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Why Low-power Cellular Will Underpin the IoT


by Peder Rand, Product Manager for Cellular IoT, Nordic Semiconductor

First generation (“1G”) cellular communications debuted in the 1970s. Analog systems handled the traffic and the handsets were cumbersome and expensive. But the idea caught on, and by 1990 the number of global subscribers reached 20 million. Fast forward 28 years and according to the GSM Association (GSMA), an organization that represents the interests of mobile operators, the subscriber base has surpassed five billion. And the latest generation of cellular technology, 4G Long Term Evolution (LTE), now reaches over 50 percent penetration in over 70 countries around the globe and supports inexpensive high-definition streaming services that couldn’t have even been imagined just a decade ago.

The prolonged gestation and maturation of cellular has allowed engineers to optimize the technology to meet consumer and commercial demands of ubiquity, reliability, security and ease-of-use. It has also given carriers the revenue and time to build and enhance the huge infrastructure required to support global coverage.

Cellular technology offers better coverage than any other wireless technology. Its reliability comes from the years of constant technical refinement and fierce competition among the carriers and device makers. Security—a major consideration for engineers building wireless systems—is an end-to-end priority for cellular networks. And high throughput is built in to meet the demands of millions of subscribers accessing streaming video and other data-intensive services. These strengths are reinforced by the high quality of service (QoS) that comes as a consequence of a robust protocol and the regulation, licensing and management of spectrum allocations used for cellular communication.

The many advantages of cellular technology have attracted the interest of engineers tasked with building the Internet of Things (IoT). Cellular promises a solution for directly connecting the IoT sensors of long-range, low power wide area networks (LPWANs) to the Cloud. In addition, cellular technology could be used as the basis of LPWANs that act as gateways to the Cloud for local area networks (LANs) powered by short-range wireless technologies such as Bluetooth Low Energy (Bluetooth LE) or Thread. But there’s still some work to do before either vision turns into reality.

Modems for IoT Applications

High-throughput cellular technology is extremely complex and expensive, and the hardware is bulky and power hungry. Consumers are willing to bear the cost and recharge their handsets daily because the technology provides seamless access to the services they crave. But for IoT engineers, high-throughput cellular technology’s high-cost, -complexity and -power consumption make it tough to build the networks of hundreds of compact, battery-powered sensors that will form the IoT.

Yet, cellular modems have found a niche for connecting expensive remote assets to the Cloud. For example, rural Intelligent Electronic Devices (IEDs) used to control smart electricity distribution grids routinely send information back to a control center via a cellular modem. And operators of commercial equipment like vending machines (sited in public places such as rail stations) can cut operating costs by using a cellular modem to send information back to HQ rather than dispatching a service operative to manually check stock levels. Cellular modems are also popular with security companies who can’t take chances with less reliable wireless technologies such as Wi-Fi.

But the modems that power these applications are unsuitable for the IoT. First, many use legacy 2G networks which are being phased out—the spectrum allocations are used inefficiently and are sorely needed for 4G and forthcoming 5G traffic—and will have virtually disappeared by 2025. Second, cellular 2G, 3G and 4G LTE modems are expensive, bulky, and power hungry because they have to be designed to meet 3rd Generation Partnership Project’s (3GPP)—a collaboration of telecoms standard associations—specifications for higher category (higher throughput) operation.

Recognizing the drawbacks of traditional modems for the unique, low-cost, -throughput, and -power demands of the IoT, the 3GPP extended the modem categories to include LTE category M1 (LTE-M) and narrow band (NB)-IoT in Release 13 of its specifications in 2015. Such a move encouraged the development of 4G LTE modems for IoT applications—applications that were impractical when based on higher category units.

Worldwide LTE infrastructure is largely in place, comprising 480 networks in 157 countries. (Source: Milonica.)

LPWAN Mass Deployment

Nordic Semiconductor and others believe LTE and NB-IoT modems offer the most promising technology for kickstarting rapid mass deployment of LPWANs and accelerating growth of the IoT. This belief is built on the fact that LTE is an open standard, operates in a licensed portion of the RF spectrum, leverages existing infrastructure for coverage, and has coexistence mechanisms that enable scaling to high-node counts per base station. In contrast, competitive LPWAN proprietary technologies include components owned and controlled by certain companies—which incur licence fees when adopted by other vendors and limit room for product differentiation—and operate in unlicensed allocations of the RF spectrum (typically at sub-1 GHz frequencies). Because these bands are a shared resource they present tough coexistence challenges.

Technologies such as IEEE 802.11 and Bluetooth wireless have repeatedly shown that open standards stimulate rapid adoption of new technology. Similarly, low power LTE is likely to lead to “massive IoT” deployment according to companies such as telecoms equipment maker, Ericsson, and GSMA, which independently forecast that the market for cellular IoT will expand at around 27 percent compound annual growth rate (CAGR) between 2017 and 2021. Both firms point to low-power LTE as a key enabler for this growth.

Low-power LTE operates in already allocated, licensed frequencies across the world. The advantages of licensed spectrum are particularly beneficial for many IoT applications; key among these are that the owners of the spectrum allocation (the carriers) can control and prioritize data, and the bands are immune from interference from other sources of RF transmissions. Second, because the spectrum allocation isn’t shared with other RF broadcasts, coexistence between connected devices is much easier to manage. LTE’s coexistence technology is based on proven frequency- and time-domain solutions, and other mechanisms such as “autonomous denials” of conflicting RF signals.

Consequently, LTE can support a node density of up to 200,000 active low-power modems per base station. Finally, data carried over the LTE protocol is safe from prying eyes because the standard has incorporated advanced security from its inception. These features ensure that carriers can offer reliability and high quality of service (QoS).

 In contrast, proprietary technologies rely on unlicensed portions of the RF spectrum which must be shared with many other services. While interference avoidance techniques are employed, because so many services are sharing the spectrum allocation, it is extremely difficult to approach, let alone match the node density, reliability and QoS of LTE. Proprietary LPWAN vendors are also faced with the major challenge of building infrastructure to support their networks. These are likely to be expensive and long-winded projects, slowing adoption.

Worldwide LTE infrastructure, comprised of 480 networks in 157 countries, is largely in place. Some upgrading (mainly of software) is required to support low-power LTE, but this is trivial compared to building the infrastructure in the first place. Because the infrastructure is installed, support for low-power LTE is likely to be added rapidly, further encouraging its uptake. Test installations are already built, and commercial deployments are already available in some countries. By the end of 2018, a significant portion of the world will feature network coverage.

Companies adopting low-power LTE for their IoT-connected products can leverage this infrastructure without bearing its build or maintenance costs, instead investing in their own services and business models.

And as the telecoms network evolves from 4G systems to 5G, low-power LTE won’t be rendered obsolete because 3GPP has ensured there’s an upgrade path for the technology. 5G, while some years away, will provide much greater throughput by using higher wireless frequencies (up to 26 GHz) and will impart even greater momentum to the IoT.

Designed for the IoT

LTE-M and NB-IoT products are already starting to trickle onto the market. At Nordic Semiconductor, the company’s Finland-based engineers have combined their LTE expertise with that of the Norwegian engineers’ ultra low power wireless know-how to design an optimized cellular IoT solution complying with the 3GPP’s LTE-M and NB-IoT specifications.

The result is the nRF91 Series System-in-Package (SiP), a low power, ultra compact cellular IoT solution. Because it has been designed to meet the unique demands of the IoT, the product’s designers have adopted a completely different approach to that employed for conventional cellular modules and have added a host of features never before seen in the cellular market.

The heart of Nordic’s nRF91 Series is formed by the company’s low power, global multimode LTE-M/NB-IoT System-in-Package (SiP). The SiP forms a complete low power cellular IoT system in a 10 by 16 by 1.2-mm package that integrates modem, transceiver, RF front end, dedicated application processor, flash memory, power management, and crystal and passive components (Figure 1). 

Figure 1: The nRF91 Series SiP has been jointly developed by Nordic’s experienced cellular design team in Finland and its low power wireless experts in Norway. The SiP comprises RF front-end, nRF91 Series SoC, and regulator.

The SiP combines all the benefits of traditional cellular modules, including tele-regulatory and cellular certifications, into a form factor with a footprint 33 percent the area, 50 percent the thickness, and 20 percent the total packaging volume of competing solutions (Figure 2). 

The SiP is based on an integrated Arm Cortex-M33 host processor. The embedded processor features TrustZone for Armv8-M together with Arm CryptoCell-310 security IP. Such an arrangement secures application data, firmware and peripherals using an isolated, trusted execution environment across the microprocessor and system. This solution provides an efficient security foundation, and reduces size, bill-of-materials (BOM), and power consumption compared to using an external host processor.

Nordic has partnered with Qorvo, a U.S.-based RF connectivity solutions company, as a strategic partner for both the RF front end and the SiP development and manufacturing. The nRF91 SiP employs Qorvo’s proven RF front-end, advanced packaging, and MicroShield technology to deliver a compact solution that combines high performance with low power consumption. The nRF91 Series supports global operation with a single SiP variant thanks to the combination of Nordic’s multimode LTE-M/NB-IoT modem, SAW-less transceiver, and the custom RF front-end solution from Qorvo.

Figure 2: The nRF91 Series SiP is a highly integrated, ultra compact, low power cellular IoT solution

Nordic’s low power cellular IoT solution also features built-in support for positioning via integrated Assisted GPS (A-GPS) technology that combines cellular and GPS technology for fast and accurate positioning.

Cellular for Everything

Through its high integration and its precertification for global operation, the nRF91 Series SiP overcomes the traditional drawbacks of cellular for LPWAN deployments as well as satisfying the comprehensive set of qualifications needed to employ cellular technology. 

A key advantage for developers who are unfamiliar with cellular engineering but want to take advantage of the technology comes from the way Nordic has implemented the nRF91 Series SiP’s design. The company has applied the strategy it used for its Bluetooth LE solutions to this new product. With Bluetooth LE technology, Nordic masked the underlying complexity of RF engineering by supplying complete single-chip (radio plus processor) wireless hardware and factory-supplied RF protocol stacks. Development and debugging is eased by keeping the RF protocol stack separated from the application software. 

While the software architecture of the nRF91 Series remains under wraps for now, Nordic’s strategy to aid developers—masking the inherent complexity of RF engineering while making it as simple as possible to code and debug wireless applications—remains. That will make cellular technology accessible to all and encourages developers with little experience in wireless to explore its advantages and unleash their creativity to come up with new products. This strategy has seen Nordic Bluetooth LE technology spread around the globe; the nRF91 Series SiP promises to do the same by bringing cellular technology to everything beyond the smartphone.

And not a moment too soon. According to Ericsson, cellular will rapidly expand to power 75 percent of the 1.8 billion LPWAN connected devices in service by 2023. 

Cellular carriers such as Norway’s Telia are already seeing a large appetite for the technology: “Telia is experiencing an unprecedented demand for dedicated IoT connectivity represented by LTE-M and NB-IoT,” said Andreas Carlsson head of Telia Next, in a statement. “That’s why Telia has been a supportive partner to Nordic Semiconductor in its development of the new product.”