Multipath aware scheduling for high reliability and fault tolerance in low power industrial networks

The Industrial Internet of Things is expected to enable the Industry 4.0 through the large deployment of low-power devices. However, industrial applications require most of the time high reliability close to 100%, and low end-to-end delays. Thus, most industrial wireless networks rely on a strict schedule of the transmissions to avoid collisions, and implement frequency hopping to combat external interference. In multihop topologies, the network has to decide both when the transmissions have to be scheduled, and which router can forward the packets. To be fault-tolerant, multipath routing consists in exploiting several paths in parallel. We exploit here a braided path routing structure, where each router has several possible next hops. Thus, we can cope with any fault along the path, while still providing a remaining operational path. We propose also a scheduling algorithm, where multiple transmitters are attached to a single cell, to the same receiver. The schedule is constructed such that only one transmitter is active at a time, and is consequently collision-free. Mutualizing the same cell for several transmitters reduces the energy consumption and increases the network capacity. Our approach is still fully compliant with the standard while minimizing idle listening. Our simulation results show the relevance of such solution to provide high-reliability and fault-tolerance. While the single and disjoint paths solutions achieve a very low reliability (20%) when two nodes crash, we keep on providing a packet delivery ratio above 80%, whatever the conditions. Besides, our scheduling algorithm is particularly energy efficient since it presents the same energy consumption as the classical single path routing scheme.