LTE CAT M1: The sweet spot for IoT connections

Jul 19, 2019

LTE CAT M1: The sweet spot for IoT connectionsThis article explains LTE CAT-M1 in relation to its competing technologies and examines some of the pros and cons of each.

The telecommunications industry now has a new, IoT-friendly standard: CAT-M1. CAT-M1, sometimes referred to as LTE-M1, LTE CAT M1 or CAT M, it is a technology that enables connection directly to a 4G network without a gateway, connecting IoT devices to the internet via the cellular network.

The first advantage

One of several technologies known collectively as an LPWA (Low Power Wide Area), the CAT-M1 network is operated by cellular network providers utilizing their own frequency bands. It is this ownership that is the first notable advantage over competitors such as SigFox and LoRa WAN.

By controlling the devices that are able to use their network, telco’s have secured the long-term quality of this service.

Meanwhile, competitors Sigfox and LoRa have opted to use unlicensed ISM (Industrial, Scientific, Medical) bands.

The blessing and curse of unlicensed bands is that they are free for everyone to use.

The blessing and curse of unlicensed bands is that they are free for everyone to use. This may jeopardize quality of service in years to come as neither Sigfox nor LoRa have any influence should the behavior of other users of these frequencies become harmful or disruptive to their customers.

The use cases are different for different regions and some rules in some countries are not kind to LPWA networks. For more information on this please see article by David Castells-Rufas, Adria Galin-Pons and Jordi Carrabina

No need to shout loud

Cellular network operators also have another advantage: they use cell technology.

As a rebuttal competitors claim that their tech needs fewer “tower points” to provide coverage compared to conventional cell operators because it can transmit over longer distances. On paper, this would seem like an enormous benefit with regard to infrastructure costs. However, this is achieved by the devices transmitting on full power at all times.

To get an idea of the implications of this, let’s relate it to human interactions. Firstly Sigfox and LoRa:

Imagine a room half full of people. Certain individuals are permitted to shout messages to others across the room. They do so by following these rules:

  • Messages can only be yelled once every 10 minutes
  • Messages must be repeated 3 times (in case someone else is also yelling at that moment)

As the room fills up the amount of messages that everyone is allowed to share has to decrease to accommodate the growing number of shouters. So this type of messaging works best with short one-way message payloads.

But with cell technology human interactions would be more like the following:

People in the room are split into small groups. They huddle together so there’s no need for shouting and relevant messages can be heard above the low volume of chatter from the other groups. Much more information can be shared this way.

LTE CAT-M1 best positioned for the coming IoT revolution

Until now the primary driver for cell network providers has been to service the insatiable human demand for live streaming HD video and music directly to mobile devices. But it has been determined that most IoT devices do not require this kind of bandwidth and so CAT-M1 has been optimized for this lower bandwidth IoT world.

While the looming 5G promises bandwidth speeds of 1Gbit per second, CAT-M1 is happy to play at around 256Kbits per second.

One of the by-products of this is a significant increase in coverage as by reducing RF bandwidth, signal-to-noise ratio increases.
A report by AT&T suggests that this technology can increase coverage by a factor of 7. In practical terms this means that in locations where 4G fizzles out CAT-M1 continues to work just fine.

Coverage Comparison

While 5G promises bandwidth speeds of 1Gbit per sec, CAT-M1 is happy to play at 256Kbits per sec.

Consider the benefits of this coverage to devices in remote country areas or deep in the basements of buildings. Where once it was virtually impossible for signals to reach these locations CAT-M1 technology now makes it possible, and best of all there is no wait time while networks are built – they already exist!

Some of the other advantages that CAT-M1 provides:

  1. Supports native TCP which features TLS (Transport Layer Security), encryption and security certificates.
  2. Direct connection to leading cloud providers like AWS, Microsoft Azure, Google cloud, et al without routing through third party servers. (Sigfox sends all data from Sigfox devices to their servers in France before redistributing it to other cloud providers.)
  3. Supports bi-directional data and always connected states. With latencies of less than a second this is perfect for alarm monitoring and remote-control applications.
  4. Bandwidth is enough to support voice calls and still photos. Also great for alarm systems
  5. Supports OTAU (Over The Air Updates) essential for future-proofing IoT applications. By enabling software updates to be deployed remotely, it removes the need to visit the (possibly far removed) location.

Initial and ongoing cost considerations

Because CAT-M1 is a more complex unit than the likes of Sigfox, the amount of silicon required is greater and costs should therefore be higher. However some prices sighted have been as little as $6.50 US. It’s likely that this pricing is the result of telecoms subsidizing traffic to enter their network. In the free market the price is a more realistic $20 US per module but these prices are expected to fall over time.

Some plans on offer start at $0.85 US per month for a limited data plan and $1.50 US per month unlimited data at 256Kbits per second. With such affordable choices an application with 150 sensors updating to the Cloud every minute could cost as little as 1 penny per month per sensor.

Into the future

CAT-M1 has been a valuable and welcome addition to the LPWA IoT landscape. Although it has arrived late to the party, it is well thought out and brings numerous advantages. It promises to be a reliable and well-maintained option. More akin to a Toyota Corolla than a pre-war Volkswagen Beetle.

Anthony Glucina is an IIoT consultant and CEO of Define Instruments, an industrial instrumentation manufacturer. He has worked in the industrial engineering space for over 25 years and holds a Master’s degree in Engineering.

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