## 2 Related Works
During the validation tests only 1.1 km transmission range was achieved within a city centre and no more than 2.7 km exploiting LoS conditions. Similar outcomes (i.e., 2.2 km and 2.5 km) were respectively achieved by the authors of Reference [21] and of Reference [22]. Each of the two groups of researchers set up tests on LoRa transmissions exploiting a comparable scenario with the one of article [3]. These results are pretty scant though if compared with the related ones of this paper where, to improve the performances of the communication channel, two diversity schemes (i.e., space and frequency) were simultaneously established. The former was achieved by setting up two Gateways whose antennas occupied different spatial locations; the latter was reached due to the fact that, conversely from the prototype presented in the former work [3], the firmware running on this sensor node implemented the LoRaWAN protocol which provides for frequency hopping amid different channels. The authors of Reference [23] also tested performances of LoRa links in an extremely high density urban area and the authors focused on assessing complete loss free communication. They installed a multi-channel LoRaWAN Gateway at a pretty high elevation (i.e., 40 m above the ground) by exploiting an existing building and then they tested a sensor node at the ground level periodically transmitting while it was carried around by a walking person. The results were in contrast with what several technical reports aver: in such a test-bed, LoRaWAN proved to be capable of tracking a person walking at street level without packet losses only within a 200 m range from the Gateway and a total loss of transmission was experienced at 600 m.  
In Reference [1] the Italian city of Padua, which is a less dense urban environment in comparison with the one of Reference [23], was exploited as application scenario. Understanding how many Gateways should be deployed throughout the city in order to ensure a full LoRa citywide coverage, with the target of realising an infrastructure for smart city contexts, was one of such paper aims. The first step was to evaluate the coverage capabilities of a single Gateway and, according to the desired specifications of the paper, it was found out that a single Gateway covered a zone having a radius of 1.2 km. Since Padua extends over an area of around 100 km\({}^{2}\), then an amount of 30 Gateways should be disposed. Similar results in terms of coverage assured by a single Gateway were also achieved within the article [24] where a slight different application scenario was proposed. However, Reference [24] shares testing methodologies and procedures with Reference [1]. With regards to long LoRa links, References [25; 26] put forward interesting clues validated by a common measurements setup exploiting an overhead location (i.e., a mountain) to install one of the two end links. While the deployment scenario described in this paper does not present such orographic properties, comparable results were achieved, in terms of correctly received packets, with the ones obtained by the authors of Reference [25]. For what concerns the covered distance, they achieved a longer link with respect to the one presented in this paper. Nevertheless, we experienced enough link margin during the tests suggesting that more extended distances might have been covered. Reference [26] deserves particular attention. Indeed, apart from exploiting LoS conditions and 60% clearance of the first Fresnel zone due to the possibility of making use of a mountain, an especially designed LoRa transceiver having enhanced characteristics, thus increased performances, was realized and employed for the tests. In so doing, the impressive covered distance of 112.5 km was obtained. On the other hand, the sensor node used in this paper to perform the validating measurements campaign is based on general purpose off-the-shelf components, and is then not optimized as that exploited within Reference [26].