8 PSM and eDRX
8.1 PSM/eDRX overview
PSM and eDRX are two different features defined in the latest 3GPP releases. The goal of
these features is to reduce the power consumption of IoT devices. To achieve this, PSM and
eDRX enable different mechanisms to reduce the signalling between the IoT device and
network. The picture above shows the two features combined. However, they can be enabled
independently.
The Power Saving Mode (PSM) in 3GPP Rel12 allows the module to skip idle mode tasks for
a longer time period while still maintaining the NAS context. This feature permits to reduce the
overall power consumption when there is no required data activity with the network for a long
time. This saves the power also related to the Paging activity. During the “PSM sleep” period
the module is NOT reachable by the network, i.e. it cannot be paged and stops access stratum
activities. The module can leave the PSM mode at any point in time when there is MO data or
when periodic TAU timer expires.
The extended DRX (eDRX) allows the module to extend the paging period. This feature allows
to reduce the overall power consumption increasing radio inactivity time in between paging
occasions. The feature is suitable for applications that support high latency communication.
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