A single-hop LoRa (Long Range) 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. INDEX TERMS two-hop LoRa network, energy balancing, relay, real-time scheduling, reliable transmission

Recently, LoRa (Long Range) technology has been drawing attention in various applications due to its long communication range and high link reliability. However, in industrial environments, these advantages are often compromised by factors such as node mobility, signal attenuation due to various obstacles, and link instability due to external signal interference. In this paper, we propose a new multi-hop LoRa protocol that can provide high reliability for data transmission by overcoming those factors in dynamic LoRa networks. This study extends the previously proposed two-hop real-time LoRa (Two-Hop RT-LoRa) protocol to address technical aspects of dynamic multi-hop networks, such as automatic configuration of multi-hop LoRa networks, dynamic topology management, and updating of real-time slot schedules. It is shown by simulation that the proposed protocol achieves high reliability of over 97% for mobile nodes and generates low control overhead in topology management and schedule updates. The protocol was also evaluated in various campus deployment scenarios. According to experiments, it could achieve high packet delivery rates of over 97% and 95%, respectively, for 1-hop nodes and 2-hop nodes against node mobility.

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A multi-hop approach can extend network coverage, including connectivity to difficult-to-access areas. This paper discusses the implementation and evaluation of the two-hop real-time LoRa (Two-hop RT-LoRa) protocol previously proposed to be used for industrial monitoring and control applications. The protocol was implemented on LoRa devices to support a multi-hop LoRa network that consists of one LoRa gateway and 40 end devices. It is shown with various campus deployment scenarios that the protocol improves reliability in data transmission significantly