Long-Range Bluetooth Low Energy Detection via Drone-Based LoRa Relays for Search and Rescue Operations in Complex Terrain

Abstract

Search and Rescue (SAR) missions in remote environments are time-critical and resource-intensive, and their effectiveness is often constrained by terrain, weather, and limited communications infrastructure. Bluetooth-based tracking offers a distinct advantage over other RF modalities due to its ubiquity in personal devices such as smartphones, smartwatches, and commercial trackers (e.g., AirTags), which continuously broadcast advertising packets that can be leveraged for localization. This work demonstrates the feasibility of using BLE advertisements as opportunistic signals for remote sensing in drone-based SAR missions to increase the efficiency of locating missing persons. A drone is used as a passive RF remote sensing node equipped with a Nordic nRF52840 scanner and different antenna configurations. To characterize the sensor’s response and detection probability under varying propagation conditions extensive field tests across diverse locations in Spain, including slot canyons with no Global Navigation Satellite System (GNSS) or cellular coverage, dense forests, and high-mountain terrain have been conducted. The proposed system detected commercial BLE devices at slant ranges close to 500 m from altitudes of up to 100 m. To overcome the lack of cellular coverage in remote areas and identify the devices, a LoRa-based data bridge has been implemented. This bridge encapsulates and forwards captured BLE payloads to a ground control station, where they are re-emitted to trigger real-time updates on crowdsourced networks (e.g., Apple’s Find My), effectively confirming the location of isolated victims to SAR command centers.