# Experimental Study of LoRa Transmission over Seawater
## 1 Introduction  
Deployment of sensors in the marine environment is a demanding task and among many implementation-related challenges, it requires reliable and low power wireless communication links between the nodes and base stations or gateways. Usually, in coastal regions, technologies like WiFi or Zigbee are used, provided that there is LOS between the access point and the node that contains the sensors. When nodes are deployed in remote sea locations, two widely adopted technologies are exploited: Global System for Mobile Communications (GSM) or data transfer over satellite constellation, such as Iridium [1]. A number of scientific works addressed the problem of data transfer from the measurement node using the technologies mentioned. For example, [PERSON] et al. [2] successfully demonstrated the use of sub-gigahertz transceiver to transfer measurement data from a buoy located \(2.5\,\mathrm{km}\) from the seashore, using narrow band type of modulation. [PERSON] et al. [3] carried out data transfer using WiFi over a distance of approximately \(300\,\mathrm{m}\), while [PERSON] et al. [4] demonstrated successful communication in coastal region combining both ZigBee and GSM. The work presented by [PERSON] [5] showed successful communication with measurement node using the Iridium satellite constellation. As can be concluded, to be able to cover different sensor deployment scenarios, various technologies have to be utilized. For example, ZigBee and WiFi are adequate technologies for deployments of up to several hundred meters from the coast, which limits their usage in remote areas. On the other hand, GSM technology can be used in remote areas, up to \(35\,\mathrm{km}\), provided that there is general network coverage of the area. However, cost of data transfer has to be taken into account since GSM technology utilizes the licensed part of the spectrum. In addition, all three technologies offer data rates which are significantly higher than it is really required for most sensor deployments. The power consumption of devices based on these technologies is significant since complex transmission protocols have to be processed per byte of the payload. Finally, deployments using satellite data transfer are rarely exploited due to the cost of the data transfer and implementation of the measurement node. LoRa, as one of the LPWAN underlying technologies, offers several advantages in deployments over seawater. First of all, it enables better range in comparison to all three technologies due to its sensitivity which goes down to \(-148\,\mathrm{dBm}\)[6]. Since it utilizes the unlicensed part of the spectrum, there is no cost of data transfer. In addition, due to low data rate and small transmission protocol overhead per byte of payload, power consumption is very low, offering extended battery-powered operating time. However, there are fewer works that tackle data transmission over seawater utilizing LoRa technology. [PERSON] et al. [7] carried out several experiments in different scenarios, including experiments over seawater. Their setup consisted of a commercial node, which was sending packets periodically with a sequence number, node status, and coordinates obtained by GPS. Packets were being received by the gateway installed on the shore on a fixed position. The node was installed on a boat which was sailing away from the shore, transmitting packets in the \(868\,\mathrm{MHz}\) band, randomly switching the channels within the band. The output power was set to \(14\,\mathrm{dBm}\), and the inter-packet delay was set to be in accordance with ETSI [8] regulation for duty cycling. The results were presented in a grossly aggregated metrics, showing a maximum communication distance of \(30\,\mathrm{km}\) with packet loss of \(32\%\) on \(3688\) packets sent. In addition, they derived a path loss model for each experimental scenario. [PERSON] et al.