Combining Dynamic Deterministic Latency Bounds and Networked Control Systems

Since network delays can severely impact Networked Control Systems (NCS), both guaranteed Quality of Service (QoS) at the network level and guaranteed stability at the application level in the presence of delays are essential. The recently developed Dynamic Priority Token Bucket (DPTB) aims to meet network-level requirements through dynamic yet deterministic latency bounds that depend on the application’s sending behavior.This concept provides great potential for a combined design method with NCS controllers, which we propose in this paper. We design and implement two approaches that combine DPTB with (1) the well-known robust input/output (DPTB-RobustIO) controller to provide provable stability and (2) a novel multi-level linear quadratic regulator (DPTB-MLQR) to improve control performance.For the evaluation of the approaches, an Ethernet-based NCS with a Linux software switch and an inverted pendulum is used. This benchmark setup for fully automated evaluations of co-designs that combine network scheduling and QoS mechanisms with NCS controllers running on real hardware components is made available as an open source implementation. DPTB-RobustIO and DPTB-MLQR reduced the data rate by up to 26% and increased the control performance by 27% compared to regular token buckets with RobustIO control.