## 5 Results and Discussion
During these trials, the LoRaWAN Node sent 2117 packets and the NB-IoT Nodes received 2086 packets (i.e., a successful complete communication paradigm was experienced in 98.54% of the times). Although this test provided better results with respect to Test #2 from the point of view of packet loss, it has to be remarked that, in Test #3, no timeouts occurred. That is also the reason why mean latency and latency standard deviation values (i.e., in turn \(\mu_{L}=32.0216\times 10^{3}\) ms and \(\sigma_{L}=19.4938\times 10^{3}\) ms) were particularly bigger than \(\mu_{RTT}\) and \(\sigma_{RTT}\) of Test #2. However, this should not be considered as a hindrance because such latency values can be commonly found whenever LoRaWAN protocol is employed for monitoring purposes due to the regional regulation concerning ISM bands temporal occupancy. On the other hand, the paradigm in which a sensor is LoRaWAN enabled and an actuator is NB-IoT enabled was proven to be a reliable and effective solution owing to the fact that NB-IoT is not devised to be capable of receiving downlinks within predefined temporal slots (as opposed to LoRaWAN). A finer analysis can be accomplished by considering the latency CDF. It can be noticed that latency is above \(\mu_{L}\), with a probability of 0.4789. Even though it could obtain a  
Figure 8: Test #2 results on RTT: (**a**) temporal trend; (**b**) CDF; (**c**) PDF; (**d**) box-and-whisker plot along with QQ plot. better result with respect to Test #2, the CDF hints at the fact that the data are more spread out than RTTs. Indeed, the latency is longer than \(42.1931\times 10^{3}\) ms, \(54.1691\times 10^{3}\) ms and \(79.9798\times 10^{3}\) ms with probabilities of 0.3015, 0.1016 and 0.0187. Accordingly, the spread of latency is remarked within the relative PDF, which shows a considerable platykurtosis apart from the outliers, which are also visible within the box-and-whisker plot. Lastly, the QQ plot confirms that, besides such outliers, the experimental data decently follow the distribution \(N(\mu_{L},\sigma_{L}^{2})\). Similar to what was said for the discussion of Test #2, the experimental data can never be negative since latency is considered; thus, a perfect overlapping with the aforementioned distribution cannot be met. Figure 10 displays the results of the Gateways power consumption test. At first glance, two main findings can be noticed: on the one hand, both current draws exhibit the same trend; on the other hand, the LoRaWAN-NB-IoT Gateway turned out to need less power than the standard LoRaWAN-4G. However, this result is far from unexpected. Indeed, NB-IoT facility was devised to be more efficient from the point of view of energy requirements than standard cellular technologies such as 4G. At the same time, it has to be said that the difference in terms of current draw is scant because the LoRaWAN-NB-IoT Gateway of this paper is only a prototype. Conversely, the exploited 4G dongle is a commercial product, and therefore, it underwent an optimisation process resulting also in power optimisation. The initialisation phase is the energy-hungrier one, requiring up to 1.25 A and 1.35 A, respectively, for NB-IoT and 4G. In addition, such procedures last 92 s and 73 s in turn for NB-IoT and 4G, hence noting the prototypical stage of the LoRaWAN-NB-IoT Gateway of this paper. After these time periods, the Gateways indefinitely listened for incoming  
Figure 9: Test #3 results on latency: (**a**) temporal trend; (**b**) CDF; (**c**) PDF; (**d**) box-and-whisker plot along with QQ plot. LoRaWAN packets averagely, drawing 877 mA and 900 mA individually for NB-IoT and 4G. During these listening periods, some peaks can be noticed, but they cannot be ascribed to reception of the LoRaWAN packets since they are not synchronised with the transmission instants (i.e., 95 s, 110 s, 125 s, 140 s, 155 s and 170 s). If it would not be so, then the current draws should be periodic from the first transmission time instant (i.e., 95 s) on.