Throughput-Delay Tradeoffs for Slotted-Aloha-based LoRaWAN Networks

LoRaWAN (Long Range Wide Area Network) is one of the most popular low power wide area networks technologies for the Internet of Things (IoT). It provides higher coverage, lower energy consumption and cost. A key parameter of LoRa modulation is the Spreading Factor (SF), which can be tuned to achieve a desired tradeoff between data rate and range. The six LoRa spreading factors (SF7 through SF12) are inherently orthogonal, which implies that communications using different SFs can coexist simultaneously on the same frequency channel without impacting performance. However, multiple devices using the same SF must compete for channel access and packet collisions must be managed. In this work, we present a comprehensive framework for Slotted-Aloha-based LoRa with random SF selection. Detailed analysis of the steady state of the system allows numerical derivation of the optimal retransmission probability. Furthermore, we assess the system's achievable performance in terms of average throughput and expected delay.