Numerical and experimental evaluation of radiohelmet-to-UAV LoRa Links

Body-worn radios exploiting the recently introduced LoRa protocol are very promising for Search and Rescue (SaR) operations in harsh environments. If the GPS signal is unavailable and there is not visual Line-of-Sight (LoS), the body-worn transmitting beacon could be localized based on the Received Signal Strength (RSS) measured by the rescuers. Moreover, an Unmanned Aerial Vehicle (UAV) equipped with a LoRa receiver could scout a vast area in little time and swiftly collect multiple RSS measurements. In this paper, the RSS seen by the UAV when a transmitting LoRa beacon is embedded in a safety helmet is evaluated through a two-ray model. The numerical values are corroborated using a flying UAV with good agreement. Search and Rescue (SaR) operations aim to localize and help a target person, usually in a harsh environment. Recently introduced Low-Power Wide-Area Networks (LPWANs) are very promising for SaR application thanks to their extended range and low power consumption. In particular, the LoRa LPWAN technology has been recently validated for mountain SaR applications involving wearable transmitters. An Unmanned Aerial Vehicle (UAV) equipped with a directive antenna could collect Received Signal Strength (RSS) measurement to localize the target to be rescued through ad-hoc algorithms. The RSS collected by a UAV equipped with a circularly polarized patch is modelled and measured when a LoRa radio is placed onto a helmet for mountaineering. The link performance is parametrized by means of the two-ray model and a simplified representation of the UAV antenna. The model is experimentally corroborated using a flying UAV with good agreement.