of PSM deep-sleep, the T3324 expires while the UE is waiting for a network response. The
network response delay can be a consequence of a temporarily server outage or packet loss in low
coverage or mobility. This can be mitigated by the usage of UDP sockets instead of TCP ones, which
also consumes less power. Like IP based applications, asynchronous AT commands, like
+UMQTTC
,
have no control on deep-sleep which could be entered before the final result of the requested
operation is received via URC.
In above cases the host application can temporarily postpone deep-sleep entry via the
AT+UPSMVER=,,,,1
command (preferred solution) or keep issuing an AT command each time the AT
interface guard timer is going to expire. To postpone deep-sleep entry during a blocking AT command
execution, AT commands can be issued on another virtual AT port. When possible, deep-sleep
temporary postponing is preferred to the disabling and re-enabling of deep-sleep via the
+CPSMS
AT
command, which would waste power in two extra deregistration-registration cycles.
8.2.2
Deep-sleep indications
The host application can monitor the entrance and exit from deep-sleep state in several ways:
•
GPIO “module status indication” (see the
+UGPIOC
AT command description in the SARA-R4 series
•
V_INT monitoring
•
RXD monitoring (if RXD is low for more than 1 character)
•
+UUPSMR
URC (printed on the AT interface when entering and exiting deep-sleep mode).
8.2.3
Deep-sleep state in out of service
The power efficient deep-sleep mode can be also entered in prolonged out-of-service conditions if the
host application has enabled the minimum functionality PSM deep-sleep mode via the
+CPSMS
AT
command. After a configurable number of unsuccessful full PLMN scans the module periodically
enters the deep-sleep mode for 4 minutes before starting new network scans. Deep-sleep state in out
of service can be tuned via the
+UPSMVER
AT command.
8.3
eDRX
SARA-R4 series modules support the 3GPP Release 13 feature Extended Discontinuous Reception
(eDRX). This feature allows power consumption reduction, cyclically listening to paging without losing
any paging indications. Paging is listened to only during short time periods (called PTW
–
Paging Time
Windows) and ignored the rest of time. There is one PTW per the eDRX cycle. The application can
enable eDRX feature negotiation via the
+CEDRXS
AT command. The command also allows
configuration of the desired eDRX parameters: the requested eDRX cycle duration, also referred as
TeDRX, and the PTW duration. If the network grants eDRX usage the assigned and finally used eDRX
values can be read via the
+CEDRXP
URC and
+CEDRXRDP
AT command. It is suggested to deliver MT
data with a pull mechanism already described for PSM. eDRX is commonly used on its own instead of
PSM in applications where MT traffic is considered in the application design, a MT data delivery delay
is affordable, but the tolerable delay is shorter than in PSM use cases. As a rule of thumb, eDRX is
preferred to PSM when the maximum admissible MT data delay is shorter than the network T3412
duration, which has a default value of almost 1 hour. In this case, to minimize power consumption, it
is suggested to set the requested TeDRX cycle duration as equal to the maximum affordable MT data
delivery delay, and to set the requested PTW to the minimum duration, which makes paging reception
