# Experimental Study of LoRa Transmission over Seawater
## 4 Experimental Results and Analysis
### Discussion  
The experimental results unambiguously show that LoRa links over seawater are feasible up to at least 22 km for any combination of LoRa parameters in both frequency bands of interest, 868 MHz and 434 MHz if LOS condition between transmitter and receiver is guaranteed. Furthermore, the links are feasible using low-cost off-the-shelf rubber duck antennas which makes the results useful also in commercial deployments. Since there is a link margin of 15 dB in 868 MHz band, and approximately 20 dB in 434 MHz, it can be assumed that maximum achievable distance is significantly longer. Moreover, the experiments also showed that there is a significant weather tolerance margin as well. Namely, it is well known that RSS decreases when ambient temperature increases [29]. This can impair signal reception if deployments are done in areas with high average temperature fluctuations during the year. Moreover, if the transceivers are mounted inside, e.g., IP-67 rated enclosure, the temperature can be even higher than ambient if the device is exposed directly to the sun [30]. Since our transceivers were deployed in unfavorable conditions in terms of weather conditions (they were mounted inside the IP-67 rated enclosure, directly exposed to the sun, with an ambient temperature of 28 \({}^{\circ}\)C), it can be easily concluded that link feasibility can be extended for even higher ambient temperatures. It is interesting to note that RSS fluctuations are smaller for a smaller spreading factor used. By increasing the spreading factor, the RSS fluctuations are increasing in amplitude in both frequency bands, resulting in a peak-to-peak value of 10 dB for \(SF=12\) at 868 MHz. Additional investigation is needed to determine the cause, however, an explanation can be related to longer packet air times (due to higher SFs) and longer RSS measurement window which increases the probability for a different kind of interference to impact the measurement. Nevertheless, this did not cause a problem in the  
Figure 22: RSS and SNR histograms for ODT: \(f=434\) MHz, \(BW=125\) kHz, \(SF=10\), \(CR=4/6\), BLOS. packet reception rate because the absolute value of RSS was substantially greater than the reception margin for the given LoRa parameters. When the SNR measurement chains are not in the saturation region of operation, the values of SNR can be used to assess the link quality. It can be seen that ODT transceiver constantly has the highest SNR, as well as the highest PRR. This is the consequence of the lowest noise floor which is provided with a special hardware design approach described in [10]. This enables the ODT to decode very weak signals and maximize range. The PRR is constantly high with negligible packet loss for all LoRa parameters tested, except for Libelium in the case of \(SF=7\). This needs further investigation since RSS and SNR are considerably above the reception margin, and the other two receivers operated flawlessly for the same LoRa parameters. Besides that, in all other experimental scenarios packet loss is negligible, which implies that LoRa parameters can be chosen only according to the application specific requirements. It is worth noting that in these experiments, compatibility between the only two manufacturers of LoRa ICs is validated since the transmitters were equipped with Semtech LoRa ICs, whereas one of the receivers was equipped with HopeRF LoRa IC. This practically means that there are no limitations in terms of hardware usage in different deployments. The experiments also revealed that LoRa links can be established even in the presence of an obstacle that blocks the line of sight, provided that higher gain antennas are used at both ends. Nevertheless, there are certain limitations when it comes to their practical implementations since costly and bulky antennas are needed on both sides and transmission reliability is not guaranteed. Results of the experiments imply that propagation over seawater does not impose any problem for LoRa transmission systems.