Power Saving Mechanisms in LTE-M

One of the biggest advantages of LTE-M is its ability to run on very low power. This feature is especially important for IoT devices that work for years in remote locations without easy access to power. Examples include sensors placed in forests, smart meters on buildings, and trackers attached to moving equipment.

In this lesson, you will learn about the two main power saving features in LTE-M:

• Power Saving Mode (PSM)
• Extended Discontinuous Reception (eDRX)

You will also learn how these features work together to help IoT devices last longer on battery power.

Why Power Saving Is Important

Most IoT devices send only small amounts of data and spend most of their time idle. For example, a temperature sensor may send one reading every few hours. Keeping the device fully connected to the LTE network all the time would waste energy.

Power saving features in LTE-M allow a device to stay connected to the network but reduce how often it communicates. This helps the device use much less power and makes the battery last several years.

Power Saving Mode (PSM)

Power Saving Mode, or PSM, is one of the key ways LTE-M reduces power consumption. When the device is not actively sending or receiving data, it can go into a sleep-like state where most of its radio components are turned off.

How PSM Works

1. The device connects to the LTE-M network and sends its data.
2. After finishing data transmission, it requests to enter Power Saving Mode.
3. While in PSM, the device turns off its radio interface but remains registered with the network.
4. The device cannot receive messages while in PSM.
5. When the preset timer expires, the device wakes up, reconnects, and sends or receives new data.

This approach allows the device to stay part of the network but use almost no power during long idle periods.

Example

A soil moisture sensor in a farm might send data every six hours. Between transmissions, it stays in PSM. During this time, its radio is off, and it draws only a very small amount of current.

Extended Discontinuous Reception (eDRX)

Extended Discontinuous Reception, or eDRX, is another power saving feature. It allows a device to reduce how often it checks for messages from the network.

Normally, an LTE device wakes up every few milliseconds to listen for messages or paging signals. This frequent activity consumes a lot of energy. With eDRX, the device can increase the time between checks to several seconds, minutes, or even hours.

How eDRX Works

• The device remains connected to the LTE network.
• It sleeps for a long time and wakes up at set intervals to listen for possible messages.
• If no messages are waiting, it goes back to sleep until the next cycle.
• The device consumes very little power while sleeping but can still receive messages periodically.

Example

A GPS tracker attached to a shipping container may use eDRX so that it can still receive occasional configuration updates from the network but remain in a low-power state most of the time.

PSM and eDRX Compared

Feature Power Saving Mode (PSM) Extended Discontinuous Reception (eDRX) Network Connection Device stays registered Device stays connected Radio Status Completely off Partially off Can Receive Messages No Yes, at longer intervals Power Consumption Very low Low Suitable For Devices that send data rarely Devices that need occasional updates

PSM saves more power but disconnects the device from receiving messages. eDRX keeps the device reachable but still reduces power usage.

Using PSM and eDRX Together

Many LTE-M devices use both features together for better energy efficiency.

For example, a wildlife tracker might use eDRX while waiting for updates and then enter PSM for long deep sleep periods. When it wakes up, it sends the next location data and repeats the cycle.

By using both mechanisms, the device balances connectivity and power saving. This combination can extend battery life up to 10 years depending on how often the device transmits data.

Summary

Example Use Cases

• Smart meters that send readings once a day usually rely on PSM.
• Asset trackers that need to receive commands occasionally use both eDRX and PSM.
• Environmental sensors that send hourly reports use PSM with short intervals.

Each device type can adjust how it uses these modes based on how often it needs to communicate.

• LTE-M is designed to reduce power use for IoT devices.
• Power Saving Mode turns off the radio completely during long idle periods.
• Extended Discontinuous Reception lets the device listen for messages less often.
• Combining both techniques can give a device battery life of several years.