LoRa, an emerging wireless technology, is examined for long range communication performance in a large area. Although LoRa shows good performance for long-distance transmission in the countryside, its radio signals can be attenuated and interfered with by buildings, trees and other signal sources. In urban areas, our observation shows that LoRa requires a dense deployment of LoRa gateways to ensure that indoor LoRa devices can transfer data back to remote servers. Mesh networking is a solution for increasing the communication range and packet delivery ratio without the need to install additional LoRa gateways. This study presents our design of a LoRa mesh-networking module for IoT applications (e.g.,collecting data from multiple, widely distributed sensors on a university campus). We deployed 19 LoRa mesh-networking devices distributed in an 800m by 600m area on campus to serve as a gateway and to collect data at one-minute intervals. The results show our LoRa mesh networking module achieved a 88.49% packet delivery ratio (PDR), while the LoRaWAN in star-network topology was only 58.7% under the same conditions.

The one of the major difficulties in deploying a wireless sensor to monitor debris flow in the real world is power consumption. Frequently replacing the battery of a sensor that is located in a remote mountainous area is not practical. In this study we examine the newly-introduced wireless debris flow sensor, SMARTCONE, which is designed to minimize the standby power consumption, but still keep alert to detecting debris flow. During standby periods, SMARTCONE turns off all major components and uses an accelerometer to sense vibration generated by moving debris flow, and it wakes up SMARTCONE for collecting the parameters of a moving debris flow. Multiple SMARTCONEs need to change operation modes between standby and wake up, collect physical parameters, and transmit data simultaneously, and these issues are kept in mind while designing the system. The performance of vibration detection, data transmission and records of GPS trajectories are evaluated to ensure the accuracy of the design.