Spreading Factor Optimization for Interference Mitigation in Dense Indoor LoRa Networks

Recent years have seen the development of several distinct Low Power Wide Area Network (LPWAN) technologies. The Long-Range Wide Area Network (LoRaWAN) is one such LPWAN solution designed for IoT communications. LoRa's low power consumption and scalability makes it a highly regarded option for low bandwidth IoT applications involving a large number of geographically dispersed devices. LoRa modulation uses symbol spreading within a constant channel bandwidth to trade off data rate for sensitivity and coverage. In LoRaWAN networks, the collision rate is highly correlated with the Spreading Factor (SF) assigned to individual nodes. The traditional method of distributing SF to devices in a LoRaWAN network reduces network performance owing to interference caused by Co-SF and Inter-SF collisions. In this work, we address this issue by allocating optimal SF to nodes who fail to transfer data with the initially assigned SF. An optimization problem is devised and addressed to improve the probability of successful transmission with specified SF. In addition, we presented an algorithm for allocating optimal SF to nodes. The results of simulation experiments indicate that the proposed method increases packet success rate and decreases collisions by designating the optimal SF.