The Challenger in the LPWA Debate: LTE CAT-1 BIS Versus CAT-M Versus NB-IoT

Mobile network operators (MNOs) are shutting down their 2G and 3G networks in markets across the globe. That’s a serious challenge for manufacturers of IoT devices, and one leading international provider of e-scooters was determined to meet it head-on. The company’s e-scooters had originally connected to cellular 2G and 3G networks. They needed to modernize and future-proof their fleet, and this meant new connectivity hardware and new SIMs—ideally with a single SIM for every market. This would allow them to create a single product stock-keeping unit (SKU), driving cost and complexity out of manufacturing and deployment processes.

Like every IoT device manufacturer scrambling to handle the sunsetting of 2G and 3G networks, this e-scooter company looked at NB-IoT and CAT-M and turned to Wireless Logic for guidance. Some national markets have great support for one or the other. A few support both. No one knows what MNO coverage for either will look like in a few years—or even a few weeks. For instance, Japan’s NTT DoCoMo discontinued its NB-IoT service in early 2020. 

For an IoT device that operates between networks and across borders, consistent operation across regional network coverage areas is a fundamental requirement that neither LTE-M nor NB-IoT can deliver on today. Wireless Logic ran a process that helped the e-scooter manufacturer understand and then assess the different trade-offs to be made. Ultimately the customer prioritized time-to-market over a modest hardware cost-saving and (for them) modest battery life benefits. They opted for the LTE CAT-1 protocol. LTE CAT-1 in general, and the single antenna version referred to as LTE CAT-1 BIS in particular (we will use CAT-1 from here on, but we’re referring specifically to CAT-1 BIS), are already present in every network’s technology stack across the globe. Everywhere MNOs support 4G networks—virtually everywhere—CAT-1 is ready to connect, with no network shut-downs anticipated.

In contrast, the customer couldn’t be certain that CAT-M or NB-IoT availability would align with their new pan-European product launch plans, nor that they would remain available throughout the life of their devices. They knew CAT-1 would. They measured the total cost of ownership (TCO) for their scooters versus the cost and lifespan of a CAT-1 module. It was a good match. Moreover, the simplicity of a single module that works in every national market made CAT-1 the right choice for these types of mobility applications. If your devices worked perfectly well on 2G or 3G networks in multiple geographies, it could be right for you, too. 

But CAT-1 isn’t a panacea. As any IoT solution provider knows, there are trade-offs for any LTE IoT standard. Here’s what you need to know about where CAT-1 sits in a debate that, too often, presents itself as a binary between CAT-M and NB-IoT. 

The Challenges of NB-IoT and CAT-M for Global Operations

To get an idea of the uneven roll-out of NB-IoT and CAT-M, look no further than the GSMA Mobile IoT Deployment Map. Glance over at Portugal, locked into NB-IoT coverage. You can’t currently roll out a CAT-M device there. Then look at Mexico, which conversely only supports CAT-M. You can’t roll out NB-IoT there. So what if you plan to sell your device in both markets? Dual-mode modules that support both CAT-M and NB-IoT are certainly available, but a single SIM that can handle both technologies in multiple countries does not exist. 

Source: GSMA

While this map is a helpful tool for device manufacturers, it also has its limitations. The GSMA doesn’t provide a lot of local detail on what works where. The map displays the U.K. as entirely purple (meaning both LTE-M and NB-IoT are supported.) That’s true at the national level, but not regionally. Coverage for LTE-M is expanding, but even as this article is published, LTE-M only covers around half of the nation. Meanwhile, NB-IoT coverage is generally more widespread than LTE-M in the U.K. but still doesn’t cover all regions currently. The point is, even this map paints an overly positive picture of CAT-M and NB-IoT support across the globe. 

We’re left with a snapshot in time that shows NB-IoT and CAT-M as a patchwork quilt of potential doubt for global device manufacturers. If one of the two technologies gets broader adoption within a certain region, MNOs may simply cut support for the other. This is already happening, as we saw with the case of NTT DoCoMo shutting down its NB-IoT service.

IoT manufacturers need to know their products will work everywhere they’re sold for the entire lifespan of the device. Ideally, they won’t face the expense of dividing their product lines into multiple SKUs, one for each market. Multiple SKUs lead to higher (and often hidden) TCO for IoT devices. CAT-1 modules provide this universal ability—and they also operate in regions of the world that don’t yet have support for CAT-M or NB-IoT, like the entire continent of Africa. These are enormous markets. For the foreseeable future, only CAT-1 can open them.

So if CAT-1 BIS provides future-proof, global functionality for IoT devices, why do NB-IoT and CAT-M get all the attention? One major reason is that they introduce novel advantages, which we’ll discuss below. Manufacturers and IoT solution providers must look closely at their markets, use cases, cost goals, and power budgets to make the right choice—and, depending on these specifics, any of these three protocols may be viable.      

Comparing CAT-1 BIS, LTE CAT-M, and NB-IoT

CAT-M and NB-IoT are grabbing headlines with their low power requirements. Of course, there are many ways to meet your device’s power budget. Your device might get parked or docked and recharge in the process, or it might get visited by a technician for normal support and service. You may use rechargeable or swappable batteries. For stationary devices, power-saving functions like Power Saving Mode (PSM) and eDRX are very valuable—although, at the moment, PSM and eDRX don’t always function when roaming across networks.   Ultimately, it’s true that when compared to CAT-M and NB-IoT, CAT-1 requires more power. At the same time, it only uses a single antenna, making CAT-1 modules easier to fit into devices. (Older CAT-1 modules used two antennas, so they took up more space.) 

All of this means CAT-M or NB-IoT may be a better option for longer-lived products. These modules can last up to 10 years, compared to less than half that for CAT-1 devices. That’s why it’s essential to consider product life when choosing an LTE IoT standard. If your devices are only meant to last for three or four years, and you want to deploy them as a single SKU across the world, CAT-1 has very real benefits.  

Then there’s the issue of cost. Depending on unit volumes, you’ll pay a bit more for CAT-1 modules than for CAT-M or NB-IoT—but over the timespan of a device lifetime, that small extra cost disappears pretty quickly. The cost per megabyte (MB) is roughly the same across all these technologies, however, and the near-universal access and roaming scenario for CAT-1 means it is far less expensive than CAT-M and NB-IoT.  

CAT-1 BIS for Global IoT Device Deployment

In short, CAT-1 is a strong contender for any global IoT device manufacturer, particularly in mobile assets. There’s evidence that it’s catching on; while the global market for cellular IoT modules shrank by 8% in 2020, CAT-1 grew to cover 23% of SIMs sold outside of China (which has invested heavily in NB-IoT—despite that technology locking users into a single MNO relationship).