Adaptive Real-Time Communication for Wireless Cyber-Physical Systems

Low-power wireless technology promises greater flexibility and lower costs in cyber-physical systems. To reap these benefits, communication protocols must deliver packets reliably within real-time deadlines across resource-constrained devices, while adapting to changes in application requirements (e.g., traffic demands) and network state (e.g., link qualities). Existing protocols do not solve all these challenges simultaneously, because their operation is either localized or a function of network state, which changes unpredictably over time. By contrast, this paper claims a global approach that does not use network state information as input can overcome these limitations. The Blink protocol proves this claim by providing hard guarantees on end- to-end deadlines of received packets in multi-hop low-power wireless networks, while seamlessly handling changes in application requirements and network state. We build Blink on the non real-time Low-Power Wireless Bus (LWB), and design new scheduling algorithms based on the earliest deadline first policy. Using a dedicated priority queue data structure, we demonstrate a viable implementation of our algorithms on re- source-constrained devices. Experiments show that Blink: (i) meets all deadlines of received packets; (ii) de- livers 99.97 % of packets on a 94-node testbed; (iii) minimizes communication energy consumption within the limits of the underlying LWB; (iv) supports end-to-end deadlines of 100 ms across 4 hops and 9 sources; and (v) runs up to 4.1× faster than a conventional scheduler implementation on popular microcontrollers.