# Experimental Study of LoRa Transmission over Seawater
## 4 Experimental Results and Analysis
### LOS Scenario
#### 4.1.1 ISM 868 MHz  
Figure 9 shows the results obtained in LOS scenario for ODT, Libelium and Uputronics transceivers, operating at 868 MHz with following parameters: \(BW=125\) kHz, \(SF=7\), and \(CR=4/6\). Figure 9: RSS, SNR, and PRR for ODT, Libelium, and Uputronics at 868 MHz in LOS trajectory for \(BW=125\) kHz, \(SF=7\) and \(CR=4/6\). We observe that the RSS is almost constant during the whole experiment and that it is nearly equal for all three transceivers. This implies that multipath propagation effects were not dominant during the experiment and that the main component of the transmitted signal was the one which traveled in direct LOS path. In addition, there can be seen two short dips in 58 and 78 min of the test. They are caused by short radio-interference bursts, but they did not produce a drop in the packet reception rate. On the other hand, the SNR follows the fluctuation trend of RSS for all three transceivers. By inspecting the SNR values of different transceivers, and rescaling Libelium SNR values using Figure 8, we observe that ODT has the highest SNR, and consequently the lowest noise floor; this implies the highest sensitivity of the ODT transceiver. The PRR for ODT and Uptronics is constantly high, with negligible packet loss; Libelium has a constant packet loss, yielding \(PL=28.68\%\) which is high and unexpected since the values of RSS and SNR are deeply inside the link margin and there is negligible interference. The additional tests are required in order to investigate the cause of the high packet loss. Figure 10 shows RSS and SNR cumulative results on the entire measurement interval for the ODT, Uptronics and Libelium transceivers at 868 MHz, for the same LoRa parameters. It can be noticed that distribution of RSS values does not indicate multipath propagation effects and fading since Rice distribution cannot be observed. Rice distribution of RSS amplitudes is characteristic when there is a multipath propagation effect in the channel and one component is dominant, usually, the one that travels in LOS path [28]. However, the distribution of the  
Figure 10: RSS and SNR histograms for ODT, Uptronics and Libelium: \(f=868\,\mathrm{MHz}\), \(BW=125\,\mathrm{kHz}\), \(SF=7,CR=4/6\), LOS. RSS amplitudes has to be interpreted cautiously since the RSS indicator measures the received power of the whole packet and cannot measure the RSS value of a single multipath component. The difference between the 1-min window moving average values and current values exhibits the Gaussian distribution. This indicates that the time window for moving average calculations has been adequately selected since that difference represents the RSS fluctuations, which can be treated as a kind of \"noise\". Figure 11 shows results for the ODT, Uputronics, and Libelium transceiver at 868 MHz, in LOS scenario, with the following parameters: \(BW=125\) kHz, \(SF=10\), \(CR=4/6\). It can be noticed that in this experiment, RSS of all three transceivers fluctuated. Since these fluctuations are relatively slow, they can be attributed to multipath propagation effects. In the first 70 min of the experiment multipath was not pronounced, however, between 70 and 140 min of the experiment fluctuations of 5 dB are recorded. Since the experiment was carried out for LOS path (60 % of the First Fresnel zone was clear), multipath was a consequence of meteorological conditions which could cause refraction and consequently reflection from the sea surface by forming air masses with different refraction indexes. However, the multipath did not cause any significant packet loss, Uputronics experienced negligible packet loss of \(PL=0.01\%\). We also observe that SNR recorded by Libelium and Uputronics follows the fluctuation trend of corresponding RSS values. On the other hand, the ODT exhibits counterintuitive behavior after 130 min of the experiment since with the increasing of the signal level at the input, SNR decreases.