## 5 Data Transmission Tests
### Measurements  
The tests were performed from offshore, by reaching the closeness of the breeding cages, towards land covering the distance \(D=8.33\) km. Figure 7 reports the position of the end node (i.e., point A), the position of the Gateways (i.e., point B) and the length of the link (i.e., the red line), whilst Table 1 lists the coordinates of points A and B. The tests were accomplished with smooth sea conditions having a maximum wave height of 50 cm. It was a sunny day with a mean temperature of 18 \({}^{\circ}\)C and a gentle breeze whose average speed was of 4 m/s. Testing the system with more severe marine and weather conditions would have been extremely interesting. Unfortunately, though, the boat we had available for the fullfilment of the tests could not cast off in such cases. However, as it will be explained later on (see Section 6.2), sub-GHz wireless links (e.g., the ones exploiting LoRa modulation) are robust to these sorts of effects. Moreover, 600 packets were transmitted by respecting the laws on temporal occupation of the transmitting band [33] in an overall amount of time of approximately 14 h. \begin{table}
\begin{tabular}{c c c} \hline
**Point** & **Latitude [\({}^{\circ}\)]** & **Longitude [\({}^{\circ}\)]** \\ \hline A & 42.895494 & 10.629385 \\ B & 42.942858 & 10.550552 \\ \hline \end{tabular}
\end{table} 
Table 1: Coordinates of points A and B of Figure 7.  
Figure 7: Map showing the positions of the end node, point A, and of the Gateways, point B along with the covered distance, red line. The measurements campaign was sorted out in 2 groups, namely #1 and #2, by covering the same link from point A to point B (see Figure 7) and by testing all the SFs by transmitting an amount of 300 packets per test collection (i.e., 50 packets per SF per collection). The test series differed from each other for the heights of the transmitting antenna above sea level (see Section 5.2). A circumstance that has to be verified is to check whether or not points A and B were in LoS. Hence, by resorting to Equation (6), by switching the transmitting antenna with the receiver one (see Figure 3) and by plugging into the Equation \(h_{RX}\) in place of \(h_{TX}\), it can be noticed that points A and B are always in LoS since the former is not behind the horizon because \(D_{h}\) is bigger than \(D\). Table 2 summarises what has just been described and it also contains the results computed by applying Equation (6). At this stage, the concepts introduced in Section 4 can be applied and evaluated to the wireless link that has just been illustrated. First of all, the maximum radius of the first Fresnel zone \(F_{1}\) can be calculated by applying Equation (5). Since a frequency diversity scheme was implemented by means of frequency hopping among the channels listed in Section 5.2, \(F_{1}\) is evaluated by exploiting as carrier frequency the mean value of the ones previously listed (i.e., 867.8 MHz). The same convention holds for all the following Equations in which the frequency of the carrier is involved. Concerning the maximum height of the Earth bulge \(H\) amid the link endpoints, it can be derived by means of Equation (7). The theoretical free space loss \(L_{FS}\) can be computed according to Equation (4), therefore an overestimation of the received signal power \(P_{RX}\) can be obtained via Equation (3). Indeed, the latter is estimated by plugging into its Equation the values cited in Sections 5.2 and 5.3 (i.e., \(G_{TX}\), \(G_{RX}\), \(L_{TX}\) and \(L_{RX}\)), by exploiting the maximum power output for the transmitter \(P_{TX}\) according to the regional regulations [33] (i.e., 14 dBm) and by considering a null value for miscellaneous losses \(L_{M}\). Actually, there are several losses of that kind due to the fact that, as it will be seen in a while, the 60% of the first Fresnel zone is not free from obstacles. Unfortunately, though, the loss introduced by such a phenomenon is hardly numerically assessable.