Experiments on LoRa Communication Used in a Relay Station Network for Disaster Management

The topography of some northern provinces of Thailand is mountainous. Hence, many areas are subject to landslides. Landslides can cause severe disruption in public utilities and services, such as transportation, electricity, and telecommunication networks. Triggers for a landslide in one area often originate from remotely mountainous or rural areas far away from towns; thus, the 3G/4G system is not available. Therefore, a relay station network based on a low-power wide-area network (LPWAN) technology is proposed to monitor environmental parameters in no-3G-signal landslide-prone areas. The relay station network consists of an array of relay stations whose function is to forward the received data from a monitored area to the next station until the data reach the destination station. Then, the data will be sent to a server via the 3G network from the base station. To achieve the final goal, we initially conduct experiments on multi-hop communication based on the LoRa protocol. This paper aims to report and discuss the implementation of simple LoRa-based relay stations in terms of packet loss and coverage area. In our experiments, each LoRa communication module was set to minimize the communication range first so that the tests could be done within a radius of one kilometer in Thammasat University. The scope was limited by setting three parameters: transmission power, coding rate, and bandwidth. Then, a relay function was designed and developed. The performance was evaluated in terms of packet receiving rate (PRR). The experimental results showed that, for the node-to-node communication with a maximum distance of 600 m, the PRR was approximately 0.994. When a relay station was added between two nodes, the maximum range extended to 800 m, with the PRR of 0.795. These results suggest that a higher layer protocol for checking the received packets is necessary.