What is LTE-M?

If you’ve been researching cellular communication you’ve probably encountered a flood of terminology. You’re likely familiar with terms like 4G and 4G LTE, but what is LTE-M?

Let’s start with the basics. 4G stands for the fourth generation of cellular connectivity. A 4G wireless network is supposed to have peak download speeds of 1GB/sec. This represents a massive improvement from 3G networks that had peak download speeds of a few MB/sec.

LTE (Long Term Evolution) is one of many technologies for implementing a 4G network -- others include WiMAX and HSPA+ -- and is by far the most widely used by US carriers. It was developed by a global organization called 3GPP (3rd Generation Partnership Project). Every few years, 3GPP publishes new enhancements to this LTE technology called “releases” Introduced in Release 13, LTE-M (also known as CAT M1) is a communication standard geared towards IoT devices.

While most 3GPP releases aim to increase the amount of data being sent between your phone (or in this case, your IoT device), LTE-M dramatically reduces the data uplink/downlink rate to 1MB/sec. Why? By decreasing the amount of data sent, devices using LTE-M technology can achieve remarkably long battery lives (several years) while still maintaining long range communication. For those familiar with the term, it qualifies as a Low Power Wide Area (LPWA) connectivity method and represents a competitor to non-cellular LPWA networks like LoRaWAN and Sigfox.

What are the advantages of LTE-M?

Energy efficiency

LTE-M is especially unique for the techniques used for minimizing power consumption. Low power consumption is crucial for any IoT device that runs on battery power. If you had to recharge your IoT devices every day (like you do with your phone), a large scale deployment would be impossible.

LTE-M uses two features -- eDRX (Extended Discontinuous Reception) and PSM (Power Saving Mode) -- to minimize power usage. How these two technologies work is out of the scope of this article, but at a high level, they allow a device to enter sleep mode more often and minimize the time the device is listening for messages from a cell tower.

LTE-M was designed so that a device could have 10 year battery life on a 5WH battery. However, the actual battery life will depend on whether hardware manufacturers can meet the design specifications outlined.

Compatibility

Another advantage of LTE-M is its compatibility with existing LTE cellular networks. Cellular companies like Verizon and AT&T only need to install new software into their base stations in order to communicate with LTE-M devices. This is not the case with other Low Power Wide Area cellular solutions like NB-IoT, which would require new hardware on the base stations. Additionally, LTE-M handles hand-overs between cell towers seamlessly (in a manner similar to your cell phone).

Voice

Finally, LTE-M also supports voice functionality (VoLTE) which opens the technology up to many new use cases. For instance, home security systems equipped with LTE-M could process sound data and alert the homeowner if suspicious noises are detected.

Conclusion

LTE-M is a promising competitor to existing LPWA technologies for IoT. It solves the battery life problem with existing cellular connectivity methods and has the added benefit of being compatible with current cellular networks. Stay tuned for the next installment of our Introduction to LTE-M where we'll cover optimal use cases for this technology.