Asynchronous Contention Resolution-Aided ALOHA in LR-FHSS Networks

Abstract

In this work, we apply an asynchronous contention resolution-aided ALOHA protocol to the recently proposed long-range frequency hopping spread spectrum (LR-FHSS) scheme, which is an amendment of widespread chirp spread spectrum (CSS)-based long-range (LoRa) modulation patented by Semtech. More specifically, we modify the so-called asynchronous contention resolution diversity ALOHA (ACRDA) protocol to comply with LR-FHSS requirements and improve LR-FHSS performance against collisions. In the proposed scheme, only the gateway requires modifications, while the ACRDA operation is transparent from the end-devices perspective, which follows the regular LR-FHSS operation. Our results, obtained using a discrete event simulator, show that the proposed scheme outperforms regular LR-FHSS in various aspects, such as average network success (up to 60% improvement in the scenarios considered), goodput (2× better) and number of supported devices for a target reliability level (more than 2×). Finally, we also evaluate the impact on the performance of the proposed scheme of parameters such as the window and the step sizes, showing that a relatively small window size (~2× the time-on-air of a single message) is sufficient to approach the asymptotic maximum network success achieved by an infinite window.