Experimental Study of LoRa Transmission over Seawater

Low Power Wide Area Networks (LPWANs) are gaining attention in both academia and industry by offering the possibility of connecting a large number of nodes over extended distances. LoRa is one of the technologies used as a physical layer in such networks. This paper investigates the LoRa links over seawater in two typical scenarios: clear Line-of-Sight (LOS) and obstructed path in two different Industrial, Scientific and Medical (ISM) radio bands: [Formula: see text] MHz and [Formula: see text] MHz. We used three different LoRa devices in the experiments: the Own Developed LoRa Transceiver (ODT) and two commercial transceivers. Firstly we investigated transceivers’ Receive Signal Strength Indicator (RSSI) and Signal-to-Noise (SNR) measurement chain linearity and provided correction factors for RSSI to correlate it with actual signal levels received at transceivers’ inputs. Next, we carried out field experiments for three different LoRa Spreading Factors, [Formula: see text] , within a bandwidth of [Formula: see text] kHz and Coding Rate [Formula: see text]. The experiments showed that LoRa links are fully feasible over seawater at distances at least [Formula: see text] km long, using only low-cost off-the-shelf rubber duck antennas in LOS path condition in both ISM bands. In addition, we showed that LoRa links can be established over [Formula: see text] km obstructed LOS oversea path in ISM [Formula: see text] MHz band, but using costly, higher gain antennas. Furthermore, the laboratory experiments revealed that RSSI is linear in a wide range, up to [Formula: see text] dBm, whereas the SNR measurement chain goes into saturation for Received Signal Strength (RSS) values higher than [Formula: see text] dBm. These findings enabled accurate interpretation of the results obtained in field experiments.