Internet of things (IoT) communications are considered as part of the last generation of wireless communication systems. As such, IoT represents a concept that leads to several design techniques to achieve different efficiency and performance objectives. In that scenario, base stations must be able to have an extended coverage for a massive number of low data rate nodes. On the other hand, IoT nodes are required to be low cost devices with restrictions on the total available power (i.e., battery operated) and processing capability. From the perspective of the nodes, the power constraints motivate the implementation of low cost, energy efficient devices operating with minimal transmission power and employing low constellation size. Regarding the base station extended coverage, depending on the frequency band used, several alternatives are considered. For the unlicensed ISM band, spread spectrum based or narrow-bandwidth based techniques are available, with very successful commercial products. For the licensed (cellular) bandwidths, there are also very interesting alternatives in terms of cost and coverage represented by: extended coverage-GSM (EC-GSM), machine-type LTE (LTE-M), and narrowband IoT (NB-IoT). Main characteristics of these techniques are related to the intensive use of repetitions and frequency diversity to obtain the extended coverage expected, the low cost premise to define the node devices and the compatibility (and simple software upgrade) with established cellular standards. Different from previous chapters, we use this chapter to illustrate design aspects of a particular IoT standard: NB-IoT. Emphasis is placed on its key features: frequency band used, cost, number of devices allowed, power consumption and capacity. To illustrate the performance of NB-IoT, we include the analysis of uplink RF impairment effects when LTE and NB-IoT coexist.
Gregorio, F., González, G., Schmidt, C., & Cousseau, J. (2020). Internet of Things. In Signals and Communication Technology (pp. 217–245). Springer. https://doi.org/10.1007/978-3-030-32437-7_9