Offline Scheduling Algorithms for Time-Slotted LoRa-based Bulk Data Transmission

LoRa-based transmissions suffer from extensive collisions due to the ALOHA-style transmission policy. As a consequence, delivering a high number of packets in a short amount of time becomes an unfeasible task. To tackle this problem we propose to schedule node transmissions in slots of different size depending on the Spreading Factor (SF). Transmissions with the same SF are scheduled in different slots to avoid collisions while those with different SF can occur in parallel. In this paper, we propose two algorithms executed in an offline manner to allocate SFs to nodes aimed at minimising the total data collection time while respecting the radio duty cycle restriction. The examined simulation scenarios and our comparison with LoRaWAN show an up to 101% improvement in terms of data collection time and an up to 250% improvement in terms of energy consumption combined with a nearly 100% packet delivery ratio.