TREMA: A traffic-aware energy efficient MAC protocol to adapt the LoRaWAN capacity

The emerging LoRa technology is quickly becoming the de facto standard for Low Power Wide Area Networks upon unlicensed frequencies. Herein, the LoRaWAN medium access sets up a lightweight network architecture able to connect very low power devices to the Internet. Traffic flows in such deployments can be variable, or even unpredictable, depending on the needs of the monitoring applications using the network. As an example, to track air quality in cities, some applications can trigger an increased need of fine grained pollution data during the daytime. However, the network capacity is currently limited by the default LoRaWAN pure ALOHA access scheme. A time synchronized scheduled access would considerably improve the achievable throughput, at the cost of an increased power consumption for synchronization duties. In such a context, this contribution introduces the traffic-aware energy efficient Medium Access Control (TREMA) protocol for LoRa networks, capable of seamlessly switching between asynchronous and synchronous schemes according to the probed traffic variations. TREMA ultimately increases the maximum capacity of LoRa deployments while always selecting the most energy efficient access scheme.