The Cellular Internet of Things -- Mobile broadband
Editor's Note: Growing requirements for increased availability of IoT devices coincide with the emergence of cellular technologies well suited for the IoT. For developers, the need has never been more acute for more detailed information about cellular technologies and their application to the IoT.
Excerpted from the book, Cellular Internet of Things, this series introduces key concepts and technologies in this arena. In part one, the authors described the evolving landscape for cellular and its role in the IoT. This article reviews massive machine-type communications (mMTC) and ultra reliable low latency communications (URLLC).
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Adapted from Cellular Internet of Things, by Olof Liberg, Marten Sundberg, Eric Wang, Johan Bergman, Joachim Sachs.
Chapter 1. Cellular Internet of Things
By Olof Liberg, Marten Sundberg, Eric Wang, Johan Bergman, Joachim Sachs
From a service, applications, and requirements point of view, the IoT market is often said to be divided into at least two categories: massive machine-type communications (mMTC) and ultra reliable low latency communications (URLLC). The Next Generation Mobile Networks Alliance is in its 5G white paper  describing these two categories in terms of typical use cases and their associated requirements. Smart Wearables and Sensor Networks are two industrial vertical features mentioned as belonging to the mMTC market category. Smart wearables comprise not only, e.g., smart watches but also sensors integrated in clothing. A main use case is sensing health-related metrics such as body temperature and heartbeat. It is clear that if this trend gains traction, the number of devices per person will go far beyond what we see today, which will put new requirements on the capacity that must be supported by cellular networks providing IoT services. It can furthermore be expected that in order for clothing manufacturers to find wearables an appealing concept, the devices must be extremely compact to support seamless integration in the clothing. The devices must also be of ultra-low cost to attract clothing manufacturers as well as consumers.
Sensor networks is a family name for various utility meters such as gas, water, and electricity meters. Potentially, every home is equipped with a multitude of sensors that will put high requirement on the capacity of the communication system providing them with connectivity. As utility meters are associated with stringent requirements on coverage, which is radio resource consuming, the task to provide sufficient capacity for these becomes even more challenging. Meters may in addition entirely rely on battery power, which will put high requirements on device energy efficiency to facilitate operation for years on small and low-cost batteries.
URLLC can, on the other hand, be exemplified by high-end applications such as automated driving, industrial automation, and eHealth. The news is filled with articles about traditional car manufacturers and giants from the ICT industry competing in the development of autonomous vehicles. If such applications are to be supported by cellular communication networks, the network needs to offer close to perfect reliability combined with support for extreme latency requirements. It is also not far-fetched to imagine remote steering as an attractive alternative to, or perhaps first step toward, fully autonomous vehicles. In this case also requirements on support for high data rates to support high-resolution video may come into the picture. Similar requirements can obviously also be mapped to the industrial automation and eHealth verticals.
Figure 1.1 summarizes the just-made observations with a high level illustration of expected requirements for the mMTC category and the URLLC category in terms of coverage, number of supported connections, latency, throughput, mobility, device complexity, and device battery life. For comparison also typical mobile broadband requirements discussed in Section 2.1 are depicted. The center of the radar chart corresponds to relaxed requirements while the outskirts of the chart map to stringent requirements.
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FIGURE 1.1 mMTC, URLLC, and mobile broadband requirements.
1.2.3 INTRODUCING EC-GSM-IOT, NB-IOT, AND LTE-M
The three technologies EC-GSM-IoT, NB-IoT, and LTE-M, described in Chapters 3-8 in this book, were to a large extent designed to serve use cases belonging to the category of mMTC. The work on LTE-M started in September 2011 with the 3GPP feasibility study named Study on Provision of Low- Cost MTC UEs Based on LTE , referred to as the LTE-M study item in the following. The main justification for this study item was to extend the LTE device capabilities in the low-end MTC domain, provide an alternative to General Packet Radio Service (GPRS) and Enhanced General Packet Radio Service (EGPRS) devices, and facilitate a migration of GSM networks toward LTE. As the aim was to replace GPRS/EGPRS as a bearer for MTC services, the study naturally used GPRS/EGPRS performance as the benchmark when setting its objectives. It was, e.g., required that data rates, spectrum efficiency, and power consumption should be at least as good as EGPRS. The main focus of the study was, however, to provide a solution with device complexity and cost on par with GPRS. In September 2012, it was decided to add a new objective on study of the feasibility of a coverage improvement of 20 dB beyond normal LTE coverage.
LTE devices have typically been considered far more expensive than GPRS/EGPRS devices, mainly because of the improved capabilities provided by LTE. Therefore for LTE to become competitive in the low-end mMTC market, a reduction in device cost and complexity was considered crucial. The coverage enhancement was considered to be needed to facilitate deep indoor coverage in locations where, for example, utility meters are expected to be located.