Battery longevity is a primary design constraint for a large share of the IoT devices eRedCap targets. Smart meters, environmental sensors, and remote asset trackers commonly operate on primary batteries for years. eRedCap provides three complementary power saving mechanisms.
Power Saving Mode (PSM)
PSM allows a device to enter a deep sleep state between reporting cycles. The device remains registered with the network but is unreachable until its next scheduled wakeup. A device in PSM consumes near-zero current from the cellular modem. Ideal for sensors reporting once per hour or less where network-initiated contact is not required between scheduled uploads.
Connected-Mode eDRX (C-eDRX)
Extended Discontinuous Reception in connected mode allows a device to sleep for extended periods between downlink monitoring cycles while staying in an active connection state. The device wakes periodically to listen for pages from the network, then returns to sleep. Useful for applications requiring lower latency than PSM allows.
eDRX in RRC_INACTIVE – Release 18 Specific
This mechanism is specific to Release 18 and is not present in RedCap (Release 17). It allows a device to sleep for extended periods while remaining registered in the RRC_INACTIVE state – an intermediate state between fully connected (RRC_CONNECTED) and fully detached.
Unlike PSM, a device in RRC_INACTIVE eDRX can be paged and wake to receive data within a configurable window, without going through the full RRC establishment procedure. This reduces wakeup latency compared to PSM while consuming far less power than staying fully connected. For applications requiring occasional server-initiated communication – firmware updates, configuration pushes, alert acknowledgements – this is a material improvement over what LTE Cat-1 or even Release 17 RedCap can offer.
Practical Impact
The combination of HD-FDD (simpler RF, lower active current), single antenna, 5 MHz bandwidth, and RRC_INACTIVE eDRX makes eRedCap meaningfully more power-efficient than LTE Cat-1 on a like-for-like basis. The exact improvement depends heavily on application duty cycle and reporting frequency, but for low-duty-cycle IoT applications the operational battery lifespan difference can be significant.