Wireless Sensor-Actuator Networks (WSANs) are an important driver for the Industrial Internet of Things (IIoT) as they easily retrofit existing industrial infrastructure. Industrial applications require these networks to provide stable communication with high reliability and guaranteed low latency. A common way is using a central scheduler to plan transmissions and routes so that all packets are delivered before a deadline. However, existing centralized schedulers are only able to achieve high reliability in the absence of interference. This limitation lowers the feasibility of using centralized schedulers in most environments susceptible to interference. This paper addresses the challenge of stable, centrally scheduled communication in low-power wireless networks susceptible to interference. We introduce MASTER, a centralized scheduler and router, for IEEE 802.15.4 TSCH (Time-Slotted Channel Hopping). MASTER uses Sliding Windows, a novel transmission strategy, which builds on flow-based retransmissions instead of link-based ones. We show in our experimental evaluation that MASTER with Sliding Windows achieves routing and scheduling stability for over 24 hours with end-to-end reliability of over 99.6%. Moreover, we show that MASTER outperforms Orchestra, a state-of-the-art autonomous scheduler, in terms of latency by a factor of 8 while achieving similar reliability under a slight duty-cycle increase.

In this paper, we present Overtake, an opportunistic routing protocol for Time-Slotted Channel Hopping (TSCH). Overtake combines (1) opportunistic routing, (2) concurrent transmissions and (3) TSCH. We show that this novel combination enables low-latency, central scheduling withstanding node failures. Our initial results show its ability to withstand node failures of up to 40% of nodes of a flow while keeping minimal latency.