SARA-R42 - Application note
UBX-20050829 - R02
Cellular technology overview
Page 8 of 58
C1-Public
2.1.3
GSM/EGPRS
To assure global coverage, the module supports also 2G legacy RAT, more precisely it supports
EGPRS class 33 with a downlink maximum speed of ~ 290 kbit/s (the peak bit rate depends on the
quality of the radio link). Being a data-only device, in 2G RAT, besides performing GPRS attach, the
module also registers for CS (Circuit Switched) services in order to enable the GSM SMS service. This
is a major difference with respect to NB-IoT RAT, where often the SMS service is granted even if the
LTE attach is accepted for EPS services only, thanks to the
“SMS only” option
negotiated during the
LTE attach. Another major difference is the fact that the host application needs to establish a PDP
context activation in order to get an
IP address and be able to use the module’s IP based applications.
2.2
Low power profile features
When integrating SARA-R4 series modules in a low power consumption device, it is recommended to
enable the power saving mode via
+UPSV
AT command. Depending on the configuration of the serial
line used, different +UPSV modes can be selected (see the SARA-R4 series system integration
manual
and the SARA-R4 series AT commands manual
).
To benefit from the enhancement of the LPWA standards, the power saving mode (PSM) can be
enabled too. In normal service in LTE Cat M1 and NB-IoT, during inactive phases the PSM feature
forces the module to enter a low power mode state, where the module is totally deactivated. The state
is exited either if the host application needs to trigger data or AT commands, or when the device has
to perform the periodic registration to the LTE network, which in PSM is done less frequently than in
normal, non-PSM operational mode (for example, after a few hours). Overall, this behavior is more
convenient with respect to usage of on-demand radio switch off/on via
AT+CFUN=0/1
but has the
disadvantage of long-lasting non-reachability periods while the device is deactivated. Similarly, host
applications using mobile-terminated user data (for example, SMS) can rely on eDRX (extended DRX)
to keep the power consumption at an optimal level while retaining reachability.
SARA-R4 series modules assure enhanced coverage thanks to the support of CE (Coverage
Enhancement) modes A and B; this benefit is balanced by longer transmission duration due to the
several repetitions, which the host application can mitigate by using a reduced transmission duty
cycle for optimal tradeoff.
