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In the LoRaWAN protocol, the confirmed message is used for the reliable transmission service. Once a server received a confirmed message from an end device, it responds with an acknowledgement message to make sure that the uplink message was successfully delivered. For doing this, the protocol reserves two receive windows that follows uplink message transmission in the specified intervals. However, when GW responds with an acknowledgement message in one of the receive windows, it fails to receive messages from other end devices since it operates in half-duplex mode. This can cause high data loss as the number of confirmed messages increases. In this paper, we study how the increase of confirmed messages and message traffic affects packet delivery ratio. The simulation results shown that up to 24% number of uplink messages is lost or collided when 1000 end devices transmit data with 0.1% duty cycle and the confirmed message ratio is 0.2.

LoRa technology draws attention for its use in industrial monitoring and control systems in which each end device or task is required to send data periodically to a (cloud) server. Despite its provision of a stable link, it suffers from data loss by signal suppression and interference. A real-time LoRa protocol is proposed that uses a slot scheduling to remove collision and device or node grouping based on signal attenuation to deal with signal suppression. Based on the definition of a frame-slot structure, a logical slot indexing algorithm is devised to tag a logical index to each slot. The logical indices enable the easy allocation of slots to nodes such that if each node sends data in the allocated slots, it can satisfy time constraint. To handle external interference caused by other networks, the protocol uses a multiple listen-before-talk (mLBT) mechanism that allows channel detection multiple times within one slot. Our protocol is compared analytically and experimentally with other ones to show its superior throughput and reliability against signal suppression and interference.