CAT-M vs NB-IoT: What are the Differences and Which Do I Need?

Who is choosing between Cat-M and NB-IoT?

Cat-M and NB-IoT are both 3GPP standardized technologies, which means they align with the standards and protocols put forward by the 3rd generation partnership project. These 3GPP standards are options for operators and enterprises looking to benefit from low-power wide area networks (LPWANs), which are an alternative to WiFi, or 2G-4G networks.

In contrast to these options which were more traditionally used for mobile phone subscribers, LPWANs can allow for wide-area networking with smaller data transfers, making them perfect for IoT applications, especially the type of IoT projects that need to cover a lot of geographical space, and use low ARPU devices that send very small data packets, for example sensors in logistics and asset tracking, fleet management, smart cities, or agriculture.

The advent of LPWANs is a huge win for IoT, as they offer a truly power-efficient network so that device batteries can last for many years, and can work on either licensed spectrum or unlicensed spectrum, depending on location and business requirements such as availability or latency. However, within the LPWAN category, stakeholders need to choose between different standards, most notably Cat-M and NB-IoT.

Cat-M vs NB-IoT: The similarities

First off, let’s consider the similarities of the two standards. Both NB-IoT and Cat-M have power-saving mode (PSM) which means that when the device is not active, it can go into a sort of hibernation, saving on the battery life. This is great for IoT, because unlike mobile phones there is no need to be always awake in case an incoming connection is being made. IoT devices often need to connect at a predictable time of day, for example to send information on rainfall, location, or speed – and the rest of the time they can remain dormant. Usually, PSM works by sending a tracking update when the device moves or when an action is taken, and at set intervals between those times. For example, smart meters can remain in PSM until someone wants to check usage manually, and outside of periodic data reports being sent to the enterprise. This can extend the battery life of IoT devices by years.

The other similarity is the ability of these standards to use extended discontinuous reception (eDRX) in order to receive messages from the operator or enterprise, like OTA updates, configuration changes, or for troubleshooting. While for mobile subscribers, the period to check for any incoming messages was 2.56 seconds, for NB-IoT and Cat-M this can now be as much as 40 minutes. As LPWAN standards, they both support wider network coverage per each base station.

Cat-M vs NB-IoT: The differences

There are some practical differences to be aware of when you’re deciding which connectivity technology is the best fit for your IoT roadmap. Firstly, the bandwidth. NB-IoT is best for very low data rate applications, especially where the radio conditions might be challenging. It can support narrow bandwidth of 200 kHz, and the data rate therefore has a ceiling at about 250Kbps. In contrast, Cat-M can achieve higher data rates of up to 1 Mbps because it uses 1.4 MHz bandwidth. This can also come at a higher cost than NB-IoT, so it’s really all about considering what you need. As Cat-M has a wider bandwidth, you can achieve lower latency and greater accuracy with where your devices are positioned. There are also benefits in terms of functionality, such as the ability for Cat-M to support voice calls and mobility. Of course – this is only a benefit if you need it, otherwise it becomes added bells and whistles at greater cost.

Understanding NB-IoT spectrum use

One benefit of NB-IoT is the way that the technology approaches spectrum use. As NB-IoT uses narrower bandwidth, as discussed above, more devices can be used within the same spectrum allocation. Radio frequency spectrum is limited, so this is a real boost for those that use NB-IoT. NB-IoT also uses something called guard bands, which uses the spectrum between the radio bands, to allow for more devices.

Maximum coupling loss between standards

Availability and coverage is an important differentiator of different IoT-friendly standards, and so 3GPP standards dictate that all LPWAN types have an MCL (Maximum Coupling Loss) awarded. This will explain how much signal will be lost from the point of transmission to the receiver, for example for indoor applications where the signal needs to go through walls etc. Of course, this is a theoretical number, but the comparison explains the potential for the standards. While Cat-M comes in at 156 dB, NB-IoT is significantly higher, at 164 dB. Practically speaking this makes NB-IoT a hardier choice for IoT connectivity, for example if devices will be competing with other signals. Remember that the higher the numbers, the more likely power consumption will be negatively impacted.

Making your choice

Remember, NB-IoT is a standard that has been built from the ground up for IoT, but it is mainly intended for massive IoT – large scale giant sensors and networks that can all be connected to a single base station. For applications with greater data needs, your maximum data speed may just not be good enough, and the latency can be as much as 10 seconds, not suitable for mission-critical applications. As NB-IoT can be less power efficient, Cat-M might be a smarter choice, especially in areas without established roaming agreements for NB-IoT, where you might need to onboard multiple mobile operator relationships in every location in which you want to deploy devices. Lastly, NB-IoT also doesn’t support handovers, so for on-the-move IoT use cases, Cat-M may be a smarter choice.

NB-IoT and Cat-M both have a lot of benefits, and can even work in a complementary way together for certain business needs. The most important thing is making sure you have a smart plan for disaster recovery and redundancy in case connectivity goes down, and that you have the flexibility for handovers and OTA switching, so that your devices are always-on. Your customers care about availability, compliance, and keeping costs low – and an intelligent partner for IoT connectivity will be able to break down your choices in line with the context of your business needs. That means you’re always two steps ahead to answer every concern, and with the right technology in place for IoT success.

Ready to discuss your IoT roadmap? We can’t wait to hear from you! Get in touch here.