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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.