A Two-Hop Real-Time LoRa Protocol for Industrial Monitoring and Control Systems.

A single-hop LoRa ( Lo ng Ra nge) network suffers from a limitation in coverage caused by high signal attenuation when deployed in industrial areas, which often include wireless unfriendly zones (WUZs). Thus, some end nodes in WUZs may fail to transmit data to the gateway (GW). This paper proposes a reliable two-hop real-time LoRa protocol in which the nodes in WUZs transmit data to another node that relays the received data to the gateway for reliable transmission. The proposed protocol allocates transmission slots to nodes with different data transmission periods, so the nodes not only achieve high reliability but also meet time constraints or periods for delivering data to a gateway. In this case, 1-hop nodes (one hop away from GW) may consume more energy than 2-hop nodes (two hops away from GW). For energy balancing, the protocol uses a data aggregation approach to minimize the number of transmissions. We show by analysis that the proposed protocol can support up to 200 nodes using a single-channel GW when every node sends one packet with a payload of 30 bytes within 17 seconds, and 30% of the nodes are 2-hop nodes. In addition, we show by experiment that the proposed protocol can achieve high reliability in data transmission.