# Experimental Study of LoRa Transmission over Seawater
## 1 Introduction
[9] deployed LoRa transceiver in a sailing monitoring system, using it to transmit the sailboat's parameters to a gateway in the \(434\,\mathrm{MHz}\) band, utilizing a bandwidth of \(BW=125\,\mathrm{kHz}\) and a spreading factor \(SF=7\). The experiment results showed a maximum distance of \(3467\,\mathrm{m}\) with packet loss of \(63.26\%\) on \(1195\) packets sent. The results were also presented in a grossly aggregated metrics fashion. The conclusions drawn from these experiments are restricted for several reasons. In both works, a relatively small number of packets was sent, with a maximum of \(3688\) packets. To assess link behavior and provide enough data for statistical processing, usual engineering practice recommends at least 10,000 packets to be transmitted. Next, data are presented cumulatively, in the form of packet loss, therefore no insight into link behavior over time can be gained. In addition, the selection of only one set of LoRa parameters deployed in the experiments cannot provide general insights in the link behavior because parameters are either selected to enable maximum sensitivity of the transceivers, as in [7] (\(SF=12\), \(BW=125\,\mathrm{kHz}\)), or to take into account trade-off between power consumption, data rate and transmission delay as in [9] (\(SF=7\), \(BW=125\,\mathrm{kHz}\)). In addition, in both works, only one frequency band is investigated, namely \(868\,\mathrm{MHz}\) in [7] and \(433\,\mathrm{MHz}\) in [9], hence advantages of using one over another frequency band cannot be quantified. Moreover, only one pair of commercial LoRatransceivers were used in the experiments; this can limit the insight in the technology capabilities, especially if we take into account the fact that commercial transceivers are usually not optimized in terms of sensitivity [10]. This is due to different trade-offs in the design which are necessary to be done in order to build general purpose transceiver. As a further matter, while in [7] RSS is logged, in [9] there is no information provided at all; additionally, both works lack data for Signal-to-Noise Ratio (SNR) for received packets, which limits gaining a deeper insight into technology and links' behavior. Besides, scaling factors for RSS indicator should be experimentally measured, and linearity and saturation region of SNR measurement chain investigated to provide an accurate interpretation of logged quantities. Finally, these two groups of experiments cover, in some aspects, one of two important deployment scenarios--when nodes are mobile, maintaining LOS, and are mounted near the seawater surface. However, there is another big group of potential deployments, which assumes that nodes are fixed and mounted well above the seawater surface. This is the case, for example, in island countries where there is a need to connect, e.g., environmental monitoring stations on different islands, or to implement early warning systems for detection of volcano eruptions, etc. The results from previous works are not fully applicable in these scenarios also because the nodes used in the experiments were deployed very close to seawater surface, which can alter the antenna radiation pattern and its resonant frequency and, consequently, degrade packet reception rate. Contrariwise, when nodes are fixed and deployed on the mainland, these effects are not dominant, and a higher packet reception rate could be possibly obtained. In our research, we aimed to investigate LoRa links over seawater in two characteristic scenarios: LOS and obstructed LOS at two different frequencies simultaneously, namely 868 MHz, and 434 MHz. In order to do so, we addressed all the potential limitations we found in currently available works. We increased significantly the number of packets sent by sending 20,000 packets in each experiment, and carried out data analysis in the time domain, exploring short and long-term variabilities in terms of RSS, SNR, and Packet Reception Rate (PRR); we also presented cumulative analysis in the form of histograms and packet loss.