Abstract
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: MHz and 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, , within a bandwidth of kHz and Coding Rate . The experiments showed that LoRa links are fully feasible over seawater at distances at least 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 km obstructed LOS oversea path in ISM MHz band, but using costly, higher gain antennas. Furthermore, the laboratory experiments revealed that RSSI is linear in a wide range, up to dBm, whereas the SNR measurement chain goes into saturation for Received Signal Strength (RSS) values higher than dBm. These findings enabled accurate interpretation of the results obtained in field experiments.
Highlights
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
The plots in time domain show current values represented by dots, while their moving average values calculated on the 1-min window are shown with solid lines
Since our transceivers were deployed in unfavorable conditions in terms of weather conditions, it can be concluded that link feasibility can be extended for even higher ambient temperatures
Summary
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. 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. Boydstun et al [3] carried out data transfer using WiFi over a distance of approximately 300 m, while Pozzebon et al [4] demonstrated successful communication in coastal region combining both ZigBee and GSM. The work presented by Trasvina-Moreno [5] showed successful communication with measurement node using the Iridium satellite constellation
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