LPWA (Low Power Wide Area) technologies for the IoT

LPWA (Low Power Wide Area) technologies are being used to build networks specific to the Internet of Things (IoT). Networks such as LoRa and Sigfox operate in the unlicensed bands and provide certain benefits but although growing, are still not so widely available as the established cellular phone networks. Mobile Network Operators (MNOs) are deploying two types of LPWA technology which are designed to work for many years on batteries alone.


The first is called NB-IoT and is designed for static applications such as meter reading. NB-IoT does not support cell handover so is not ideal for mobile applications.


LTE-M, also known as Cat M1 is an LPWA technology designed for applications on the move. LTE-M is being rolled out by Mobile Network Operators (MNOs) across the world with the UK already having over 10,000 cell sites, these deployed in the first half of 2020. LTE-M has the advantage of supporting mobility in the same way that established technologies such as 2G, 3G and 4G can. An LTE-M connected device is handed from cell to cell as it moves along.

How LTE-M technology conserves power

LTE-M standards allow for simpler and cheaper chipsets to be manufactured. These standards also give the IoT application developers and customer options on how best to conserve power. There are two ways of doing this, depending on what is best for your application:

  • PSM (Power Saving Mode)

  • eDRX (Extended Discontinuous Reception)

LTE-M Power Saving Mode (PSM)

You can put an LTE-M connection into PSM, telling the network that your device is going dormant for an indefinite period of time. A timer or other logic in your application can decide when to wake your device and request to transmit. After transmission, PSM keeps your device in receive mode for 4 idle frames so that it can be reached if needed. Depending on the demands of your application, an LTE-M connection in PSM can be more energy efficient even than NB-IoT, Sigfox or LoRa. This is due to the higher transmission (TX) rates of LTE-M, where speeds of 100 to 150 kbps are typical, allowing your device to do the work quickly before dropping back into sleep mode. If your device makes one transmission a day in PSM it should last for 10 years on 2 x AA batteries.

LTE-M Extended Discontinuous Reception

PSM is not the only way to manage power consumption on an LTE-M connection. The normal ‘paging cycle’ of an LTE device is 1.28 seconds, this is where the device ‘checks in’ with the cell tower to make sure it is connected. This may be fine for mobile phones or IoT devices where there is a mains or vehicular power supply, but not if your device is relying on batteries. LTE DRX extends the paging cycle, allowing the device to ‘sleep’ for 10.24 seconds, these extended sleep cycles are called hyper frames (HFs). DRX is useful for some IoT applications but still not enough to achieve a battery life of many years. The eDRX (extended) feature on LTE-M has been developed to use hyper frames in a different way. eDRX allows your device to specify how many HFs it would like to sleep before checking back in. The maximum number of HFs you can have is set by the operator but should be at least 40 minutes, which is about 240 HFs. Running your application in eDRX with your device checking in ever 10 minutes (60 Hyper Frames), should give a battery life (2 x AA) of 4 to 5 years.

eDRX allows more flexibility than PSM if you do need to communicate with your device in an asynchronous way, either to grab some data following an event or deliver a firmware update.

More information about LTE-M power saving modes

For those of you designing your IoT solution, writing the application or simply wanting to know more about LPWA cellular technology, here is a link to a GSMA document that gives more detail on LTE-M power saving modes (pages 10-13) and pages 6 to 8 explain more of those IoT acronyms we love so much.

LTE-M Deployment Guide to Basic Feature Set Requirements Version 2.0 05 April 2018