Closeness Centrality-Based Scheduling for IoT Transmissions in LEO Satellite Networks

Low-Earth-Orbit (LEO) communication systems are fundamental for ubiquitous coverage, providing new opportunities in precision agriculture, smart cities, wildlife and environmental monitoring. In this context, it is very desirable that Internet of Things (IoT) devices can directly transmit information to LEO satellites. However, practical Direct-to-Satellite IoT (DtS-IoT) networks still require the development of modern and efficient multiple access protocols to support massive connectivity. For high-density scenarios, many devices appear simultaneously in the satellite footprint. Rise-based schemes like first-come-first-served (FCFS) can lead to considerably frequent collision events and thus reduced scheduling efficiency. This work presents a novel scheduling strategy for a DtS-IoT scenario, where a constellation of LEO satellites covers clustered IoT devices distributed across the target area. The proposed scheme utilizes the concept of closeness centrality to evaluate cluster transmission suitability and improve success probability, focusing on the shortest distance between IoT devices within that cluster and the satellite. Additionally, devices are equipped with a satellite trajectory predictor and utilize LoRa modulation to transmit data packets. Simulation results include real satellite orbits and demonstrate improvements in success probability comparing with a regular ALOHA (337.66%) protocol and the FCFS (83.15%) method for dense scenarios with hundreds of devices per cluster.