A Duty-Cycle-Efficient Synchronization Protocol for Slotted-Aloha in LoRaWAN

In the current context of massive IoT, the Pure-Aloha scheme used in LoRaWAN is reaching its limit, and Slotted-Aloha is being considered as an alternative, as it offers twice Pure-Aloha's packet success rate. It however requires synchronization across the nodes. In this paper, we propose a new slot structure adapted to devices with low quality clock, and a duty-cycle efficient synchronization protocol for LoRaWAN class A devices with the lowest overhead to date. We discuss the conditions of its integration into LoRaWAN. The experimental results confirm that it succeeds in tracking each device's synchronization state, identifying the exact moment they desynchronize and resynchronizing them. The proposed protocol is also proven to be more duty-cycle efficient than existing fixed-rate synchronization solutions.