Fast Feedback Control over Multi-hop Wireless Networks with Mode Changes and Stability Guarantees

Abstract

Closing feedback loops fast and over long distances is key to emerging cyber-physical applications; for example, robot motion control and swarm coordination require update intervals of tens of milliseconds. Low-power wireless communication technology is preferred for its low cost, small form factor, and flexibility, especially if the devices support multi-hop communication. Thus far, however, feedback control over multi-hop low-power wireless networks has only been demonstrated for update intervals on the order of seconds. To fill this gap, this paper presents a wireless embedded system that supports dynamic mode changes and tames imperfections impairing control performance (e.g., jitter and message loss), and a control design that exploits the essential properties of this system to provably guarantee closed-loop stability for physical processes with linear timeinvariant dynamics in the presence of mode changes. Using experiments on a cyber-physical testbed with 20 wireless devices and multiple cart-pole systems, we are the first to demonstrate and evaluate feedback control and coordination with mode changes over multi-hop networks for update intervals of 20 to 50 milliseconds.

Scaling beyond Bandwidth Limitations: Wireless Control with Stability Guarantees under Overload

“…In prior approaches capable of distributed control over wireless multi-hop networks [6,8,32] the latency to exchange M messages scales as O (MT ), with T the time required for the dissemination of a single message. With this scaling behavior the number of messages that can be exchanged in a given update interval is rather small.…”

The Wireless Control Bus: Enabling Efficient Multi-Hop Event-Triggered Control with Concurrent Transmissions

“…as long as n i=1 θ i = 0 for n state variables. This enables using each of the i-th conditions in the right-hand side of Equation (7) independently at each sensor. The triggering parameters θ i can be designed offline or adapted online.…”

“…LWB has been exploited also specifically for control. The system in [7] supports feedback control, stability guarantees, and mode changes over multi-hop wireless networks for systems with fast dynamics (tens of milliseconds). Latency is therefore the main focus rather than reliability, for which dedicated mechanisms are not provided.…”

“…Centralized controllers are generally easier to design and provide better performance than controllers accounting for network topology constraints; further, in the specific case of ETC they usually lead to fewer events being triggered. Unfortunately, the use of CTX in control is hitherto largely unexplored, apart from a few recent exceptions [7,9,37] that, however, focus on periodic and self-triggered sampling rather than ETC. Methodology and contributions.…”

Dynamic Network Slicing for the Tactile Internet

“…In the context of wireless embedded systems, several works have attempted to guarantee communication quality to ensure the stable control of remote devices. Some of these works also address how to dynamically change the communication path between a controller and a remote device without compromising on stability (see [30] and references therein), a concept that bears some similarity to the concept of dynamic network slicing discussed in this paper. These works, however, focus only on embedded wireless systems working on a limited number of hops.…”