The IoT technology landscape
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 an earlier series, the authors described the evolving landscape for cellular, its role in the IoT, and technologies for massive machine-type communications (mMTC) and ultra reliable low latency communications (URLLC).
This series dives more deeply into options for IoT connectivity, compares the alternatives, and describes key selection criteria for choosing among the options. This excerpt is presented in the following installments:
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Adapted from Cellular Internet of Things, by Olof Liberg, Marten Sundberg, Eric Wang, Johan Bergman, Joachim Sachs.
Chapter 9. The competitive Internet of Things technology landscape
By Olof Liberg, Marten Sundberg, Eric Wang, Johan Bergman, Joachim Sachs
This chapter provides an overview over connectivity solutions for Internet of Things (IoT) devices. An overview of short-range radio and low power wide area technologies that operate in unlicensed spectrum is given. Also the characteristics of using unlicensed spectrum are described. The properties of unlicensed technologies are compared with the CIoT technologies that operate in licensed spectrum. Finally, the performance of the different CIoT technologies, Extended Coverage Global System for Mobile Communications Internet of Things (EC-GSM-IoT), Long-Term Evolution for Machine-Type Communications (LTE-M), and Narrowband Internet of Things (NB-IoT) is reviewed and compared with each other. Benefits of the different CIoT technologies are discussed.
9.1 IoT CONNECTIVITY TECHNOLOGIES IN UNLICENSED SPECTRUM
9.1.1 UNLICENSED SPECTRUM
188.8.131.52 Unlicensed Spectrum Regulations
CIoT networks, such as EC-GSM-IoT, LTE-M, and NB-IoT operate in licensed spectrum. This means that mobile network operators have acquired long-term spectrum licenses from regulatory bodies in the country/region after, for example, an auction process. Such licenses provide an operator with exclusive spectrum usage right for a carrier frequency. Such spectrum licenses may also be combined with an obligation to build out a network and provide network coverage and communication services in a certain area within a certain time frame. This obligation in combination with the cost of the license motivates mobile network operators to invest upfront into a network infrastructure. This exclusive spectrum usage right provides the prospect of good financial returns on the investment obtained via communication services within the lifetime of the license. There are also other spectrum bands, which do not abide to the rules of licensed spectrum. In unlicensed or license-exempt spectrum any device is entitled to transmit as long as it fulfills the regulation without requiring any player from holding a license. These regulatory requirements have the objective to harmonize and ensure efficient use of the spectrum.
Unlicensed spectrum bands differ for different regions in the world. In the following an overview of the usage of unlicensed spectrum is provided for two bands, one at around 900 MHz and one at 2.4 GHz. These are of particular relevance due to their ability to cater for IoT services and popular wireless communication standards such as Wi-Fi and Bluetooth have been specified for these bands. The sub-GHz range around 900 MHz provides attractive propagation characteristics in terms of facilitating good coverage. The 2.4 GHz range is interesting because it is considered to be a global band, which is important for systems targeting a global footprint. While the 2.4 GHz band is globally harmonized, the sub-GHz range has regional variations. However, most regions have some unlicensed spectrum allocation even if they differ in their specifics. A more detailed description is here provided for the US unlicensed spectrum at 902-928 MHz and the European unlicensed spectrum at 863-870 MHz. In Europe, some differences in the allocations of the 863-870 MHz band exist on a per country basis. There has been significant market traction for IoT connectivity solutions operating in the unlicensed frequency domain in these two regions. In other regions, the unlicensed spectrum allocation in the sub-GHz range varies for different countries. For example, the allocations in Korea and Japan are overlapping with the US spectrum region, and China has an allocation that is below the European spectrum allocation, see e.g., Reference . Radio technology standards that are addressing the unlicensed spectrum around 900 MHz, such as, IEEE 802.11ah, are typically designed in a way, in which they provide a common technology basis for different channelization options in this spectrum range; the detailed channelization is then adopted to the region where it is deployed, see e.g., Reference  for the channelization of IEEE 802.11ah. IEEE 802.11ah is the basis upon which Wi-Fi HaLow is built.
For the United States, the usage of unlicensed spectrum for communication devices is regulated by the Federal Communications Commission (FCC) and it is specified in Title 47 Code of Federal Regulations Part 15 . For Europe, the spectrum rules are specified by the European Conference of Postal and Telecommunications Administrations (CEPT), which is a coordination body of the telecommunication and postal organizations within Europe. As of today, 48 countries are members of CEPT . The CEPT recommendation for usage of short-range devices in unlicensed spectrum is described in Reference . This recommendation is the basis for European Telecom Standards Institute (ETSI) harmonized standards, which specify technical characteristics and measurement methods for devices that can be used by device implementers to validate their devices for conforming with the regulated rules. Such ETSI standards are as follows:
- ETSI standard EN 300 220 for short-range devices operating in 25 MHze1 GHz [5,6],
- ETSI standard EN 300 440 for radio equipment to be used in the 1e40 GHz frequency
- ETSI standard EN 300 328 for data transmission equipment operating in the 2.4 GHz ISM band
and using wide band modulation techniques. Direct-sequence spread spectrum (DSSS), frequency hopping spread spectrum (FHSS), and Orthogonal Frequency-Division Multiplexing (OFDM) are considered to be wide band modulation techniques .
Table 9.1 European unlicensed spectrum at 863-870 MHz, for more details see Reference 
Table 9.2 US unlicensed spectrum at 902-928 MHz, for more details see Reference 
Some of the more relevant spectrum usage rules for unlicensed spectrum at 863-870 MHz in Europe is given in Table 9.1 and for 902-928 MHz in the United States in Table 9.2. The tables present, e.g., the maximum allowed radiated power and requirements for interference mitigation. While the ETSI regulations in the band 863-870 MHz mandate the power in terms of Effective Radiated Power (ERP), i.e., the radiated power assuming a half-wave dipole antenna, the FCC setsrequirements in terms of conducted power in combination with allowed antenna gain. Here we have converted these requirements to Equivalently Isotropically Radiated Power (EIRP), i.e., the radiated power assuming an isotropic antenna, according to the following equation:
EIRP = ERP + 2:15 dB …. (9.1)