Multi-hop, Multi-channel Protocol for Tree Topology in LoRa

Abstract

In the upcoming Internet of Things (IoT) era, smart system, such as energy management and surveillance control systems, are expected to be widely deployed in buildings, industrial area or city. New transceiver technologies have emerged which enable power efficient communication over very long distances. LoRa is one of them recently has been developed as a crucial IoT access network technology in terms of long distance and low power consumption. This technology has some feature make it different with others such as long time on air, CAD (carrier activity detection) mechanism, channel separation using different spreading factor (SF), and capture effect. Although improved communication range, some researches showed that under many real deployments there are so many obstacles that will strongly affect to communication range, so a multi-hop protocol will be efficient in not only this problem but also power efficient and reliability. In this paper, we firstly have performed comprehensive experiment to investigate CT performance of LoRa under variation of power offsets and timing offsets in the real environment. Then we propose a scheme to construct a tree topology that included assigning channel and time slot for upward data transmission in one-time flooding. By the channel and time slot assignment in upward data transmission, we show a method to allow downward data and perform aligning cycle timing in data transmission period. With analysis power consumption in tree construction period and evaluation performance of protocol from experiment in real environment, this protocol is feasible to apply in some specific IoT applications with large coverage and high reliability.