A Real-Time LoRa Protocol for Periodic and Aperiodic Data Transmission

Abstract

Due to the provision of a long-range and robust link, the LoRa technology draws attention for its use in industrial data collection networks. In such networks, an end device or task can either transmit data periodically or transmit data in an event-driven manner to a server. This Ph.D. dissertation proposes a real-time LoRa protocol that can deal with both periodic and aperiodic data effectively. Based on the definition of a frame-slot architecture, a logical slot indexing algorithm is devised to tag a logical index to each slot in a frame. The slots are logically partitioned such that they are first scheduled for periodic data by the slot scheduling algorithm and then the remaining unscheduled slots are used for event-driven aperiodic data. In this logical frame partitioning, the unscheduled slots appear in an interleaved fashion so that aperiodic tasks can transmit data with low delay and fairness while every periodic task still completes data transmission before the beginning of the next period. To deal with the problems of data collision and traffic congestion for aperiodic data, a two-level collision avoidance scheme is proposed that adopts the notion of contention window and delay slot. To evaluate the performance of the proposed protocol, we utilize two evaluation methods: (1) conducting experiments on the testbed of the real LoRa devices to evaluate the data transmission of periodic tasks and (2) performing simulations with various scenarios to evaluate the data transmission of aperiodic tasks. It was proven by experiment and simulation that the proposed protocol achieves better performance compared with other recent protocols, LoRWAN, ILoRa and RT-LoRa. Specifically, it can not only guarantee the timely delivery of periodic data, but also deal with aperiodic data with high reliability, fairness, and low delay compared with others. Therefore, it is expected that the proposed protocol is highly suitable for industrial monitoring and control systems that require the support for the transmission of both periodic and aperiodic data.