Towards a novel gateway selection strategy for LoRaWAN downlink communications

In a LoRaWAN network, a number of end-devices communicate with one or more gateways that forward the messages exchanged between the end-devices and the network server. The LoRaWAN downlink transmissions, i.e., the ones from the network server to the end-devices, have to comply with the strict regional duty cycle constraints that the relevant authorities (e.g., ETSI in Europe) impose on the gateways. However, as the gateways handle the downlink traffic of a large number of end-devices, they reach their duty cycle limits faster than the individual end-devices. This determines a traffic bottleneck, as no downlink transmissions are possible as long as the gateway exceeds the duty cycle limits. Ultimately, this situation can prevent the delivery of important downlinks, e.g., the acknowledgments, in mission-critical applications. This paper explores the rationale behind the introduction of a novel gateway selection strategy, called DL+, that dynamically schedules downlink traffic to enhance the downlink packet delivery ratio. DL+ leverages a weighted decision metrics that takes into account both signal quality parameters, such as RSSI and SNR, and the available duty cycle. Preliminary simulation results are presented that demonstrate the significant improvement of the downlink packet delivery ratio introduced by DL+ compared to existing baseline approaches, especially in dense network scenarios.