What are PSM and eDRX
Quick definition
PSM (Power Saving Mode) and eDRX (extended Discontinuous Reception) are 3GPP-defined mechanisms that let a cellular IoT device draw microamps while idle. PSM turns the modem off between long windows (up to days); eDRX spaces paging listening in short intervals (seconds to minutes) without losing network registration.
When to use PSM
When the device initiates all communication (scheduled or event-based telemetry push) and nobody needs to reach it during downtime. Typical for meters, environmental sensors, asset trackers.
When to use eDRX
When the device needs to receive commands from the server with some regularity (remote parameter changes, alerts) without burning battery. eDRX lets paging windows be 20-40 seconds apart instead of every 1.28 s in classic DRX.
FAQ
Can I use PSM and eDRX together?+
Yes. The typical pattern is eDRX during active hours and PSM at night or between long cycles. The network must negotiate and accept the timers the device requests.
Does every carrier support PSM?+
In Spain yes, on LTE-M and NB-IoT. International support varies: always check with your provider before shipping product that relies on specific PSM timers.
Related terms
What is NB-IoT
NB-IoT (Narrowband IoT) is a 4G/5G LPWA technology optimized for small messages from static, multi-year battery devices. It runs in a 200 kHz sub-band and prioritizes deep coverage and extreme power efficiency over throughput.
What is LTE-M
LTE-M (also LTE Cat-M1) is an LTE variant designed for IoT: moderate bandwidth (up to 1 Mbps), very low power, voice support, and real cell-to-cell mobility. It is the sweet spot between NB-IoT (cheaper but static) and Cat-1 (faster but power-hungry).
What is LTE Cat-1
LTE Cat-1 is the LTE device category targeted at general-purpose IoT: up to 10 Mbps down, 5 Mbps up, voice support, and works on any 4G network worldwide. Its Cat-1 bis variant runs on a single antenna, cutting hardware cost. It is the workhorse behind POS terminals, alarms, gateways, and low-bitrate CCTV.