## 2 Related Works
#### LoRa Transmission over Water Basins  
This Subsection exposes related works on LoRa links in marine and lacustrine environments that a priori confirmed the feasibility of such broadcasting. Indeed, as it was said earlier on,telecommunications over water, especially over the sea, are a tough problem since water basins act as huge ground planes entailing odd reflection occurrences. Thus they can be labelled to all intents and purposes as harsh environments. The conference article in Reference [27] shows a LoRa network to implement a sailing monitoring system. The system was tested on a lake by installing sensor nodes on board of sailboats whose antennas were placed at 1.5 m above the water level while the one of the Gateway was installed at 4 m above the water level. Such elevations are comparable with the ones tested in this paper. The big differences between our tests and the ones of the aforesaid paper are the exploited Industrial, Scientific and Medical (SM) band (868 MHz and 433 MHz respectively), the transmitter power output (in turn, 25 mW and 100 mW), the tested SFs (all the SFs and only three SFs severally) and the tested Bandwidths (BWs) (125 kHz for our tests while both 250 kHz and 500 kHz where selected by the authors of Reference [27]). Notwithstanding these dissimilarities, similar outcomes may be observed: we were able to cover longer distances though ensuring lower rates of received packets. Saline lakes are a hybrid scenario between a freshwater lake and the sea. They are massively exploited to mine salt by means of brine pumps. Hence, a remote real-time monitoring for such machineries is required in order to prevent them from failures. What has just been described is exposed in Reference [28] where a group of researchers set up a LoRa based LPWAN to monitor brine pumps installed in brine wells. The entire system was tested on the field for a timespan of a month showing an effective and dynamic monitoring of those machineries. However, no more than 700 m were covered since longer distances were not requested for this application scenario. LoRaWAN technology has been also under investigation to be employed for emergency conditions monitoring for ships [29]. Sensor nodes were placed on board of boats sending emergency notifications via LoRa to Gateways, which are installed ashor, by covering a 5.11 km distance. Then, the latter ones forward these information to a cloud service that enables the harbor police to be aware if an emergency event occurred offshore by consulting an Android mobile application. This scenario resembles the one proposed in this paper since sensor nodes were installed offshore, sending packets ashor to Gateways. Another work on real-time tracking and monitoring of boats, in particular of the lightweight ones, is exposed in Reference [30]. The authors implemented a LoRa LPWAN architecture to retrieve data from ships and make them accessible to users by means of a data visualization platform. Once again, sensor nodes were installed offshore on board of boats whilst a Gateway was situated ashor on the roof of a building. System performances were evaluated during some training sessions for sailboats races within a port area which entailed various spots of non-LoS conditions. Indeed, the entire infrastructure was supposed to be exploited for the remote and real-time monitoring of sailboats races. Several transmission parameters were analyzed throughout different sets of trials and the maximum coverage range experienced within such a scenario was 4 km. LoRaWAN networks may be exploited as well for the assessment of potential tidal energy in sites at risk like the Philippines [31]. By means of specially designed buoyant sensor nodes such energy was sensed and wirelessly sent towards land, covering the maximum distance of 14.6 km. While this transmission distance is larger than the one achieved in this paper, the residual link margin measured during our tests suggests similar results. The same conclusion can be drawn by considering Reference [17].