A LoRa Based Wireless Relay Network for Actuator Data

This paper describes a novel approach to the design of low complexity, robust, wireless relay networks based on the LoRa physical layer for transmission of short and infrequent messages such as sensor and actuator data. Relay networks comprise a message source, one or more relays that forward the message and a destination. These networks are sometimes described as 'long and thin'. Relay networks are a natural fit for pipes, underground mines, tunnels, communications along international borders and on transport links such as rail and road. Of particular interest to us are dynamic environments, in particular underground mining, where networks need to be deployed quickly with minimal time spent on site surveys and configuration. A key design feature of a relay network is relay forwarding. Relays must forward messages they receive but manage collisions caused by other relays. Collision management in wireless relay networks is challenging because there may be coverage overlap between multiple relays. In underground mines and tunnels, wireless coverage may be affected by the movement of machinery, dust or other environmental causes. Since relay coverage may overlap, multiple relays may be visible to and receive messages from each other, potentially leading to collisions that may corrupt the message. In this paper we propose a forwarding scheme based on broadcast scheduling where the schedule is such that regardless of overlapping transmissions, a collision will not occur. We have simulated and implemented the approach in an experimental network for detonation of explosives. The approach appears to be effective.