A LoRaWAN Adaptive Retransmission Mechanism

LoRaWAN is a widely used protocol for low-power Internet of Things devices. Due to duty cycle restrictions imposed in sub-GHz unlicensed spectrum, the downlink time resources of the gateways are limited. If many end-devices request acknowledgments for their uplink transmissions, the gateway resources will be depleted fast, especially if retransmissions occur. Apart from the obvious effect on the network congestion, this also has a negative effect on the number of unique transmissions that an end-device can send, because repeated retransmissions of the same uplink may postpone scheduled transmissions of new data and violate the application requirements. This paper examines the impact of retransmission attempts on network performance and proposes an adaptive retransmission mechanism with the main goal of increasing the unique packet transmissions and, at the same time, meeting the application requirements. Simulation results show that, even though the packet delivery ratio is dropped, the proposed mechanism not only increases the unique packets, but it also achieves a better energy consumption as compared to an existing approach in the literature and to an approach that always uses the maximum number of retransmissions.