Automating Reliable and Fault-Tolerant Design of LoRa-based IoT Networks

Low-Power Wide-Area Networks (LPWAN) has recently been scaling rapidly, targeting at large-scale and low-power applications. LoRa and LoRaWAN have been adopted in many practical deployments. While the advantages of LoRa have been well-demonstrated, challenges in scalability and reliability impede LoRa networks from further expansion. Traditional deployment strategies for reliability and fault tolerance, which ensure that multiple networking paths are available, are not directly applicable because of LoRa's single-hop and Aloha medium-access design. In this paper, we study how to design LoRa networks in large regions so that their transmission reliability and fault tolerance against gateway failures and interference are met for LoRaWAN technology. We first introduce m-gateway connectivity to guarantee fault tolerance due to LoRa's unique properties. Next, we leverage state-of-the-art transmission reliability model based on estimated path loss from satellite maps. Combining the above two contributions, we formulate an Integer Nonlinear Program (INLP) that minimizes the number of gateways through strategic gateway placement and resource allocation. Constraints are imposed to achieve (i) fault tolerance, (ii) reliable transmission (i.e., satisfactory QoS), (iii) sufficiently long lifetime. Due to high complexity of INLP, we design a greedy heuristic, RFT-LoRa, to acquire a high-quality solution for larger size problems. Comprehensive evaluation is performed with ns-3 simulator using realworld datasets. The results demonstrate that RFT-LoRa enhances average packet delivery ratio by 10% - 54% over the existing heuristic under gateway failures and interference.