Multi-hop LoRa Network with Pipelined Transmission Capability

LoRa (Long Range) has been developed as an attractive IoT (Internet of Things) access network technology in terms of long distance and low power consumption. LoRaWANa network standard based on LoRa, is an infra-structured network with star topology between LoRa motes, LoRa gateways, and a network server. Even though LoRaWAN has a long distance communication capability, it is difficult to apply LoRa technology in a large area with no communication infrastructure. In those environments, an ad-hoc network based on LoRa can cover a large area easily. In this paper, we propose a multi-hop LoRa network protocol, called pm-LoRa (pipelined multi-hop LoRa), with time-slotted and pipelined transmission capability which can be deployed easily on demand. In our protocol, a converge-cast tree topology is constructed at first for uploading and downloading communication between LoRa motes and a sink node. During the tree construction step, a channel and time-slot is assigned to each tree link, and each node transmits its data on the assigned channel and time-slot during the uploading and downloading data transmission cycles. We developed our multi-hop LoRa node prototype using Multi-tech mDot and made an experiment in the university. The experiment result showed that we could construct a multi-hop LoRa network easily on demand and collect sensor data from LoRa motes with high reliability by removing collisions among neighbor nodes.