## 1 Introduction  
The Internet of Things (IoT) has emerged as a potential game changer for the way people interact with technology on a daily basis, seamlessly connecting the physical and digital worlds by using the Internet. Although the general public strongly associates the IoT with concepts such as \"home automation\" or \"home appliances\", the truth is that the IoT aims at being (and has the potential to be) employed pervasively in many other environments--from industrial machinery to the water supply chain, Smart Cities (SC), Smart Grids (SG), etc. One of the main additional advantages of applying IoT technologies to these industrial fields is that we can rapidly improve infrastructure or industry performance in an affordable and cost-effective way [1]. Among these industrial fields, one particularly excels for its potential to have a particularly positive impact on the society via the application of the IoT: the SG [2]. The SG is called to revolutionize the way electricity is generated, distributed and finally consumed by every of us. By the inclusion of two-way communication systems, the electricity grid will become a more efficient, reliable, and flexible infrastructure [3], and although there are other technologies that could also be applied in the SG (like traditional centralized, wired communications), inexpensive deployment costs and the flexible and easy-to-configure nature of the IoT make it one of the most appropriate approaches for renovating the traditional power grid [1]. Nonetheless, like most Information and Communication Technologies (ICTs), the IoT strongly relies on wireless communications as its main enabling technology. Thus, deep insights into this form of transmission are of paramount importance to unleash the true potential of the IoT - and this is even more so in the SG where the complex and heterogeneous environments they operate in play a major role in the communication process. Many of these underlying wireless technologies that IoT systems employ, have been directly borrowed from Wireless Sensor Networks (WSN) or Mobile ad hoc Networks (MANET), as they originally paved the way for the emergence of these new paradigms [4]. Thus, communication technologies employed by most IoT devices are those used in WSNs or MANETs--either Mobile Telecommunications Technologies (MTT), such as 3G/4G [5; 6], Cognitive Radio (CR)-based solutions [7; 8; 9] or technologies operating in the 2400 MHz ISM unlicensed band, such as WiFi, ZigBee or Bluetooth [10; 11; 12]. Since IoT-based SG should strive for high levels of self-independence and cost-effectiveness, it is not generally advisable to rely on private or licensed bands (such as those used in MTT). Unexpected and uncontrolled MTT failures or high expenditure costs can make deployments economically or technically unfeasible. On the other hand, although wideband Cognitive Radio (CR) approaches have also been thoroughly studied in the literature, the increased cost multi-band transceivers makes this approach unfeasible if intended to be used in every device of an IoT network - note that the IoT is envisaged to consists of more than hundreds or thousands of devices [13]. For these reasons, most battery-powered IoT devices that are conceived to operate in SG use ISM bands [14], generally the 2400 MHz one, and employ low-power standards such as the 802.15.4, 6 LoWPAN or ZigBee [15; 16; 17]. Although there are other ISM unlicensed bands that have also been exploited since the emergence of the WSN (apart from the 2400 MHz), the evolution to the IoT left them practically unused. The reason to do so was the higher transmission rate that the aforementioned standards provide for the 2400 MHz band (250 Kb/s) along with lower power consumption (orders of magnitude smaller than other non-low-power 2400 MHz standards, such as WiFi, or other ISM bands such as the 5 GHz). Another key aspect known by the research community is that most of IoT-based SGs do not make extensive use of the network; they transmit information very occasionally [18].