Four Bars: Low-Power Cellular for IoT at Scale

Cellular connectivity has traditionally been a small slice of the pie when it comes to IoT deployments. Despite being a nearly ubiquitous source of wireless connectivity, cellular connections were impractical for all but very few projects. One of the biggest obstacles to the broader use of cellular for IoT was the high cost of its hardware for IoT devices and the expense of ongoing data transfer costs. Those two price tags were fine for media-intensive consumer devices like smartphones and tablets but far too costly for the vast majority of IoT projects with large numbers of low-cost devices delivering small, intermittent data packets.

Battery Power

The other major obstacle to the greater use of cellular for IoT was how fast it drained battery power. The high energy usage of cellular’s “always-on” radio architecture may have been ideal for phones. Still, it was a huge disadvantage for IoT devices expected to stay in the field for years without the need, or possible opportunity, for a battery change.

Those two disadvantages overshadowed multiple cellular strengths for IoT, including the biggest advantage: the widespread LTE network infrastructure that already exists in so many geographies. That massive infrastructure built and maintained by major telecom companies represented already-built, highly-reliable backhaul infrastructure for IoT if only those two drawbacks above could be overcome. Two low-power, low-cost versions of cellular technology—LTE-M and NB-IoT—accomplish exactly that, allowing cellular IoT to become a practical option at scale for the first time.

LTE-M and NB-IoT

These two new versions of LTE cellular solve both drawbacks that prevented cellular from being practical in the past. Unlike the always-on architecture of the primary specification of cellular technology, LTE-M and NB-IoT are designed to preserve battery life through sleep cycles and other energy-saving features (known as eDRX and PSM modes) that enable devices to go 10 years or more without a battery change. LTE-M and NB-IoT also solve the cost issue with hardware and data costs that make them competitive with other wireless connectivity technologies. Using the cell network only intermittently for delivering batches of occasional data, operating costs are minimized with LTE-M and NB-IoT. LTE-M and NB-IoT also remove the expense of a company having to build out and maintain network infrastructure by using public LTE network infrastructure.

By removing those disadvantages, LTE-M and NB-IoT turn cell towers into ubiquitous infrastructure for IoT. Anywhere you have bars on your phone, you can deploy IoT devices that tap into the same digital infrastructure. That is significant for a long list of use cases, including smart city initiatives, the cold supply chain for food and vaccines, telehealth monitoring of remote medical devices, remote monitoring of industrial equipment – all of which have connectivity challenges that are solved by the ubiquity of cell connectivity.

Low-Power Cellular Versions

Low-power cellular was created as two versions. This gives engineers the ability to pick which set of features is best suited for their given device and network. LTE-M gives engineers the ability to design with a wider bandwidth, offers a higher transfer data rate than NB-IoT, and achieves a battery life of up to 10 years. Engineers typically use LTE-M when higher-throughput is a top priority for a given project’s performance and when coverage penetration is lower. NB-IoT gives engineers better coverage penetration and longer projected battery life than LTE-M. Engineers typically use NB-IoT when a device’s use case and deployment environment make coverage penetration a higher priority than maximizing throughput.

One of the key design considerations for engineering teams to keep in mind about low-power cellular is that you do not face a high stakes choice between the two versions at the beginning of an IoT project. Cellular IoT allows you to embed both technologies in a device so that your team can use one or the other based on how the device will be used later on and where geographically your product will be used. The provisioner can later optimize the device’s and IoT network’s performance by leveraging whatever makes the most sense on a device-by-device basis.

One important thing for engineering teams to keep in mind when they work with cellular technology is certifications. Certifications can be arduous for any cell-connected device because of the additional certification hurdles for products with a cellular radio, including regulatory agencies (e.g., FCC/IC, etc.), network approvals (e.g., PTCRB/GCF), and carrier approvals (e.g., AT&T certifications). But that process can be accelerated and simplified using pre-certified cellular IoT socket modems and by having an experienced wireless design company as a partner.

Power-Saving Modes

One of the most important pieces of advice I give to engineers starting to work with cellular IoT is working with power-saving modes. LTE-M and NB-IoT give engineers a lot of control over sleep settings to balance performance and power consumption. The key features to know are PSM and eDRX, which work in concert to make the battery life of up to 10 years possible. PSM, which stands for Power Saving Mode, allows devices to be programmed to go into a deep sleep mode while still being reachable. You can program the sleep cycle with various parameters, sleeping for a moment or more than a year. It saves power almost to the same degree that powering a device off would achieve, yet the device remains registered with the network. It does not need to expend time and energy reestablishing network connections. The other sleep cycle feature to take advantage of is eDRX (Extended Discontinuous Reception), which allows engineers to optimize the length of time between paging cycles by programming customized pauses between paging cycles that is far longer than the default. This extension of paging cycles by as many seconds or minutes as an engineering team wants reduces power consumption significantly.

Cloud Connectivity

Another important piece of advice I give to engineering teams about cellular IoT is about cloud connectivity. Cloud is essential for cellular IoT because data management can have such a big impact on operational costs. Even though NB-IoT and LTE-M are designed to minimize data costs, engineering teams can carefully control those costs through the cloud strategy used. By carefully weighing what you want a device to send to the cloud, what you don’t want to send, how often you want that to happen, etc., you can minimize your network’s data transfer periods in ways that give you a lot of control over those costs.

Antenna Selection

One last important consideration for low-power cellular projects is antenna selection. Choosing any antenna is a complex process, particularly for cellular projects because the frequency range is so broad and with segments of the band owned by different carriers. That selection process becomes even more complex when combining LTE-M and NB-IoT with a short-range technology like Bluetooth. Working with a consultant or firm with expertise in antenna selection and implementation can ensure that you choose the right antenna, install it in the right location on the device, and optimize performance for the implementation's exact role and physical location.