Design and analysis of a LoRa-based system with scheduled transmissions from IoT nodes to UAV in rural areas

This paper considers Low Power Wide Area Network (LPWAN) IoT devices deployed in rural areas without terrestrial Internet connectivity and local energy supply. These devices are equipped with sensors to continuously monitor ground conditions and deliver measurements to the Internet using the LoRa/LoRaWAN technology, exploiting the occasional connectivity to fixed-wing Unmanned Aerial Vehicles (UAVs). This work proposes an approach to coordinate the UAV pass with the transmissions of ground nodes for smart agriculture to allow scheduled access to the LoRa gateway onboard the UAV. A testbed has been developed to study the propagation in the LoRa ISM band at 868 MHz. Then, a waypoint-based UAV closed path is devised, where the waypoints are determined as the centroids of the k-means clustering scheme on IoT node locations. Based on the Matlab UAV simulator, we determine the UAV flight trajectory and identify the intervals during which each ground node can transmit to the UAV; these intervals are used to schedule the transmissions of these nodes. We evaluate the performance of this UAV access scheme in terms of different indicators related to outage events, packet collisions, and the risk that the visibility interval of the UAV is too short for a certain node to allow it to send data to the UAV. We investigate different tradeoffs, showing that using small Spreading Factor (SF) values and selecting the maximum possible UAV flight altitude is more convenient for achieving a high probability of collecting data from the nodes in one UAV flight cycle.